Investigation of Co2FeSi: The Heusler compound with highest Curie temperature and magnetic moment

Wurmehl, S.; Fecher, Gerhard H.; Kandpal, H.C.; Ksenofontov, Vadim; Felser, Claudia; Lin, Hong‐Ji

doi:10.1063/1.2166205

Cited by 423 publications

(218 citation statements)

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“…These two features are typical of those for bulk samples or thin films of Co 2 MnZ ͑Z =Si,Ge͒. 6,9,12 In particular, a shoulder in the Co XAS spectrum has been commonly observed for bulk samples 12,13 or thin films 6,9 of Co 2 YZ with the L2 1 structure.…”

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confidence: 91%

X-ray absorption spectroscopy and x-ray magnetic circular dichroism of epitaxially grown Heusler alloy Co2MnSi ultrathin films facing a MgO barrier

Saito

Katayama

Ishikawa

et al. 2007

Applied Physics Letters

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We element specifically studied the electronic and magnetic states of epitaxially grown full-Heusler alloy Co 2 MnSi ͑CMS͒ 1.1 nm ͑4 ML͒ thick ultrathin films facing an epitaxial MgO͑001͒ tunnel barrier by means of x-ray absorption spectroscopy ͑XAS͒ and x-ray magnetic circular dichroism ͑XMCD͒. In situ reflection high-energy electron-diffraction observations indicated that the CMS films grew into the L2 1 structure. The observed XAS and XMCD spectra revealed that the CMS ultrathin film was not oxidized. The ratio of Mn and Co spin magnetic moments obtained by applying the sum rules was about 2.7, close to a theoretical value of 2.8 for CMS with the L2 1 structure. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2824856͔Co-based full-Heusler alloys ͑Co 2 YZ͒ have attracted much interest as a desirable ferromagnetic electrode material for spintronic devices. [1][2][3][4][5] This is because of their potentially high spin polarization arising from the half-metallic ferromagnetic nature theoretically predicted for some of these alloys, and because of their high Curie temperatures, which are well above room temperature ͑RT͒. Some of the present authors recently developed fully epitaxial magnetic tunnel junctions ͑MTJs͒ with a Co 2 YZ thin film of Co 2 Cr 0.6 Fe 0.4 Al ͑CCFA͒, Co 2 MnSi ͑CMS͒, or Co 2 MnGe as a lower electrode and a MgO͑001͒ tunnel barrier, 3-5 and demonstrated relatively high tunnel magnetoresistance ͑TMR͒ ratios of 109% at RT ͑317% at 4.2 K͒ for CCFA/ MgO / Co 50 Fe 50 MTJs ͑Ref. 4͒ and 90% at RT ͑192% at 4.2 K͒ for CMS/ MgO / Co 50 Fe 50 MTJs. 3 The electronic and magnetic states of the interfacial region of ferromagnetic electrodes with a tunnel barrier play an essential role in the spindependent tunneling characteristics in MTJs. It has recently been shown that x-ray absorption spectroscopy ͑XAS͒ and x-ray magnetic circular dichroism ͑XMCD͒ measurements are powerful techniques for obtaining microscopic information about the element-specific electronic and magnetic states in the interfacial region of MTJs. [6][7][8][9] Our purpose of the present study is to clarify the electronic and magnetic states of the interfacial region of Co 2 YZ thin films facing a MgO barrier. For this study, we fabricated epitaxial CMS ultrathin films as typical Co 2 YZ films with an epitaxial MgO barrier and performed XAS and XMCD measurements at the Mn-L 2,3 and Co-L 2,3 edges. To investigate the interfacial region selectively, we fabricated CMS ultrathin films with a 4 ML thickness ͑=1.1 nm͒. The fabricated sample layer structure ͑from the substrate side͒ was as follows: MgO buffer ͑10 nm͒ / Fe underlayer ͑50 nm͒ / CMS ultrathin film ͑1.1 nm= 4 ML͒/MgO barrier ͑2 nm͒ / Ru cap ͑2 nm͒ ͑hereafter called Fe/CMS ͑4 ML͒/MgO͒, grown on a MgO͑001͒ single-crystal substrate. The monolayer of Co 2 MnSi consists of a Co plane and a Mn-Si plane, and a unit cell of CMS, whose lattice parameter is 0.5654 nm ͑Ref. 10͒, corresponds to 2 ML of CMS. To stabilize the ferromagnetism of ultrathin CMS films at RT, we grew them on the ...

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confidence: 91%

X-ray absorption spectroscopy and x-ray magnetic circular dichroism of epitaxially grown Heusler alloy Co2MnSi ultrathin films facing a MgO barrier

Saito

Katayama

Ishikawa

et al. 2007

Applied Physics Letters

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“…In the XAS spectrum for the 50-nm-thick CMS film, there is a small distinct shoulder at the higher photon energy ͑about 3 eV͒ side of the Co-L 3 peak. This shoulder at the Co-L 3 peak is characteristic of full-Heusler alloys ͑Co 2 YZ͒ with the L2 1 structure and has been commonly observed for bulk samples 15 or thin films. 9,12 The XAS and XMCD spectra for the 4-ML-thick CMS film are similar to those for the 50-nm-thick film in terms of the structure and magnitude.…”

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Electronic and magnetic properties of Heusler alloy Co2MnSi epitaxial ultrathin films facing a MgO barrier studied by x-ray magnetic circular dichroism

Saito

Katayama

Emura

et al. 2008

Journal of Applied Physics

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The electronic and magnetic states of an epitaxially grown full-Heusler alloy Co 2 MnSi ͑CMS͒ 1.1 nm ͑4 ML͒ thick ultrathin film and a CMS 50-nm-thick film both facing an epitaxial MgO͑001͒ tunnel barrier were element-specifically studied by means of x-ray absorption spectroscopy ͑XAS͒ and x-ray magnetic circular dichroism ͑XMCD͒. The observed XAS and XMCD spectra revealed that both the CMS films were not oxidized. The Co and Mn spin magnetic moments for the 4 ML thick CMS film obtained by applying the sum rules were close to those for the 50-nm-thick one and the theoretical values for bulk CMS with the L2 1 structure. These results indicate that 4 ML thick CMS ultrathin films facing a MgO barrier still retain the electronic and magnetic states for the L2 1 structure. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2836676͔Co-based Heusler alloys ͑Co 2 YZ͒ are promising ferromagnetic electrode materials for spintronic devices. [1][2][3][4][5][6][7][8] This is because of their potentially high spin polarization arising from the half-metallic ferromagnetic nature theoretically predicted for some of these alloys, and because of their high Curie temperatures, which are well above room temperature ͑RT͒. We have recently developed fully epitaxial magnetic tunnel junctions ͑MTJs͒ with a Co 2 YZ thin film and a MgO͑001͒ tunnel barrier, and demonstrated a relatively high tunnel magnetoresistance ratio at RT. [3][4][5][6][7][8] The spin-dependent tunneling characteristics in MTJs are very sensitive to the electronic and magnetic states of the interfacial region of ferromagnetic electrodes with a tunnel barrier.Recently, x-ray absorption spectroscopy ͑XAS͒ and x-ray magnetic circular dichroism ͑XMCD͒ have proved to be effective techniques for obtaining microscopic information about the element-specific electronic and magnetic states in the interfacial region of MTJs. [9][10][11][12] In this work, we fabricated an epitaxial Co 2 MnSi ͑CMS͒ 1.1 nm ͑4 ML͒-thick ultrathin film and a CMS 50-nm-thick film with an epitaxial MgO barrier in order to investigate the interfacial region selectively by XAS and XMCD measurements at the Mn-L 2,3 and Co-L 2,3 edges.The sample layer structure was grown on a MgO͑001͒ single-crystal substrate and, from the substrate side, consisted of MgO buffer ͑10 nm͒ / Fe underlayer ͑50 nm͒/CMS ultrathin film ͑4 ML͒/MgO barrier ͑2 nm͒ / Ru cap ͑2 nm͒. A monolayer of Co 2 MnSi consists of a Co plane and a Mn-Si plane, and a unit cell of CMS, whose lattice parameter is 0.5654 nm ͑Ref. 13͒, corresponds to 2 ML of CMS. We grew the 4-ML-thick CMS ultrathin film on the Fe underlayer to stabilize its ferromagnetism at RT. Each layer in the sample layer structure was successively deposited in an ultrahigh vacuum chamber ͑base pressure: about 6 ϫ 10 −8 Pa͒ through the combined use of magnetron sputtering ͑for Fe, CMS, and Ru͒ and electron beam evaporation ͑for MgO͒; the fabrication procedure was the same as in previous work. [3][4][5][6][7][8]14 The CMS film deposited at RT were annealed in situ at 325°C for...

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“…Co-based compounds were synthesized and investigated in the 1970s [5]. They attracted a great deal of interest due to their high Curie temperatures [6,7] and being predicted to be half metallic ferromagnets [8,9]. Many of the Co 2 -based compounds are now used in magnetic tunnel junctions [10,11].…”

Section: Introductionmentioning

confidence: 99%

Crystal Structure of New Heusler Compounds

Graf

Casper

Winterlik

et al. 2009

Zeitschrift anorg allge chemie

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Investigation of Co2FeSi: The Heusler compound with highest Curie temperature and magnetic moment

Cited by 423 publications

References 24 publications

X-ray absorption spectroscopy and x-ray magnetic circular dichroism of epitaxially grown Heusler alloy Co2MnSi ultrathin films facing a MgO barrier

X-ray absorption spectroscopy and x-ray magnetic circular dichroism of epitaxially grown Heusler alloy Co2MnSi ultrathin films facing a MgO barrier

Electronic and magnetic properties of Heusler alloy Co2MnSi epitaxial ultrathin films facing a MgO barrier studied by x-ray magnetic circular dichroism

Crystal Structure of New Heusler Compounds

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