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 .     

Low-frequency resonance of domain walls in the iron garnet Tb3Fe5O12 near the magnetic compensation point

The vibrational motion dynamics of domain walls (DWs) in the iron garnet Tb₃Fe₅O₁₂, a low-frequency magnetic field, and the temperature range 200–295 K (which includes the magnetic compensation point of this ferrimagnet, T _c ≈ 249 K) is studied by a magnetooptical method. The temperature dependence of the DW vibration amplitude in this garnet crystal near T _c has a resonance character. A theoretical model of the magnetic resonance of DWs is proposed to interpret the obtained experimental results; according to this model, the DW mass tends to infinity and the resonance frequency tends to zero when temperature approaches the magnetic compensation point.     

Technical magnetization of Tb3Fe5O12 garnet ferrite near the magnetic compensation point

The domain structure and technical magnetization of a single-crystalline Tb₃Fe₅O₁₂ garnet ferrite sheet near its magnetic compensation point (T _c ≈ 250 K) are studied. It is found that above this temperature the domain structure persists and considerably influences the field and temperature dependences of the Faraday effect. It is shown that the behavior of Tb₃Fe₅O₁₂ during technical magnetization near T _c is not fully described by the existing thermodynamic theory of the domain structure. The features of the domain structure and technical magnetization of Tb₃Fe₅O₁₂ are related to the transition of the magnetic structure to a non-collinear phase.     

Remanent magnetizations of gadolinium iron garnet sublattices near the compensation point

Gadolinium iron garnet Gd₃Fe₅O₁₂ has been studied near the compensation point T _cm by Mössbauer spectroscopy. It has been shown that the remanent magnetizations of the ferrite sublattices abruptly increase near T _cm. The phenomenon has been explained by the increase in the domain sizes in the ferrite with approaching T _cm. The Mössbauer spectroscopy can be used to investigate the magnetization and magnetization reversal processes in individual sublattices of a ferrimagnet.     

Induced magnetic phase transitions in GdCo/Co-type multilayer films

The magnetic structure transformation of the layered ferrimagnet [Co/Gd₃₆Co₆₄]₄/Co in an external magnetic field was comprehensively studied. Using magnetometrical, magnetooptical, and magnetoresistive techniques, it is established that, when magnetized in fields exceeding a threshold value H _cr, the collinear magnetic structure formed by the magnetic moments of the Co and GdCo layers is distorted. The value H _cr varies nonmonotonically with temperature T and reaches a minimum at the temperature of magnetic compensation of the layered ferrimagnet. The H _cr(T) dependence is well described in terms of the homogeneous ferrimagnet model with an adequately chosen phenomenological intersublattice interaction constant taking into account the weakened coupling of the surface Co layers with the internal part of the actual layer structure.     

Effect of magnetization of the rare earth sublattice on the domain structure of a two-layer ferrite-garnet film

The temperature behavior of the domain structure in a two-layer ferrite-garnet film with one of the layers having a compensation point T _c , as well as in single-layer witness films, has been experimentally investigated. It is shown that the rare earth sublattice affects phase transitions in the domain structure of a two-layer film. The phase transitions observed were explained in terms of the concept of magnetostatic pressure in the domain structure.     

Magnetic properties of the CuCoAlBO<Subscript>5</Subscript> single crystal

High-quality CuCoAlBO₅ single crystals have been grown, and their crystal structure, magnetic susceptibility, and magnetization have been studied. It has been established that the CuCoAlBO₅ compound is an uncompensated antiferromagnet or ferrimagnet with a small magnetic moment and the magnetic ordering temperature T _N = 28 K. A model has been proposed for the magnetic structure. A strong anisotropy of the magnetic properties has been revealed.     

The kinetics of relaxation of magnetization fluctuations near the phase transition from paramagnetic state to ferromagnetic state with domain structure

The equations of motion describing relaxation of magnetization fluctuations in the paramagnetic state for a uniaxial ferromagnet have been solved. In the Landau-Ginzburg functional the demagnetization energy has been taken into account. The finite dimensions of a sample have been considered. It has been shown, that a phase transition is generated by fluctuations containing information about the period of the domain structure at the phase transition point T_c¹. The obtained formulae describe T_c¹ and the period of the domain structure. The results can be used both for bulk materials and thin films.     

Modulated magnetic structure in quasi-one-dimensional clinopyroxene NaFeGe<Subscript>2</Subscript>O<Subscript>6</Subscript>

The magnetic structure of the NaFeGe₂O₆ monoclinic compound has been experimentally investigated using the elastic scattering of neutrons. At a temperature of 1.6 K, an incommensurate magnetic structure has been observed in the form of an antiferromagnetic helix formed by a pairs of the spins of the Fe³⁺ ions with helical modulation in the ac plane of the crystal lattice. The wave vector of the magnetic structure has been determined and its temperature behavior has been studied. The analysis of the temperature dependences of the specific heat and susceptibility, as well as the isotherms of the field dependence of the magnetization, has revealed the existence of not only the order-disorder magnetic phase transition at the point T _N = 13 K, but also an additional magnetic phase transition at the point T _c = 11.5 K, which is assumingly an orientation phase transition.     

AC susceptibility and temperature modulation studies of gadolinium near the Curie point

Measurements of the ac susceptibility and temperature modulation studies of the ac and dc magnetic properties of polycrystalline gadolinium in the vicinity of the Curie point T_c are reported. Field-independent exchange-enhanced paramagnetism was observed above T_c. Below T_c the initial field-independent susceptibility was observed for applied fields < 8 A/m rms and exhibited a frequency dependence characteristic of a magnetic after-effect. Within about 3 K of T_c this susceptibility is strongly influenced by domain nucleation and a temperature dependent magnetic relaxation time was observed.     

Reflexivity and Correlation of Magnetic States of Nanostructures in the Nb(70 nm)/Ni<Subscript>0.65</Subscript>Cu<Subscript>0.35</Subscript>(6.5 nm)/Si Ferromagnet–Superconductor Heterostructure

We have studied the Nb(70 nm)/Ni_0.65Cu_0.35(6.5 nm)/Si layered structure in the temperature range T = 1.5–10 K using polarized neutron reflectometry. The correlation of the states of magnetic structures is observed at temperature T = 9 K, which is slightly higher than the superconducting transition temperature T_c = 8.5 K of the structure. At temperature T = 4 K, which is lower than T_c, the effect of reflexivity of magnetic states existing at T = 9 K was observed.     

57Fe Mössbauer effect studies of spinreorientational transitions near the compensation point in Y1.6Gd1.4Fe5O12

Existence of spin-reorientational (SR) transitions near the magnetic compensation point (T_c) is shown for a polycrystal sample of Y_1.6Gd_1.4Fe₅O₁₂ (YGG) with no external magnetic field (H_ext).     

Crystal structure of the inverse weberite ZnFeF5(H2O)2, magnetic and mössbauer study of the antiferromagnet ZnFeF5(H2O)2 and ferrimagnet Mn FeF5(H2O)2

The room temperature crystal structure of the inverse weberite ZnFeF₅ (H₂O)₂ is refined from powder X-ray diffraction. The cell is orthorhombic (S.G. Imma, a = 7.475(1) →A, b = 10.766(1) →A, c = 6.594(1) →A, z = 4). Below T_N = 9(2) K, ZnFeF₅(H₂O)₂ becomes a 1-D antiferromagnet. This behaviour was characterized by susceptibility and magnetization measurements and Mössbauer spectroscopy. On the contrary, isotypic MnFeF₅(H₂O)₂ is confrimed to be a ferrimagnet below T_c = 39.5(1)K. Its magnetic and Mössbauer characteristics are, above and below T_c,and agree with a 3-D magnetic character. Ferrimagnetism could be due to frustration effects as in previously described Fe₂F₅(H₂O)₂.     

Vortex structure and anisotropy of electric resistance in Bi2Sr1.65La0.35CuO6 + δ single crystals

The vortex structure of Bi₂Sr_1.65La_0.35CuO_6+δ single crystals in tilted magnetic fields has been studied by the decoration method. From the observed pattern of vortex chains in the basal plane, the parameter of anisotropy in the superconducting state has been estimated as γ_S = 460 ± 40. The electric resistance of Bi₂Sr_1.65La_0.35CuO_6+δ single crystals has been studied in a broad range of temperatures (T _c < T < 300 K) and magnetic fields (up to 16 T). The ratio of resistivities in the direction perpendicular to the basal plane and in plane near the critical temperature T _c amounted to ρ⊥/ρ‖ = 3.2 × 10⁵. A possible relationship between the anisotropy in the normal and superconducting states is discussed.     

Dissociative hydrogen adsorption on nickel surfaces: Absence of a magnetocatalytic effect

The temperature dependence of the rate of dissociative hydrogen adsorption on Ni(111) and Ni(110) surfaces was determined by monitoring the rate of HD production from a mixed H₂ and D₂ molecular beam striking the sample surfaces. No anomaly was found in the vicinity of the Curie point T_c if the surfaces were rigorously kept clean. A step-like increase of the rate was, however, observed near T_c if the surfaces were slightly contaminated with carbon which dissolves in the bulk in this temperature range and segregates back upon cooling. The results are discussed in view of the present knowledge of the magnetic properties of nickel surfaces.     

Preparation,Structure, and Dielectric and Magnetic Properties of SrFe<Subscript>2/3</Subscript>W<Subscript>1/3</Subscript>O<Subscript>3</Subscript> Ceramics

Polycrystalline samples of SrFe_2/3W_1/3O₃ (SFWO) ceramic were obtained by solid-phase reactions with subsequent sintering using conventional ceramic technology. X-ray diffraction analysis showed that at room temperature, the SFWO ceramic is single-phase and has a perovskite-type structure with tetragonal symmetry and parameters a = 3.941(9) Å, c = 3.955(6) Å, and c/a = 1.0035. In studying the magnetic properties and the Mössbauer effect in SFWO ceramics, it is found that the material is a ferrimagnet, and the iron ions are only in the valence state of Fe³⁺. It is suggested that in the temperature range of T = 150–210°C, a smeared phase transition from a cubic (paraelectric) phase to a tetragonal (ferroelectric) phase takes place in SFWO with decreasing temperature.     

Magnetic properties of RFe6Al6 alloys with R=Y,Dy

Intermetallics crystallizing in ThMn₁₂ type structure were investigated. Magnetostatic measurements showed that the magnetic ordering temperature and the magnetic moment of YFe₆Al₆ samples depend strongly on thermal and mechanical treatment. These measurements for a powdered sample of YFe₆Al₆ showed that the alloy was a ferromagnet with a Curie temperatureT _C =265 K and a magnetic moment μ=5.1 μ_B/f.u. at 77.4 K. From X-ray, magnetostatic and Mössbauer effect measurements it appears that the Fe atoms prefer the 8j and 8f crystallographic positions. Magnetostatic measurements for a powdered sample of DyFe₆Al₆ showed that this alloy was a ferrimagnet with the ordering temperatureT ₀=311 K and magnetic moment μ=1.1 μ_B/f.u. at 77.4 K.     

Dynamical behavior of spin-glass Cd1-xMnxTe from low field faraday rotation measurements

The low field Faraday rotation effect has been used to the investigation of the dynamic magnetic properties of the spin-glass Cd_1-xMn_xTe. The temperature and time dependence of the Faraday angle was investigated at T<T_c. It was shown that the thermal and magnetic history of the sample above T_c has the essential influence on the behavior below the critical temperature.     

A neutron small angle scattering study of the onset of ferromagnetism in TiBe2-xCux alloys

The onset of ferromagnetic order in TiBe_2-xCu_x alloys, with x = 0.5, 0.4, 0.3, 0.2 and 0.15, has been examined using the technique of neutron small-angle scattering. The Curie temperature, T_c, for these alloys has been determined from the temperature dependence of the magnetic critical scattering. A linear extrapolation of T_c versus copper concentration yields a critical concentration for ferromagnetic order of x_c = 0.05 ± 0.02. For the alloys with x = 0.4, 0.5 the lineshape of the magnetic critical scattering, at and above T_c, is well explained by the Ornstein-Zernicke form of the spin correlation function. For the lower concentration alloys the exact form of the spin correlation function is still unclear.