Energy level crossing and magnetic anomalies in PrVO4 in strong fields

The magnetic anomalies due to the interaction of the energy levels of a rar e-earth ion in a strong magnetic field are studied experimentally and theor etically for the van-Vleck paramagnet PrVO4. A maximum is discovered in the differential susceptibility dM/dH in a field H-c approximate to 45 T, wher e the lower energy levels cross. The magnetocaloric effect in pulsed fields is calculated assuming the magnetization process to be adiabatic. This eff ect is characterized by the absence of initial heating of the sample when t he field is turned on and strong cooling as H-c is approached. It is shown that in PrVO4, which is an enhanced nuclear magnet, the hyperfine interacti on plays an extremely important role for the magnetic anomalies associated with crossover. For another van-Vleck paramagnet, HoVO4, it is shown that a second crossover occurs near 310 T and the magnetocaloric effect is calcul ated. (C) 2000 MAIK "Nauka/ Interperiodica".