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Cobalt doping's influence on the structural, magnetic, and electronic properties of the double spinel LiFeCr 4 O 8 was systematically investigated. Rietveld refinement revealed a consistent increase in lattice parameter a and unit cell volume with cobalt incorporation. Magnetic susceptibility measurements indicated three distinct transitions: an increase in the ferrimagnetic transition temperature (T N), a decrease in the magnetostructural transition temperature (T MS), and an increase in the spin gap transition by cobalt doping. Through diffuse reflectance spectroscopy the direct optical band gap (E og) was obtained with values of 1.169 eV, 1.303 eV, 1.396 eV, and 1.230 eV for x = 0.0, 0.1, 0.2, and 0.5, respectively. The observed increase in E og with cobalt doping suggests a widening of the band gap, which could be beneficial for optoelectronic applications. By means of X-ray photoelectron spectroscopy (XPS) the core levels of Li 1s , Co 3p , Fe 3p , Cr 3p , Fe 2p , Cr 2p , and O 1s were identified. XPS valence band (VB) analysis revealed a decreasing intensity at binding energy BE = 0 eV with respect to x = 0.0. Density functional theory calculations with Hubbard U correction (DFT + U) confirmed a ferrimagnetic semiconductor behavior with a direct electronic band gap (E eg) of 1.085 eV. [ABSTRACT FROM AUTHOR]

We have investigated, for the first time, the hyperthermia properties, antibacterial, anticancer and antioxidant activities, as well as their toxicity, of Mn 0.25 Mg 0.25 Co 0.5 Fe 2 O 4 nanoparticles synthesized by the sol-gel auto-combustion method. X-ray diffraction results revealed a pure phase and good crystallinity of the synthesized. In addition, the Fourier transform infrared (FTIR) spectrum confirmed the formation of the crystallographic sites of the synthesized structure. In terms of morphology, scanning electron microscopy (SEM) showed that the nanoparticles were agglomerated. In addition, transmission electron microscopy (TEM) revealed that the nanoparticles had a cubic shape and a nanometric size of around 32 nm. Energy-dispersive X-ray spectroscopy (EDS) confirmed the chemical composition of the nanoparticles. With regard to magnetic properties, magnetic measurements showed almost ferrimagnetic behavior, with a saturation magnetization of 38.90 emu/g at room temperature. Hyperthermia measurements revealed relatively good heating efficiencies, with SAR value of 33W/g, good temperature rise and short time to reach magnetic hyperthermia temperature 42 °C (8 min). For biological activities the nanoparticles showed an excellent capacity to neutralize free radicals, eliminating 97% of DPPH and 95% of hydrogen peroxide. The dose of 40 mg/kg of the nanoparticles caused significant alterations in hematological and biochemical profiles. The material showed a significant effect on various bacterial strains, including Staphylococcus aureus and Bacillus subtilis. The synthesized nanoparticles also showed significant activity against various cell lines, including MCF-7 and HeLa. These results strongly suggest the promising utilization of Mn 0.25 Mg 0.25 Co 0.5 Fe 2 O 4 , in many applications as a potential candidate for magnetic-mediated hyperthermia. [ABSTRACT FROM AUTHOR]

Samples with inversion parameter values (δ) ranging from 0.27 to 0.14 while maintaining the crystallite size value have been successfully fabricated from commercially available powders by mechanical grinding and thermal annealing treatments at temperatures ranging between 400 and 600 °C. Detailed characterization studies of these samples using X-ray, neutron diffraction and magnetic measurements have confirmed for the first time the simultaneous coexistence at 2 K of short range antiferromagnetic and ferrimagnetic ordering for a wide range of the inversion parameter. The magnetic phase diagram obtained is different from the one previously reported, which shows at 2 K the coexistence of long range antiferromagnetic order and short range order for values of inversion parameters less than 0.1 and the presence of a ferrimagnetic order only for values of δ > 0.2. At room temperature, the Rietveld analysis of NPD patterns and the magnetization curves showed a paramagnetic behavior in the samples with δ ≤ 0.1. For the samples with higher cationic inversion, typical hysteresis curves of ferrimagnetic materials were observed and the saturation magnetization values obtained agree quite well with the net magnetic moment obtained from the Rietveld refinement of the neutron diffraction patterns. [ABSTRACT FROM AUTHOR]

The crystal structure of the first-synthesized compound EuErCuS 3 was determined from X-ray powder diffraction data: orthorhombic crystal system, space group Pnma , structural type Eu 2 CuS 3 : a = 10.1005(2) Å, b = 3.91255(4)Å, c = 12.8480(2) Å; V = 507.737(14) Å3, Z = 4, and ρ x = 6.266 g/cm3. The temperatures and enthalpies of reversible polymorphic transitions and incongruent melting of the compound were determined by DSC: T α↔β = 1524 K, ΔН α↔β = 2.3 ± 0.2 kJ∙mol−1; T β↔γ = 1575 K, ΔН β↔γ = 0.7 ± 0.1 kJ∙mol−1; T γ↔δ = 1602 K; ΔН γ↔δ = 1.3 ± 0.1 kJ∙mol−1 and T cr = 1735 ± 10 K, ΔН cr = −3.5 ± 0.3 kJ∙mol−1. IR spectra were recorded in the range from 50 to 400 cm−1. The compound was found to be IR-transparent in the range 4000–400 cm−1. The compound was characterized by Raman spectroscopy. The observed spectra featured both Raman lines and luminescence. Ab initio calculations of the EuErCuS 3 crystal structure and phonon spectrum were performed, the frequencies and types of fundamental modes were determined, and the involvement of constituent ions in the IR and Raman modes was assessed from an analysis of the ab initio displacement vectors. The vibrational spectra were interpreted. EuErCuS 3 manifests a ferrimagnetic transition at 4.8 K. Its microhardness is 2850 MPa. The obtained data can serve as the basis for predicting the properties of EuLnCuS 3 compounds. Valence states for Eu (2+) and Er (3+) are proved both by the XRD and optical methods. Optical band gap was found to be 1.934 eV from diffuse reflectance spectrum. Image 1 • The EuLnCuS 3 compound exhibit ferrimagnetic properties at low temperature. • The polymorphic transitions for EuLnCuS 3 are identified at high temperature. • EuErCuS 3 is a wide-gap semiconductor. • Valence purity of Eu2+ is proved via both XRD and optical techniques • The ab initio calculation of the Raman and infrared spectra of EuErCuS 3 , made for Pnma symmetry, agrees well with experiment. [ABSTRACT FROM AUTHOR]

Di-phase ferroelectric-ferrite composites with the same composition close to the percolation limit (0.66BaTiO 3 -0.33CoFe 2 O 4) and with different phase arrangements (randomly mixed phases and tri-layer structures) have been consolidated by using spark plasma sintering and their properties were comparatively analyzed. The intrinsic effective dielectric constant has been estimated by using finite element method and a value almost ten times higher was predicted for the randomly mixed composite, as result of different field distributions inside the ferrite and ferroelectric phases. At room temperature, experimental permittivity contains an intrinsic behavior overlapped onto a very strong extrinsic component determined by the interfaces and by local charge inhomogeneity. The extrinsic dielectric behavior has been discussed in terms of thermally activated relaxation mechanisms developed in both types of investigated structures, as revealed by the temperature-dependence impedance spectroscopy. The magnetic properties are derived as "sum property" from the ferrimagnetic character of CoFe 2 O 4 and show the lowest magnetization for the randomly mixed composites and a weak magnetic anisotropy when the magnetic field was applied in-plane or out-of-plane in the layered structure. Due to the different levels of interface doping specific to the different types of interfaces, the magnetic Curie temperature of the two composites ranges from 720 K in the randomly mixed structure to 746 K for the layered one. The ferroelectric P (E) loops and a modest ME coefficient of 14 mVOe−1cm−1 at 100 Hz were determined only for the layered structure, due to the high leakage and to the small grain size (below 200 nm) in the ferroelectric BaTiO 3 component. • Randomly mixed and tri-layered structure composites were comparatively investigated. • Role of the phase arrangement on the dielectric properties was predicted by FEM. • Experimental dielectric data contains a strong influence from extrinsic phenomena. • Magnetic properties slightly depend on the phase arrangement. [ABSTRACT FROM AUTHOR]

Here, we report structural and magnetic phase transitions in NiCr 1.9 Fe 0.1 O 4 nanoparticles of size ∼60 nm synthesized through cost-effective co-precipitation route. X-ray diffraction pattern shows a stable cubic phase at RT in contrast to tetragonal phase in bulk NiCr 2 O 4. Decreasing the temperature, a complete tetragonal symmetry is observed at 50 K, while a coexistence of cubic and tetragonal phases in the intermediate temperature range. Interestingly, no tetragonal to orthorhombic phase transformation has been observed down to 12 K as observed in NiCr 2 O 4 at 70 K. The local structure examined from temperature dependent EXAFS demonstrates that although no change in distribution of cations among tetrahedral (A) and octahedral (B) sites down to 10 K has been observed, Fe3+ ions occupy A site replacing equivalent amount of Ni2+ towards B site which is contradicting to the bulk NiCr 2 O 4 where Ni2+ occupies only A site. Magnetic studies demonstrate a two-fold increase in para to long-range ferrimagnetic transition, T C , due to increase in A-B exchange interaction and no change in spiral ordering temperature, T S indicates strong B-B interaction. In addition, these nanoparticles exhibit unusually high spontaneous exchange bias of ∼1.265 kOe at 60 K. We discuss the temperature dependent exchange bias on the basis of competition between uncompensated B site moments and ferromagnetically ordered spins at A site. The tunable exchange bias without field highlight the potential applications of these materials in spintronics devices. [ABSTRACT FROM AUTHOR]

Abstract Exchange bias behaviors up to room temperature have been observed in NiCo 2 O 4 /NiO nanoparticle system. The field-cooled magnetic hysteresis loops exhibit shifts both in the field and magnetization axes simultaneously. The variation of exchange bias field and magnetization shift depends strongly on the measuring temperature. In addition, the dependence of exchange bias effect on measuring temperature is not monotonous, which is reflected in the different tendency during the decrease process of magnetization shift and exchange bias field. The exchange bias field is decreased firstly at the range of 10–50 K followed by an increase of 50–200 K and decreased again of 200–320 K. By analyzing various magnetic measurements, the special exchange bias effect in NiCo 2 O 4 /NiO can be owing to the spin glass state and the ferrimagnetic/antiferromagnetic coupling during different temperature ranges. [ABSTRACT FROM AUTHOR]

Exfoliated graphite (EG) is a promising sorbent for oil and organic pollutants, which has a high sorption capacity and hydrophobicity. Modifying the EG with ferrimagnetic compound allows EG with sorbed oil to be collected from the water surface with the use of a magnetic field. The aim of this work is to obtain a sorbent based on exfoliated graphite with ferrimagnetic maghemite (γ-Fe 2 O 3) and investigate its structure and functional properties. The preparation of iron-containing EG includes the impregnation of expandable graphite with a FeCl 3 water solution and the thermal treatment of impregnated expandable graphite at temperatures between 400 and 1000 °C. Mossbauer spectroscopy, X-ray diffraction analysis, scanning electron microscopy and energy dispersive X-ray spectroscopy show the evolution of the iron-containing phase from FeOCl to the mixture of α-Fe 2 O 3 and γ-Fe 2 O 3 , which grants magnetic properties to the samples. EG obtained at 1000 °C has a saturation magnetization of 22.7 emu g−1. High macropore and meso-/micropore volume investigated by mercury porosimetry and nitrogen adsorption-desorption method results in a high sorption rate and sorption capacity of EG up to 30 g g−1 toward oil and liquid hydrocarbons. At the same time, the EG sorption capacity toward water is ten times lower. [Display omitted] • Exfoliated graphite/γ-Fe 2 O 3 is obtained from expandable graphite/FeCl 3. • Evolution of the iron-containing phase was investigated by Mossbauer spectroscopy. • Consequent formation of FeOCl, α-Fe 2 O 3 and γ-Fe 2 O 3 is observed. • γ-Fe 2 O 3 content increases when increasing the thermal treatment temperature. • EG/γ-Fe 2 O 3 has high saturation magnetization and oil sorption capacity. [ABSTRACT FROM AUTHOR]

Polycrystalline sample of Bi 2 Cu 5 B 4 O 14 was synthesized and its structural and magnetic properties were investigated by means of temperature dependent x-ray diffraction, magnetization, and heat capacity measurements. Bi 2 Cu 5 B 4 O 14 is found to be a spin-1/2 layered compound with repeating Cu-pentamer units. DC magnetic susceptibility at high temperatures follows the Curie-Weiss law with a large and negative Curie-Weiss temperature θ CW ≃ −39 K, suggesting the dominant ferromagnetic interaction between Cu 2+ ions. A positive curvature in inverse susceptibility and a magnetization hysteresis with reduced ordered moment at T = 2.1 K pinpoint the ferrimagnetic nature of the compound with T C ≃ 25 K. The modified Arrott analysis shows that Bi 2 Cu 5 B 4 O 14 is a good example of Heisenberg ( β = 0.367 and γ = 1.388) ferrimagnet. Heat capacity data at low temperatures (i.e. in the ordered state) follows a power law ( γT α ) with a reduced exponent ( α ≃ 2.58). The change in magnetic entropy is calculated to be S mag ≃ 28 J/mol K at around 100 K which is close to the expected theoretical value of 28.81 J/mol K for Bi 2 Cu 5 B 4 O 14 . [ABSTRACT FROM AUTHOR]

• Mn Zn ferrite particles with a size of ≈ 12 nm are prepared by hydrothermal synthesis. • Analysis by Mössbauer spectroscopy and neutron diffraction reveals a metastable state. • Mn 0.6 Zn 0.4 Fe 2 O 4 particles show a non-equilibrium distribution of Zn and Mn. • Superparamagnetism is studied on time scales of Mössbauer and magnetic measurements. • Transition to superparamagnetic state is easily controlled by Zn content. Magnetic behaviour of nanoparticles deviates from their bulk equivalents not only due to finite-size and surface effects but it may be also affected by occurrence of metastable states, such as non-equilibrium cation distribution. The chemical composition along with the specific cation distribution are decisive for magnetic properties of spinel ferrites, the nanoparticles of which can be easily tailored to exhibit peculiar properties suitable for various applications. The present study is devoted to hydrothermally prepared Mn Zn ferrite nanoparticles; namely to five samples with approximate composition Mn 1− x Zn x Fe 2 O 4 , where x = 0.21–0.63, that were prepared by a surfactant-free hydrothermal procedure at a rather low temperature of 180 °C. XRD measurements evidenced the cubic spinel structure and a gradual decrease of the mean crystallite size from 14 to 10 nm with increasing zinc content, which was further confirmed by TEM analysis. 57Fe Mössbauer spectroscopy and temperature-variable magnetic measurements provided valuable insight into the blocking behaviour of particles on two dramatically different time scales and demonstrated that Néel relaxation can be enhanced by increasing the zinc content. Nanoparticles of the selected composition Mn 0.62 Zn 0.41 Fe 1.97 O 4 were subjected to neutron diffraction study at 2 K to determine the ferrimagnetic order and in combination with Mössbauer spectroscopy to analyse the cation distribution. The non-zero occupancy of Zn2+ in octahedral sites evidenced a metastable distribution, and the supplemental DFT study revealed that the distribution of Mn2+ is non-equilibrium as well. [ABSTRACT FROM AUTHOR]

The GdTi 0.05 Fe 0.95- x Mn x Si, х = 0–0.95 intermetallic compounds with a tetragonal crystal structure of the CeFeSi type (space group P4/nmm, N 129, tP6) have been studied. The lattice parameter c and the Curie temperature T C increase quickly, whereas the lattice parameter a is almost unchanged in the system when the content of Mn increases. The saturation magnetization, magnetocaloric effect MCE and refrigerant capacity RC change non-monotonically with a dip at intermediate compositions that is presumably due to the canted ferrimagnetic structure of these compounds. The MCE and RC vary in a field changing to 17 kOe within the small ranges of 1.6–2.7 J/kgK and 60–117 J/kg around T C , respectively, while T C changes in a wide range around the room temperature from 160 to 360 K. • The lattice parameter c and T C increase and lattice parameter a is almost unchanged. • Presumably, the canted ferrimagnetic structure is formed in the system. • М sat. , MCE, RC change non-monotonically with a dip at intermediate compositions. • MCE, RC , T C vary in the ranges 1.6–2.7 J/kgK, 60–117 J/kg at 17 kOe field, 160–360 K. [ABSTRACT FROM AUTHOR]

The synthesis, structural characterization, and magnetic properties of La 3 Mn 2 NbO 9 double perovskite are reported. The crystal structure has been refined by X-ray and neutron powder diffraction data in the monoclinic space group P2 1 /n. The Mn2+, Mn3+ and Nb5+ cations are distributed at the 2d and 2c Wyckoff sites, with a high cation order degree in the latter, mainly occupied by Mn2+/Mn3+. The Mn3+ presence was established from X-ray Emission Spectroscopy and X-ray Photoelectron Spectroscopy. Rietveld refinements of powder neutron diffraction data show that at room temperature the cell parameters are a= 5.6063(3) Å, b= 5.8155(3) Å, c= 7.9877(2) Å y β= 89.89(1)°. Magnetization measurements indicate the presence of ferromagnetic and antiferromagnetic interactions with T C ∼19 K and T N ∼11 K, respectively, with a magnetic cell of symmetry Γ 1 (A g). The analysis of the neutron data suggests a canted ferrimagnetic spin structure where an antiferromagnetic unit-cell in a and c axis, and ferromagnetic in b axis with a propagation vector k = (0 ½ 0) was used. The effective magnetic moment obtained experimentally is μ eff = 5.50 μ B /mol Mn2+/3+, slightly lower than the theoretical one for spin only (5.83 μ B). • Synthesis of new double perovskite La 3 Mn 2 NbO 9. • Canted ferrimagnetism due to the high degree of structural distortion. • Effective existence of Mn2+/Mn3+ mixture. • Multiple possible magnetic interactions and huge distortion of the octahedral network allow AFM and FM couplings. [ABSTRACT FROM AUTHOR]

Search for low-moment magnetic materials with high spin-polarization is important for emerging spintronics applications. In this work, we have conducted detailed growth and characterization along with complementary first-principles calculations to investigate the structure and magnetism of Mn 2 FeSi, which is a prospective inverse-Heusler material. We confirm that Mn 2 FeSi adopts a cubic inverse-Heusler structure, in excellent agreement with theory. The magnetic and resistivity measurements show an antiferromagnetic behavior with a Néel temperature of 48 K, which is consistent with prior experimental reports. We find that a low-moment state with higher ordering temperature (150–200 K) can be stabilized under certain growth conditions. Supporting calculations show that Neel-type antiferromagnetic states are energetically very close to the ferrimagnetic ground state. Our work provides evidence that Mn 2 FeSi may be interesting for exploring newer applications with low-moment materials, but the ordering temperatures are low for viable practical applications. • The experimental work reported here confirms a theory prediction into the structure of a relatively unexplored magnetic Heusler material (Mn 2 FeSi). • Such materials can be promising to explore the emerging area of antiferromagnetic spintronics. [ABSTRACT FROM AUTHOR]