Zinc-blende CrTe Research Articles

Symmetry-Induced Hybridization in Hexagonal and Zinc-Blende CrTe Crystals

Symmetry-Induced Hybridization in Hexagonal and Zinc-Blende CrTe Crystals

Stability and half-metallicity of the (001) and (111) surfaces of CrTe with rocksalt structure

We extend the recent study on above-room-temperature half-metallic ferromagnetism in bulk rocksalt CrTe [Y. Liu, S. K. Bose, and J. J. Kudrnovský, Phys. Rev. B 82, 094435 (2010)] to the (001) and (111) surfaces by using the first-principles calculations. We show that the Te-terminated (111) surface is energetically more stable than both the (001) and the Cr-terminated (111) surfaces over the whole effective Cr chemical potential, and the surface stability of the Te-terminated (111) surface of rocksalt CrTe is comparable with that of the Te-terminated (001) surface of experimental zinc-blende CrTe. In addition, both the (001) and (111) surfaces of rocksalt CrTe retain the bulk half-metallicity. The atomic magnetic moments at the (111) surfaces are greatly different from those in the bulk rocksalt CrTe due to the breakdown of Cr-Te bond at the (111) surface, but the differences are very small for the case of the (001) surface due to the existence of Cr-Te bond at the (001) surface. These results indicate that it is feasible to fabricate the half-metallic CrTe thin films with rocksalt structure other than zinc-blende one.

Magnetocrystalline anisotropy of zinc-blende CrTe (001) surface: A first-principles study

By using the highly precise all-election full potential linearized augmented plane-wave method based on density functional theory within the generalized gradient approximation, we investigated magnetocrystalline anisotropy and magnetism of zinc-blende CrTe (001) surface. We observed that both of the Cr- and Te-terminated zinc-blende CrTe (001) surfaces maintain the half-metallicity by analyzing the density of states. The magnitudes of the calculated magnetic moments for the Cr(S) and Cr(S-1) atoms are calculated to be 3.92 and 3.16 μ B for the Cr- and Te-terminated surfaces, respectively. The Te atoms show significantly induced negative spin polarizations of 0.13–0.30 μ B. The spin orientations at the Te-terminated (Cr-terminated) surfaces were found to be in-plane (out-of-plane) regardless of its thickness. Since a Te-terminated surface is known as to be more stable than a Cr-terminated one, our result is consistent with an experiment which observed in-plane magnetic anisotropy at a CrTe (001) surface.

Robust half-metallicity at the zincblende CrTe(001) surfaces and its interface with ZnTe(001)

Abstract All electron full potential calculations based on spin density functional theory are performed to study cubic zincblende (ZB) and hexagonal NiAs structures of bulk CrTe, free (0 0 1) surfaces of ZB CrTe, and interface of ZB CrTe with ZnTe(0 0 1). The ferromagnetic NiAs structure is reported to be about 0.26 eV more stable than the ferromagnetic ZB phase while ZB CrTe is found to be a half-metallic ferromagnet with a half-metallic gap of about 2.90 eV. Thermodynamic stability of CrTe(0 0 1) surfaces are studied in the framework of ab-initio thermodynamic. The obtained phase diagram evidences more stability of the Te terminated surface compared with the Cr termination. We discuss that both Te and Cr ideal terminations of CrTe(0 0 1) retain bulk-like half-metallic property but with a reduced half-metallic gap compared with bulk value. The structural, electronic, magnetic, and band alignment properties of the ZB CrTe/ZnTe(0 0 1) interface are computed and a rather large minority valence band offset of about 1.09 eV is observed in this heterojunction.

Fluorescence XAFS analysis of local structures in iodine-doped Zn1-xCrxTe

Geometric structures for II-VI diluted magnetic semiconductor iodine-doped Zn1-xCrxTe films (x = 0.05) grown by molecular-beam epitaxy with high-temperature ferromagnetism were investigated by using fluorescence x-ray absorption fine structure (XAFS) measurement in order to elucidate the relationship between the geometric structure and the magnetic properties. The XAFS analysis has revealed that the local structures around Cr atoms are dependent on the growth temperature. For the samples grown at 360 and 390 °C, the majority of Cr atoms are tetrahedrally coordinated to Te atoms, indicating the formation of substitutional Cr on Zn-site in ZnTe lattice and/or zinc-blende (ZB) CrTe. On the contrary, for the samples grown at 300 and 330 °C the additional formation of secondary phases such as Cr-Te compounds was suggested. Therefore, it is deduced that the formation of secondary phase such as Cr-Te compounds are related to the increase of Curie temperature. The XAFS analysis has also revealed that the local structures do not depend on the I concentration. For the samples with different I concentrations, the Cr atoms form substitutional Cr on Zn-site in ZnTe lattice and/or ZB CrTe, corresponding to the result of TEM measurement.

Exchange bias in zinc-blende CrTe–MnTe bilayer

We have studied the exchange bias at the ferromagnetic (FM)/antiferromagnetic interface in the zinc-blende transition-metal chalcogenides, CrTe (5 nm)/MnTe(40 nm) bilayer grown on GaAs (100) substrate by molecular-beam epitaxy. A negative exchange bias shift in the hysteresis loop is observed when the bilayer is cooled in the applied magnetic field. The temperature-dependent remanent magnetization shows a clear enhancement of the Curie temperature and magnetization in the bilayer as compared to a single FM layer. The effects of temperature, cooling field, and angular dependence on the exchange bias have been investigated.

Systematic investigation of structural and magnetic properties in molecular beam epitaxial growth of metastable zinc-blende CrTe toward half-metallicity

We report a systematic investigation on the structural and magnetic properties of molecular-beam epitaxial growth of CrTe thin films with different layer thicknesses and Cr∕Te flux ratios. A phase diagram of the growth parameters is established based on the detailed analyses of the reflection high-energy electron diffraction patterns, atomic force microscopy, and magnetization. Our high-resolution transmission electron microscopy results show that under appropriate growth conditions, a metastable zinc-blende (ZB) phase of CrTe film can be achieved with a nominal thickness of 5nm. The magnetic properties of ZB CrTe exhibit a strong in-plane anisotropy with an easy axis along the [001] direction and hard axes along the [011] and [01¯1] directions. Correspondingly, the uniaxial (KU) and cubic (KC) anisotropy constants are obtained through the fitting of the [011] hard-axis direction. The temperature dependence of the remanent magnetization indicates the TC∼100K of ZB CrTe is attained.

Observation of strong magnetic anisotropy in zinc-blende CrTe thin films

We report the growth of zinc-blende CrTe thin films with a nominal thickness of 5 nm by low-temperature molecular-beam epitaxy. Reflection high-energy electron diffraction patterns, atomic force microscopy and high-resolution transmission electron microscopy analyses established that a quasi-two-dimensional layer-by-layer growth mode is achieved. We observe a strong magnetic anisotropy in the film with an easy axis along the [0 0 1] direction. The uniaxial (KU) and cubic (KC) anisotropy constants are obtained through the fitting of the hard axes along the [0 1 1] and directions of the magnetization curves. A Curie temperature of 100 K is obtained from the temperature-dependent remanent-magnetization measurement.

Half-metallic ferromagnetism and structural stability of zincblende phases of the transition-metal chalcogenides.

An accurate density-functional method is used to study systematically half-metallic ferromagnetism and stability of zincblende phases of 3d-transition-metal chalcogenides. The zincblende CrTe, CrSe, and VTe phases are found to be excellent half-metallic ferromagnets with large half-metallic gaps (up to 0.88 eV). They are mechanically stable and approximately 0.31-0.53 eV per formula unit higher in total energy than the corresponding nickel-arsenide ground-state phases, and therefore would be grown epitaxially in the form of films and layers thick enough for spintronic applications.