Determination of superconducting anisotropy from magnetization data on random powders as applied to LuNi2B2C, YNi2B2C, and MgB2 -: art. no. 180506

The recently discovered intermetallic superconductor MgB2 appears to have a highly anisotopic upper critical field with H-c2(max)/H-c2(min) = gamma > 5. in order to determine the temperature dependence of both H-c2(max) and H-c2(min) we propose a method of extracting the superconducting anisotropy from the magnetization M(H,T) of randomly oriented powder samples, The method is based on two features in (partial derivativeM/partial derivativeT)(H): the onset of diamagnetism at T-c(max), that is commonly associated with H-c2, and a kink in partial derivativeM/partial derivativeT at a lower temperature T-c(min). Results for LuNi2B2C and YNi2B2C powders are in agreement with anisotropic H-c2 obtained from magnetotransport measurements on single crystals. Using this method on four different types of MgB2 powder samples we are able to determine H-c2(min)(T) and H-c2(min)(T) with gamma approximate to 6.