Minority-spin t2gstates and the degree of spin polarization in ferromagnetic metallic La2−2xSr1+2xMn2O7 (x = 0.38)

摘要

Using angle-resolved photoemission spectroscopy (ARPES), we investigate theelectronic band structure and Fermi surface of ferromagneticLa$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ ($x=0.38$). Besides the expected two holepockets and one electron pocket of majority-spin $e_g$ electrons, we show anextra electron pocket around the $Gamma$ point. A comparison withfirst-principles spin-polarized band-structure calculations shows that theextra electron pocket arises from $t_{2g}$ electrons of minority-spincharacter, indicating this compound is not a complete half-metallicferromagnet, with similar expectations for lightly-doped cubic manganites.However, our data suggest that a complete half-metallic state is likely to bereached as long as the bandwidth is mildly reduced. Moreover, the band-resolvedcapability of ARPES enables us to investigate the band structure effects onspin polarization for different experimental conditions.