Hard X-ray photoelectron spectroscopy on buried, off-stoichiometric Co x Mn y Ge z (x:z=2:0.38) Heusler thin films

Ouardi, Siham; Fecher, Gerhard H.; Chadov, Stanislav; Balke, Benjamin; Kozina, Xeniya; Felser, Claudia; Taira, Toshio; Yamamoto, Mikio

doi:10.1007/s00339-013-7565-y

Cited by 12 publications

(6 citation statements)

References 50 publications

(31 reference statements)

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“…Another way to avoid spurious photoemission results due to degraded sample surfaces is the use of less surface-sensitive hard x-ray photoemission spectroscopy (HAXPES). The identification of several experimentally obtained intensity features with the density of states (DOS) was possible for materials like NiTi 0.9 Sc 0.1 Sn, NiMnSb or Co x Mn y Ge z (x : z = 2 : 0.38) thin Heusler films 50,51 . However, due to the low intensities of HAXPES experiments no spin resolved results are available up to now.…”

Section: B Experimental Detailsmentioning

confidence: 99%

Monitoring surface resonances onCo2MnSi(100)by spin-resolved photoelectron spectroscopy

et al. 2015

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The magnitude of the spin polarization at the Fermi level of ferromagnetic materials at room temperature is a key property for spintronics. Investigating the Heusler compound Co2MnSi a value of 93% for the spin polarization has been observed at room temperature, where the high spin polarization is related to a stable surface resonance in the majority band extending deep into the bulk. In particular, we identified in our spectroscopical analysis that this surface resonance is embedded in the bulk continuum with a strong coupling to the majority bulk states. The resonance behaves very bulk-like, as it extends over the first six atomic layers of the corresponding (001)-surface. Our study includes experimental investigations, where the bulk electronic structure as well as surface-related features have been investigated using spin-resolved photoelectron spectroscopy (SR-UPS) and for a larger probing depth spin-integrated high energy x-ray photoemission spectroscopy (HAXPES). The results are interpreted in comparison with first-principles band structure and photoemission calculations which consider all relativistic, surface and high-energy effects properly.

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Section: B Experimental Detailsmentioning

confidence: 99%

Monitoring surface resonances onCo2MnSi(100)by spin-resolved photoelectron spectroscopy

et al. 2015

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“…The CMFS thin film was deposited at RT using radiofrequency magnetron cosputtering from three targets, i.e., nearly stoichiometric CMS, Mn, and Fe, in an ultrahigh vacuum chamber (that has a base pressure of 6 × 10 [47], electronic, and magnetic properties [33][34][35][36][37][38][48][49][50]. The MgO buffer and barrier were deposited by electron beam evaporation in the same chamber at 400°C and RT, respectively.…”

Section: A Experimental Methodsmentioning

confidence: 99%

Enhanced half-metallicity of off-stoichiometric quaternary Heusler alloy Co2(Mn,Fe)Si investigated through saturation magnetization and tunneling magnetoresistanc

et al. 2016

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We investigated the factors that critically affect the half-metallicity of the quaternary Heusler alloy Co 2 (Mn,Fe)Si (CMFS) by examining the film composition dependence of the saturation magnetization per formula unit, μ s , of CMFS thin films and the tunneling magnetoresistance (TMR) ratio of CMFS/MgO/CMFS magnetic tunnel junctions (MTJs). We also investigated the origin of the giant TMR ratio of up to 2610% at 4.2 K (429% at 290 K) obtained for CMFS MTJs with Mn-rich, lightly Fe-doped CMFS electrodes. Co antisites at the nominal Mn/Fe sites (Co Mn/Fe antisites) can consistently explain the μ s for (Mn + Fe)-deficient CMFS thin films being lower than the half-metallic Z t − 24 value and the TMR ratio for MTJs with (Mn + Fe)-deficient CMFS electrodes being lower than that for MTJs with (Mn + Fe)-rich CMFS electrodes. It was revealed that the Co Mn/Fe antisite is detrimental to the half-metallicity of the CMFS quaternary alloy, as it is in the Co 2 MnSi (CMS) ternary alloy. It was also shown that (Mn + Fe)-rich compositions are critical to suppressing these harmful antisites and to retaining the half-metallic electronic state. In addition, a relatively small Fe ratio, rather than a large one, in the total (Mn + Fe) composition led to a more complete half-metallic electronic state. Half-metallicity was more strongly enhanced by increasing the Mn composition in Mn-rich, lightly Fe-doped CMFS than in Mn-rich CMS. This phenomenon is the cause of the giant TMR ratio recently reported for CMFS MTJs. Our findings indicate that the approach to controlling off-stoichiometry and film composition is promising for fully utilizing the half-metallicity of quaternary CMFS thin films as spin source materials.

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“…Picozzi et al predicted from first principles that half-metallicity in CMS and Co 2 MnGe (CMG) is lost for Co Mn antisites, where a Mn site is replaced by a Co atom, because of the appearance of minority-spin in gap states near E F , while half-metallicity is retained for Mn Co antisites, where a Co site is replaced by a Mn atom [33]. The effect of off-stoichiometry on the half-metallicity of CMS and CMG has been systematically investigated recently using various experimental approaches, including the tunneling magnetoresistance (TMR) ratios of MTJs [9][10][11][12], the saturation magnetization per formula unit of thin films [12], the surface spin polarization [42], the magnetic states as investigated by x-ray absorption spectroscopy and x-ray magnetic circular dichroism [43][44][45], and the electronic states as investigated through spin-resolved low-energy and hard x-ray photoelectron spectroscopy [46][47][48]. These experimental studies, along with first-principles calculations, demonstrated that Co Mn antisites induced by a Mn-deficient composition (the Mn composition α < 2 − β in the composition expression of Co 2 Mn α Si β ) is detrimental to the half-metallicity of CMS.…”

Section: Introductionmentioning

confidence: 99%

Temperature dependence of spin-dependent tunneling conductance of magnetic tunnel junctions with half-metallicCo2MnSielectrodes

Moges

Honda

et al. 2016

Phys. Rev. B

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In order to elucidate the origin of the temperature (T ) dependence of spin-dependent tunneling conductance (G) of magnetic tunnel junctions (MTJs), we experimentally investigated the T dependence of G for the parallel and antiparallel magnetization alignments, G P and G AP , of high-quality Co 2 MnSi (CMS)/MgO/CMS MTJs having systematically varied spin polarizations (P ) at 4.2 K by varying the Mn composition α in Co 2 Mn α Si electrodes that exhibited giant tunneling magnetoresistance ratios. Results showed that G P normalized by its value at 4.2 K exhibited a notable, nonmonotonic T dependence although its variation with T was significantly smaller than that of G AP normalized by its value at 4.2 K, indicating that an analysis of the experimental G P (T ) is critical to revealing the origin of the T dependence of G. By analyzing the experimental G P (T ), we clarified that both spin-flip inelastic tunneling via a thermally excited magnon and spin-conserving elastic tunneling in which P decays with increasing T play key roles. The experimental G AP (T ), including its stronger T dependence for higher P at 4.2 K, was also consistently explained with this model. Our findings provide a unified picture for understanding the origin of the T dependence of G of MTJs with a wide range of P , including MTJs with high P close to a half-metallic value.

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Hard X-ray photoelectron spectroscopy on buried, off-stoichiometric Co x Mn y Ge z (x:z=2:0.38) Heusler thin films

Abstract: Hard X-ray photoelectron spectroscopy on buried, off-stoichiometric Co x Mn y Ge z (x : z = 2 : 0.38) Heusler thin films.

Cited by 12 publications

References 50 publications

Monitoring surface resonances onCo2MnSi(100)by spin-resolved photoelectron spectroscopy

Monitoring surface resonances onCo2MnSi(100)by spin-resolved photoelectron spectroscopy

Enhanced half-metallicity of off-stoichiometric quaternary Heusler alloy Co2(Mn,Fe)Si investigated through saturation magnetization and tunneling magnetoresistanc

Temperature dependence of spin-dependent tunneling conductance of magnetic tunnel junctions with half-metallicCo2MnSielectrodes

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