Residual resistivity ratio and its relation to the magnetoresistance behavior in LaMn₂Ge₂-derived alloys

Abstract

Results of low temperature magnetoresistance (Δρ/ρ) and isothermal magnetization (M) measurements on polycrystalline ferromagnetic(T_C close to 300 K) natural multilayers, LaMn_2±xGe_2−ySi_y, are reported. It is found that the samples with large residual resistivity ratio, ρ(300K)/ρ(4.2K), exhibit large positive magnetoresistance at high magnetic fields. The Kohler's rule is not obeyed in these alloys. In addition, at 4.5 K, there is a tendency towards linear variation of Δρ/ρ with magnetic field with increasing ρ(300K)/ρ(4.2K); however, the field dependence of Δρ/ρdoes not track that of M, thereby suggesting that the magnetoresistance originates from non-magnetic layers. It is interesting that these experimental findings on bulk polycrystals are qualitatively similar to what is seen in artificially grown multilayer systems recently.