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Two- and tree-component spinel-polymer composites were produced by thermal pressing. The initial components were chosen as CoFe 2 O 4 and Ni 0.4 Cu 0.2 Zn 0.4 Fe 2 O 4 spinels that were produced using the sol-gel method. The ratio between spinel phases varied from 1:3 to 3:1. As a polymer, fluorinated ethylene propylene was used. The concentration of the spinels in the polymer matrix was fixed at 20 mass.%. Using XRD, SEM, and high-frequency spectroscopy, the correlation between the composition, structure, and electrodynamic characteristics of composites was established. It was found that the parameters of the unit cell of ferrite fillers do not change when filling the polymer. The RL values for the initial CoFe 2 O 4 /FEP and Ni 0.4 Cu 0.2 Zn 0.4 Fe 2 O 4 /FEP were in the range of −14.5 ... -24.2 dB and −10.4 ... -14.1 dB, respectively, which is lower than for ferrites without a polymer matrix. The maximum values of RL (as a module) were marked for CoFe 2 O 4 /FEP. Obtained values of the reflection loss coefficient in the range of 5–10 GHz open broad perspectives for the development of materials for electromagnetic absorption and 5G technology. [ABSTRACT FROM AUTHOR]

Abstract Jacobsite is a relatively rare mineral of composition MnFe2O4, found in Urandi (Bahia State) in Brazil. It is also a common species in the deep-sea manganese nodules, attracting the interest of many mineral-extracting companies. Because of its spinel constitution similar to magnetite, Jacobsite is commonly called a manganese-ferrite. However, the manganese/iron content may vary substantially according to its origin, demanding specific studies in each case. The Jacobsite mineral inspired our laboratory synthesis of the analogous manganese ferrite nanoparticles. The direct synthesis by the coprecipitation method has not been successful; however, it can be carried in the presence of citrate ions, yielding strongly magnetic nanoparticles, with a maximum magnetization of 45.6 emu.g1. Although they were structurally identical to Jacobsite, the mineral from Bahia exhibited a rather weak magnetism, because it involves a ferrimagnetic coupling. For this reason, the synthetic method seems to provide a better way of obtaining strongly magnetic manganese ferrites. These magnetic nanoparticles have been investigated in detail, including their interaction with diatoms, providing interesting magnetic bio-silicate carriers in drug delivery.

It is well‐established that oxidation of a stepped surface can lead to the formation of 1D metal oxide nanowires along the steps. However, it is still uncertain how the extent of surface oxidation impacts the characteristics of these nanowires. Ab initio study of the effect of the oxidation state of a nonmagnetic vicinal Au surface on the magnetic properties of 1D Mn nanowires formed on the step edge is presented. Herein, the magnetic properties and electronic structure of two different types of nanowires are investigated: 1D manganese oxides (MnO) and 1D dioxides (MnO2), which correspond to different levels of oxidation of the substrate surface. [ABSTRACT FROM AUTHOR]

Controlling the magnetic anisotropy of materials is important in a variety of applications including magnetic memories, spintronic sensors, and skyrmion‐based devices. Ru‐substituted La0.7Sr0.3MnO3 (Ru‐LSMO) is an emerging material, showing tilted magnetic anisotropy (TMA) and possible nontrivial magnetic topologies. Here anisotropic in‐plane magnetization is reported in moderately compressed Ru‐LSMO films, coexisting with TMA. This combination is attractive for technological applications, such as spin‐orbit torque (SOT) based devices and other spintronic applications. A microstructural analysis of films of this material is presented, and Ru single ion anisotropy and strain‐induced structural mechanisms are found to be responsible for both the in‐plane anisotropy and the TMA. The manifestation of these properties in a correlated oxide with Curie temperature near room temperature highlights an attractive platform for technological realization of SOT and other spintronic devices. Illustrating the mechanisms behind these properties provides the necessary engineering space for harnessing these phenomena for practical devices. [ABSTRACT FROM AUTHOR]

Abstract Controlling the magnetic anisotropy of materials is important in a variety of applications including magnetic memories, spintronic sensors, and skyrmion‐based devices. Ru‐substituted La0.7Sr0.3MnO3 (Ru‐LSMO) is an emerging material, showing tilted magnetic anisotropy (TMA) and possible nontrivial magnetic topologies. Here anisotropic in‐plane magnetization is reported in moderately compressed Ru‐LSMO films, coexisting with TMA. This combination is attractive for technological applications, such as spin‐orbit torque (SOT) based devices and other spintronic applications. A microstructural analysis of films of this material is presented, and Ru single ion anisotropy and strain‐induced structural mechanisms are found to be responsible for both the in‐plane anisotropy and the TMA. The manifestation of these properties in a correlated oxide with Curie temperature near room temperature highlights an attractive platform for technological realization of SOT and other spintronic devices. Illustrating the mechanisms behind these properties provides the necessary engineering space for harnessing these phenomena for practical devices.

A new double double perovskite of ideal composition CaMnCoWO6 has been synthesised at high pressure. The structure is tetragonal (P42/n, a=7.6651(3), c=7.6822(3) Å) and disorder between A‐site Mn2+ and B‐site Co2+ leads to a Co‐rich off‐stoichiometric composition CaMn0.8Co1.2WO6 [Ca(Mn0.65Co0.35) (Co0.86Mn0.14)WO6]. An unusual combination of commensurate and incommensurate spin orders (A‐site Mn/Co spins with propagation vector (0.5 0.5 0.5) and B‐site Co/Mn spins with (0.5 0.42 0.5)) is observed below a magnetic transition at TC=18 K. This is the first discovery of complex magnetism in the double double perovskite family. [ABSTRACT FROM AUTHOR]

A new double double perovskite of ideal composition CaMnCoWO6 has been synthesised at high pressure. The structure is tetragonal (P42/n, a=7.6651(3), c=7.6822(3) Å) and disorder between A‐site Mn2+ and B‐site Co2+ leads to a Co‐rich off‐stoichiometric composition CaMn0.8Co1.2WO6 [Ca(Mn0.65Co0.35) (Co0.86Mn0.14)WO6]. An unusual combination of commensurate and incommensurate spin orders (A‐site Mn/Co spins with propagation vector (0.5 0.5 0.5) and B‐site Co/Mn spins with (0.5 0.42 0.5)) is observed below a magnetic transition at TC=18 K. This is the first discovery of complex magnetism in the double double perovskite family. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the magnetic properties of mixed nanocrystalline Zn/manganese oxide compounds synthesized by a hydrothermal method. These compounds are designed as (ZnO)1−n(MnO)n, where index n ranges from 0.05 to 0.60. The results of magnetic measurements, including AC magnetic susceptibility as a function of temperature (up to 160 K) and frequency (from 7 Hz up to 9970 Hz), as well as DC magnetization in magnetic fields up to 9 T and temperature up to 50 K, are reported. We observed various types of magnetic behavior depending on the nominal weight content of MnO. Samples with a low nominal content (up to n = 0.10) of MnO exhibited Curie–Weiss behavior at higher temperatures. For samples with high nominal weight contribution (from n = 0.30 to 0.60), spin-glass-like or/and weak ferromagnetic behavior is observed. [ABSTRACT FROM AUTHOR]

The extent of interfacial charge transfer and the resulting impact on magnetic interactions were investigated as a function of sublayer thickness in La0.7Sr0.3MnO3/La0.7Sr0.3CoO3 ferromagnetic superlattices. Element-specific soft x-ray magnetic spectroscopy reveals that the electronic structure is altered within 5-6 unit cells of the chemical interface, and can lead to a synthetic ferromagnet with strong magnetic coupling between the sublayers. The saturation magnetization and coercivity depends sensitively on the sublayer thickness due to the length scale of this interfacial effect. For larger sublayer thicknesses, the La0.7Sr0.3MnO3 and La0.7Sr0.3CoO3 sublayers are magnetically decoupled, displaying two independent magnetic transitions with little sublayer thickness dependence. These results demonstrate how interfacial phenomena at perovskite oxide interfaces can be used to tailor their functional properties at the atomic scale.

Cerium-substituted yttrium iron garnet (Ce:YIG) thin films are promising magneto-optical (MO) materials for the application in optical isolators. Ce:YIG can be grown on the YIG seed layer, and the change of layer thickness ratio for Ce:YIG to YIG may result in different magnetic properties. In this work, Ce:YIG (Ce1Y2Fe5O12) to YIG (Y3Fe5O12) bilayer films, with different thickness ratios of 2:1, 4:1, 6:1, and 8:1, were grown by pulsed laser deposition (PLD); 2:1 and 4:1 films consist of pure YIG phase; 6:1 and 8:1 films consist of YIG phase, Y2Fe4O9 phase with hexagonal structure, and Y2O3 phase with cubic structure. Y2Fe4O9 and Y2O3 phases induce the decrease of saturation magnetization ($M_{s}$). The concentration of Fe2+ and Ce4+ ions increases with layer thickness ratio increasing, resulting in the decrease of saturation magnetization ($M_{s}$), coercivity ($H_{c}$), and magnetic anisotropy energy ($E$). It is found that the best magnetic properties, including $H_{c}$ (26.9 Oe), $M_{s}$ (140.6 emu/cm3), and $E$ (257.5 J/cm3), are obtained in the 2:1 film. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the magnetic properties of mixed nanocrystalline Zn/manganese oxide compounds synthesized by a hydrothermal method. These compounds are designed as (ZnO)1−n(MnO)n, where index n ranges from 0.05 to 0.60. The results of magnetic measurements, including AC magnetic susceptibility as a function of temperature (up to 160 K) and frequency (from 7 Hz up to 9970 Hz), as well as DC magnetization in magnetic fields up to 9 T and temperature up to 50 K, are reported. We observed various types of magnetic behavior depending on the nominal weight content of MnO. Samples with a low nominal content (up to n = 0.10) of MnO exhibited Curie–Weiss behavior at higher temperatures. For samples with high nominal weight contribution (from n = 0.30 to 0.60), spin-glass-like or/and weak ferromagnetic behavior is observed.

The rapid urbanization and industrialization is causing worldwide water pollution, calling for advanced cleaning methods. For instance, pollutant adsorption on magnetic oxides is efficient and very practical due to the easy separation from solutions by an magnetic field. Here we review the synthesis and performance of magnetic oxides such as iron oxides, spinel ferrites, and perovskite oxides for water remediation. We present structural, optical, and magnetic properties. Magnetic oxides are also promising photocatalysts for the degradation of organic pollutants. Antimicrobial activities and adsorption of heavy metals and radionucleides are also discussed. [ABSTRACT FROM AUTHOR]

We investigate the ultrafast spin dynamics of an antiferromagnet in a ferromagnet/antiferromagnet heterostructure Fe/GdFeO3 via an all-optical method. After laser irradiation, the terahertz spin precession is hard to be excited in a bare GdFeO3 without spin reorientation phase but efficiently in Fe/GdFeO3. Both quasi-ferromagnetic and impurity modes, as well as a phonon mode, are observed. We attribute it to the optical modification of interfacial exchange coupling between Fe and GdFeO3. Moreover, the excitation efficiency of dynamics can be modified significantly via the pump laser influence. Our results elucidate that the interfacial exchange coupling is a feasible stimulation to efficiently excite terahertz spin dynamics in antiferromagnets. It will expand the exploration of terahertz spin dynamics for antiferromagnet-based opto-spintronic devices. [ABSTRACT FROM AUTHOR]

In present research six samples of nano X-type hexagonal ferrites with general formula SrBaMg2-xCoxDyyFe28-yO46 (x = 0–1; y = 0–0.1 with step size of 0.2 and 0.02, respectively) were synthesized by sol–gel technique. The temperature required for the phase formation of these materials was estimated using thermogravimetric analysis. X-ray diffraction patterns revealed the pure phase of the prepared materials up to the doping concentration of x = 0.4, y = 0.04 along with the second phase for higher doping concentration. The secondary phase appeared due to the solubility limit of higher ionic radius Dy3+ ions into the hexagonal lattice. The mean crystalline size decreased from 29 to 18 nm while unit cell volume, bulk density, and X-ray density were increased with Dy-Co doping. Hysteresis loops showed that by incorporation of Dy-Co ions the saturation magnetization (Ms) was enhanced from 50 to 60 emu.g−1. Also, coercivity (Hc) varied in the range 1573–3251 Oe, such high values of Ms and Hc propose the utilization of these X-type materials as permanent magnets and perpendicular recording media. The dependence of dielectric parameters (dielectric constant, ac conductivity, Q-value) on frequency (1 MHz–3 GHz) as well as composition was discussed. Inclusion of Dy-Co in X-type lattice modified dielectric parameters i.e. dielectric constant, ac conductivity was increased. Complex modulus studies directed to elucidate Nyquist plots which exhibited a single half-circle for all X-type ferrites, thus depicting Debye sort of behavior. [ABSTRACT FROM AUTHOR]

Summary: Considering accelerated discovery of half‐metallic alloys has substantially created a research curiosity due to their potential technological considerations and multi‐functional applications. In this work, we have delivered a theoretical overview on experimentally determined Ba2XNbO6 (X = Ho,Yb) alloys first time to understand their basic structural chemistry and other physical properties by Density Functional Theory (DFT). The exploitation of the Birch‐Murnaghan equation to obtain their lattice parameters, designates a clear‐cut consistency with the experimental results. Quantum description of identifying electronic structures of Ba2XNbO6 (X = Ho,Yb) is achieved by the insertion of Generalised gradient approximation (GGA), Hubbard correlation correction (GGA + U) and Tran‐Blaha modified Becke‐Johnson (TB‐mBJ) potential. The exhibition of spin‐polarisation creates ferromagnetism of (4 and 1) μB respectively has been put forwarded in this report. Moreover, phonon dispersions decisively certifies the dynamical stability by using density functional perturbation theory (DFPT). The Seebeck coefficient of Ba2HoNbO6 (Ba2YbNbO6) obeys half‐metallic trend with their outcomes values at room temperatures −347.65 μV/K (−261.11 μV/K) in spin‐up and −69.29 μV/K (3.42 μV/K) in spin‐dn respectively. The summed‐up properties catch a magnificent and dynamic view to see these alloys in spintronics and thermoelectric progressive technologies. [ABSTRACT FROM AUTHOR]

• Ce 1-x Sm x O 2 (x = 0–10 % Sm, Δx = 2) co-precipitation synthesized nanomaterials. • FCC structure of Sm-doped CeO 2 nanomaterials with no impurity phases. • XAS indicate presence of valence states of Ce4+, Ce3+ and Sm3+ cations. • FM ordering in the CeO 2 nanoparticles is improved by the oxygen vacancies. • Formation of various complexes mediated by oxygen vacancies for F+ centres to promote FM ordering. The present study reports crystalline structure, electronic structure and magnetic properties for nanoparticles undoped CeO 2 and C e 1 - x S m x O 2 (x = 0.02 to 0.10, @ 0.02). The nanoparticle samples are synthesized by the co-precipitation method. XRD data shows the successful incorporation of Sm3+ ions at Ce4+ sites in the face-centered cubic (fcc) lattice. The soft X-ray absorption spectroscopy technique is utilized to get an insightful overview of electronic structural properties due to structural defects, chemical states and the development of oxygen vacancies in C e 1 - x S m x O 2 nanoparticles. The soft XAS spectra show a significant Ce and Sm peak in the M 4,5 domain, along with the well-defined O K-edge peak. Analysis of Ce M 4,5 -edges indicates that Ce-ions have both 3 + and 4 + oxidation states. With the incorporation of Sm+3 ions, there is a reduction of Ce4+ states and oxidation of Ce3+ states, as well as a substantial increase in oxygen vacancy concentration. The room-temperature magnetic properties of C e 1 - x S m x O 2 nanoparticles reveal ferromagnetic behavior. The origin of ferromagnetism is explained by F-center exchange (FCE) coupling mechanisms mediated via development of oxygen vacancy and defects. [ABSTRACT FROM AUTHOR]

Supercapacitors are increasingly used for energy conversion and storage systems in sustainable nanotechnologies. Graphite is a conventional electrode utilized in Li-ion-based batteries, yet its specific capacitance of 372 mA h g−1 is not adequate for supercapacitor applications. Interest in supercapacitors is due to their high-energy capacity, storage for a shorter period and longer lifetime. This review compares the following materials used to fabricate supercapacitors: spinel ferrites, e.g., MFe2O4, MMoO4 and MCo2O4 where M denotes a transition metal ion; perovskite oxides; transition metals sulfides; carbon materials; and conducting polymers. The application window of perovskite can be controlled by cations in sublattice sites. Cations increase the specific capacitance because cations possess large orbital valence electrons which grow the oxygen vacancies. Electrodes made of transition metal sulfides, e.g., ZnCo2S4, display a high specific capacitance of 1269 F g−1, which is four times higher than those of transition metals oxides, e.g., Zn–Co ferrite, of 296 F g−1. This is explained by the low charge-transfer resistance and the high ion diffusion rate of transition metals sulfides. Composites made of magnetic oxides or transition metal sulfides with conducting polymers or carbon materials have the highest capacitance activity and cyclic stability. This is attributed to oxygen and sulfur active sites which foster electrolyte penetration during cycling, and, in turn, create new active sites. [ABSTRACT FROM AUTHOR]

The compound Ca3Co2O6 undergoes a transition into a spin-density wave (SDW) state near 24 K. Below ∼10 K, this unstable SDW state coexists with a nearly- degenerate commensurate antiferromagnetic state as well as short-range magnetic order. Clear signatures of this strong magnetic disorder have been observed in the response of entropy to changing magnetic field and temperature. We performed a calorimetry study of Ca3Co2O6 and Ca3Co1.9Zn0.1O6 in order to compare their entropic responses at low temperature. Our results for Ca3Co2O6 reveal that ΔS(T, H) ≡ S(T, H)−S(T, H = 0) increases as either temperature or magnetic field increase. In contrast, ΔS data for Ca3Co1.9Zn0.1O6 were relatively unresponsive to changes in temperature or field, suggesting that Zn substitution may reduce the low-temperature magnetic disorder observed in Ca3Co2O6. These results are discussed within the context of two cases (Ca3Co2O6 under applied pressure and Ca2.75R0.25Co2O6 (R = Dy, Lu)) in which a single magnetic ground state is stabilised. [ABSTRACT FROM AUTHOR]

The enhanced magnetoelectric properties of Ba0.5Sr1.5Zn2(In0.08Fe0.92)12O22 are demonstrated. This hexaferrite exhibits great magnetoelectric tunability and high electrical resistivity. Mutual modulation of ferroelectricity and magnetism is simultaneously achieved near room temperature. Moreover, the reversal of M direction by an electrical field is obtained at low magnetic field. This study illuminates a potential application in magnetoelectric devices. [ABSTRACT FROM AUTHOR]

La0.7Ca0.3MnO3 perovskite and its composites with graphene nanoplatelet (GNP) were prepared using a wet chemical method. The structural, magnetic and magnetocaloric properties of La0.7Ca0.3MnO3: GNP composites were investigated to determine the effect of GNPs. The results of XRD analysis show that the synthesised powders can be almost indexed to pure phase orthorhombic La0.7Ca0.3MnO3. The magnetic measurements demonstrate that 0.7 and 1% GNP amounts cause an increase in the Curie temperature (TC), and for larger amounts of GNP, the TC monotonically decreases, except for the sample with 10% GNP. The results obtained from the Arrott plots show that the magnetic phase transition of the samples transforms from the first to second order with increasing GNP amount. The changes in the magnetocaloric properties are interpreted in terms of perovskite phase formations via structural analysis. The amounts of graphene nanoplatelets in the oxide powders are correlated with the observed magnetocaloric properties. The best magnetocaloric performance with the maximum magnetic entropy change of 3.99 Jkg−1K−1 and refrigeration capacity of 90 Jkg−1 was obtained at a 2 T magnetic field. [ABSTRACT FROM AUTHOR]

The general magnetic characterisation of a series of materials in the BaNi2V2O8-BaNi2P2O8 layered honeycomb spin-1 system is reported. A change from dominantly 2-dimensional (2D) to dominantly 3-dimentional (3D) magnetic character is observed on progressing from the pure V to the pure P material. The change is continuous with composition in BaNi2(V1−xPx)2O8. But a variety of features in the temperature-dependent magnetic susceptibilities at low temperatures suggest that the magnetic system is complex. Although the Curie–Weiss temperature becomes less strongly negative on increasing the P content, an indication of increased competition between different types of magnetic coupling, the system does not appear to be approaching a quantum spin liquid state at low temperatures. [ABSTRACT FROM AUTHOR]

Abstract Epitaxial superlattices of ferromagnetic/paramagnetic La 0.67 Sr 0.33 MnO 3 /SrIrO 3 materials have been prepared on SrTiO 3 (100) substrate using pulse laser deposition technique. An unexpected onset of interface magnetic interaction has been observed around 40 K. Interestingly, magnetic exchange bias effect has been observed in both field cooled and zero field cooled magnetization loops, however, the shifting of loop is opposite in both measurements. Exchange bias field vanishes as temperature increases to interface magnetic ordering temperature. Moreover, exchange bias field is found to decrease with increasing cooling field. We believe that tuning of magnetic exchange at interface during field cooling induces this evolution in nature of exchange bias field. Highlights • Superlattice of [La 0.67 Sr 0.33 MnO 3 /SrIrO 3 ] 3 on SrTiO 3 (100) substrate is prepared. • Constituent materials are paramagnetic and ferromagnetic in nature. • Unusual exchange bias effect has been observed in both FC and ZFC magnetization. • The exchange bias is observed at low temperature below around 40 K. • This effect is attributed to magnetic ordering of SrIrO 3 at low temperature which renders an antiferromagnetic type interaction at the interface. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Granular activated carbon was efficiently impregnated with magnetic Fe oxides. • Isotherm models considering adsorption in two surface sites were developed. • The two-site monolayer model describes the phosphorus adsorption in the adsorbent. • The maximum monolayer capacity increases with the reduction of pH. • The internal mass transfer step has been shown as the limiting rate of adsorption. Abstract This study investigates the impregnation of iron oxide in a granular activated carbon (GAC-Fe), to employ for the adsorption of phosphorous from aqueous solution. Physical and chemical characterization of GAC-Fe was performed including Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS), Thermogravimetric analysis (TGA), N 2 physisorption, and zero point charge (pH ZPC) analyses. Adsorption isotherms were developed considering the presence of two active sites on the adsorbent surface. The two-site monolayer model was shown as the best isotherm model to describe the system equilibrium. The results indicated the high relation of the adsorption with the pH solution, showing the best adsorption capacity in pH 3.0 (q m = 2.874 mg g−1). An analysis of the surface charge of the adsorbent indicated a positive value at pH lower than 3.5, explaining the higher affinity to phosphate. The process was spontaneous and favorable at the temperatures studied (25, 35 and 45 °C). The thermodynamic results suggest two types of adsorption mechanisms on the surface, related to chemisorption processes. The best kinetic model of adsorption considers the internal mass transfer as the rate-limiting step. The temperature and initial concentration do not show any influence on the effective diffusion coefficient. Hence, the study brings an alternative material for phosphorus adsorption and contributes for a better knowledge of the mechanism involved in the process and equilibrium of the system. [ABSTRACT FROM AUTHOR]

Abstract Conditions of synthesis, such as concentration, temperature and pH, determine physico-chemical properties of nanoparticles. Mechanochemical method is an alternative approach to synthesize nanoparticles in shorter time and using lower amount of solvent. Milling is an underestimated mechanochemical process that has been rediscovered by researchers chiefly as an economical and fast process. This paper presents the synthesis and the characterization of iron and cobalt magnetic oxides based on the mechanochemical preparation by milling the metal salt precursors in the presence of sodium borohydride. Moreover, the advantages in relation to the ordinary methodologies are presented and discussed. Characterization of the synthesized magnetic iron and cobalt particles showed amorphous products of average particle size in the range of 30–150 nm. The nanoparticle structures were obtained and confirmed by TEM, SEM and XRD analyses. N 2 adsorption-desorption isotherm showed narrow distribution of the nanopores in the range of 4 nm, which indicates a promising material for application as solid catalysts and feedstock for the fine chemistry industry. Highlights • Mechanochemical synthesis was effective for Fe 3 O 4 and Co 3 O 4 nanoparticles. • Morphological analyzes showed crystallinity and atomic ordering. • Material possess a great potential to be applied as a catalyst. • Average size of 60 nm for Fe 3 O 4 and 120 nm for Co 3 O 4 were exhibited. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The observed unusual co-existence of AFM with GP in nanometric SCCMO sample is rare in nature. • The glassy behavior in bulk SCCMO is attributed to the antisite disorders (∼7.12%) along with magnetic frustration. • Magnetic spin dynamics and aging effect are suggesting different spin relaxation processes. Abstract Griffiths phase like behavior has been investigated in details in size modulated Sm 1.5 Ca 0.5 CoMnO 6 double perovskite, having ferromagnetic entities in the paramagnetic matrix. Temperature dependent real and imaginary part of ac susceptibility confirms that Sm 1.5 Ca 0.5 CoMnO 6 -1150 °C bulk-sample has spin-glass like ordering below T g ∼ 34.88(3) K. This glassy behavior is attributed to the antisite disorders (∼7.12%) along with and magnetic frustration in the system. However, the ground state of Sm 1.5 Ca 0.5 CoMnO 6 -600 °C nanometric-sample is observed to be antiferromagnetic in nature due to the presence of large antisite disorder (∼53.58%). The observed unusual co-existence of antiferromagnetism with Griffiths-like phase in Sm 1.5 Ca 0.5 CoMnO 6 -600 °C sample is rare in nature. Interesting magnetic spin dynamics and aging effect are also observed in both the compounds suggesting different spin relaxation processes in low temperature regime. The observed magnetism in these compounds can be tuned by nearest neighbor Co-O-Mn and/or Co-O-Co/Mn-O-Mn exchange interactions as well as the next nearest neighbor Co-O-O-Co/Mn-O-O-Mn interactions. [ABSTRACT FROM AUTHOR]

Abstract We report the evolution of temperature and magnetic field dependent magnetic properties of Mn substituted spinel cobalt chromite Co ( C r 0.7 M n 0.3 ) 2 O 4 compound. It is observed that 30 % 'Mn' substitution for Cr-site in C o C r 2 O 4 results in magnetic compensation and huge reversal of temperature dependent magnetization below compensation temperature, T c o m p ∼ 83 K under low applied fields which was absent in the parent compound C o C r 2 O 4. For large applied fields magnetization reversal disappears but ends in field induced transition across T c o m p. Magnetic hysteresis loops exhibit gigantic coercivity at 3 K, and dramatically drops on increasing temperature. The exchange-bias-like behavior is observed below 10 K and as well as in the vicinity of compensation point, T c o m p (∼ 83 K). Low temperature neutron powder diffraction (NPD) experiment shows the possible magnetic structure and ordering in Co ( C r 0.7 M n 0.3 ) 2 O 4. Non-monotonic change in bond lengths and bond angles around the compensation temperature (T c o m p) revealed that there is a correlation between crystal and magnetic structure. Possible origin behind such exotic magnetic properties has been discussed in detail in the paper. [ABSTRACT FROM AUTHOR]

Abstract: Interatomic distance considerations and site occupancy refinements indicate that Zn2+ is exclusively located on tetrahedral sites in both Z and X-type hexagonal ferrites. Zinc is more strongly enriched in four layer thick spinel blocks of X-type hexaferrite than in the two layer thick spinel blocks of both magnetic oxides. No zinc was incorporated in the tetrahedra of the T blocks of Z-type hexaferrite. Bond valence analyses reveal different local charge compensation requirements as origin of the unequal distribution of diamagnetic Zn2+ over the tetrahedral sites, which strongly modify the magnetic properties.Graphical Abstract: Diamagnetic zinc is more strongly enriched on the tetrahedral sites in the four layer thick spinel blocks of X-type hexaferrite than in the two layer thick spinel blocks of both compounds which strongly modifies their magnetic properties. [ABSTRACT FROM AUTHOR]

Abstract: Interatomic distance considerations and site occupancy refinements indicate that Zn2+ is exclusively located on tetrahedral sites in both Z and X-type hexagonal ferrites. Zinc is more strongly enriched in four layer thick spinel blocks of X-type hexaferrite than in the two layer thick spinel blocks of both magnetic oxides. No zinc was incorporated in the tetrahedra of the T blocks of Z-type hexaferrite. Bond valence analyses reveal different local charge compensation requirements as origin of the unequal distribution of diamagnetic Zn2+ over the tetrahedral sites, which strongly modify the magnetic properties.Graphical Abstract: Diamagnetic zinc is more strongly enriched on the tetrahedral sites in the four layer thick spinel blocks of X-type hexaferrite than in the two layer thick spinel blocks of both compounds which strongly modifies their magnetic properties. [ABSTRACT FROM AUTHOR]

We report on the response of magnetic domains in thin magnetite microstructures to weak external magnetic fields. Magnetite islands were grown by high-temperature oxygen-assisted molecular beam epitaxy on Ru(0001). The islands, micrometric wide and tens of nanometers thick are of high structural quality, each having been grown from a single nucleation center. Their magnetic domain structure is dominated by shape anisotropy, i.e., they present Landau flux-closure domain configurations. The magnetic domains of the in situ grown microstructures have been imaged directly by means of x-ray magnetic circular dichroism in photoemission electron microscopy while applying external, in-plane magnetic fields along different directions. Upon application of an external field the Landau state vortex core experiences a displacement along a direction perpendicular to the excitation field. The behavior of the Landau state under the applied magnetic field is quantified and compared with micromagnetic simulations. The results highlight the bulk-like magnetic properties of the nanometer-thick microstructures, opening the way to their possible use in technological applications. [Display omitted] • High quality magnetic oxides. • Vortex movement under applied magnetic field. • Custom sample holder for high temperature growth and magnetic field application. • Micromagnetic simulation. [ABSTRACT FROM AUTHOR]

The demand for water is predicted to increase significantly over the coming decades; thus, there is a need to develop an inclusive wastewater decontaminator for the effective management and conservation of water. Magnetic oxide nanocomposites have great potentials as global and novel remediators for wastewater treatment, with robust environmental and economic gains. Environment-responsive nanocomposites would offer wide flexibility to harvest and utilize massive untapped natural energy sources to drive a green economy in tandem with the United Nations Sustainable Development Goals. Recent attempts to engineer smart magnetic oxide nanocomposites for wastewater treatment has been reported by several researchers. However, the magnetic properties of superparamagnetic nanocomposite materials and their adsorption properties nexus as fundamental to the design of recyclable nanomaterials are desirable for industrial application. The potentials of facile magnetic recovery, ease of functionalization, reusability, solar responsiveness, biocompatibility and ergonomic design promote the application of magnetic oxide nanocomposites in wastewater treatment. The review makes a holistic attempt to explore magnetic oxide nanocomposites for wastewater treatment; futuristic smart magnetic oxides as an elixir to global water scarcity is expounded. Desirable adsorption parameters and properties of magnetic oxides nanocomposites are explored while considering their fate in biological and environmental media.

Abstract In this work, we review three models of magnetic ordering in typical magnetic materials that have been proposed based on atomic physics. The first model we discuss is the O 2 p itinerant electron model for magnetic oxides, which is called the IEO model. Using this model, the magnetic structures of spinel ferrites M Fe 2 O 4 , where M = Ti, Cr, Mn, Fe, Co, Ni, or Cu, and perovskite manganites La 1 − x Sr x MnO 3 , where 0. 0 ≤ x ≤ 0. 4 , can be explained. The second model considered is a new itinerant electron model for magnetic metals, called the IEM model. The IEM model can be employed to explain the relation between the average magnetic moment per atom and resistivity for Fe, Ni, and Co metals. According to this model, free electrons in magnetic metals should be distinguished from itinerant electrons. Then, when the free electrons are excluded, the itinerant electrons transitioning between adjacent metal ions in magnetic metals have similar characteristics to those transitioning between adjacent cations and O anions in magnetic oxides. The third model we address is the Weiss electron pair (WEP) model, which is based on the IEO and IEM models. The WEP model is used to explain the origin of the magnetic ordering energy in magnetic metals and oxides and provides a reason for the different Curie temperatures observed in typical magnetic metals and oxides. [ABSTRACT FROM AUTHOR]

The influence of rare earth site substitution on structural, transport and magnetic characteristics of polycrystalline Ln 2 CoMnO 6 (Ln = La, Sm and Gd) has been systematically investigated in details. The room temperature X-ray diffraction data confirm the monoclinic crystal structure of the samples, having P2 1 /n space group. The magnetic study reveals that the ferromagnetic transition temperature (T C1  ∼ 233.2 K) of La 2 CoMnO 6 decreases very fast due to a decrease of ionic radii in Ln site and T C2 (∼150 K) disappears in the Gd 2 CoMnO 6 system due to the presence of only Co 2+ and Mn 4+ ion pair. The field dependent magnetization data at 5 K exhibit antiferromagnetic ordering induced in the Sm 2 CoMnO 6 and Gd 2 CoMnO 6 systems due to structural distortion and 4f-3d negative magnetic interactions. The temperature dependent resistivity data of La 2 CoMnO 6 display semiconductor like behavior in a temperature range of 150–300 K and this behavior has been best described by the variable range hopping conduction mechanism. On the other hand, the resistivity of Sm and Gd based samples follows variable range hopping model in the temperature range of 200–300 K. Large magnetoresistance of ∼−26.35% has been observed at 160 K at a magnetic field of 60 kOe in La 2 CoMnO 6 and it decreases to −8.28% for Sm 2 CoMnO 6 , and −1.01% for Gd 2 CoMnO 6 as ionic radii decrease at the Ln site. [ABSTRACT FROM AUTHOR]

Neutron and X-ray diffraction, magnetic susceptibility, and specific heat measurements have been used to investigate the magneto-structural phase transitions in 20% Cu substituted multiferroic CoCr 2 O 4 spinel. The Jahn-Teller active Cu 2+ ion in the tetrahedral A -site of the spinel configuration induces the Jahn-Teller distortion slightly above the Néel temperature. In this compound, we observe a Jahn-Teller distortion of the crystal structure at 90 K. It was further observed that the high temperature cubic ( Fd 3 ‾ m ) structure coexists with the low temperature orthorhombic ( Fddd ) structure till the lowest temperature of measurement. [ABSTRACT FROM AUTHOR]

We report the evolution of physical properties due to partial substitution of Gd on the Y site in a mixed metal oxide YFe 0.5 Cr 0.5 O 3 . This compound exhibits negative magnetization at low applied fields. Our investigations on Y 1-x Gd x Fe 0.5 Cr 0.5 O 3 (x = 0.0, 0.2, 0.4 and 0.6) compounds is carried out through magnetization and Raman spectroscopy studies. It is observed that even with 20% Gd substitution, the negative magnetization observed in YFe 0.5 Cr 0.5 O 3 is suppressed. Due to magnetic rare earth ion Gd 3+ , additional exchange interaction of the form Gd-O-Fe/Cr dominates the magnetic interaction arising due to the transition metal ions. This results in positive magnetization in Gd-substituted compounds. Temperature dependent Raman spectroscopy along with magnetization studies revealed that the observed shifts of Raman mode is due to spin-phonon coupling. Hardening of Raman mode observed below 240 K in YFe 0.5 Cr 0.5 O 3 weakens and softening of phonon modes was observed for Y 0.4 Gd 0.6 Fe 0.5 Cr 0.5 O 3 compound. This implies that additional magnetic interactions due to Gd ions play a dominating role in dictating the behavior of the Gd-substituted compounds. [ABSTRACT FROM AUTHOR]

In magnetic materials, a large magnetocaloric effect is expected in those with large magnetocrystalline anisotropy in the vicinity of their magnetic phase transition temperature. Here we report a comparative study of rotating magnetocaloric effect in TbMn 1- x Fe x O 3 (x = 0, 0.75) single crystals by rotating them in a constant external field within a c plane from 2 to 50 K. We observed a large magnetic entropy change between a and c axes with strong magnetocrystalline anisotropy in TbMnO 3 as well as TbMn 0.25 Fe 0.75 O 3 . For TbMn 0.25 Fe 0.75 O 3 , the large magnetocaloric effect appears close to a spin reorientation from Γ 1 ( A x , G y , C z ) to Γ 4 ( G x , A y , F z ) magnetic configuration at ∼16 K, which is distinguished from that of TbMnO 3 near the antiferromagnetic ordering of Tb 3+ ions at ∼9 K. The maximum of magnetic entropy change and refrigerant capacity of TbMnO 3 (TbMn 0.25 Fe 0.75 O 3 ) reach as high as 19.20 J/Kg K (14.84 J/Kg K), 411.97 J/Kg (260.80 J/Kg) under 7 T, respectively. Furthermore, using Lorentz transmission electron microscopy technique, we show the TbMn 0.25 Fe 0.75 O 3 material displays a large single domain structure with dimension up to about 3 μm × 3 μm , as an indicative of a large magnetocrystalline anisotropy in this system. Based on nonextensive thermodynamics, we further employ the q - Fermi Dirac statistics to demonstrate the good consistency between computed and experimental results of magnetization versus rotating angles. Our results clearly indicate the magnetocrystalline anisotropy energy plays a decisive role in the large differences of the magnetic properties and magnetocaloric properties in TbMn 1- x Fe x O 3 system. [ABSTRACT FROM AUTHOR]

Monoclinic Nb12O29 undergoes a charge ordering transition to form antiferromagnetic Nb4+ chains (TN ~ 12 K) spaced 15.7 Å apart, which are coupled through mediation from a subset of metallic electrons which are present over all temperature regimes. We present the effects of disrupting the delicate electronic equilibrium in monoclinic Nb12O29 through doping Nb4+ (d1) with Ti4+ (d0) ions in the series, TixNb12−xO29. Powder neutron diffraction demonstrates that Ti is distributed over all of the 6 crystallographically distinct Nb positions. Magnetic susceptibility measurements reveal a rapid suppression of the magnetic ordered state on Ti doping, with a 3% percolation threshold consistent with the existence of one-dimensional Nb4+ chains. The reduction of the number of unpaired electrons on Ti4+ doping is shown to depopulate both localised and itinerant electron subsets, demonstrating that they are intrinsic to the properties of the system, which is argued to be a direct consequence of the mixture of bonding schemes within the lattice.

The pyrochlore structure (A2B2O7) has been an object of consistent study by materials scientists largely due to the stability of the cubic lattice with respect to a wide variety of chemical species on the A or B sites. The criterion for stability under ambient conditions is controlled by the ratio of these cations, which is empirically 1.36 < RA/RB < 1.71. However, under applied pressure synthesis conditions, the pyrochlore lattice is stable up to RA/RB ∼ 2.30, opening up possibilities for new compounds. In this review, we will highlight recent work in exploring new rare-earth pyrochlores such as the germanates RE2Ge2O7 and platinates RE2Pt2O7. We highlight recent discoveries made in these pyrochlores such as highly correlated spin ice behavior, spin liquid ground states, and exotic magnetic ordering.

Temperature-dependent DC electrical resistivity of polycrystalline samples with orthorhombic perovskite structure GdCaMnCrO ( x = 0.0-0.5) has been reported. The samples were prepared by the solid-state reaction method. The resistivity of all the samples indicates a semiconducting nature. In the high-temperature region, the electrical conduction process follows the small polaron hopping (SPH) mechanism showing exponential variation of resistivity with temperature. The activation energy increases with Cr concentration. The low-temperature resistivity data follows Mott's ln( ρT )∼ T law of variable-range hopping (VRH) conduction mechanism. The estimated values of hopping distances ( R) and hopping energies ( W) of the samples start to increase with increasing Cr concentrations from and above x = 0.5 and satisfy essential conditions of the Mott VRH, i.e., αR>> 1 ( α = inverse localization length) and W/ K T>> 1. This signifies that evaluation of these parameters being logical and the effect can be attributed to high density of doping which introduces simultaneously potential disorder and localized states. The magnetic field-dependent magnetoresistance has been explained by a phenomenological model considering spin-polarized tunneling at grain boundaries in the samples. [ABSTRACT FROM AUTHOR]

Polycrystalline Ce:YIG thin films deposited on silicon are promising material candidates for integrated nonreciprocal photonic devices. So far, the reported Faraday rotation of polycrystalline Ce:YIG thin films on silicon is much lower than that of their single crystal or epitaxial thin film counterparts, limiting the magneto-optical figure of merit, device bandwidth and fabrication tolerance. In this paper, we report the growth of Ce:YIG thin films on silicon from targets with high Ce concentration up to nominally Y 1.5 Ce 1.5 Fe 5 O 12 by pulsed laser deposition. The polycrystalline Y 1.5 Ce 1.5 Fe 5 O 12 thin film showed pure garnet phase, smooth surface roughness of 0.7 nm, a dominant Ce 3+ valence state and a bulk-like saturation magnetization of 125 emu/cm 3 at room temperature. This material shows high Faraday rotation of −6410 deg/cm at 1550 nm wavelength, exceeding that of an Y 2 Ce 1 Fe 5 O 12 epitaxial thin film on a GGG (100) substrate. However higher loss and lower figure of merit is also observed at 1550 nm wavelength compared to Y 2 Ce 1 Fe 5 O 12 thin films, possibly due to the low oxygen partial pressure during fabrication. Low deposition oxygen partial pressure is essential to enhance the Ce solubility and Ce 3+ concentration, which results in large Faraday rotation. [ABSTRACT FROM AUTHOR]

Rare earth manganites under hole doping, R1-xBxMnO3 (R = La, Nd, Pr and B = Sr, Ca, Ba), have a rich charge carrier-temperature-magnetism phase diagram. The phases are tunable by applying external constraints, such as strain and boundary conditions. For example, the ferromagnetic phase dominated by the double-exchange mechanism can be transformed into an antiferromagnetic phase by controlling the doping level. In this work, using first principles calculations based on density functional theory, we study the bilayer system La0.67Sr0.33MnO3 (LSMO)/SrRuO3 (SRO) composed of two ferromagnetic materials. The original ferromagnetism in LSMO becomes A-type antiferromagnetism at the interface. Such intriguing behavior at transition-metal oxide interfaces in the LSMO/SRO bilayer, stemming from coexisting interdiffusion and charge transfer from the SRO layer, is similar to a hole-doped LSMO layer attached to a substrate with electric polarization. Our result qualitatively and quantitatively explains recent experimental evidence of a dramatic change in the strength of magnetization for different terminations of LSMO/SRO bilayers. [ABSTRACT FROM PUBLISHER]

• First-ever magnetic Compton profiles (MCPs) of non-stoichiometric Ni 0.9-x Pr x Fe 2.1 O 4 inverse spinel ferrites. • Decomposed experimental MCPs into constituent profiles of Ni, Fe, Pr-4f and diffuse electrons. • Validated MCP based total and site-specific spin moments using FP-LAPW calculations. • Explored role of orbital magnetic moments using MCP data and magnetization data. • Revealed effect of Pr-4f states in amending the spin moments and electronic properties. Magnetic Compton profiles of 5 % and 15 % Pr-doped non-stoichiometric NiFe 2 O 4 have been measured using synchrotron radiations of energy 182.65 keV at SPring-8, Japan. An analysis of MCPs measured at 6 and 300 K show that the total spin moment decreases with increasing temperature and Pr concentration in Ni 0.9-x Pr x Fe 2.1 O 4 which is consistent with the magnetic moment (spin + orbital) as observed from magnetization measurements data. Spin moments at different sites are deduced using decomposition of MCPs in the elemental profiles of Ni, Pr-4f, Fe and diffused electrons. Spin moments at Ni-site have been found to play crucial role in emergence of absolute spin moments. Spin moments at Pr-site is aligned antiparallel to that of Ni and Fe sites. The orbital magnetic moment is also deduced from the subtraction of MCP based spin moments from the magnetization data. Theoretical FP-LAPW based total and atom specific spin moments are found in consonance with the MCP based data. Total and spin projected density of states are also computed using the FP-LAPW method to validate role of Pr-4f and Fe-3d (O h) states in amending the total magnetic moment with Pr concentration. The M−H based saturation magnetization derived at 6 and 300 K temperature show that the saturation magnetic moments reduce from 2.21 → 2.05 μ B /f.u. at 6 K and 2.10 → 1.98 μ B /f.u. at 300 K with increase in Pr concentration from 5 % → 15 %. On the basis of hysteresis curve and coercive force, both the doped compounds show soft magnetism. [ABSTRACT FROM AUTHOR]