Spin-resolved low-energy and hard x-ray photoelectron spectroscopy of off-stoichiometric Co2MnSi Heusler thin films exhibiting a record TMR. (8th April 2015)

• Record Type: Journal Article
• Authors: Fetzer, Roman; Ouardi, Siham; Honda, Yusuke; Liu, Hong-xi; Chadov, Stanislav; Balke, Benjamin; Ueda, Shigenori; Suzuki, Motohiro; Uemura, Tetsuya; Yamamoto, Masafumi; Aeschlimann, Martin; Cinchetti, Mirko; Fecher, Gerhard H; Felser, Claudia
• Is Part Of: Journal of physics. Volume 48:Number 16(2015)
• Publication Date: 2015-04-08
• Subjects: Heusler thin films -- photoelectron spectroscopy -- electronic structure -- dichroism -- magnetic tunnel junctions -- HAXPES -- spin resolved PES; Physics -- Periodicals; 530
• DOI: 10.1088/0022-3727/48/16/164002
• Languages: English
• ISSNs: 0022-3727

Abstract

Abstract: Half-metallic Co2 MnSi-based Heusler compounds have attracted attention because they yield very high tunnelling magnetoresistance (TMR) ratios. Record TMR ratios of 1995% (at 4.2 K) are obtained from off-stoichiometric Co2 MnSi-based magnetic tunnel junctions. This work reports on a combination of band structure calculations and spin-resolved and photon-polarisation-dependent photoelectron spectroscopy for off-stoichiometric Heusler thin films with the composition Co2 Mn1.30 Si0.84 . Co and Mn are probed by magnetic dichroism in angle-resolved photoelectron spectroscopy at the 2 p core level. In contrast to the delocalised Co 3 d states, a pronounced localisation of the Mn 3 d states is deduced from the corresponding 2 p core level spectra. The valence states are investigated by linear dichroism using both hard x-ray and very-low-photon-energy excitation. When a very low photon energy is used for excitation, the valence bands exhibit a spin polarisation of about 30% at the Fermi energy. First principles calculations reveal that the low spin polarisation might be caused by a spin-flip process in the photoelectron final states.