The resonance properties of a new Cu 2 OSeO 3 ferrimagnet have been investigated in a wide range of frequencies (17-142 GHz) at liquid helium temperature. The resonance data were used to plot the frequencyfield dependence of the ferrimagnetic spectrum described within the model of an anisotropic two-sublattice ferrimagnet. The effective magnetic anisotropy corresponding to the gap in the spin wave spectrum has been estimated (3 GHz). It is found that the spectrum has a multicomponent structure which is due to the diversity of the types of magnetization precession. As the amplitude of the high-frequency magnetic field increased, an additional absorption was observed in the external magnetic field lower than the field of the main resonance. The detected additional absorption corresponds to the nonuniform nonlinear parametric resonance, connected with nonuniformity of magnetic structure in the ferrimagnetic crystal Cu 2 OSeO 3 .

The temperature dependence of the magnetic susceptibility along the principal magnetic axes of rubidium–dysprosium tungstate RbDy(WO4)2 is measured in the temperature interval 0.5–300 K. Strong anisotropy of the susceptibility is observed at all temperatures in that range. At TN=0.8 K the susceptibility along all three magnetic axes exhibits a sharp anomaly due to the phase transition to a magnetically ordered state. At 0.5 K the measured field dependence of the magnetization along all three axes demonstrates a metamagnetic orientational phase transition in the directions of the magnetic axes y and z. Another type of anomaly of the magnetic susceptibility is observed at temperatures of around 5, 8, and 50 K. Analysis shows that these anomalies correspond to structural phase transitions in this compound.

X-ray studies of the magnet KTb(WO4)2 have shown that this compound belongs to the monoclinic class C2∕c with a chain structure. The susceptibility and magnetization of KTb(WO4)2 single crystals are investigated experimentally in the temperature region 0.4–100 K and at magnetic fields up to 2 T. The angular dependence of the susceptibility shows that at low temperatures a purely Ising anisotropy is realized in this compound: there exists but one component of the moment, along the b axis. The temperature dependence of the susceptibility has a maximum at T=1.2K, and the M(H) curve obtained at 0.5 K exhibits substantial nonlinearity at low fields, as is characteristic of an ordered state. Analysis of the experimental data in the mean field approximation suggests that this state is a singlet Ising antiferromagnet with TN≈0.7K, a value determined from the susceptibility data. At extremely low temperatures a collinear antiferromagnetic structure with equivalent sublattices is realized in the sample, according to estimates made. The high-temperature behavior of the susceptibility is evidence of the presence of an excited quasi-doublet in the vicinity of 35 K.