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We report a study on the interfacial antiferromagnetic coupling between ferrimagnetic TbIG/YIG thin films. TbIG/YIG bilayers are grown on YAG (110) substrates. The crystal structure and magnetic properties of the films are characterized. The temperature and directional dependences of the antiferromagnetic coupling effect are observed at low temperatures. This work enriches the magnetic research of ferrimagnetic oxide films with complex structures, providing new ideas for the design of antiferromagnetically coupled spintronics devices. [ABSTRACT FROM AUTHOR]

Fault kinematics can provide information on the relationship and assembly of tectonic units in an orogen. Magnetic fabric studies of faults where pseudotachylytes form have recently been used to determine direction and sense of seismic slip in prehistoric earthquakes. Here we apply this methodology to study magnetic fabrics of pseudotachylytes in field structures of the Köli Nappe Complex (central Swedish Caledonides), with the aim to determine fault kinematics and decipher the role of seismic faulting in the assembly of the Caledonian nappe pile. Because the pseudotachylyte veins are thin, we focused on small (ca. 0.2 to 0.03 cm 3) samples for measuring the anisotropy of magnetic susceptibility. The small sample size challenges conventional use of magnetic anisotropy and results acquired from such small specimens demand cautious interpretation. Importantly, we find that magnetic fabric results show inverse proportionality among specimen size, degree of magnetic anisotropy and mean magnetic susceptibility, which is most likely an analytical artifact related to instrument sensitivity and small sample dimensions. In general, however, it is shown that the principal axes of magnetic susceptibility correspond to the orientation of foliation and lineation, where the maximum susceptibility (k1) is parallel to the mineral lineation, and the minimum susceptibility (k3) is dominantly oriented normal to schistosity. Furthermore, the studied pseudotachylytes develop distinct magnetic properties. Pristine pseudotachylytes preserve a signal of ferrimagnetic magnetite that likely formed during faulting. In contrast, portions of the pseudotachylytes have altered, with a tendency of magnetite to break down to form chlorite. Despite magnetite breakdown, the altered pseudotachylyte mean magnetic susceptibility is nearly twice that of altered pseudotachylyte, likely originating from the Fe-rich chlorite, as implied by temperature-dependent susceptibility measurements and thin-section observations. Analysis of structural and magnetic fabric data indicates that seismic faulting occurred during exhumation into the upper crust, but these data yield no kinematic information on the direction and sense of seismic slip. Additionally, the combined structural field and magnetic fabric data suggest that seismic faulting was postdated by brittle E–W extensional deformation along steep normal faults. Although the objective of finding kinematic indicators for the faulting was not fully achieved, we believe that the results from this study may help guide future studies of magnetic anisotropy with small specimens (<1 cm 3), as well as in the interpretation of magnetic properties of pseudotachylytes. [ABSTRACT FROM AUTHOR]

Terbium (Tb) and Thulium (Tm) co-doped strontium hexaferrites (SHFs), with composition SrFe 12-2x Tb x Tm x O 19 (0.00 ≤ x ≤ 0.04), were prepared via sol-gel auto-combustion method. The effect of Tb3+ and Tm3+ (as co-dopants) on SHFs were investigated in detail. XRD pattern of the prepared SHFs revealed the formation of M-type SHFs. A secondary phase of Fe 2 O 3 starts to appear for x ≥ 0.02. The optical band gaps (E g) of the prepared SHFs were widened with the increase in doping levels. Mössbauer study showed that the Tm3+ and Tb3+ ions have the preference to occupy 12k and 2a octahedral sites. M(H) measurements were recorded at room temperature (RT; T = 300 K) and low temperature (T = 10 K). The hysteresis loops of various SHFs revealed their ferrimagnetic (FM) nature at both RT and 10 K. Magnetic parameters including saturation magnetization (M s), remanence (M r), coercivity (H c), squareness ratio (SQR = M r /M s) and magnetic moment ( n B ) were determined. Compared to the pristine (undoped) sample, lower content of Tm3+ and Tb3+ co-substitution (x = 0.01) improves significantly the magnetic properties of SHFs. With further increasing co-substitution contents (x > 0.01), an impurity phase appears and as a result the magnetization reduces. The observed SQR values of the proposed SHFs above 0.5 clearly indicated their single domain character with uniaxial magnetocrystalline anisotropy. Our systematic synthesis strategy and characterization may constitute a basis for achieving high quality co-doped SHFs in a customized way. [ABSTRACT FROM AUTHOR]

The effects of Fe substitution on the structural and magnetic properties of the HoCo 12- x Fe x B 6 (0 ≤ x ≤ 2) series of intermetallic compounds have been studied. All of the compounds form in the rhombohedral SrNi 12 B 6 -type structure, the lattice constants increasing linearly with x. These compounds are ferrimagnets with a small transition metal magnetic moment and exhibit a spin reorientation transition. The Curie temperature decreases from 147 K for x = 0–105 K for x = 2. The Fe for Co substitution leads also to a progressive decrease of the spontaneous magnetization. The spin reorientation transition temperature is significantly reduced upon Fe for Co substitution whereas the compensation temperature is much less sensitive to the Fe composition. • Ferrimagnetic ground state. • Compensation point. • Spin reorientation transition. • Magnetocrystalline anisotropy. • Monotonic decrease of T C , T SR and M S upon Fe for Co substitution. [ABSTRACT FROM AUTHOR]

Co(Fe 1 -x Cr x) 2 O 4 (x = 0.02, 0.10, 0.15, 0.30, 0.50) samples are synthesized by the sol-gel method. The XRD patterns and subsequent Rietveld refinement provided structural analysis and confirmation of the samples' single-phase formation. XPS measurement reveals the existence of the elements Co, Cr and Fe in 2+ and 3+ oxidation states. The saturation magnetization (M s), coercivity (H c) and magnetocrystalline anisotropy (K 1) are observed to decline to as low as 10 emu/g, 35 Oe and 0.50 (106 erg/cm3) following Cr substitution, which indicated that the samples transform to a soft magnetic material. Cr substitution also lowers the ferrimagnetic (FiM) to paramagnetic (PM) transition temperature, T c , from 752 K for x = 0.02 to 307 K for x = 0.50. With Cr replacement, the dielectric constant and dielectric loss values decrease, indicating it to be a potential contender for high frequency applications. The dielectric constant for x = 0.30 and x = 0.50 samples rises sharply around 1 MHz owing to the LC resonance effect between the samples and the measurement leads. The ac conductivity plots are found to be in conformity with Jonscher's single power law, and the conduction process is revealed to be attributable to the small polaron hopping mechanism. • Cr substituted Cobalt ferrites has been synthesized in single phase form by sol-gel method. • Co, Cr and Fe exists only in 2+ and 3+ oxidation state. • Cr occupies only the octahedral sites. • Saturation magnetization, Coercivity and magnetocrystalline anisotropy are observed to decline following Cr substitution. • Dielectric constant and dielectric loss decreases with Cr substitution. [ABSTRACT FROM AUTHOR]

The Monte Carlo simulation has been used to investigate the magnetic properties of a mixed spin-1 (sublattice A) and spin-1/2 (sublattice B), where each sublattice has a rectangular structure and the whole lattice system forms a 2-D centered rectangular lattice. Five possible interactions are considered. Namely, two S–S interactions and two $\sigma $ – $\sigma $ interactions depend on crystal direction, and an antiferromagnetic interaction between the two sublattices is taken. Our results show that the critical temperature increases with increasing the variation of any exchange interactions. The existence of the compensation temperature depends on the balance between the S–S interactions along and $\sigma $ – $\sigma $ interactions along [01] directions. [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]

We have separately assessed the contributions of isolated Fe3+ ions and the ferrimagnetic subsystem to the total magnetization of an aligned magnetite (Fe3O4) nanowire array grown in pores of an anodized alumina membrane and evaluated the magnetic anisotropy field of the nanowires, which has been found to be an order of magnitude weaker than the expected shape anisotropy field. The reduction in magnetic anisotropy in the nanowires can be accounted for by dipole–dipole interaction between individual nanowires in the array. In electron spin resonance spectra of the nanowires, we have identified a phase-inverted line, corresponding to their microwave magnetoresistance. The Verwey transition in the magnetite nanowires has been shown to be suppressed due to deviations from stoichiometry and size effects. [ABSTRACT FROM AUTHOR]

Tunability of structural and magnetic properties of Mn 3- x Co x Ga films is presented by Co substitution, where critical behavior emerges 0.37 ≤ x ≤ 0.56 exhibiting a transition from tetragonal hard ferrimagnetic with perpendicular magnetic anisotropy (PMA) to a cubic soft ferrimagnetic phase with in-plane magnetic anisotropy (IMA). In the critical regime, coexisting state of tetragonal and cubic phases possesses significantly low coercive field (H C = 1.9 kOe) with relatively low saturation magnetization (M S = 100~150 emu/cc) while maintaining the PMA. From first-principles calculations, moments of two Mn sites do not change upon Co substitution. However, moments of substituted Co almost vanish in tetragonal while giving around 1 μ B in cubic phase, which agrees with overall M S behaviors of the experimental results. These findings not only uncover the hidden magnetic state in Mn 3- x Co x Ga by altering the parallel and antiparallel coupling between Mn and Co, but also provide an additional degree of freedom for spintronic applications using Mn-based Heusler compounds. • Critical regime during the transition from hard ferrimagnetic tetragonal to soft ferrimagnetic cubic in Co-substituted Mn3Ga. • Dramatic reduction of the coercive field on remaining perpendicular magnetic anisotropy in the critical regime. • Compensation point near this critical regime due to a large reduction of the Co moments when substituted in Mn 3 Ga. [ABSTRACT FROM AUTHOR]

NiCr 2 O 4 nanoparticles have been successfully prepared by chemical co-precipitation method. Desired crystallographic phase of NiCr 2 O 4 is confirmed by analyzing x-ray diffractrograms. With increasing annealing temperature, crystal transition from cubic to tetragonal phase is observed. The increasing average particle size from ∼80 to ∼280 nm is studied by SEM and TEM micrographs as annealing temperature increases. Exchange bias behavior is detected at 10 K accompanied by the shift of magnetic hysteresis loops along field axis. This effect is gradually weakening as annealing temperature increases. The magnetization depending on temperature under zero-field-cooled and field-cooled conditions suggests the ferrimagnetic transition at ∼72 K and the spiral magnetic order at ∼25 K. Furthermore, the ferrimagnetic transition point shifts slightly to low temperature with increasing annealing temperature. Based on the measurement results, the appearance and evolution of exchange bias effect in NiCr 2 O 4 nanoparticles with improving annealing temperature should be simultaneously derived from the lattice transition and the surface spin effects. • Annealing temperature evidently affects the microstructure and magnetism of NiCr 2 O 4 nanoparticles. • Increasing annealing temperature results in crystal transition from cubic to tetragonal phase. • Increasing average particle size from ∼80 to ∼280 nm is observed as annealing temperature increases. • Magnetic behavior is regulated by crystal transition and particle size due to annealing temperature. [ABSTRACT FROM AUTHOR]

This paper described to the ceramics (inorganic) two-component composites with controllable magnetic and electrical properties. Ceramic composite samples were produced via solid state reaction method (standard ceramic technique) from initial magnetic (BaFe 11.9 Al 0.1 O 19 or BF) and ferroelectric (BaTiO 3 or BT) phases. BT and BF initial compounds were mixed in stoichiometric ratios (BF) 1-x - (BT) x (x = 0, 0.25, 0.5, 0.75 and 1) and sintered. Initial compounds BaFe 11.9 Al 0.1 O 19 (x = 0) and BaTiO 3 (x = 1) were also produced via standard ceramic technique. The constituent materials were chosen considering their perspective ferrimagnetic and ferroelectric properties, respectively for BF and BT. Moreover, Ba-hexaferrites are reported to exhibit ferroelectricity at room temperature as well, and the combination of two ferroelectric phases is of interest. Systematic investigations of the structural, magnetic and electrical properties versus chemical composition (x) were performed. As structural properties we have defined the features of crystal structure (a and c lattice parameters, volume of unit cell) and peculiarities of microstructure (density, porosity, average grain size). The ferrimagnetic phase transition temperature is almost independent of the content of BT, which is determined by the exchange interactions Fe3+-O2--Fe3+in the magnetic phase. However, the coercivity of composite samples is lower which is due to the contribution of the microstructure dependent shape-anisotropy to the total magnetic anisotropy energy. The permittivity vs. temperature behavior confirmed the existence of two ferroelectric phase transitions corresponding to structural phase transitions in BT (at about 400 K) and BF (at about 700 K). It was observed that the electrical properties of composite samples, including the temperatures of the phase transitions, critically depended on concentration x which affects the composite microstructure. This behavior was discussed in terms of microstructure analysis (grain size, porosity and density). [ABSTRACT FROM AUTHOR]

The effects of deposition order on the magnetic properties of the NiFe/NiMn exchange couple were studied. The use of a thin underlayer, to enhance these properties, was also investigated for the deposition order NiMn/NiFe. We found that the use of such an underlayer was essential for the exchange field to be greater than the coercivity. We observed that the underlayer film thickness did not have a dramatic effect on the final exchange field obtained. X-ray diffraction studies did not reveal a strong correlation between film texture and exchange fields. The blocking temperature was also measured for the deposition order NiFe/NiMn. [ABSTRACT FROM PUBLISHER]