Magnetic properties of La 0.7−x Pr x Ca 0.3 MnO 3 single crystals: When is Banerjee criterion applicable?

The magnetic properties of ferromagnetic single crystals of La0.7−xPrxCa0.3MnO3 with x≤0.3 are studied. It is shown that the transition temperature TM determined from the position of an inflection point in the magnetization-versus-temperature curve is linear in magnetic field: TM(H)=TM(0)+BMH with TM(0)=(229−270x)K, BM=0.8K/kOe for x=0.0, 0.1, 0.2 and BM=1.2K/kOe for x=0.3. The magnetic moments of Pr and Mn are shown to be parallel to each other. The data obtained are employed in order to analyze when Banerjee criterion for distinguishing first and second order transitions can be used in inhomogeneous ferromagnets. Phenomenological theory for the Arrott–Belov plots is also developed. It is found experimentally and theoretically that in inhomogeneous ferromagnets, the slope of the Arrott–Belov plots is not a universal tool for determining the type of transition, in fact, Banerjee criterion may be used only in the paramagnetic state beyond the transition region.