Half-metallic Heusler Research Articles

Surface-specific thermal spin-depolarization on the half-metallic Heusler films

Half-metallic ferromagnets exhibit a perfect spin-polarization at the Fermi energy. Among many candidates, Co2MnSi Heusler alloy is the most investigated material due to its half-metallic nature and high Curie temperature (TC). Magnetic junction devices using Co2MnSi show remarkable performance at low temperatures. However, the performance is significantly degraded at room temperature, which requires a detailed understanding of the temperature-dependent electronic structure of Co2MnSi films. Here, using surface-sensitive spin- and angle-resolved photoelectron spectroscopy combined with first-principles calculations, we verify the temperature- and momentum-dependent spin-polarization of Co2MnSi thin-film. The recorded spin-polarization reaches ~ 60-75% at 50 K, while it reduces ~ 30-50% at 300 K. The observed surface-specific spin-depolarization behavior can be described by the thermally excited magnon model even well below TC, and we conclude that the spin-fluctuation is markedly enhanced on its surface. Our findings provide insights into the temperature-dependent electronic structure of half-metallic Heusler films, which could have significant implications for future spintronic applications.

Large magnetoresistance and high spin-transfer torque efficiency of Co2MnxFe1−xGe (0 ≤ x ≤ 1) Heusler alloy thin films obtained by high-throughput compositional optimization using combinatorially sputtered composition-gradient film

Half-metallic ferromagnetic Heusler alloys having high spin polarization are promising candidates to realize large magnetoresistance (MR) ratio and high spin-transfer torque (STT) efficiency in next-generation spintronic devices. Since the Heusler alloy properties are sensitive to composition, optimizing the composition is crucial for enhancing device performance. Here, we report the fabrication of high-performance current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices using Co2MnxFe1−xGe (0 ≤ x ≤ 1) Heusler alloy, employing a high-throughput and detailed composition optimization method. The method combined composition-gradient films and local measurements to enable the composition variation from Co2FeGe to Co2MnGe to be efficiently studied on a single library sample with a small composition interval. The CPP-GMR devices fabricated from stacks annealed at 250 °C showed a clear composition dependence of MR with the maximum of MR ratio ∼38% in the Mn-rich region of x = 0.85. By increasing the annealing temperature to 350 °C, the MR ratio increased to ∼45% along with high STT efficiency ∼0.6 in the broad composition range of 0.2 ≤ x ≤ 0.7. The optimal composition for the highest MR changed with annealing temperature because of the stability of the GMR stack being higher in the lower x range. The record high MR for the all-metal CPP-GMR devices, at low annealing temperature of 250 °C was achieved by the detailed composition optimization. These results present the high potential of Co2MnxFe1−xGe and provide a comprehensive guidance on the composition optimization for achieving large MR ratio and high STT efficiency in the CPP-GMR devices.

Atomic disorder and intrinsic anomalous Hall effect in a half-metallic ferromagnet Co2VAl

Atomic disorder and intrinsic anomalous Hall effect in a half-metallic ferromagnet Co2VAl

First Principles Study of Structural, Electronic, Mechanical and Density of State Properties of the Half - heusler Alloy NaCrGe

In this study, the investigated structural parameters revealed that NaCrGe is stable at beta phase. We obtained that the material is a narrow bandgap semiconductor half-Heusler alloys with measured gap of 1.050 eV. The structure NaCrGe conduction band minimum (CBM) position at gamma(Γ) and the valence band maximum (VBM) located at X-point of the Brillouin zone. This indicates that the alloy NaCrGe has indirect bandgap semiconductors. The material NaCrGe is considered hybrids between metals and semiconductors. Hence, NaCrGe is Half-metallic heusler alloy. The calculated mechanical properties indicate that NaCrGe possesses good mechanical stability, making it suitable for structural applications. B/G ratio for NaCrGe is 2.40. This implies that NaCrGe is “ductile” in nature at ambient condition. Also NaCrGe is confirmed “ductile” in nature at positive value of C11 – C44 (+48.07). PDOS shows that Na-4p, Cr-4p and Ge- 2p has the highest orbital contribution for Na, Cr and Ge atoms respectively. At fermi energy both spin up and spin down is at zero point in the plot of projected density of state (PDOS) against energy. This revealed that NaCrGe is a half metallic heusler alloy.

Half-metallic Heusler alloy/AlP based magnetic tunnel junction

Exploring the spin transport characteristics of magnetic tunnel junctions based on half-metallic Heusler holds significance, not only in unraveling the fundamental physics at play but also in advancing applications of spintronic devices. Here, density functional theory in conjunction with non-equilibrium Green’s functions has been systematically employed to investigate two prominent Heusler alloys, Co2CrAl and CoFeCrAl, which are of direct interest to the candidates of magnetic tunnel junction. The electronic structures of two Hesler alloys reveal that both exhibit characteristics of half-metallic ferromagnets, featuring a substantial spin-down bandgap and achieving 100% spin polarization. The tunneling magnetoresistance ratios obtained for Co2CrAl/AlP/Co2CrAl and CoFeCrAl/AlP/CoFeCrAl magnetic tunnel junctions are determined to be 173% and 59%, respectively, with the former exhibiting superior device characteristics. Therefore, the Co2CrAl/AlP-based magnetic tunnel junction demonstrates ideal performance, providing new opportunities for two-dimensional spintronics.

Surface effects for half-metallic Heusler alloy CrYCoAl

Surface effects for half-metallic Heusler alloy CrYCoAl

Density functional study of electrode material for magnetic tunnel junction designed using Co2TiZ (Z = Ge, Si) Heusler alloys

Density functional study of electrode material for magnetic tunnel junction designed using Co2TiZ (Z = Ge, Si) Heusler alloys

Spin dependent tunneling and strain sensitivity in a Co2MnSb/HfIrSb magnetic tunneling junction: a first-principles study.

Half-metallic Co-based full Heusler alloys have captured considerable attention of researchers in the realm of spintronic applications, owing to their remarkable characteristics such as exceptionally high spin polarization at the Fermi level, ultra-low Gilbert damping, and a high Curie temperature. In this comprehensive study, employing the density functional theory, we delve into the electronic stability and ballistic spin transport properties of a magnetic tunneling junction (MTJ) comprising a Co2MnSb/HfIrSb interface. An in-depth investigation of k-dependent spin transmissions uncovers the occurrence of coherent tunneling for the Mn-Mn/Ir interface, particularly when a spacer layer beyond a certain thickness is employed. It has been found that the Co-terminated Co2MnSb/HfIrSb interface shows perpendicular magnetic anisotropy, while those with Mn-Sb and Mn-Mn termination exhibit in-plane magnetic anisotropy. Furthermore, our spin-dependent transmission calculations demonstrate that the Mn-Mn/Ir interface manifests strain-sensitive transmission properties under both compressive and tensile strain and yields a remarkable three-fold increase in majority spin transmission under tensile strain conditions. We find a tunnel magnetoresistance of ∼500% under a bi-axial strain of -3%, beyond which the tunnel resistance is found to be theoretically infinite. These compelling outcomes place the Co2MnSb/HfIrSb junction among the highly promising candidates for nanoscale spintronic devices, emphasizing the potential significance of the system in the advancement of the field.

Electronic, magnetic, and structural properties of NiFeMnAl

Half-metallic Heusler compounds have been extensively studied in the recent years, both experimentally and theoretically, for potential applications in spin-based electronics. Here, we present the results of a combined theoretical and experimental study of the quaternary Heusler compound NiFeMnAl. Our calculations indicate that this material is half-metallic in the ground state and maintains its half-metallic electronic structure under a considerable range of external hydrostatic pressure and biaxial strain. NiFeMnAl crystallizes in the regular cubic Heusler structure, and exhibits ferromagnetic alignment. The practical feasibility of the proposed system is confirmed in the experimental section of this work. More specifically, a bulk ingot of NiFeMnAl was synthesized in A2 type disordered cubic structure using arc melting. It shows a high Curie temperature of about 468 K and a saturation magnetization of 2.3 . The measured magnetization value is smaller than the one calculated for the ordered structure. This discrepancy is likely due to the A2 type atomic disorder, as demonstrated by our calculations. We hope that the presented results may be useful for researchers working on practical applications of spin-based electronics.

Structural stability, opto-electronic, magnetic and thermoelectric properties of half-metallic ferromagnets quaternary Heusler alloys CoFeXAs (X = Mn, Cr and V)

Structural stability, opto-electronic, magnetic and thermoelectric properties of half-metallic ferromagnets quaternary Heusler alloys CoFeXAs (X = Mn, Cr and V)

Combinatorial optimization for high spin polarization in Heusler alloy composition-spread thin films by anisotropic magnetoresistance effect

Half-metallic Heusler alloys are promising candidates for spintronic applications due to their high spin polarization. However, the spin polarization strongly depends on the atomic composition, which is time-consuming to optimize from various compositional combinations. Here, we demonstrate a high-throughput compositional optimization method for high spin polarization in Co2(Mn, Fe)Ge Heusler alloys by combining composition-spread films and anisotropic magnetoresistance (AMR) measurement. Two types of composition-spread films of polycrystalline Co2(Mn1−xFex)Ge and (Co2Mn0.5Fe0.5)1−yGey are fabricated on SiO2/Si substrates by combinatorial sputtering deposition, followed by post-annealing. The compositional dependence of AMR shows the largest negative AMR ratio of −0.13% and the smallest temperature dependence of the resistance change of AMR for y = 0.25 in the (Co2Mn0.5Fe0.5)1−yGey composition-spread film, suggesting the highest spin polarization and the closest nature to the ideal half-metal at this composition ratio. To verify this, we also develop a new technique to measure the compositional dependence of spin polarization by measuring the spin accumulation signals of nonlocal spin-valve devices fabricated on the composition-spread films and observe the highest spin polarization of 82% for y = 0.24. This confirms a clear qualitative correlation between the large negative AMR ratio and high spin polarization. Our combinatorial method using the composition-spread films and the AMR measurement proves to be a facile way for optimizing the fabrication conditions of half-metallic Heusler alloys with high spin polarization.

Experimental and first-principles investigation on magnetic properties and electronic structure in half-metallic Mn-Co-V-Al Heusler alloy

Experimental and first-principles investigation on magnetic properties and electronic structure in half-metallic Mn-Co-V-Al Heusler alloy

Slater-Pauling Behavior in Half-Metallic Heusler Compounds.

Heusler materials have become very popular over the last two decades due to the half-metallic properties of a large number of Heusler compounds. The latter are magnets that present a metallic behavior for the spin-up and a semiconducting behavior for the spin-down electronic band structure leading to a variety of spintronic applications, and Slater-Pauling rules have played a major role in the development of this research field. These rules have been derived using ab initio electronic structure calculations and directly connecting the electronic properties (existence of spin-down energy gap) to the magnetic properties (total spin magnetic moment). Their exact formulation depends on the half-metallic family under study and can be derived if the hybridization of the orbitals at various sites is taken into account. In this review, the origin and formulation of the Slater-Pauling rules for various families of Heusler compounds, derived during these two last decades, is presented.

First-Principles Studies on Spin-Dependent Transport of Magnetic Junctions with Half-Metallic Heusler Compounds

Two types of magnetoresistance (MR), i.e., tunnel magnetoresistance (TMR) and current perpendicular to plane giant magnetoresistance (CPP-GMR), are theoretically discussed for systems with half-metallic (HFM) Co-based full Heusler compounds. In TMR, the non-collinear spin structure at the Co2MnSi(CMS)/MgO(001) interface that results from thermal spin fluctuations significantly reduced the TMR ratio at room temperature (RT). Enhancement of the exchange stiffness of CMS/MgO was essential to suppress the reduction in TMR at RT. Furthermore, it is proposed that inserting of a B2-CoFe layer between CMS and MgO is a promising way to enhance the interface exchange stiffness constant. In CPP-GMR, the interface spin asymmetry γ in the Valet-Fert model was essential to enhance GMR at RT, because the temperature dependence of γ in experiments was much larger than that of the bulk spin asymmetry β. I showed that the experimental CPP-GMR ratio increases with the decrease in the theoretical resistance-area product RPA, which is roughly consistent with the RP dependence of γ. This means that matching of the conductive channel between HMF and a non-magnetic metallic spacer is a key parameter to enhance γ. These findings will be very important for room temperature spintronics devices applied in future artificial intelligence hardware.

Study of structural, electronic, elastic, magnetic and thermal properties of the new half-metallic Heusler alloys Cr2LuSn1−xPbx: by DFT approach

Study of structural, electronic, elastic, magnetic and thermal properties of the new half-metallic Heusler alloys Cr2LuSn1−xPbx: by DFT approach

Soft magnetism in single phase Fe3Si thin films deposited on SrTiO3(001) by pulsed laser deposition

The development of devices relying on spin phenomena requires of an ideal spin polarized electron source. This can be achieved by taking advantage of half-metallic full Heusler alloy thin films. However, their implementation requires a controlled growth of stoichiometric films with large activation volumes. In this work, we report on the growth of epitaxial Fe3Si ultra-thin films by pulsed laser deposition on SrTiO3(001) substrates, analyzing the effect of deposition temperature in the structural, morphological and magnetic properties of the deposited films. We conclude that optimal compromise between phase purity and interface quality is obtained at 200 ºC, obtaining the best magnetic response under this condition.

Magnetization dynamics of a CoFe/Co2MnSi magnetic bilayer structure

Half-metallic Heusler alloys are receiving significant attention for spintronic applications utilizing magnetic tunnel junctions and requiring large spin polarization. Co2MnSi (CMS) is one of the most promising candidates for this purpose. Here, we report the magnetization dynamics of a thin, epitaxial CMS film in a magnetic CoFe/CMS bilayer structure sputtered on an MgO substrate. The magnetic precession frequency response of the CoFe/CMS bilayer shows a fourfold symmetry with respect to the azimuthal applied field angle, reflecting the crystal symmetry of the CMS layer and not the underlying CoFe film. Moreover, the effective Gilbert damping parameter exhibits inhomogeneous broadening at lower applied magnetic fields. At large fields, however, the azimuthal angle dependence disappears, and the intrinsic Gilbert damping is observed. This study provides insight into the dynamics of a magnetic bilayer structure that forms an integral element in spintronic applications.

Experimental studies of Cr2NiAl half-metallic inverse Heusler compound for spintronic applications

Experimental studies of Cr2NiAl half-metallic inverse Heusler compound for spintronic applications

Half metallic Heusler alloys XMnGe (X = Ti, Zr, Hf) for spin flip and thermoelectric device application – Material computations

Half metallic Heusler alloys XMnGe (X = Ti, Zr, Hf) for spin flip and thermoelectric device application – Material computations

Low magnetic damping constant in half-metallic Co2FeAl Heusler alloy thin films grown by molecular beam epitaxy

Half-metallic Co2FeAl Heusler alloy thin films with various thickness were prepared by MBE method and its magnetic and crystalline properties were investigated. At the thickness of 20 nm and above, good magnetic properties and high B2-order parameter was obtained. In addition, magnetic damping constant was evaluated from peak-to-peak linewidth measured by FMR and ultra-low magnetic damping constant below 0.001 was obtained at the film thickness of 30 nm. These results are thanks to the excellent half-metallicity in the Co2FeAl films prepared by MBE.