Nonlocal effects in angular dependence of in-plane magnetization of tetragonal superconductors

The reversible magnetization M of Lu(Ni1-xCox)(2)B2C with x = 0 and 0.06 is measured in a broad temperature domain as a function of field orientation theta in the basal crystal plane. The data are interpreted within London th eory extended for nonlocality of the current-field relation in superconduct ors. The dependence M (theta) diminishes on warming, vanishes at T* < T-c, and changes sign for T > T*. The low-T sign is opposite to what is expected from the known angular dependence of the upper critical field and therefor e cannot be attributed to the latter. Upon doping with Co, the effect disap pears with decreasing mean-free path in agreement with theory. [S0163-1829( 99)51742-6].