Chemically Induced Magnetism and Magnetoresistance in La0.8Sr1.2Mn0.6Rh0.4O4

It is shown by magnetometry and muSR spectroscopy that short-range magnetic interactions between the Mn cations in the nonmetallic K2NiF4-like phase La0.8Sr1.2Mn0.6Rh0.4O4 become significant below �200 K. Negative magnetoresistance (rho/rho(0) ~� 0.5 in 14 T at 108 K) is apparent below this temperature. Neutron diffraction has shown that an applied magnetic field of 5 T is sufficient to induce saturated (3.38(7)muB per Mn) long-range ferromagnetic ordering of the atomic moments at 2 K, and that the induced ordering persists up to a temperature of 50 K in 5 T. Spin glass behavior is observed below 20 K in the absence of an applied field. The induced magnetic ordering is attributed to the subtle changes in band structure brought about by the external field, and to the controlling influence of Rh3+ over the relative strength of competing magnetic exchange interactions.