Residual resistivity ratio and its relation to the magnetoresistance behavior in LaMn<SUB>2</SUB>Ge<SUB>2</SUB>-derived alloys

Results of low temperature magnetoresistance (&#916;&#961;/&#961;) and isothermal magnetization (M) measurements on polycrystalline ferromagnetic(T<SUB>C</SUB> close to 300 K) natural multilayers, LaMn<SUB>2&#177;x</SUB>Ge<SUB>2&#8722;y</SUB>Si<SUB>y</SUB>, are reported. It is found that the samples with large residual resistivity ratio, &#961;(300K)/&#961;(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 &#916;&#961;/&#961; with magnetic field with increasing &#961;(300K)/&#961;(4.2K); however, the field dependence of &#916;&#961;/&#961;does 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