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In this study, the structural, morphological, and magnetic properties of hydrothermally synthesized Co0.5Ni0.5BixFe2-xO4 (x=0.00–0.10) nanosized spinel ferrites, (CoNiBiFO (x=0.00–0.10) NSFs), were investigated. The formation of CoNiBiFO NSFs phase was confirmed by X-ray diffraction (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the morphology of the NSFs. Magnetization revealed that undoped Co0.5Ni0.5Fe2O4 and Co0.5Ni0.5BixFe2-xO4 NSFs (except with x = 0.04) exhibit ferrimagnetic magnetism at 300 K. Only the hysteresis loops recorded from Co0.5Ni0.5Bi0.04Fe1.96O4 NSFs have superparamagnetic characteristics. Mixed Co0.5Ni0.5Fe2O4 NSFs have maximum remnant magnetization (Mr) of 23.5 emu/g, maximum saturation magnetization (MS) of 63.38 emu/g, and maximum magneton number (nB) 2.66 μB. However, Co0.5Ni0.5Bi0.04Fe1.96O4 NSFs have minimum MS of 28.25 emu/g and minimum nB as 1.22 μB among Bi3+ doped and undoped samples. The coercivity (HC) of undoped Co0.5Ni0.5Fe2O4 NSFs is 656 Oe. However, the Bi3+ ion-doped samples have a wide range of HC values between 101 Oe and 1038 Oe. The squareness ratios are in the range of 0.092–0.418 and multi-domain structure is assigned for all types of samples. The measured positive exchange bias (HE) magnitudes are 268 Oe and 290 Oe, respectively. Hysteresis loops recorded at 10 K proved that the products are ferrimagnetic. These coercivities showed that all the samples are magnetically harder at low temperatures. Positive HE values of 165 Oe and 297 Oe were measured from the nanoparticles (NPs) with x = 0.08 and x = 0.10 at 10 K. The SQR of the Co0.5Ni0.5Bi0.04Fe1.96O4 sample at 10 K is almost equal to the critical value of 0.5, and a single domain structure with uniaxial symmetry can be attributed for this sample. The other samples have SQRs in the range of 0.632–0.782 and multi-domain wall structure is assigned for them at 10 K.

Gd3+-substituted nano-sized Sr-hexaferrite, SrGd(x)Fe(12-x)O19 (0.00

We fabricated high-quality ferrimagnetic CoFe2O4 (CFO) thin films on a mica substrate using a pulsed laser deposition technique. High-resolution X-ray diffraction and transmission electron microscopy revealed that the film grew epitaxially with the relationships of CFO || Mica [010] and CFO [111] || Mica [001]. The films were highly flexible in terms of both inward and outward bending, and exhibited clear ferrimagnetic hysteresis with weak anisotropy in both the in-plane and out-of-plane directions. We observed that the magnetization of CFO films was robust against mechanical stimuli without microcracks. The remnant magnetization and coercive field were within 8% and 11% over a strain of ±0.54%. As the number of bending cycles increased, the magnetic easy axis became more closely aligned to the out-of-plane direction, without any noticeable change in domain size.

The use of additives as a sintering aid for promoting densification is well-known in processing structural ceramics. In leaky ferroelectric ceramics (e.g., BiFeO3-based systems), additives are also used to reduce the leakage current, improve the poling efficiency and the piezoelectric response of a material. A less investigated aspect is how additives affect the multiferroic (ferroelectric and magnetic) features of BiFeO3-based ceramics. In this work, we report a systematic study of the effect of different additives viz, MnO2, CuO, K2CO3 and KMnO4 on the microstructural, electromechanical, and magnetic properties of Dy-modified BiFeO3–PbTiO3. We found that all the additives help in the precipitation of the ferrimagnetic dysprosium iron garnet phase. The additives containing potassium (K) tend to suppress the grain size. We found that the best combination of ferroelectric and ferromagnetic behaviour was found in a mixture of additives.

Intermetallic compounds based on rare-earth metals and iron are by far the most promising materials for permanent magnets. In this work, the multicomponent compound Sm1.2Ho0.8Fe17 was prepared by induction melting. The hydride Sm1.2Ho0.8Fe17H4.4 with a high hydrogen content was obtained by direct hydrogenation of the intermetallic compound. The rhombohedral Th2Zn17-type of structure (space group R 3 ¯ m ) is inherent to parent compound and hydride as well. The effect of hydrogenation on the magnetic properties of Sm1.2Ho0.8Fe17 was investigated. Curie temperature of the hydride Sm1.2Ho0.8-Fe17H4.4 is higher than that of parent compound by ΔTC = 138 K. The hydrogen embedded in Sm1.2Но0.8Fe17 crystal lattice increases the saturation magnetization (σS) at T = 300 K, but does not significantly affect σS at Т = 4.2 K. The ferrimagnetic structure is retained in magnetic fields up to 58 T in the parent compound, while, in the hydride, there is a spin-reorientation phase transition observed at 55 T. It is found that the parameter of the intersublattice exchange interaction decreases significantly in the hydride Sm1.2Ho0.8Fe17H4.4 (and in the nitride Sm1.2Ho0.8Fe17N2.4) which is associated with boosting of the unit-cell volume and distances between magnetic ions.

Al–Cr substituted CoFe2O4 nano spinels (CoAlxCrxFe2−2xO4 where x = 0.1 to 0.6) were successfully prepared for the first time via sucrose sol–gel auto-combustion technique. The structural parameters as well as magnetic and electrical properties of the prepared ferrites have been investigated. X-ray diffraction (XRD) confirmed single-phase formation and showed a decrease in the calculated values of lattice parameters by substitution attributed to the difference in the ionic radii. Based on the obtained structural parameters, an appropriate cation distribution was proposed and discussed. In this distribution, most of Al3+ and Cr3+ ions preferred octahedral sites occupation however, small amount of Al3+ seek the tetrahedral sites. Accordingly, the magnetic characterization via vibrating sample magnetometer (VSM) measurements revealed a decrease in the saturation magnetization (Ms) by successive substitution from 57.9 to 4.7 emu/g, indicating the incorporation of non-magnetic Al3+ and anti-ferromagnetic Cr3+ ions in the octahedral sites instead of Fe3+ ions. The much lower magnetization values obtained than that prepared by other methods could be attributed to the present lower sizes. The coercivity measurements indicated soft ferrimagnetic properties favoring their uses as high frequency transformers. Ac-conductivity as well as dielectric properties, as a function of frequency and temperature, indicated semiconducting behavior with decreasing trend by Al–Cr substitution due to decreasing in the Fe3+-Fe2+ hopping probability in octahedral sites. The obtained results suggest the using of the present materials in electronic inductors, electromagnets and transformers and microwave devices.

Structural, magnetic, and optical properties along with N2 absorption-desorption features of Sm3+–Dy3+ ions co-substituted BaSr hexaferrite microspheres (HFMSs) engineered through a hydrothermal gel approach were investigated. The microstructural and morphological features were examined by powder X-ray diffraction (XRD), surface area and pore size distribution (BET), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HR-TEM), and transmission electron microscopy (TEM) techniques. Rietveld analysis proved the purity of products. The BET revealed a slight variation in textural characteristics with increasing Sm3+–Dy3+ substitution. The surface area (11–16 m2/g) exhibits a pore volume of ~0.07 cm3/g and average pore size distributions of 26.6 nm. The 300 K and 10 K field-dependent hysteresis loops were registered. Remanent magnetizations (Mr) and coercive fields (HC) are in a range of 29.15–34.05 emu/g and 1420–5391 Oe at 300 K, respectively. The estimated saturation magnetizations (Ms) vary between 53.22 emu/g and 71.08 emu/g, and magneton numbers (nB) are in a range of 10.51–13.93 μB. At 10 K, the Mr = 35.18–46.83 emu/g, HC = 1487–4760 Oe, Ms = 81.82–99.17 emu/g, and nB = 14.83–19.44 μB, which are greatly higher compared to room temperature. All magnetic parameters exhibit strong ferrimagnetic features of pristine Sr0·5Ba0·5Fe12O19 and Dy3+ and Sm3+ co-doped HFMSs at both temperatures. Squareness ratios (SQRs), which are very close to 0.50 assign the single domain uniaxially symmetric structured HFMSs. δ M type of remanence plots was applied to specify the intensity and type of interparticle interactions as a function of the externally magnetic field, H. The Schuster-Kubelka-Munk theory provides to estimate direct energy band gaps (Eg). Undoped or co-doped HFMSs have a very narrow magnitude of Eg data between 1.795 and 1.865 eV depending on the couple ion concentrations.

Recognizing the crucial properties exhibited by FeAlO3 perovskite, its stabilization with the inclusion of bigger sized Pr3+ (f-block ion) in place of Fe3+ (d-block ion) is examined by preparing the samples employing an epoxide mediated sol-gel route and characterizing them extensively. Up to 40 mol % substitution of iron, hexagonal PrAlO3 with rhombohedral symmetry (R-3c spacegroup) was retained. At 50 mol % of iron substitution, it transformed into orthorhombic symmetry (Pnma spacegroup). At 80 mol % substitution of iron, X-ray pattern was amorphous. The metal-oxide bonding and symmetries were further verified by FTIR and Raman measurements. EPR and XPS measurements, performed at room temperature, confirmed the presence of Fe2+ and Fe3+ in the samples. Besides, praseodymium existed in III and IV oxidation states in these samples. Both field and temperature-dependent measurements showed ferromagnetic/ferrimagnetic behavior in the iron substituted samples. The ferrimagnetic transition occurred above room temperature (321 K) in 70 mol % iron substituted PrAlO3. Such a high TF is not reported till now among the available polymorphs of PrAlO3 or FeAlO3. 50 and 70 mol % iron substituted PrAlO3 samples showed ferroelectric behavior at room temperature, qualifying them to be multiferroics.

The effects of site occupation on the phase stability, martensitic transformation, and the magnetic and electronic properties of a full series of Ni-Mn-In alloys are theoretically studied by using the ab initio calculations. Results indicate that the excess atoms of the rich component directly take the sublattices of the deficient components of the Ni2Mn1+xIn1-x, Ni2-xMn1+xIn, and Ni2+xMn1-xIn alloys. Nevertheless, the mixed and indirect site occupations may coexist in the Ni2+xMnIn1-x system. The relevant magnetic configurations of the austenite for the four alloy systems have also been determined. The results show that, except for the austenite in the Ni2-xMn1+xIn alloys, which tend to be ferrimagnetic, the other alloys all present ferromagnetic austenite. Thus, the site occupation and associated magnetic states are the crucial influencing factors of the phase stability, martensitic transformation, and the total magnetic moment. The electronic structure of the austenite phase also shows that the covalent bonding plays an important role in the phase stability. The key finding of this work is both Ni2Mn1+xIn1-x and Ni2+xMnIn1-x alloys serve as the potential shape memory alloys.

In this comparative study, Tb and Tm substituted Sr-hexaferrites (HFs) with the chemical compositions of SrTbxFe12−xO19 and SrTmxFe12−xO19 (x = 0.00, 0.02 and 0.04) were fabricated via citrate sol-gel approach. The AC susceptibility and FC-ZFC magnetization were investigated. The product structure and morphologies were also investigated via XRD, TEM and SEM along with EDX. Measurements of temperature dependence of magnetization M-T and AC magnetic susceptibility versus temperature were carried out. The various synthesized HFs displayed ferrimagnetic behavior within 10–325 K. At lower temperatures, super-spin glass-like behavior was noticed. Neel-Arrhenius and Vogel-Fulcher models were employed to explore the experimental data of AC susceptibility.

Quaternary Ni1-xCuxFe2-yCeyO4 complex nano-ferrites system with different cerium content ratio and copper substitution degree were synthesized via co-precipitation wet chemical technique. The newly obtained nanoparticles, with general formula Ni1-xCuxFe2-yCeyO4 (where x = 0.0, 0.3, 0.6 and y = 0.00, 0.03, 0.05, 0.08 and 0.10) were heated up to 600 °C to stabilize the specific crystalline spinel structure. The limit of cerium content was quantitively determined to be around 0.08 and up to 0.10. Furthermore, the powders were pelletized in a 13 mm wide pellets and thermally treated at 950 °C. The thermal treatment affected even more the phases segregation process, as CeO2 was identified in the sample with lowest degree of cerium insertion – 0.03. Also, a difference in color and size of pelletized samples was noticed after the 950 °C thermal treatment. The Rietveld refinement, crystal structure confirmation, morphology magnetic and electrical properties of samples have been deeply studied. The cation distribution carried out from Rietveld refinement confirms the occupancy of (Fe3+) on tetrahedral sites and [Ni2+], [Cu2+], [Fe3+] and [Ce2+] on octahedral sites in the crystal lattice. Preliminary information regarding the cation distribution in spinel structures were suggested by FTIR spectral results, precisely in the 650-520 cm−1 region, as a consequence of peak shape and lack of shiftiness of MTd – O bond. Spherical-shaped quaternary nano-ferrites of 17–28 nm were determined from FE-SEM analysis and the samples composition was confirmed by EDX analysis. Hysteresis loops shows modifications in coercivity, magnetization and magnetic remanence with Ni2+ and Cu2+ ions doping in Ni1-xCuxFe2-yCeyO4 complex systems with typical ferrimagnetic behavior. Dielectric measurements were employed in order to determine the electrical permittivity, dielectric losses and conductivity values in a 10 Hz – 1 MHz frequency range.

Pure B a F e 12 O 19 and T i 4 + − M 2 + co-doped B a F e 11 T i 0.5 M 0.5 O 19 (M = Co2+, Ni2+, Zn2+) hexaferrites were synthesized by a co-precipitation method. X-ray diffraction (XRD) patterns confirmed the formation of single-phase M-type hexagonal structure with P 6 3 / m m c space group. The structural analysis indicated that T i − N i and T i − Z n co-doped samples enhanced the values of lattice parameters ( a , c ) and cell volume ( V ) in comparison to T i − C o sample. Scanning electron microscopy (SEM) was used to investigate the effects of co-doping on the microstructure, whereas the elemental composition of prepared samples was verified by the energy dispersive X-ray spectroscopy (EDX). Impedance spectroscopy measurements revealed a significant variation in the dielectric properties of T i 4 + − M 2 + co-doped samples which can be associated with the values of grain and grain boundary resistance. The magnetic hysteresis loops exhibited a ferrimagnetic behavior at room temperature. However, T i − N i and T i − Z n co-doped samples showed considerably high values of magnetization along with reduced coercivity. These variations in the obtained results are elucidated based on the site preferences of co-doped ions, mobility of charge carriers, and microstructure. Here, our findings of high dielectric permittivity, diminished dielectric tangent loss, better conduction, moderate magnetization and reduced coercivity for the T i − N i co-doped B a F e 11 T i 0.5 N i 0.5 O 19 sample make this composition favorable for electromagnetic absorbing applications.

The Phase diagrams of a ferrimagnetic mixed-spin (1/2, 3/2) hexagonal Ising nanotube with Core-Shell structure are investigated using the mean field approximation. For this, we have studied the effects of the exchange interactions and crystal field on the magnetic properties of the system. The results obtained show the appearance of critical and compensation behaviors, as well as first-order phase transitions terminating at isolated end-points in the ferrimagnetic phase domain at low temperatures.

A series of FeCo2O4 powders was initially synthesized using a hydrothermal method and subsequently calcined at various temperatures to produce the final product. Pure phase FeCo2O4 powders can only be formed in the temperature range of 950–1050 °C. In this work, we study the cation occupation, cation valence, bond length and bond angle changes of the pure phase FeCo2O4 powders formed in such a narrow temperature range. Octahedral lattice distortion in the pure phase FeCo2O4 samples has been observed. More tetrahedral Fe3+ and octahedral Co2+ are excited and exchanged their sites as the calcination temperature increases from 950 °C to 1000 °C, and part of Co3+ ions are reduced to Co2+ in the sample calcined at 1050 °C. The structure of the sample calcined at 1000 °C is close to that of the ideal FeCo2O4 spinel. Magnetic measurements show that ferrimagnetism and anti-ferromagnetism coexist in the pure phase FeCo2O4 samples. Interaction changes between ferrimagnetism and antiferromagnetism caused by the structural changes of the samples have been studied. Due to the pinning of the local anti-ferromagnetism to ferrimagnetism in the sample, the sample shows a Barkhausen jump below 150 K. As the measurement temperature increases further, the system enters into a reentrant spin glass state.

The structural and magnetic properties of Mn doped Nickel Chromite (Ni1-xMnxCr2O4, x = 0, 0.2, 0.3, 0.4, 0.6, 0.8) nanoparticles (NPs) were studied in detail. The X-ray diffraction analysis affirms normal spinel structure for all the samples and average crystallite size was found in the range 31–58 nm. The spinel structure of these nanoparticles was also confirmed by Fourier transform infrared spectroscopy which revealed the formation of tetrahedral and octahedral vibrational bands in the range 607 -628 cm−1 and 486 - 491 cm−1, respectively. Transmission electron microscopy images depicts less agglomerated and non-spherical shaped NPs. The temperature dependent zero field cooled and field cooled magnetic measurements revealed a paramagnetic to ferrimagnetic transition Tc at 87 K for NiCr2O4 NPs, which is shifted to low temperatures by Mn doping. This effect was attributed to cationic distributions between adjacent sites produced by Mn doping. M − H loops of Ni1-xMnxCr2O4 NPs revealed enhanced saturation magnetization with increase in Mn doping which is attributed to a large magnetic moment of Mn ions. Ni1-xMnxCr2O4 (x = 0.6 and 0.8) NPs show steps in their M − H loops because of exchange interactions between two sites of these NPs.

This study reports the first morphology and crystalline structure details of iron oxide nanoparticles in a comprehensive manner. A series of iron oxide nanoparticles were synthesized in 1-octadecene from iron(III) acetylacetonate with the aid of oleic acid surfactant and then followed by post thermal processes. Quantitative small and wide angle X-ray scattering analyses using synchrotron radiation sources were performed together with electron microscopy, infrared spectroscopy and thermogravimery, providing morphology and crystalline structure details. Larger size of nanoparticles are synthesized by higher loading of the surfactant. Prolate ellipsoidal nanoparticles, rather than spherical particles, are always synthesized in single unimodal and narrow size distribution. The individual particles are composed of core, core-shell interface, shell, and shell-surfactant interface, regardless of the sizes. Magnetite-like crystalline phases are predominant. In addition, wuestite-like crystalline phases are discernible as minor components. For a given particle, the size and distribution are varied very little by the post thermal proccesses. Nevertheless, the other morphology characteristics, as well as the crystalline phases are significantly influenced through the post thermal process with a mixture of nitrogen and oxygen. In particular, the core part is thickened, the density gap between the core and the shell is reduced, and ferrimagnetic magnetite-like crystallites are enlarged and more populated. Paramagnetic wuestite-like crystalline phases are decreased substantially or disappeared completely. These enhanced morphology and crystalline characteristics make great contributions to improve magnetization performances significantly. Overall, this study provides the well-controlled synthetic schemes and morphology/crystalline structure details that are essential for better applications of iron oxide nanoparticles in various advanced fields including biomedicine and nanotechnology.

A new hexaferrite with the composition (Ba,Pb)(Fe,Ti)9O15 was synthesized from lead(II) oxide flux, which lead to the incorporation of Pb2+ into the structure on the barium position. Like other ferrites, its structure can be described as the stacking of characteristic building blocks along [001]. Within the structure, the barium site is mixed occupied with lead. Octahedrally coordinated interstices are filled by iron and titanium in different ratios. Tetrahedra and trigonal bipyramids are solely occupied by iron. Wavelength dispersive X-ray spectroscopy provides the composition Ba0.69(1)Pb0.34(2)Fe7.28(7)Ti1.52(3)O15. Lastly, the compound shows ferrimagnetic behavior with a Curie temperature of TC = 309.3 °C and a strong indication for a magnetic phase transformation to ferromagnetic state at high magnetic field strengths and at temperatures below −123 °C.

The physical properties of the double perovskite A2BB'O6 are closely related to the B-site cationic arrangement, which directly affects the crystal morphology, magnetic coupling and electronic structure. Herein, the impact of B-site antisite defects on the magnetic and electronic properties of double perovskite Pb2FeOsO6 has been investigated using spin-polarized first-principles calculations. Our calculations demonstrate that B-site ordered Pb2FeOsO6 is a ferrimagnetic semiconductor with the saturated magnetic moment of ~2.27 μB f.u.−1, mainly generated from B-site Fe and B′-site Os antiferromagnetic coupling. With the introduction of B-site antisite defects, the crystal lattices nearly maintain the original structure of the ordered Pb2FeOsO6, although the internal atomic arrangements are reconstructed. Nevertheless, the saturated magnetic moment is sharply reduced in Fe/Os disordered configurations, which originates from the additional Os–Os and Fe–Fe antiferromagnetic coupling, and consequently induces Os–Os, Os–Fe and Fe–Fe spins interaction competition. Further electronic structure analyses indicate that the B-site antisite defects do not alter the semiconducting performance of Pb2FeOsO6. Our study sharpens the understanding of the effects of cationic ordering on the physical properties of double perovskites and provides an alternative avenue for tailoring their characteristics.

Ferrites are also termed as Ferrimagnetic ionic crystalline materials, with general formula MFe2 O4. Depend on the particle size, ferrite shows significant applications in the wide area. We have prepared Cr doped Zn Ferrite by co-precipitation method. The prepared ferrite materials were confirmed by XRD analysis. The XRD data confirms the formation spinal phase structure and by applying the debye scherrer formula, the particle was found in the nano range. The temperature dependent DC electrical conductivity was studied. The obtained result shows materials have semiconductor behaviour with the rise of temperature.

Ultrafine nickel ferrite and nickel ferrite/reduced graphene oxide nanocomposite materials have been synthesized by self-combustion method using glycine, citric acid and urea as chelating agent. The comparative analysis of structural and magnetic properties of the obtained materials in a temperature range of 300–900 °C has been performed. The changes in average particle sizes of spinel phase for NiFe2O4 and NiFe2O4/reduced graphene oxide materials have been analyzed from the point of view of the metal-organic complexes interaction and different mechanisms of gel formation for glycine, citric acid and urea based materials. The conditions of ferrimagnetic and superparamagnetic states formation of nickel ferrite nanoparticles have been investigated by Mossbauer spectroscopy.

Giant magneto-optical properties were achieved by adding Ce to ferrimagnetic YIG (Y3Fe5O12) ceramics. The amount of change in Faraday rotation was 144 deg./cm when 1at.% of Ce was substituted on the Y site of YIG ceramics, and the Faraday rotation of 990 deg/cm was obtained by 8at.% Ce substitution. Doping Ce in iron garnet can give a Faraday rotation function around 5 times higher than that of Bi (29 deg./cm per 1at.% of Bi), which is currently used in optical isolators for telecommunications. The in-line transmittance of 4at.% Ce:YIG ceramics (t = 0.5 mm) at 1550 nm was 62 %, and this ceramic exhibited excellent characteristics as an optical isolator.

This paper outlines the magnetic properties of a tri-layers nano-dicoronylene like-structure, using Monte Carlo simulations under the Metropolis algorithm in the Blume Capel model. The top and bottom layers are composed by S-spins (S = 0, ±1), While the middle layer is composed by σ-spins (σ=±3/2, ±1/2). Each layer contains 48 atoms. We establish, in six various planes, the ground state phase diagrams. Still, we present the thermal variation of partials and total magnetization and susceptibility for several values of exchange coupling interactions and crystal field. Also, the hysteresis cycles have been reported for selected values of temperature and exchange coupling interaction. The compensation and blocking temperatures values increases when increasing the exchange coupling parameter in the extreme layers.

Chronic kidney disease (CKD) is an increasing problem worldwide, usually detected by an increase of uremic toxins in the human bloodstream. In this study, Zn1-xMgxFe2O4 nanoparticles were synthesized and characterized as possible candidates for the adsorption of uremic toxins, such as urea, creatinine, and uric acid. The synthesis of nanoparticles from magnetic oxides of Fe, Zn, and Mg (Zn1-xMgxFe2O4, x = 0.0, 0.25, 0.5, 0.75, and 1.0) was carried out by sol-gel method at a heat treatment temperature of 500 °C for 60 min. The study evaluates the effect of replacing Zn2+ with Mg2+ cations within a zinc ferrite (ZnFe2O4), the crystalline structure, and the magnetic properties of nanoparticles. The synthesized samples were identified as ZnFe2O4 ferrite (JCPDS 22-1012) by X-ray diffraction. By the Vibration Sample Magnetometry technique, it was possible to observe an increase in the saturation magnetization value (Ms), as the content of Mg2+ cations decrease (x ≤ 0.5). The remnant magnetization (0.47–0.91 emu/g) and the coercive field (5–9 Oe) indicate a ferrimagnetic behavior of the synthesized nanoparticles. The samples have a quasi-spherical morphology and a size smaller than 16 nm, as determined by transmission electron microscopy (TEM). The Fourier Transform Infrared (FT-IR) technique showed characteristic absorption bands of the spinel ferrite M − O bonds for the ferrites ZnFe2O4 and Zn0·5Mg0·5Fe2O4. Hemolysis tests of the selected ferrites showed a hemolysis percent of less than 2.0% of cytotoxicity for suspensions of 10 mg of ferrite per milliliter of the aqueous medium. The selected samples of ZnFe2O4 and Zn0·5Mg0·5Fe2O4 were tested as adsorbent materials for uremic toxins removing up to 20% for uric acid, 77% for creatinine, and 85% for urea.

Composition dependence of martensitic transformations as well as the magnetic properties for the Ni2Mn1+xIn1-x (0.25 ≤ x ≤ 0.58) alloys were investigated by using the first-principles calculations. Key results demonstrate that the stability of parent austenite (A) decreases gradually with increasing Mn content whilst it is opposite for the martensitic phase. This causes the total energy difference between the austenite and martensite phases increscent with increasing Mn contents. When x = 0.33, the martensite transformation during cooling is PA→FA→NM. When x ≥ 0.42, an intermartensitic transformation occurs from modulated 6 M martensite to non-modulated (NM) martensite with the martensite transformation sequence of PA→FA→6M→NM. The martensitic transformation from austenite to martensite accompanies the transition from ferromagnetic to ferrimagnetic state. This is a typical magneto-structural coupling transformation. The analysis of the density of states demonstrates that the Ni 3d state plays an important role in the phase stability.

In the present work, we reveal a novel finding, that is, self-assembled grain boundary precipitates for realizing the magnetic-field-induced metamagnetic transition by employing low melting point metal in materials. This strategy has been experimentally verified in a well-established ferrimagnetic compound Mn2Sb by doping the bismuth (Bi) element with a low melting point of just 271.3°C. Bi solidifies later than the Mn2(Sb,Bi) main phase in (Mn2Sb)1-xBix system (the melting point of ~948°C for Mn2Sb), and aggregates spontaneously along the grain boundaries, forming Bi-rich grain boundary precipitates to coat main phase grains. This is very similar to the Nd-rich grain boundary phase in Nd-Fe-B permanent magnets. The fraction of Bi-rich grain boundary phase can be controlled by Bi-content. As a result, the magnetic field induced steep magnetoelastic transition from antiferromagnetic to ferrimagnetic is achieved in (Mn2Sb)0.89Bi0.11 alloy with giant multiple functional properties in Bi-doped Mn2Sb. Especially, the magnetic entropy change maximum nearly quadruples when Bi-doping increases from 0.03 to 0.11. Giant negative magnetoresistance of more than 65% under μ0∆H = 0–5 T, and magnetostrain of ~1802 ppm under μ0H = 8.5 T are obtained in (Mn2Sb)0.89Bi0.11. It should pave a way to achieve the magnetic transition and enhance the magnetoresponsive effects in designing similar coherent materials by employing low melting point metal doping to form the dual-phase heterogeneous structure.

The synthesis of the Ni0.5-xZn0.5-xCu2xFe2O4 (x = 0; 0.10 and 0.15) ferrite with the differential of pilot-scale production by the combustion reaction method was investigated for RAM application purposes. Combustion temperatures ranging from 682 °C to 738 °C were observed. All ferrites were sintered at 1200 °C for 1 h. A comprehensive study of the influence of substitution with Cu2+ in a partial and proportional way to the Ni2+ and Zn2+ ions, doping mode little reported in the literature, and also of the sintering process over the structural, textural, morphological, magnetic and electromagnetic properties of NiZnCu ferrites was performed. The XRD patterns of the ferrites as synthesized revealed the formation of the cubic structure of the inverse spinel as majoritary phase, and traces of hematite and zinc oxide as segregated phases. After sintering, it was proven the single-phase formation of cubic spinel ferrite structure. The introduction of Cu led to a reduction in the lattice parameter, whose values ranged from 8.337 to 8.385 A. The EDX results confirm the composition of oxides. The textural and morphological analyses confirmed the densest characteristic, with increase of particle size and reducing of surface area and pore volume after Cu-doping. All ferrites showed characteristics of soft ferrimagnetic material, where the increase in Cu content contributed to a slight reduction in saturation magnetization, whose values were of ~22–29 emu/g for the as synthesized ferrites and ~71–85 emu/g for the sintered ones. The best result of electromagnetic absorption in X-band was presented by the sintered ferrite with 0.3 mol of Cu, reaching an attenuation of 99.8% at 11.5 GHz frequency, thus confirming the efficiency of the pilot-scale combustion synthesis in obtaining a ferrite with great potential for RAM application.

With the aim to produce a material with magnetic and semiconductor properties, a lanthanide bismuth-ferrite type material is proposed in this work. Polycrystalline samples of Dy2Bi2Fe4O12 were produced following the standard solid-state reaction method. Structural characterization through the X-ray diffraction technique evidences that the synthesized ceramic crystallizes in a perovskite-like orthorhombic structure, belonging to the Pnma (#62) space group. Scanning electron microscopy images revealed the granular nature of the samples with mean grain sizes of nanometric order. X-ray energy dispersion spectra allowed establishing that in the samples there are no elements different from those expected in the stoichiometric proportions suggested by the chemical formula of the compound. Studies of electrical behavior were carried out using I–V curves and electrical permittivity as a function of frequency and temperature, which show the diode varistor feature of this material with a marked Maxwell–Wagner-type trend. The semiconductor band gap was determined from the analysis of diffuse reflectance spectra that reveal Eg = 1.88 eV. Temperature-dependent magnetization curves for applied fields of 1.0, 5.0 and 10 kOe showed the behavior expected for ferromagnetic type materials, with strong evidence of magnetic frustration causing irreversibility in curves obtained from Zero Field Cooling and Field Cooled measurement procedures. The magnetization hysteresis curves at temperatures of 50, 200 and 300 K exhibit a ferromagnetic response with evidence of superparamagnetic effects due to the significant presence of nano-sized ferromagnetic grains. Based on the obtained results, it can be affirmed that the material behaves like a soft ferrimagnetic semiconductor with low coercive field (between 500 Oe and 700 Oe) and remnant magnetization (between 2.15 × 10−4 emu/g and 3.25 × 10−4 emu/g) that would have eventual technological implications in the spintronic industry.

Zero thermal expansion (ZTE) materials, particularly metals, have important applications in precision manufacturing. Here, ultra-low thermal expansion over a significantly broadened temperature interval is realized by tuning Gd content in ferrimagnetic(FIM) Gdx(Dy0.5Ho0.5)1-xCo2 compounds. The achieved coefficients of thermal expansion αl ~+1.3 × 10−6K−1 (5-220K), -1.5 × 10−6K−1 (220-280K) for x=0.5 are even better than the well-known ZTE Invar alloy Fe0.65Ni0.35, while the operation temperature interval is much wider. The origin is closely related to the regulation of magnetostrictive process by rare earth ions along c-axis in the rhombohedral FIM structure. Our work highlights the advantageous ways to generate ultra-low thermal expansion in magnetocaloric materials.

This study compares the AC susceptibility, FC-ZFC and hyperfine interactions of Sr(CoxZrx) Fe12-2xO19 and Sr(NixZrx)Fe12-2xO19 hexaferrites (HFs) manufactured via ultrasonic route. The formation of M-type hexaferrites have been confirmed by X-ray powder diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR) and high-resolution transmission electron microscopy (HR-TEM) techniques. Scanning electron microscopy (SEM) presented the hexagonal-platelet morphology of products. The variation in isomer shift, line width, quadrupole splitting and hyperfine magnetic field values of them have been governed by Fe-57 Mossbauer spectroscopy which showed that Co2+ and Zr4+ ions located at generally octahedral and 2b sites, while Ni2+ and Zr4+ ions located at octahedral 12k and 4f(2) sites. Measurements of magnetization versus temperature (M-T) and AC susceptibility versus temperature were carried out. The various synthesized HFs displayed ferrimagnetic behavior in the temperature interval of 10-325 K. Super-spin glass-like behavior was noticed at lower temperatures. Neel-Arrhenius and Vogel-Fulcher models were used to explore the experimental AC susceptibility. It was showed that a lower Co-Zr substitution content leads to strengthen the magnetic exchange interactions, however even low Ni-Zr substitution content provoke a reduction in magnetic exchange interactions. WOS:000560004300010 2-s2.0-85087295384

The solid-state magnetic cooling (MC) relying on magnetocaloric effect (MCE) of magnetic materials is recognized as a promising energy efficiency and environmentally friendly technology. However, there is still a large gap between the fundamental materials in the laboratory developing stage and the practically realizable applications. In this paper, a new series of B-site ordered RE2ZnMnO6 (RE = Gd, Dy and Ho) perovskites are successfully fabricated, and their structural and magnetic properties together with the cryogenic magnetocaloric performances are studied in detail. All the RE2ZnMnO6 compounds are found to crystallize in the B-site ordered orthorhombic (double perovskites) structure with the space group of P121/C1. The magnetic ground state are confirmed to be a ferromagnetic (FM) coupling for Gd2ZnMnO6, whereas, ferrimagnetic (FIM) coupling for Dy2ZnMnO6 and Ho2ZnMnO6 based on the magnetic measurements and first principle calculations. The ordering temperatures (TM) are determined to be ~6.4 K for Gd2ZnMnO6, ~10.4 K for Dy2ZnMnO6, and ~6.8 K for Ho2ZnMnO6, respectively. Furthermore, several vital parameters for determining the magnetocaloric performances including -ΔSMmax (magnetic entropy change peak values), TEC(2) (temperature-averaged magnetic entropy change) and RCP (relative cooling powers) are evaluted to be 15.17, 14.44 J/(kgK) and 226 J/kg for Gd2ZnMnO6, 8.32, 8.17 J/(kgK) and 208 J/kg for Dy2ZnMnO6, and 13.19, 12.68 J/(kgK) and 246 J/kg for Ho2ZnMnO6, with the field change ΔH = 50 kOe, respectively. It is worthly noted that Gd2ZnMnO6 exhibits relatively great magnetocaloric performances below 10 K, which suggests that Gd2ZnMnO6 is a competitive candidate for cryogenic magnetic cooling.

In order to enhance the magnetoelectric property of LaFeO3, we have considered co-substitution of Al3+ and Ti4+ in La3+ and Fe3+ sites. Rietveld refinement of the observed XRD patterns confirms that the pristine (LaFeO3, LFO) crystallizes in orthorhombic Pbnm (centrosymmetric) space group whereas the doped samples (La0.9Al0.1Fe0.9Ti0.1O3, LAFTO) crystallizes in orthorhombic Pna21 (non-centrosymmetric) space group due to co-doping of Al3+- Ti4+ in LFO. Analysis of magnetic data confirms the antiferromagnetic phase of LFO and LAFTO possess ferrimagnetic spin structure with enhanced magnetization. Besides this ferroelectric polarization at room temperature is also improved in the co-doped sample of LAFTO (Pmax = 0.25 µC/cm2). Spontaneous polarization is predicted from first principle calculation for LAFTO to be ~ 12.31 µC/cm2. The dielectric loss factor of LAFTO reduces significantly and the dielectric strength is also enhanced compared to that of LFO. Experimental results are in agreement with these findings extracted from ab initio calculations using density functional theory. The present doped sample LAFTO has improved magnetic, dielectric, ferroelectric properties and magnetoelectric coupling compared to that of LFO, would have the high potential for applications in multiferroic devices.

Indium-substituted yttrium iron garnet samples, Y3Fe5−xInxO12 (x = 0–0.7, step 0.1), were prepared using a citrate solgel method. Synchrotron X-ray diffraction (SXRD) measurements combined with the Rietveld refinement technique were used to investigate the crystallization, structure parameters and lattice distortion in the samples. Magnetization and Curie temperature of the samples were measured with the SQUID and VSM equipments. The non-magnetic indium ions were found to reside at the octahedral sites, leading to an increase of the total magnetization and a decrease in the Curie temperature. Molecular field coefficients Naa, Ndd and Nad were determined by fitting the experimental thermomagnetization curves in the framework of a two-sublattice ferrimagnetic model. The stiffness constant of the spin waves, D, in these samples was calculated based on the exchange interaction constants, Jij, and its temperature dependence was derived for the sublattice magetizations. The calculated results for D(T) are in good agreement with the experimentally measured data and are significantly large around room temperature.

A detailed study has been carried out of the static and dynamic magnetic properties of ferrimagnetic spinel MgFe1.2Ga0.8O4 nanoparticles (NPs), including the measurements of low-field dc-magnetization M(T) under zero-field-cooled (ZFC) and field-cooled (FC) conditions and ac-susceptibility χac(T) at different frequencies (f) and amplitudes of the ac-field (Hac). Below, a Curie temperature (TC), a clear magnetic irreversibility (MZFC(T) ≠ MFC(T)), as well as a broad peak in both MZFC(T)–MFC(T) magnetizations have been observed. At T ≪ TC, the two distinct, frequency-dependent peaks at Tp1 ≈ 9 K and Tp2 ≈ 14 K in the imaginary part of the ac-susceptibility χac''(T) have been found. Their positions have been consistent with those of the anomalies detected on the temperature dependence of the magnetic contribution to the heat capacity Cmag(T), and a sharp decrease of the MZFC(T) magnetization near ≈ 10–20 K. It was revealed that the fitting of the frequency dependence of the peaks’ positions (Tp1(f) and Tp2(f)) in the imaginary part of ac-susceptibility χac''(T) using the Neel-Arrhenius law yields unphysical values of the relaxation time (τ0) and, therefore, these results ruled out a possibility of an existence of superparamagnetic (SPM) clusters in the system. On the other hand, the Tp1(f) and Tp2(f) dependences followed both the Vogel-Fulcher law and the power law. These observations indicate that, a complex magnetic state in MgFe1.2Ga0.8O4, realized in the low temperature region, may likely be related to a progressive freezing of magnetic clusters.

In the present work, the influence of cationic surfactant CTAB (cetyltrimethylammonium bromide) on size, shape and coalescence behaviour of cobalt ferrite nanoparticles (CFNPs) synthesized via hydrothermal method is reported. Pure CFNPs show no additional peaks, whereas α-Fe2O3 phase is observed in CTAB added CFNPs upon annealing. FT-IR analysis confirms the formation of M − O vibrational bands (metal -oxygen) at tetrahedral A-site and octahedral B-site for both samples. SEM observations reveal less agglomeration and smaller particle size for surfactant added CFNPs. Raman spectral study confirms the formation of cubic spinel structure and Raman active modes of CTAB added CFNPs. UV–Vis spectra indicate a decrease in the energy band gap with annealing. The dielectric constant of surfactant added CFNPs decreases with increasing applied frequencies for both real and imaginary, but ac conductivity increases with increasing frequencies. Two sextet patterns of Fe3+ trivalent ions from tetrahedral and octahedral sites are observed in Mossbauer spectra. VSM study indicate the ferrimagnetic nature of CTAB added CFNPs. The electrochemical analysis reveals the pseudocapacitive nature of working electrode prepared by CTAB added CFNPs.

Polycrystalline samples of Mg substituted lithium ferrites (Li1-xMg2xFe5-xO8 (LMFO) (x = 0, 0.003, 0.005, 0.007 and 0.01) have been prepared by conventional solid-state reaction. X-ray diffraction patterns revealed the formation of a single-phase cubic structure with P4132 space group. The dielectric constant of lithium ferrite increased with Mg substitution attaining a maximum value for x = 0.005 (er = 3034, tan δ = 0.001at 1 MHz) at room temperature. Temperature-dependent dielectric response in the high frequency range (1 MHz–1 GHz) showed the relaxor behaviour of the dipoles, evident from the shift in the loss tangent with frequency. The activation energy of LMFO is found to be in the range of 1.39 - 0.35 eV. An enhanced permeability is found to be ∼29 for x = 0.007 at 1 MHz, RT. The variation in permeability is attributed to the variation in thickness of the domain walls and magneto-crystalline anisotropy. The temperature-dependent magnetization curves reveal the ferrimagnetic transition of LFO at 600 °C, which reduced with Mg substitution. Magnetic hysteresis loops showed the highest saturation magnetization (Ms = 54.6 emu/g) for x = 0.007 among all the samples. The magnetic properties are explained by considering Neel’s two sub-lattice model. Thus, LMFO samples, (especially with x = 0.005) are very promising for circulator and phase shifter applications.

In this paper, we have studied the magnetic properties of a bi-layer naphthalene-like nano-structure with RKKY (Ruderman-Kittel-Kasuya-Yoshida) interactions, using Monte Carlo simulations. The system consists of two naphthalene-like magnetic planes, with mixed spins σ = 7/2 and S = 1, separated by L non-magnetic layers. In the first part of this study, the ground state phase diagrams for zero temperature are reported and discussed. In the second part, we investigate the effect of the RKKY interactions on the magnetizations and susceptibilities of the system, for non-zero temperature values. It is found that the value of the blocking temperature decreases when increasing the number of non-magnetic layers. Furthermore, the effect of the ferrimagnetic parameter (JSσ) on the blocking temperature behavior has been investigated. Finally, the effect of different physical parameters, namely the number of non-magnetic layers, the ferrimagnetic parameter, the crystal field and the temperature, on the magnetic hysteresis cycles are illustrated.

Zinc and cadmium based cobalt ferrites ZnxCd0.375-xCo0.625Fe2O4 (where x = 0, 0.075, 0.125, 0.25) were successfully synthesized by a facile co-precipitation technique. Structural, optical and magnetic characteristics of the doped ferrites were systematically analyzed. X-ray Diffraction (XRD) pattern confirmed the formation of cubic spinel structure in all samples. Scanning electron microscopic analysis of surface morphology revealed cubic and spherical shaped ferrite particles. Fourier transform infrared (FTIR) spectroscopy confirmed the existence of metal oxygen (M − O) bonding in the prepared samples. Moreover, the prepared samples exhibited two frequency bands corresponding to phonon vibrational stretching in both octahedral and tetrahedral lattice positions. The optical properties were investigated in detail through photoluminescence (PL) spectroscopy and Raman spectroscopy. The PL spectrum confirmed the strong emission peaks in the ultraviolet to visible region of all the samples. Further, four active Raman modes, associated with cubic spinel structure are identified in all prepared samples. Finally, the magnetic characteristics are evaluated by using vibrating sample magnetometer (VSM) revealing ferrimagnetic and soft magnetic behavior of the samples. As the Zn and Cd co-doping in Co was increased, the Hc was decreased. The magnetic studies show the maximum Hc of 576 Oe for Cd doped cobalt ferrite, and maximum saturation magnetization (Ms) for Zn–Cd doped cobalt ferrite. It is envisaged that the newly prepared Zn–Cd co-doped cobalt ferrite would be appropriate for a number of important applications, for example, magnetic recording devices, sensors, actuators, high-density data storage devices, and biomedical equipments.

We report the successful synthesis of Ba0.83Ca0.10Sr0.07TiO3–MnFe2O4 multiferroic composites showing significant improvement in electromechanical and magnetoelectric properties. All the composite samples have formed a diphasic perovskite-ferrite composite without the presence of any impurity or intermediate phase. The bare as well as composite samples have shown classical dielectric behavior even at higher ferrite substituted samples. The electrical characteristics of composite samples have shown slight deterioration, which is mainly attributed to non-ferroelectric MnFe2O4. However, the composites still exhibit high enough piezoelectric behavior and the modification in the electromechanical response of composites is mainly caused by a change in applied stress with MnFe2O4 addition. The M-H loops of composites have demonstrated a ferrimagnetic behavior with a substantial increase in saturation magnetization on increasing the ferrite concentration. Further, the composites have shown better coupling between the ferroelectric and ferrimagnetic phases, which has resulted in an improved magnetoelectric characteristic. The role of oxygen vacancies on ferroelectric and magnetic properties of prepared composites has been systematically studied.

Here we report ambient pressure synthesis, magnetic and dielectric properties of BiCu3Ti3(Fe/Mn)O12 and BiCu2.5Mn0.5Ti2.5Fe1.5O12. Both the samples are crystallized in a cubic Im-3 space group. The antiferromagnetic ground state of A-site copper in Bi2/3Cu3Ti4O12 is differently affected by substitution of nonmagnetic Ti4+ by magnetic Fe and Mn ions in B-site. In contrast to the Mn substitution, the antiferromagnetic ordering of A-site Cu is robust towards Fe substitution. The substitution of iron for Ti4+ initially weakens the antiferromagnetic structure of A-site Cu and eventually it results in the crossover from antiferromagnetic to ferrimagnetic state, whereas the Mn substitution quickly turns antiferromagnetic to ferrimagnetic state. For x > 1.0 Fe-doped sample and low Mn-doped samples exhibit phase separation where the ferromagnetic like phase coexists with antiferromagnetic phase. The glassy magnetic state is realized for x = 1.0 Fe doped sample. The magnetic ground state strongly influences the dielectric behavior of the samples. Near room temperature the dielectric constant value is ~2000 for BiCu3Ti3FeO12, whereas for BiCu2.5Mn0.5Ti2.5Fe1.5O12 the value is much lower (

Two-dimensional (2D) nanostructures with robust room-temperature ferromagnetism or ferrimagnetism have attracted significant attention because of their potential applications in fundamental research, integrated circuits, and next-generation spintronic devices. Magnetic order in 2D nanostructures can be divided into intrinsic and defect-induced magnetism. In this review, we highlight recent progress on the synthesis and magnetic properties of intrinsic 2D magnetic van der Waals nanostructures, such as VS2, CrI3, and 2D metal-organic frameworks. In addition, defect-induced magnetism in several systems such as graphene, MoS2 nanosheets, and Ni3N nanosheets are briefly introduced. Finally, we discuss future prospects for this booming research area.

We demonstrated domain wall (DW)-induced anomalous magnetoresistance (MR) generated in asymmetric and symmetric ferrimagnetic Tb/Co multilayered, and Tb–Co alloyed wires. The extraordinary Hall effect (EHE)-induced circulating currents in the vicinity of DWs between longitudinal voltage probes are assigned to the anomalous MR. A large anomalous MR ~1.5% was obtained in the asymmetric Tb/Co multilayered wire. The large MR can be attributed to an addition of spin Hall current with a long coherence length from an adjacent Pt layer. These results open new possibilities for the use of ferrimagnetic multilayered wires beyond multi-function devices.

Spinel ferrite Co1–2xNixMnxFe2–yCeyO4 (0.0 ≤ x = y ≤ 0.3) nanoparticles (NPs) were prepared by sol-gel auto-combustion method. The synthesized NPs were examined using several techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) coupled with EDX and elemental mapping, transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), and a vibrating sample magnetometer (VSM). The analysis of the crystal structure and the phase identification of samples indicates the formation of spinel cubic phase with the occurrence of CeO2 as secondary phase when the content of Ce substitution element increases. In addition, all produced samples exhibit cubic symmetry with space group Fd3m. TEM confirms the presence of two phases, i.e., the cubic spinel ferrite and the cubic cerium oxide (CeO2). The characteristics of hysteresis loops reveal the soft ferrimagnetic nature of the different synthesized samples. The saturation (Ms) and remanent (Mr) magnetizations fall on increasing the content of substituting elements. Compared with pure CoFe2O4 NPs, the value of coercive field (Hc) slightly increases for x = y = 0.1 and x = y = 0.2 NPs. Then, Hc reduces with further increasing the x and y contents. The squareness ratio is found to be in the 0.528–0.400 interval, indicating the single domain NPs with uniaxial anisotropy for the different produced NPs. The magneto crystalline anisotropy constant (Keff), anisotropy field (Ha), magneton number (nB) and the demagnetizing field (N) were also determined and discussed.

Co-substitution of iron and manganese in ZrO2 and the subsequent structural analysis, mechanical, magnetic and in vitro evaluation is presented. Five different compositions have been synthesized by varying the concentrations of iron and manganese addition in ZrO2 system. Characterization results revealed the concomitant effect of dopant concentration and annealing temperature in influencing the phase behaviour of ZrO2 alongside the formation of secondary phase comprising bixbyite [(Fe,Mn)2O3] structure. XPS analysis confirmed the oxidation state of constituent elements in the composite system. Iron and manganese inclusions in ZrO2 facilitated ferrimagnetic characteristics and moreover enhanced magnetization is noticed during the crystallization of (Fe,Mn)2O3. Pore free microstructures together with the enhanced hardness and Young's modulus values have been determined in the investigated compositions. In vitro studies displayed good biocompatibility, cell viability and negligible toxicity of ZrO2 system comprising iron and manganese.

Maghemite nanoparticles were synthesized using sol–gel method. The structural study of the samples was done using XRD technique. Zero-field-cooled (ZFC) and field-cooled (FC) magnetization versus applied field (M−H) measurements were conducted between −5 T and +5 T at several temperatures and several field cooled values. The XRD study revealed that the average diameter of the nanoparticles to be around 20 nm. XRD patterns show mainly maghemite phase with very slight hematite phase. The coercively was found to decrease sharply with temperature up to 200 K above which it remains almost constant. Negative and positive horizontal exchange bias was obtained in the ZFC state and only negative exchange bias was obtained at all field cooled values. The magnitudes of the exchange bias were found to decrease sharply with temperature and disappearing above 100 K. Negative and positive vertical loop shifts were obtained in the ZFC state and only positive loop shifts were obtained at all field cooled values. The magnitudes of the loop shifts were found to decrease sharply with temperature and disappearing above 50 K. These results are discussed and attributed mainly to the exchange coupling between the maghemite (ferrimagnetic) and hematite (antiferromagnetic) phases in the nanoparticle system.

Multiferroic particulate composites have been fabricated by taking the morphotropic phase boundary composition of ferroelectric phase Bi(Ni1/2Ti1/2)O3–PbTiO3 and magnetic phase (Ni,Zn)Fe2O4. The ferroelectric phase has coexisting monoclinic and tetragonal perovskite structures with space group Pm and P4mm, respectively whereas the magnetic phase has spinel cubic structure with space group Fd 3 ‾ m. Rietveld structural analysis for the each components of composite reveals that the tetragonality (c/a) of the ferroelectric phase continuously increases with increasing the concentration of magnetic phase and finally transform in rhombohedral (R 3 ‾ c) phase suggesting partial ionic diffusion between ferroelectric and magnetic phases. Composition dependent Mossbauer spectra of (1-x)Bi(Ni1/2Ti1/2)O3–PbTiO3/x(Ni,Zn)Fe2O4 reveals the superparamagnetic like behavior for the ferroelectric rich composition with x = 0.2. The magnetic ordering increases for the composition with x = 0.4 and 0.6 which completely transforms into ferrimagnetic for the composition with x = 0.9. Unlike the ferroelectric or magnetic components that do not exhibit the magnetoelectric response separately, significant value of magnetoelectric coefficient (> 30 mV/Oe-cm) in (1-x)Bi(Ni1/2Ti1/2)O3–PbTiO3/xNi0.6Zn0.4Fe2O4 composite makes it promising for multifunctional applications.

This paper emphasizes the structure, morphology, optical, and magnetic properties of sonochemically prepared terbium-substituted cobalt ferrite nanoparticles, CoTbxFe2-xO4 (0.00 ? x ? 0.10). The formation of cubic spinel nanosized ferrite structure was confirmed by X-ray diffraction (XRD), Field-emission scanning electron microscopy (FE-SEM), and Fourier-transform infrared (FT-IR) spectroscopy. The crystallites sizes were found in the range of 11–14 nm. Ultraviolet–visible percentage diffuse reflectance investigations were performed on pristine and Tb3+-doped cobalt spinel ferrite CoFe2O4 nanoparticles. The direct energy band gap (Eg) values were determined by applying the Kubelka–Munk theory and Tauc plots were found to be in a narrow band range of 1.37–1.44 eV. Analyses of magnetization versus the magnetic field (M(H)) were performed. The magnetic parameters, including the saturation magnetization (Ms), squareness ratio (SQR = Mr/Ms), magnetic moment (nB), remanence (Mr), and coercivity (Hc) were evaluated. The M(H) curves exhibited a soft ferrimagnetic nature. It was demonstrated that the Tb3+ substitutions strongly influenced the magnetization data. Indeed, the Ms, Mr, Hc, and nB values decreased with increasing Tb3+ substitution. © 2019 Elsevier Ltd and Techna Group S.r.l. Deanship of Scientific Research, King Saud University: 2018-209-IRMC, 2017-576-IRMC This study was supported by the Deanship of Scientific Research (project applications 2017-576-IRMC and 2018-209-IRMC ) of Imam Abdulrahman Bin Faisal University (Saudi Arabia).

Sr-substituted polycrystalline lithium ferrites (Li1-xSr2xFe5-xO8 (LSFO); x = 0, 0.003, 0.005, 0.007, 0.01) have been synthesized by solid-state reaction method. The effect of Sr substitution on structural, microstructural, dielectric and magnetic properties of LSFO ferrites are studied systematically. The Rietveld refinement of the XRD patterns revealed a single phase cubic structure for all the compositions and the lattice constants and unit cell volume are enhanced with Sr concentration. Further, Sr substitution led to a structral distortion and modified Fe - O bond length and Fe - O - Fe in both the tetradedral and octahedral positions. The surface morphology of LSFO ferrites displayed a dense microstructure and the average grain size is found to be reduced with Sr concentration, which showed that Sr inhibited the grain growth. The dielectric and magnetic properties of these samples are measured as a function of frequency (1MHz to 1GHz) and temperature (−140 °C to 250 °C). The sample with x = 0.003 exhibited the best dielectric response (er = 5986, tanδ = 1.17 @1MHZ, at RT). A shift in the critical temperature (160 oC– 200 °C) with diffuse transition has been observed which signifies a relaxor behavior, and analyzed by using Vogel– Fulcher and modified Curie Weiss laws. This behavior is complimented by the magnetic measurements also. The activation energies have been calculated by using the Arrhenius relation and found to be in the range of 0.142 eV - 0.07 eV. The variations in the permeability values are attributed to the magneto-crystaline anisotropy, thickness of domain walls and inner stress. The M-T measurements showed that the Tc of the samples decreased with Sr content whereas magnetization value at RT enhanced significantly. However, the M-H curves shifted towards negative fields and displayed the soft ferrimagnetic response. The maximum saturation magnetization is found to be 61.5 emu/g for x = 0.007 sample.

This paper focused on the structure, optic and magnetic properties of niobium substituted Co0.5Mn0.5NbxFe2-xO4 nanoparticles (NPs) that synthesized by hydrothermal method. The synthesis of cubic spinel ferrite structures was confirmed via XRD, SEM along with EDX and elemental mapping, TEM and FT-IR. The crystallite size of the products was found between 17 and 18 nm. The %DR-UV-visible spectrophotometer revealed that the band gap values are 0.37, 0.52, 0.54, and 0.46 eV for each substitution respectively. Room temperature (RT) and 10 K magnetization measurements were performed on spinel Co0.5Mn0.5Fe2-xNbxO4 (0.00 ≤ x ≤ 0.10) NPs by VSM. The specific magnetic parameters such as saturation magnetization (Ms), remanence (Mr), coercivity (Hc), magnetic moment ( n B ) and squareness ratio (SQR = Mr/Ms) were determined and evaluated. The M(H) curves showed ferrimagnetic nature at RT and 10 K. The Nb3+ ion substitution significantly improves the magnetizations data. An enhancement in the Ms, Mr, and n B values was observed in substituted products compared to pristine one. The highest values were obtained for x = 0.04 product. The obtained magnetic data are primarily derived from the substitution of Fe3+ ions with Nb3+ ions that will strengthen the super-exchange interactions.

Manifold degeneracy in the zero field cooled (ZFC) state of the Ising like spin system, Ca3Co2O6, is progressively alleviated by magnetic field (H) at low temperature (T). Field excursion after ZFC stabilizes ferrimagnetic (FIM) state above Tsf ~7K which converts to ferromagnetic (FM) state at high-H. Whereas, various metastable states have been created by H excursion of degenerate ZFC state below Tsf and finally it switches to FM state. In contrast, field cooling at 5kOe supports stable FIM ordering for all temperatures in low fields, which converts to the FM state at increasingly higher-H with decrease in T. This thermomagnetic irreversibility (TMI) below ~7K indicates non-ergodic nature of the ZFC state and it persists till the system fully saturates. It is obvious that both the hindered kinetics of H-T induced first order intermediate phase to FIM transformation and interplay of different interchain interactions like 1st nearest neighbor (nn) and 2nd nn with thermal energy are playing a crucial role in appearance of such type of TMI in this spin system.

The ferrite having the general chemical formula Mg1-xZnxFe2-xCrxO4 (x = 0.0, 0.1, 0.3, 0.5 and 0.7) prepared by the solid state technique. The XRD analysis depicted the presence of single phase cubic spinel structure. They showed an increasing trend of lattice parameter with the expansion of the spinel lattice which resulted from the partial incorporation of larger radii. The FT-IR absorption bands are observed at 590 and 430 cm−1 for tetrahedral and octahedral location. These bands are shifting toward 604.7 and 474.15 cm−1 for Zn–Cr substitution due to the change in Me–O covalence. DC electrical resistivity has found to show the highest magnitude 107 Ω cm at x = 0.1, decreases with further increase in content. The hysteresis curves measured at 300 K demonstrate the coercivity and it varies from 146.33 to 9.427 Oe for increasing the content which confirms decreasing the grain size as well as soft ferrimagnetic material.