Critical exponents of inhomogeneous ferromagnets

A method for the analysis of temperature and field dependent magnetization data near the Curie temperature T-C is devised, which allows the reliable determination of critical exponents even in strongly inhomogeneous ferromagnets. It is shown, both experimentally and theoretically, that the field-induced broadening of the ferromagnetic phase transition follows a power law with a characteristic critical exponent beta.delta, where beta and delta are the conventional temperature and field dependent critical exponents of the magnetization. Experimental results on inhomogeneous La2/3Ca1/3MnO3 films yield critical exponents beta=0.3682+/-0.0033 and delta=4.76+/-0.32, even though the intrinsic T-C distribution width is larger than the field-induced effect. (C) 2002 American Institute of Physics.