Minority-spin impurity band in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi mathvariant="normal">n</mml:mi></mml:math>-type (In,Fe)As: A materials perspective for ferromagnetic semiconductors
Masaki Kobayashi, Le Duc Anh, Jan Minár, Walayat Khan, Stephan Borek, Pham Nam Hai, Yoshihisa Harada, Thorsten Schmitt, Masaharu Oshima, Atsushi Fujimori, Masaaki Tanaka, Vladimir N. Strocov
Abstract
Fully understanding the properties of n-type ferromagnetic semiconductors (FMSs), complementary to the mainstream $\mathrm{p}$-type ones, is a challenging goal in semiconductor spintronics because ferromagnetism in $\mathrm{n}$-type FMSs is theoretically nontrivial. Soft-x-ray angle-resolved photoemission spectroscopy (SX-ARPES) is a powerful approach to examine the mechanism of carrier-induced ferromagnetism in FMSs. Here our SX-ARPES study on the prototypical $\mathrm{n}$-type FMS (In,Fe)As reveals the entire band structure, including the Fe-$3d$ impurity bands (IBs) and the host InAs ones, and provides direct evidence for electron occupation of the InAs-derived conduction band (CB). A minority-spin Fe-$3d$ IB is found to be located just below the conduction-band minimum (CBM). The IB is formed by the hybridization of the unoccupied Fe $3d$ states with the occupied CBM of InAs in a spin-dependent way, resulting in the large spin polarization of CB. The band structure with the IB is varied with band filling, which cannot be explained by the rigid-band picture, suggesting a unified picture for realization of carrier-induced ferromagnetism in FMS materials.