Large positive magnetoresistance at low temperatures in a ferromagnetic natural multilayer, LaMn2Ge2

The results of magnetoresistance measurements on a naturally occurring multilayer LaMn2Ge2, which is ferromagnetic below 326 K, are reported. The magnitude of magnetoresistance is found to be positive below 70 K gradually increasing to an unusually large value (nearly 100%) at 4.2 K in the presence of a field of 70 kOe as the temperature is lowered, similar to the recent observations by Verbanck, Temst, Mae, Schad, Van Bael, Moshchalkov, and Bruynseraede [Appl. Phys. Lett. 70, 1477 (1997)] in Cr/Ag/Cr trilayers. The positive sign of magnetoresistance for a ferromagnet is unexpected and possible explanations are offered. (C) 1997 American Institute of Physics.