Antiferromagnetic resonance and magnetic anisotropy in PrxY1-xFe3(BO3)4 crystals in the region of the magnetic structure transformation «easy axis – easy plane»

The spin dynamics, magnetic structures and magnetic anisotropy of single crystals Pr x Y 1-x Fe 3 (BO 3 ) 4 have been studied using antiferromagnetic resonance (AFMR) in a wide range of frequencies, magnetic fields, and temperatures. The frequency-field dependences of AFMR for the crystals with x=0.25 and 0.45 are characteristic of antiferromagnets with the easy plane (EP) anisotropy. The crystals with x=0.75 and 1.0 exhibit frequency-field dependences that are typical for antiferromagnets with the easy axis (EA) anisotropy. In these crystals, a significant decrease in the effective anisotropy fields of praseodymium upon the transition to the spin-flop state has been found. It is shown that this is the main reason for the large lability intervals, within which the regions of coexistence of the collinear and spin-flop states overlap. In the crystal with x=0.67, the magnetic field applied along the trigonal axis of the crystal leads to the spin reorientation transition from the EA to the EP state. A magnetic phase diagram of the states on the plane "magnetic field - temperature" is built. In this crystal, the effective anisotropy field of praseodymium also decreases upon the transition to the field-induced EP state. Diamagnetic dilution of the praseodymium subsystem leads to the contribution of this subsystem to the total anisotropy field depending almost linearly on the praseodymium concentration. • In crystal with х=0.67 magnetic field H||c causes spin reorientation transition EA→EP. • For х=0.67÷1.0 a decrease in praseodymium anisotropy upon transition to field-induced EP or spin-flop state is found. • Large interval of coexistence of collinear and spin-flop states in crystals with х=0.75÷1.0