Exchange interactions and temperature dependence of magnetization in half-metallic Heusler alloys

Şaşıoğlu, E.; Sandratskii, L. M.; Bruno, P.; Galanakis, I.

doi:10.1103/physrevb.72.184415

Cited by 287 publications

(190 citation statements)

References 81 publications

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“…Calculating the latter one as explained in Ref. 27 we get a value of 1505 K within the mean field approximation (MFA) and 1129 K within the random-phase approximation (RPA) (see Table I) close to the calculated value of 1050 K in Ref. 69.…”

Section: Robustness Of Half-metallicity and Ferromagnetismsupporting

confidence: 79%

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Ab initio electronic and magnetic properties of half-metallic NiCrSi and NiMnSi Heusler alloys: The role of defects and interfaces

Galanakis

Özdoğan

Şaşıoğlu

2008

Journal of Applied Physics

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Using state-of-the-art first-principles calculations we study the properties of the ferromagnetic Heusler compounds NiYSi where Y stands for V, Cr or Mn. NiCrSi and NiMnSi contrary to NiVSi are half-metallic at their equilibrium lattice constant exhibiting integer values of the total spin magnetic moment and thus we concentrate on these two alloys. The minority-spin gap has the same characteristics as for the well-known NiMnSb alloy being around ∼1 eV. Upon tetragonalization the gap is present in the density of states even for expansion or contraction of the out-of-plane lattice parameter by 5%. The Cr-Cr and Mn-Mn interactions make ferromagnetism extremely stable and the Curie temperature exceeds 1000 K for NiMnSi. Surface and interfaces with GaP, ZnS and Si semiconductors are not half-metallic but in the case of NiCrSi the Ni-based contacts present spinpolarization at the Fermi level over 90%. Finally, we show that there are two cases of defects and atomic-swaps. The first-ones which involve the Cr(Mn) and Si atoms induce states at the edges of the gap which persists for a moderate-concentration of defects. Defects involving Ni atoms induce states localized within the gap completely destroying the half-metallicity. Based on single-impurity calculations we associate these states to the symmetry of the crystal.

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Section: Robustness Of Half-metallicity and Ferromagnetismsupporting

confidence: 79%

“…We have used the formalism presented in Ref. 27 and in Fig. 7 we present the Cr-Cr and Mn-Mn exchange constants as a function of the distance between the atoms.…”

Section: Robustness Of Half-metallicity and Ferromagnetismmentioning

confidence: 99%

Ab initio electronic and magnetic properties of half-metallic NiCrSi and NiMnSi Heusler alloys: The role of defects and interfaces

Galanakis

Özdoğan

Şaşıoğlu

2008

Journal of Applied Physics

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“…Using the calculated energies in Table I for lattice-matched ZB-CrAs, J is estimated to be 15 meV, in good agreement with previous calculations. 31 This nearest-neighbor exchange interaction in ZB-CrAs is one order of magnitude larger than for some strong ferromagnets such as Co 2 MnSi Heusler alloy, 32 although the range of exchange interaction is considerably shorter in ZB-CrAs. 31 Due to this strong exchange interaction, a high Curie temperature of about 1000 K for ZB-CrAs is predicted by first-principles calculations, 33 which has not been confirmed by experiments up to now.…”

Section: Magnetic Propertiesmentioning

confidence: 96%

Stable structure and magnetic state of ultrathin CrAs films on GaAs(001): A density functional theory study

2010

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Density functional theory calculations using the pseudopotential-plane-wave approach are employed to investigate the structural and magnetic properties of epitaxial CrAs thin films on GaAs͑001͒. Motivated by recent reports of ferromagnetism in this system, we compare zinc-blende CrAs films ͑continuing the lattice structure of the GaAs substrate͒ and CrAs films with a bulklike orthorhombic structure epitaxially matched to three units of the GaAs͑001͒ lattice. We find that even for very thin films with three Cr layers the bulklike crystal structure is energetically more favorable than zinc-blende CrAs on GaAs͑001͒. CrAs films with orthorhombic structure, even if under epitaxial strain, preserve the antiferromagnetic order of CrAs bulk. In the light of our calculations, it appears likely that the magnetic hysteresis loop measured in ultrathin CrAs/GaAs͑001͒ films originates from uncompensated antiferromagnetic moments near the CrAs/GaAs interface. In conclusion, our results do not support earlier proposals that thick CrAs films could be employed as perfectly matched spin-injection electrode on GaAs. I. MOTIVATION AND BACKGROUNDSpin injection from a ferromagnet into a semiconductor is a major prerequisite for semiconductor spintronics. In recent years it has become clear that the efficiency of spin injection not only depends on the degree of spin polarization in the ferromagnet but the ferromagnet-semiconductor interface also plays a crucial role. Using electrodes fabricated from conventional ferromagnetic ͑FM͒ materials, such as Fe or Co, only a limited amount of spin-polarized current could be injected into GaAs. 1,2 As possible reasons, the conductivity mismatch in the metal and the ͑doped͒ semiconductor has been discussed 3 but the unsatisfactory results could also be due to technological problems in fabricating high-quality interfaces.As an alternative, Akinaga et al. 4 suggested to grow CrAs epitaxially, in the zinc-blende ͑ZB͒ structure, on GaAs. As advantages over conventional ferromagnetic electrodes, it has been pointed out that the use of a zinc-blende CrAs layer on GaAs not only avoids ͑possibly detrimental͒ interface states 5 but in addition zinc-blende CrAs is a half-metallic ferromagnet according to DFT calculations, i.e., it offers the highest possible spin polarization of 100%. By growing a superlattice of alternating CrAs and GaAs layers, Akinaga et al. managed to fabricate heterostructures showing ferromagnetic behavior at room temperature. Following this work, several research groups studied epitaxial CrAs films on GaAs, 6-11 and confirmed the ferromagnetic hysteresis of the samples. The saturation magnetization was found to correspond to about 2 B up to 3 B per Cr atom. However, the remanent magnetization was typically much lower, less than 10% of the saturation magnetization. Transmission electron microscopy ͑TEM͒ images of the samples demonstrated pseudomorphic growth of CrAs on GaAs, and most researchers claimed the formation of zinc-blende CrAs. However, Etgens et al., 12 using in situ refl...

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“…We calculate the exchange interactions between the Mn atoms following the same methodology as in Ref. 23. We use the augmented spherical waves ab initio method 24 within the atomic-sphere approximation 25 to calculate the electronic structure.…”

mentioning

confidence: 99%

Structural-induced antiferromagnetism in Mn-based full Heusler alloys: The case of Ni2MnAl

Galanakis

Şaşıoğlu

2011

Appl. Phys. Lett.

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Exchange interactions and temperature dependence of magnetization in half-metallic Heusler alloys

Cited by 287 publications

References 81 publications

Ab initio electronic and magnetic properties of half-metallic NiCrSi and NiMnSi Heusler alloys: The role of defects and interfaces

Ab initio electronic and magnetic properties of half-metallic NiCrSi and NiMnSi Heusler alloys: The role of defects and interfaces

Stable structure and magnetic state of ultrathin CrAs films on GaAs(001): A density functional theory study

Structural-induced antiferromagnetism in Mn-based full Heusler alloys: The case of Ni2MnAl

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