K.A. Sablina

Weak ferromagnetism in CuB2O4 copper metaborate

Abstract The results of the magnetic susceptibility, magnetization, specific heat and μSR measurements of the tetragonal CuB 2 O 4 single crystals are presented. CuB 2 O 4 is a paramagnet at temperatures above 21xa0K. The paramagnetic Neel temperature and effective magnetic moment determined from high-temperature magnetic susceptibility measurements are equal to θ =−9.5 K, μ eff =1.77 μ B , respectively. The easy plane magnetic structure with a weak spontaneous magnetic moment was determined in the temperature range 21–10xa0K. The value of the weak spontaneous magnetic moment is m 0 =0.56xa0emu/g at T =10xa0K. Morin magnetic phase transition was observed at the temperature T M =10xa0K. The μSR measurements confirm the existence of two magnetic phase transition at T =21 and 10xa0K.

Magnetic, resonance, and electrical properties of single crystal and amorphous Bi2CuO4

Abstract Single crystal and amorphous samples Bi 2 CuO 4 were prepared. The magnetic susceptibility, magnetization, magnetic resonance and electrical resistivity measurements for wide range of temperatures and magnetic fields are presented. The anisotropic exchange interactions and 3-d antiferromagnetic behaviour were revealed for single crystal Bi 2 CuO 4 . The effective magnetic moments per copper ion were determined. The sharp differences between single crystal and amorphous samples properties were shown.

Magnetic state and spin dynamics of Bi2CuO4

Abstract The magnetic properties, neutron scattering and magnetic resonance of high quality large single crystals Bi 2 CuO 4 with Neel temperature of 45 K have been studied. Two branches of the spin wave spectrum with large energy gaps and low frequency AFMR with a little gap due to weak basal plane anisotropy were found.

Magnetic properties of copper metaborate CuB2O4

The results of experimental research on the magnetic and resonance properties, heat capacity, muon spin relaxation, and neutron scattering of single-crystal copper metaborate CuB2O4 are reviewed. The results of a symmetry analysis and of modeling by the method of the phenomenological thermodynamic potential are presented. The magnetic structure of the crystal in various temperature intervals of the magnetic ordering region is discussed.

Microwave resonance absorption in antiferromagnet Bi2CuO4

Abstract The resonance absorption in Bi2CuO4 single crystals was found in the frequency range 35–80 GHz for H⊥C4 case and it was absent for H∥C4 case. The frequency-field dependence for H⊥C4 case at 4.2 K is typical for easy-plane antiferromagnets with weak magnetic anisotropy in this plane. In contrast to the sublattice magnetization of Bi2CuO4 the resonance parameters depend strongly on the temperature below 20 K. Besides, the resonance field has a considerable jump at TN which is not typical for second order phase transitions.

The magnetic structure of Cu5Bi2B4O14. Neutron scattering

Abstract The neutron scattering measurements have been carried out on powdered sample Cu 5 Bi 2 B 4 O 14 at temperature range 2–35xa0K in order to investigate the low-temperature magnetic structure. The ferrimagnetic easy-axis structure was confirmed with the spin canting for one of the sublattice. No doubling of the crystal unit cell below the transition temperature T N =25xa0K was observed.

The magnetostriction of CuGeO3

Abstract We have measured the magnetostriction of CuGeO 3 single crystal at temperature range 2–25 K. The magnetostriction was measured along the c -axis of the crystal in a magnetic field up to 12 T applied along c - and b -crystal axes. It was found, that the magnetostriction grows when the temperature is decreased from 15 K and after reaching of maximum at 7 K it decreases down to zero at a temperature 2 K. Our interpretation of the experimental data is based on the two levels model of a spin-Peierls magnet.

Synthesis and Magnetic Properties of Crystalline and Amorphous CuB2O4

Single-crystal and amorphous CuB2O4 samples are prepared, and their magnetic properties (temperature-dependent susceptibility and magnetic resonance) are compared. Crystalline CuB2O4 has a small magnetic moment in the basal plane in the temperature range 10–21 K and an incommensurate magnetic structure below 10 K. The effective exchange interaction is found to be stronger in amorphous CuB2O4.

Magnetostriction in the spin-Peierls state of CuGeO3 single crystals

Abstract The forced magnetostriction in the spin-Peierls phase of CuGeO 3 was measured in a magnetic field up to 12 T. The magnetostrictive strains were determined for magnetic field directed along the a,b and c axes. The strong increase of the magnetostriction constants is observed near the transition from spin-Peierls phase to incommensurate phase. The mechanism responsible for forced magnetostriction in CuGeO 3 is discussed.

Magnetic resonance probe of the phase separation in Eu0.7Pb0.3MnO3 single crystal

Abstract The magnetic resonance measurements show that the mixed two-phase state takes place in the Eu 0.7 Pb 0.3 MnO 3 single crystals. The coexistence of the magnetic phases is observed in vicinity of the magnetic phase transition, where the sample exhibits the effect of the CMR. The frequency-field dependences of the spectra allow to conclude that these phases are the paramagnetic and the ferromagnetic ones. Moreover the study of the frequency dependences shows the sensitivity of the mixed-phase state to the external magnetic field. This suggests that the scenario of the phase separation is realized in this case and the mixed two-phase state is not related to simple chemical inhomogeneity.