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Our study highlights spin-polarization mechanisms in metals by focusing on the mobilities of conducting electrons with different spins instead of their quantities. Here, we engineer electron mobility by applying chemical disorder induced by nonstoichiometric variations. As a practical example, we discuss the scheme that establishes such variations in tetragonal Mn3Ga Heusler material. We justify this approach using first-principles calculations of the spin-projected conductivity components based on the Kubo-Greenwood formalism. It follows that, in the majority of cases, even a small substitution of some other transition element instead of Mn may lead to a substantial increase in spin polarization along the tetragonal axis. [ABSTRACT FROM AUTHOR]

We demonstrated electrical spin injection from a half-metallic Heusler alloy Co2MnSi electrode into a GaAs channel through observation of a spin-valve signal and a Hanle signal in the four-terminal nonlocal geometry. Furthermore, we electrically detected a nuclear field acting on electron spins, which was produced by the dynamic nuclear polarization, through observation of transient oblique Hanle signals. Samples with a Co2MnSi spin source exhibited higher spin-injection efficiency and a larger nuclear field compared to samples with a Co50Fe50 spin source, suggesting that the spin polarization of Co2MnSi is higher. This higher polarization is promising for realizing future spintronic devices and for understanding spin interactions as well as spin-dependent transport properties in a semiconductor channel. [ABSTRACT FROM AUTHOR]

The electronic structure and magnetism of the quaternary Heusler alloy NiFeMnSn are studied using the full-potential linearized augmented plane-wave (FPLAPW) method. The calculation for the perfectly LiMgPdSn-type ordered crystal structure (type I) of NiFeMnSn shows a high spin polarization (~ 76%) with a ferromagnetic ground state. The total spin magnetic moment is in good agreement with the Slater-Pauling rule. The structural investigations using neutron diffraction at 500 K, and Mössbauer spectroscopy at 300 K on the NiFeMnSn alloy, prepared using an arc melting, show the presence of atomic site disorder. The electronic structure calculation for the disordered structure shows that the site disorder destroys the nearly half-metallic nature of this alloy. The magnetization measurements indicate that the Curie temperature is well above room temperature (~ 405 K) as desired for the spintronics application. [ABSTRACT FROM AUTHOR]

Heusler compounds offer potential as spintronic devices due to their spin polarization and half-metallicity properties, where electron spin-majority (minority) manifold exhibits states (band gap) at the electronic chemical potential, yielding full spin polarization in a single manifold. Yet, Heuslers often exhibit intrinsic disorder that degrades its half-metallicity and spin polarization. Using density-functional theory, we analyze the electronic and magnetic properties of equiatomic Heusler (L21) CoMnCrAl and CoFeCrGe alloys for effects of hydrostatic pressure and intrinsic disorder (thermal antisites, binary swaps, and vacancies). Under pressure, CoMnCrAl undergoes a metallic transition, while half-metallicity in CoFeCrGe is retained for a limited range. Antisite disorder between Cr-Al pair in CoMnCrAl alloy is energetically the most favorable, and retains half-metallic character in Cr-excess regime. However, Co-deficient samples in both alloys undergo a transition from half-metallic to metallic, with a discontinuity in the saturation magnetization. For binary swaps, configurations that compete with the ground state are identified and show no loss of half-metallicity; however, the minority-spin band gap and magnetic moments vary depending on the atoms swapped. For single binary swaps, there is a significant energy cost in CoMnCrAl but with no loss of half-metallicity. Although a few configurations in CoFeCrGe energetically compete with the ground state, the minority-spin band gap and magnetic moments vary depending on the atoms swapped. This information should help in controlling these potential spintronic materials. [ABSTRACT FROM AUTHOR]

Half metal magnets are of great interest in the field of spintronics because of their potential full spin polarization at the Fermi level (EF) and low magnetization damping. The high Curie temperature and the predicted 0.7 eV minority spin gap make the Co2MnSi Heusler compound very promising for applications. We investigated the half-metallic magnetic character of this compound using spin-resolved photoemission, ab initio calculation, and ferromagnetic resonance. At the surface of Co2MnSi, a gap in the minority spin channel is observed, leading to 100% spin polarization. However, this gap is 0.3 eV below EF, and a minority spin state is observed at EF. We show that a minority spin gap at EF can nevertheless be recovered either by changing the chemical composition of the compound or by covering the surface by Mn, MnSi, or MgO. This spin-gap recovery results in extremely small damping coefficients, reaching values as low as 7?10-4. [ABSTRACT FROM AUTHOR]