Magnetic homogeneity of colossal-magnetoresistance thin films determined by alternating current magnetic susceptibility

We report measurements of the alternating current (ac) magnetic susceptibility, chi(ac) = chi' + i chi ", performed on colossal-magnetoresistance (CMR) materials. We have studied thin film samples of La0.67Ca0.33MnO3 and Nd0.7Sr0.3MnO3. For homogeneous samples, the temperature of the peak observed in chi "( T) is in agreement with the temperature of peak resistivity (T-p) obtained from transport measurements. This agreement is not found for inhomogeneous samples, where chi "(T) shows multiple peaks. The analysis of chi "(T) enables one to determine the quality of the CMR materials. The results obtained in thin films of La0.67Ca0.33MnO3 and Nd0.7Sr0.3MnO3, are consistent with those obtained from an homogeneous single crystal of La0.80Sr0.20MnO3. We show that the contactless ac magnetic susceptibility technique is a quick method to reveal inhomogeneities which are not directly evident in direct current transport measurements. (C) 1998 American Institute of Physics. [S0003-6951(98)01049-3].