Direct evidence for minority spin gap in theCo2MnSiHeusler compound

Half metal magnets are of great interest in the field of spintronics because of their potential full spin polarization at the Fermi level (E F) and low magnetization damping. The high Curie temperature and the predicted 0. 7 eV minority spin gap make the Co 2 MnSi Heusler compound very promising for applications. We investigated the half-metallic magnetic character of this compound using spin-resolved photoemission , ab initio calculation , and ferromagnetic resonance. At the surface of Co 2 MnSi , a gap in the minority spin channel is observed , leading to 100% spin polarization. However , this gap is 0. 3 eV below E F , and a minority spin state is observed at E F. We show that a minority spin gap at E F can nevertheless be recovered either by changing the chemical composition of the compound or by covering the surface by Mn , MnSi , or MgO. This spin-gap recovery results in extremely small damping coefficients , reaching values as low as 7 × 10 −4 .