TEMPERATURE DEPENDENCES OF THE HIGH-FIELD MAGNETIZATION OF DILUTE FRUSTRATED FERRIMAGNETIC SPINELS

Results are presented of an investigation of the magnetic properties o f dilute frustrated ferrimagnetic spinels Li0.5Fe2.5-xGaxO4 (x = 0.8 - 1.2), which characterize the main parameters of the ferrimagnetic sta le and provide evidence of local violation of collinear spin ordering and frustrations. In particular, measurements were made of the concent ration dependences of the magnetic moment n(0)(x) and the Curie point T-c(x), the magnetization isotherms sigma(T)(H) at T = 4.2 K and H les s than or equal to 10 kOe, and also the low- and high-field magnetizat ion polytherms sigma(T)(T). It was established that for x greater than or equal to 0.8 in fields exceeding the technical saturation field H- s similar to 2 kOe, the temperature dependences of the high-field magn etization sigma(H)(T) between 4.2 and 230 K cannot he described by the Bloch T-3/2 law whereas this law is satisfied for undiluted Li spinel (x = 0). Over the entire temperature range (4.2-230 K) the experiment al curves sigma(H)(T) may be approximated by sigma(H)(T) = sigma(0)(1 - AT(3/2) - BT5/2) for x = 0.8-1.0 and sigma(H)(T) = sigma(0)[1 - CT(3 /2)exp(mu(H-H-0)/k(B)T)] for x = 1.1, 1.2, where mu H-0 similar to 15 K is the internal field produced by competition between exchange inter actions and frustrations. (C) 1998 American Institute of Physics.