CoS2 has recently been predicted to be highly spin-polarized, but very little is known about its magnetotransport properties. We find that this system exhibits a large anomaly in the resistivity at the Curie temperature (TC), which shows a pronounced shift with applied field, resulting in negative magnetoresistance below TC and positive magnetoresistance above it. Magnetization measurements indicate an almost first-order character to the ferromagnetic transition, indicating that CoS2 is close to a tricritical point. Analyzing the field dependence of the magnetization and resistivity, we are able to prove that the resistivity near TC is controlled only by the magnetization, regardless of whether the ferromagnetic state is induced by cooling or by application of a field. We propose that the increase in resistivity on entering the ferromagnetic state is due to a spin-dependent band structure effect where exchange splitting results in a distinct decrease in the density of states at the Fermi level for the minority spins. Point-contact Andréev reflection measurements on sulfur-stoichiometric polycrystals give a spin polarization of 56%, consistent with indications of electron-magnon scattering in our transport measurements as well as our proposed spin-dependent band structure mechanism for the magnetotransport anomalies.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Jan 1 2004|