A.I. Pankrats

Antiferromagnetic resonance and phase diagrams of gadolinium ferroborate GdFe3(BO3)4

Antiferromagnetic resonance in single crystals of rhombohedral gadolinium ferroborate GdFe3(BO3)4 was studied. The frequency-field dependences of antiferromagnetic resonance over the frequency range 26–70 GHz and the temperature dependences of resonance parameters for magnetic fields oriented along the crystal axis and in the basal plane were determined. It was found that the iron subsystem, which can be treated as a two-sublattice antiferromagnet with anisotropy of the easy-plane type, experienced ordering at T=38 K. At temperatures below 20 K, the gadolinium subsystem with the opposite anisotropy sign strongly influenced the anisotropic properties of the crystal. This resulted in a spontaneous spin-reorientation transition from the easy-plane to the easy-axis state at 10 K. Below 10 K, magnetic field-induced transitions between the states were observed. Experimental phase diagrams on the temperature-magnetic field plane were constructed for fields oriented along the crystal axis and in the basal plane. A simple model was used to calculate the critical transition fields. The results were in close agreement with the experimental values measured at T=4.2 K for both field orientations.

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.

Copper Metaborate CuB 2 O 4 Phase Diagrams Based on the Results of Measuring the Magnetic Moment

The magnetic phase transitions and the phase diagrams of the CuB2O4 multiferroic are studied. Phase diagrams of copper metaborate in a magnetic field directed along the [100] and [001] axes are plotted using the results of measuring the magnetic moment. Evidences for the existence of polycritical points are obtained.

Magnetic and Dielectric Properties of PbFeBO4 and PbMnBO4 Single Crystals

PbFeBO4 and PbMnBO4 single crystals were synthesized. The X-ray, magnetic, dielectric, Mössbauer, and resonance investigations of the crystals were fulfilled. It is established that single-crystal PbFeBO4 is an antiferromagnet with a Néel temperature TN =114 K, while PbMnBO4 is a ferromagnet with a Curie temperature TC = 31 K. Both single-crystal compounds have a strong anisotropy of the magnetic and dielectric properties.

Magnetic-resonance and thermophysical studies of the magnetic phase diagram for a GdFe2.1Ga0.9(BO3)4 single crystal

The antiferromagnetic resonance, heat capacity, magnetic properties, and magnetic phase diagram of a GdFe3(BO3)4 crystal in which some of the iron ions were substituted by diamagnetic gallium ions have been investigated. It has been found that the Neél temperature upon diamagnetic substitution decreased to 17 K compared to 38 K in the unsubstituted crystal. The effective exchange and anisotropy fields for GdFe2.1Ga0.9(BO3)4 have been estimated from the field dependences of magnetization and resonance measurements. The magnetic phase diagram of the crystal has been constructed from magnetic and resonance measurements. In GdFe2.1Ga0.9(BO3)4, there is no spontaneous reorientation and, in the absence of a magnetic field, the crystal remains an easy-axis one in the entire domain of magnetic ordering. The critical field of the reorientation transition to an induced easy-plane state in a magnetic field along the trigonal axis has been found to increase compared to that in the unsubstituted crystal.

Synthesis and Magnetic Properties of β-Cu3Fe4(VO4)6 Single Crystals

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.

Magnetic Properties of PrхY1-xFe3(BO3)4

The magnetic properties of trigonal PrxY1-xFe3(BO3)4 compound have been investigated. Anomalies on the magnetization curves induced by a magnetic field are observed for each composition. The calculations were performed using a molecular-field approximation and a crystal-field model for the rare-earth subsystem. Extensive experimental data on the magnetic properties of PrxY1-xFe3(BO3)4 have been interpreted and good agreement between theory and experiment has been achieved.

Role of Magnetic Subsystems to Form a Complex Magnetic Structure Mn2GeO4 Single Crystals

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.