Professor Stephen Blundell

Abstract:

We report structural, magnetic, and magnetotransport properties of the two-dimensional chromium sulfide Cr2S2.92, which contains both Cr3+ and Cr2+ ions. Below its magnetic-ordering temperature (TN=118 K), Cr2S2.92 exhibits a weak spontaneous magnetization with a maximum around 90 K and a value of 0.013(4) μB per Cr ion at 5 K. The resistivity and magnetoresistance exhibit pronounced local maxima around TN (MR=48% in a field of 14 T). The magnetotransport properties are discussed in terms of magnetic-polaron formation.

Abstract:

It is shown by magnetometry and microSR spectroscopy that short-range magnetic interactions between the Mn cations in the nonmetallic K(2)NiF(4)-like phase La(0.8)Sr(1.2)Mn(0.6)Rh(0.4)O(4) become significant below approximately 200 K. Negative magnetoresistance (rho/rho(0) approximately 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)mu(B) 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 Rh(3+) over the relative strength of competing magnetic exchange interactions.