In their recent Kerr rotation studies Bandaru et al. [P. Bandaru et al., Appl. Phys. Lett. 72, 1 (1998)] were able to lower the Curie temperature of MnBi by doping it with 5-20 at. % Cr thereby decoupling the magnetic phase transition from the structural phase transition at 630 K. This development makes much-studied MnBi a promising candidate for magneto-optic applications. Here we report first-principle electronic structure calculations to study the magnetic and magneto-optical properties of MnBiCr alloys as functions of the Cr concentration. Both interstitial and substitutional occupancies of Cr in MnBi are investigated. The exchange interaction parameters calculated show that Cr substitution for Mn results in antiferromagnetic coupling between Mn and Cr along the c axis but ferromagnetic coupling in the a-b plane. This effectively decreases the Curie temperature of MnBi. The calculated Kerr rotation and ellipticity are in good agreement with the experimental data for Mn1-xCrxBi. The Kerr rotation of MnBi decreases with the substitution of Cr. The decrease is stronger for the "red" peak at 1.96 eV (633 nm) than for the "blue" peak at 3.35 eV (370 nm), in qualitative agreement with the experiment. Interstitial Cr also lowers the Kerr rotation but the occupancy of interstitial sites is expected to be much smaller than that of substitutional sites.
|Original language||English (US)|
|Number of pages||3|
|Journal||Journal of Applied Physics|
|Issue number||8 II A|
|Publication status||Published - Apr 15 1999|
ASJC Scopus subject areas
- Physics and Astronomy(all)