THE INFLUENCE OF AN EXTERNAL MAGNETIC FIELD ON THE MAGNETIC PROPERTIES OF QUASI-ONE-DIMENSIONAL HALDANE MAGNETS (Y1-X NDX)2BANIO5 (X = 0.25 И 0.04)

Abstract

In the compounds of the (Y1-xNdx)2BaNiO5 family, the paradoxical coexistence of the Haldane phase and spin waves is realized. The magnetic ordering in the system is caused by the interaction of Nd3+ ions through spin fluctuations of a nickel chain, which remains internally disordered. Nd3+ magnetic moments do not deviate from the c axis of the crystal even in the presence of an external magnetic field. In this paper, for compounds (Y1-xNdx)2BaNiO5 with x = 0.25 and x = 0.04, an experimental study of the field dependence of the magnetization M(B) and the temperature dependence of the heat capacity C( T ), measured in fields B = 0; 2 and 5 T. For compounds with x = 0.25 on the dependence M(B) measured at T = 4.2 K, an anomaly was detected indicating a metamagnetic transition. Changes in the parameters of the magnetic interaction between the magnetic moments Nd along the c axis of the crystal leads to the periorientation of the magnetic moments of all Nd3+ ions along the direction of the external field B||c. For the connection with x = 0.04, no anomalies were detected on the dependence M(B), the magnetic moments of both neodymium sublattices lie along the direction of the applied magnetic field. The presence of a Schottky anomaly on the dependence C( T ) at B =0 indicates the existence of an internal magnetic field acting on the Nd3+ ion from the side of the nickel subsystem, and leading to the splitting of the main Kramers doublet of the Nd3+ ion. For a connection with x = 0.04, the Schottky anomaly shifts towards higher temperatures with an increase in the external magnetic field, and for a connection with x = 0.25, the Schottky anomaly shifts towards low temperatures only in the field B = 5 T. The displacement of the Schottky anomaly in the presence of a field is due to the ratio between the magnitude of the applied magnetic field and the component of the internal magnetic field fields с along the c axis of the crystal. For connection with x = 0.25 , the magnetic moments of the two neodymium sublattices are oppositely directed, and the Schottky anomaly of the 1st sublattice shifts towards higher temperatures, and the Schottky anomaly of the 2nd sublattice shifts towards lower temperatures. For connection with x = 0.04 с The magnetic moments of the two neodymium sublattices are directed towards the applied field, and the Schottky anomaly of both sublattices shifts towards higher temperatures, which is consistent with the experimen