Bludov O. Features of resonant properties and magnetic phase transformations in praseodymium ferroborate and rare earth chromoborates

The dissertation is devoted to research of features of magnetic resonance and magnetic phase transformations in praseodymium ferroborate crystals and rare earth chromoborates with La, Gd, Tb and Dy. For the PrFe3(BO3)4 crystal, the value of the effective field of magnetic anisotropy was determined and the contribution to it from the praseodymium subsystem was estimated. It was also established that the phase transition induced by an external magnetic field is a first-order phase transition. It was found that the spin ordering in compounds RCr3(BO3)4 with R = La, Gd, Tb and Dy is antiferromagnetic and Neel temperatures were determined. It was shown that the chromium subsystem of these crystals can be represented as a system of antiferromagnetic spin S = 3/2 chains with ferromagnetic interchain interactions. In TbCr3(BO3)4 and DyCr3(BO3)4 at low temperatures the antiferromagnetic state with “easy axis” magnetic anisotropy is realized, and there is a spontaneous phase transition to the antiferromagnetic phase with “easy plane” anisotropy as temperature rise. The H–T phase diagrams were constructed for GdCr3(BO3)4 and TbCr3(BO3)4 crystals and magnetic field-induced electric polarization was detected.