Magnetorefractive effect in La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> in the infrared spectral range

The reflection and magnetic reflection spectra, magnetic resistance, electrical properties, and equatorial Kerr effect in La_0.7Ca_0.3MnO₃ crystals have been complexly investigated. The measurements have been performed in wide temperature and spectral ranges in magnetic fields up to 3.5 kOe. It has been found that magnetic reflection is a high-frequency response in the infrared spectral range to the colossal magnetore-sistance near the Curie temperature. Correlation between the field and temperature dependences of the magnetic reflection and colossal magnetoresistance has been revealed. The previously developed theory of the magnetorefractive effect for metallic systems makes it possible to explain the experimental data at the qualitative level. Both demerits of the theory of the magnetorefractive effect in application to the magnets and possible additional mechanisms responsible for the magnetic reflection are discussed.     

Magnetocaloric properties of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>K<Emphasis Type="Italic">x</Emphasis>MnO<Subscript>3</Subscript> manganites

A technology for obtaining single-phase ceramic samples of La_{1 − x} K _x MnO₃ manganites, as well as the dependence of their structure parameters on the potassium content, is described. The magnetocaloric effect in the samples has been measured by two direct methods, the classical method and the magnetic field modulation method, and has been calculated from the specific heat data. The values of the magnetocaloric effect obtained by these methods are significantly different. The observed discrepancies have been explained. Correlation between the doping level and the value of the effect has been found. It has been shown that the magnetic-field dependence of variation of the magnetic entropy near T _C in weak fields corresponds to theoretical calculations and that the value of the magnetocaloric effect in high magnetic fields can be predicted using this dependence.     

Magnetostructural phase transitions in manganese arsenide single crystals

The effect of an external magnetic field with a strength up to 140 kOe on the phase transitions in manganese arsenide single crystals has been investigated. The existence of unstable magnetic and crystal structures at temperatures above the Curie temperature T _C = 308 K has been established. The displacements of manganese and arsenic atoms during the magnetostructural phase transition and the shift in the temperature of the first-order magnetostructural phase transition in a magnetic field have been determined. It has been shown that the magnetocaloric effect in a magnetic field of 140 kOe near the Curie temperature T _C is equal to ??T ?? 13 K. A model of the superparamagnetic state in MnAs above the temperature T _C has been proposed using the data on the magnetic properties and structural transformation in the region of the first-order magnetostructural phase transition. It has been demonstrated that, at temperatures close to T _C, apart from the contribution to the change in the entropy from the change in the magnetization there is a significant contribution from the transformation of the crystal lattice due to the magnetostructural phase transition.     

Effect of temperature conditions of ion implantation on percolation ferromagnetism in Ge0.98Mn0.02 thin films

The effect of temperature conditions of ion implantation on the magnetic properties of Ge_0.98Mn_0.02 thin films has been studied. It has been shown that a decrease in the implantation temperature significantly increases the temperature of percolation magnetic ordering in the subsystem of dispersed Mn²⁺ ions. It has been demonstrated that the observed effect can be due to suppression of the thermally activated aggregation of Mn²⁺ ions into Ge₃Mn₅ clusters and increase in their concentration in the dispersed state.     

Nuclear orientation study of low temperature magnetization of54Mn impurity in ferromagnetic PtFe alloys

Low-temperature nuclear orientation of⁵⁴Mn in ferromagnetic Pt₉₅Fe₅ and Pt₉₀Fe₁₀ hosts has been investigated in 12–50 mK temperature range at external magnetic fields up to 1.2 T. Temperature dependence of the effective magnetic field B_eff on Mn has been observed and interpreted as an effect of misalignment of Mn magnetic moments with respect to the macroscopic magnetization direction at host magnetic saturation.     

Magnetic and ferroelectric properties of exchange-frustrated multiferroics (Ni1 ? xTx)3V2O8 (T = Co, Mn, Zn)

The effect of the substitution of Co²⁺, Mn²⁺, and Zn²⁺ ions for Ni²⁺ ions on the magnetic, dielectric, and ferroelectric properties of vanadate single crystals (Ni_{1 − x} T _x )₃V₂O₈ has been analyzed. It has been found that the low-level (x ≤ 0.1) substitution of both magnetic and nonmagnetic ions stabilizes the ferroelectric state with a cycloidal magnetic structure. The existence region of this state is expanded to low temperatures down to 3 K for Zn²⁺ and below 1.8 K for Co²⁺ and Mn²⁺ owing to the suppression of a low-temperature weak ferromagnetic phase. At the same time, the ferroelectric phase disappears completely at large concentrations of Co and Mn. The effect of magnetic fields on the magnetic and ferroelectric states has been analyzed. It has been shown that the magnetic field along the c axis suppresses the ferroelectric state, whereas the magnetization along the antiferromagnetism axis (a axis) induces the reentrant phase transition from a paraelectric weak ferromagnetic structure to a ferroelectric structure. The corresponding H-T phase diagrams have been drawn.     

High frequency behaviours and Mssbauer study of field annealed FeCuNbSiB alloy ribbons

This paper investigates the high frequency behaviours and magnetic anisotropy of rapidly solidified FINEMET (Fe73.5Si13.5B9Nb3Cu1) alloy ribbons annealed in an applied magnetic field. It finds that the ribbons annealed with the applied magnetic field show much higher resonance frequencies and have even higher permeability at higher frequencies than the samples annealed without the magnetic field and the non-annealed ribbons. Mssbauer spectroscopy had been employed to study the spatial distribution of the magnetic moments of five selected FINEMET alloy ribbons in different heat-treated conditions. The results show that an easy plane has been established after annealling in the magnetic field, while for the other ribbons this effect is not significant. Hence, the relationship between magnetic field annealing and high frequency property has been bridged by the bianisotropic theory.     

Features of magnetic and magnetoelectric properties of rare-earth multiferroic PrFe3(BO3)4 with the singlet ground state

The features of magnetization of rare-earth multiferroic PrFe₃(BO₃)₄ with the singlet ground state have been investigated theoretically. The magnetic anisotropy of the crystal has been studied. The temperature dependences of anisotropy constants have been calculated. The phase H-T diagram has been constructed. The dependences of the behavior of magnetization vectors of magnetic sublattices on the external magnetic field have been obtained. The magnetoelectric effect has been investigated, and the dependences of polarization on the temperature and field have been found for its various orientations. The theoretical data have been compared with the experimental data and their good agreement has been established.     

Magnetocaloric effect and magnetic properties in YMnO3 perovskite

The magnetic properties and magnetocaloric effect in YMnO₃ have been investigated using Monte Carlo simulations. The thermal magnetization, specific heat and magnetic entropy have been obtained for different values of exchange interactions and for a several external magnetic field values. The variation of adiabatic temperature change with the temperatures has been obtained for several values of external magnetic field. It has been found that the sample exhibited a paramagnetic to ferromagnetic phase transition at 30 K. The transition temperature of YMnO₃ has been deduced for different values of size (1/L) and different values of exchange interactions. The relative cooling power with several values of external magnetic field has been established.     

Magnetocaloric effect in (La<Subscript>0.6</Subscript>Ca<Subscript>0.4</Subscript>)<Subscript>0.9</Subscript>Mn<Subscript>1.1</Subscript>O<Subscript>3</Subscript>

The results of investigations of the magnetization, susceptibility, and magnetic-field-induced changes in the entropy of polycrystalline manganite (La_0.6Ca_0.4)_0.9Mn_1.1O₃ near the magnetic phase transition have been presented. Magnetic measurements have been carried out at temperatures in the range from 210 to 310 K in magnetic fields of up to 9 T. The magnetocaloric effect has been revealed by measuring the magnetic-field dependences of magnetization. The magnitude of the magnetocaloric effect is compared with similar results obtained for other manganites.     

Heat capacity and magnetocaloric properties of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>K<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> manganites

The magnetocaloric effect and the heat capacity of La_{1 − x} K _x MnO₃ (x = 0.1, 0.15, 0.175) ceramic samples have been studied at temperatures in the range 77–350 K and in magnetic fields of up to 27 kOe. The technique for preparing the samples has been described. The heat capacity anomalies related to the ferromagnetic-paramagnetic magnetic phase transition have been revealed and interpreted. It has been demonstrated that the change in the magnetic entropy ΔS calculated from the data on the heat capacity C _p and direct measurements of the magnetocaloric effect ΔT reaches values that are of practical interest.     

Specific features of the magnetoresistance in multilayer systems of magnetic nanoislands in weak magnetic fields

New magnetic structures such as multilayer systems of magnetic nanoislands being alternating layers of nanoislands of various magnets have been proposed. The electric, magnetic, and magnetooptical properties of the systems have been studied. The magnetoresistance of ～2% related to the anisotropic effect has been revealed. In multilayer structures of magnetic nanoislands, a unidirectional axis of predominant magnetization has been found, which changes its orientation depending on the structure parameters. The magnetic field required to reorient the axis in the opposite direction has been estimated to be 2 kOe < H _A < 20 kOe. The periodic multilayer structures of magnetic nanoislands are very sensitive to hyperweak magnetic fields (to 10^?6 Oe).     

Anomalous Hall effect and ferromagnetism in the new diluted magnetic semiconductor Sb<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript>x</Subscript>Te<Subscript>3</Subscript>

The magnetic and galvanomagnetic properties of single crystals of the new diluted magnetic semiconductor p-Sb_2?xCr_xTe₃ (0 ≤ x ≤ 0.02) have been studied in the temperature range 1.7–300 K. A ferromagnetic phase with the Curie temperature T_c ≈ 5.8 K and the maximum Cr content x = 0.0215 has been revealed. The easy magnetization axis is parallel to the C₃ crystallographic axis. In the presence of strong magnetic fields, the Shubnikov-de Haas effect has been observed. Analysis of this effect shows that doping with chrome reduces the concentration of holes. Negative magnetoresistance and the anomalous Hall effect are observed at liquid helium temperature.     

Colossal magnetodielectric effect in SmFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> multiferroic

The colossal (more than threefold) decrease in the dielectric constant ɛ in the easy-plane SmFe₃(BO₃)₄ ferroborate in a magnetic field of ∼5 kOe applied in the basal ab plane of the crystal has been found. A close relation of this effect to anomalies in the field dependence of the electric polarization has been established. It has been shown that this magnetodielectric effect is due to the contribution to ɛ from the electric susceptibility, which is related to the rotation of spins in the ab plane, arises in the region of the antiferromagnetic ordering T < T _N = 33 K, and is suppressed by the magnetic field. A theoretical model describing the main features of the behavior of ɛ and electric polarization in the magnetic field has been proposed, taking into account the additional anisotropy in the basal plane induced by the magnetoelastic stresses.     

Magneto-optical properties of the iron garnet Tb3Fe5O12 near the magnetic compensation temperature

The magneto-optical susceptibility and magnetic hysteresis loops of the Faraday effect, which accompany the technical magnetization of the iron garnet Tb₃Fe₅O₁₂, have been investigated experimentally in the temperature region near the magnetic compensation point of this ferrimagnet T _c = 249 K. It has been found that, during the technical magnetization as the temperature approaches the magnetic compensation point T _c , the velocity of domain walls increases, whereas the magneto-optical susceptibility has local maxima to the right and to the left from T _c . Mentioned features of magneto-optical properties of the iron garnet Tb₃Fe₅O₁₂ are associated with the resonance natural frequency of the domain wall oscillations in the crystal with the frequency of the alternating magnetic field. It has been shown that the used theoretical model of the magnetic resonance of domain walls makes it possible to consistently describe (at the qualitative level) the revealed regularities of the variation of the Faraday effect in the iron garnet Tb₃Fe₅O₁₂ near T _c .     

Interrelation of anisotropy of magnetic properties and magnetodielectric effect in a Cu<Subscript>3</Subscript>B<Subscript>2</Subscript>O<Subscript>6</Subscript> single crystal

The effect of an external magnetic field on permittivity has been studied in a Cu₃B₂O₆ single crystal with a layered structure in the direction perpendicular to layers (bc-planes). It has been found that the appreciable magnetodielectric effect in the temperature range below the Néel temperature (≈10 K) takes place only at one magnetic field orientation H and one crystallographic direction, i.e., H || b. Such “selectivity” of the magnetodielectric effect correlates with the anisotropic behavior of magnetic properties of the crystal.     

Study of magnetic flux pinning in granular YBa2Cu3O7 − y /nanoZrO2 composites

In this work, the effect of ZrO₂ nanoparticles prepared in a low-pressure arc discharge plasma on magnetic flux pinning of granular YBa₂Cu₃O_{7 ? y} /nanoZrO₂ composites has been studied. It has been shown that the ZrO₂ nanoparticles do not change the superconducting transition and the microstructure of superconductors. At a temperature of 5 K, the addition of 0.5 and 1 wt % of ZrO₂ nanoparticles may lead to the additional effect of magnetic flux pinning and the increase in the critical current density J _c. The J _c value for composites with 1 wt % is two times larger than that for the reference sample. The fishtail effect is observed for YBa₂Cu₃O_{7 ? y} /nanoZrO₂ composites at the temperatures of 20 and 50 K. The problems associated with the additional effect of magnetic flux pinning of granular YBa₂Cu₃O_{7 ? y} /nanoZrO₂ composites and the appearance of the fishtail effect have been discussed.     

Interface induced exchange bias effect in La0.67Sr0.33MnO3/SrIrO3 multilayer

Epitaxial superlattices of ferromagnetic/paramagnetic La_0.67Sr_0.33MnO₃/SrIrO₃ materials have been prepared on SrTiO₃ (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.     

Effect of pressure on magnetic phases of (Fe1-x Ni x )49Rh51

The effect of high pressure and magnetic field on the stability of magnetic phase transitions in (Fe_1?x Ni _x )₄₉Rh₅₁ has been studied. It has been shown that the increase in the Ni content suppresses the stability of the low-temperature antiferromagnetic phase and leads to its disappearance. Pressure on the other hand restores the stability to the antiferromagnetic order. These findings are explained using first-principles band-structure calculations.