Solid State Phenomena Vols. 233-234

Abstract: Present paper reports of resonance properties of Mn₂GeO₄ single crystals. The data confirm the formation of a complex spiral magnetic structure at low temperatures. It is shown that the spin reorientation may be associated with the competition anisotropic contributions of the various subsystems of the manganese ions.

Abstract: Temperature-field and orientational magnetization dependences of single crystals were measured. Both samples demonstrate significant field-depending temperature hysteresis and low-temperature counter field magnetization. The correlation of orientational dependences of these effects and magnetic anisotropy is analyzed; the role of spin-lattice interactions is discussed.

Abstract: β-Cu₃Fe₄(VO₄)₆ single crystals were synthesized. The X-ray, magnetic, Mössbauer, and EPR investigations of the crystals were fulfilled. It is established that single-crystal β-Cu₃Fe₄(VO₄)₆ is a spin glass at low temperatures. Freezing temperature varies considerably depending on the orientation of the magnetic field relative to the crystal axes. Spin-glass state is confirmed by the relaxation of the magnetization.

Abstract: Thermopower α and magnetothermopower ∆α/α were studied in the Sm_0.55Sr_0.45MnO₃ samples, containing clusters of three types: ferromagnetic clusters with the Curie temperature T_C = 126 K, A-type antiferromagnetic clusters with the Neel temperature T_NA ≥ T_C and CE-type antiferromagnetic clusters with the T_NCE = 240 K. The curves of temperature dependence of α (T) have a large maximum including T_C and T_NCE and the sharp minimum on the {∆α/α}(T) curves in the T_C-region. Negative magnetothermopower in minimum achieves the giant value ~ 85% in magnetic field 14.17 kOe. It is shown that thermopower is largely caused by the presence of ferromagnetic nanoclusters of ferron-type and to a lesser degree of CE-type antiferromagnetic clusters, in which there is a charge ordering, displacing oxygen ions.

Abstract: It has been found that the temperature dependences of the Young’s modulus for rare-earth cobaltites RBaCo₄O₇ (R = Dy - Er, Y) exhibit significant hysteresis and irreversible effects over a wide range (80–280) K between the structural and magnetic phase transition temperatures. At the magnetic phase transition temperature, there are weak and smoothed anomalies of the Young’s modulus, which correlate with the low dimensionality and frustration of the exchange interactions in the Kagome lattice of the Co subsystem for the studied rare-earth cobaltites.

Abstract: Transient optical anisotropy in the hexagonal manganite YMnO₃ excited by linearly and circularly polarized laser pulses has been observed. The photo-induced anisotropy was investigated by the pump-probe technique based on a femtosecond Ti:sapphire laser generating optical pulses at the photon energy of 1.55 eV. Temporal and spectral dependencies of the photo-induced optical rotation and ellipticity were analyzed by a theoretical model considering ultrafast population and relaxation processes near the interband transitions from the hybridized O²⁻(2p)-Mn³⁺(3d) (Γ₁) to the Mn³⁺(3d³_z2−r2) (Γ₅) states at photon energies of the laser excitation. Very short relaxation time of ~10 fs, which is the Raman coherence time between the excited Γ₅|x> and Γ₅|y> states, has been determined. It is found that this coherence time is much shorter than a charge relaxation time of ~500 fs between the Γ₅|x,y> and Γ₁|g> states for the interband electronic transition Γ₁→Γ₅.

Abstract: Influence of the substitution of Hg by Cd on Kerr effect, magnetoreflection, and magnetotransmission of unpolarized light for Hg_1-xCd_xCr₂Se₄ (0≤x≤1) single-crystals is studied. The changes in the magnetooptical properties of the ferromagnetic spinels are shown to occur in compositions with x>0.1. The giant values of magnetooptical effects in Hg_1-xCd_xCr₂Se₄ spinels can be used in the magnetooptoelectronics.

Abstract: The dependences of the resistivity and complex magnetic permeability of (Co₄₁Fe₃₉B₂₀)_33.9(SiO₂)_66.1 composite–based multilayer films on the thickness of different metallic and semiconducting spacers are studied. It is found that in the presence of a continuous spacer with a resistivity on the order of 0.01 Ω·m, the superparamagnetic state of these heterogeneous systems changes to ferromagnetic ordering.

Abstract: The experimental evidence for the existence of chain paramagnetic Curie-type contribution to the temperature dependence of the normal (non-superconducting) state magnetic susceptibility χ (T) was obtained for pure high-Tc superconductors (HTSC) YBa₂Cu₃O_6+δ series with different oxygen contents (0.6 < δ ≤ 1). It was shown that this contribution became clearly evident on curves χ (T) only at the temperature T < 150 K. It increases with the amount of oxygen vacancies increase in Cu1–O4 chains, and also depends on the way of the oxygen vacancies ordering.

Abstract: Greigite (Fe₃S₄) is an iron sulfide with inverse spinel structure, same as the structure of magnetite. Half-metallic properties in combination with ferrimagnetic nature of greigite puts this mineral in a fairly narrow group of materials that are potentially suitable for spintronics [1]. In this paper, we have conducted a comparative study of magnetic properties of two crystalline greigite samples obtained by hydrothermal synthesis with different parameters.Conducted Mossbauer spectroscopy study has shown that there are two magnetically non-equivalent B-site iron positions. The interpretation of this result was given using a model for magnetite from [2]. Unusual temperature dependencies of effective magnetic fields for A-and B-site iron atoms were obtained. It was found that coercive magnetic parameters as well as greigite stability depend on the synthesis procedure. Stepwise thermomagnetic analysis in saturating field allowed us to obtain the synthesized greigite critical temperatures of structural stability (T ~ 240oC), after which the sequential process of greigite transformation to pyrite, metastable maghemite (or magnetite) and finally to hematite begins. All of the found greigite peculiarities not only expand the knowledge about this complicated ferrimagnetic phase but can be used as guidance for optimal synthesis conditions.