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Register a new userSpin-charge conversion in NiMnSb Heusler alloy films
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Half-metallic Heusler alloys are attracting considerable attention because of their unique half-metallic band structures which exhibit high spin polarization and yield huge magnetoresistance ratios. Besides serving as ferromagnetic electrodes, Heusler alloys also have the potential to host spin-charge conversion which has been recently demonstrated in other ferromagnetic metals. Here, we report on the spin-charge conversion effect in the prototypical Heusler alloy NiMnSb. Spin currents were injected from Y3Fe5O12 into NiMnSb films by spin pumping, and then the spin currents were converted to charge currents via spin-orbit interactions. Interestingly, an unusual charge signal was observed with a sign change at low temperature, which can be manipulated by film thickness and ordering structure. It is found that the spin-charge conversion has two contributions. First, the interfacial contribution causes a negative voltage signal, which is almost constant versus temperature. The second contribution is temperature dependent because it is dominated by minority states due to thermally excited magnons in the bulk part of the film. This work provides a pathway for the manipulation of spin-charge conversion in ferromagnetic metals by interface-bulk engineering for spintronic devices.
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We report the structure, magnetic property and spin polarization of CoFeMnGe equiatomic quaternary Heusler alloy. The alloy was found to exist in the L21 structure with considerable amount of DO3 disorder. Thermal analysis result indicated the Curie temperature is about 711K without any other phase transformation up to melting temperature. The magnetization value was close to that predicted by the Slater-Pauling curve. Current spin polarization of P = 0.70 {plus/minus}0.1 was deduced using point contact Andreev reflection (PCAR) measurements. Half-metallic trend in the resistivity has also been observed in the temperature range of 5 K to 300 K. Considering the high spin polarization and Curie temperature, this material appears to be promising for spintronic applications.
We determine experimentally the spin structure of half-metallic Co2FeAl0.4Si0.6 Heusler alloy elements using magnetic microscopy. Following magnetic saturation, the dominant magnetic states consist of quasi-uniform configurations, where a strong influence from the magnetocrystalline anisotropy is visible. Heating experiments show the stability of the spin configuration of domain walls in confined geometries up to 800 K. The switching temperature for the transition from transverse to vortex walls in ring elements is found to increase with ring width, an effect attributed to structural changes and consequent changes in magnetic anisotropy, which start to occur in the narrower elements at lower temperatures.
Spin gapless semiconductors (SGS) form a new class of magnetic semiconductors, which has a band gap for one spin sub band and zero band gap for the other, and thus are useful for tunable spin transport based applications. In this paper, we report the first experimental evidence for spin gapless semiconducting behavior in CoFeMnSi Heusler alloy. Such a behavior is also confirmed by first principles band structure calculations. The most stable configuration obtained by the theoretical calculation is verified by experiment. The alloy is found to crystallize in the cubic Heusler structure (LiMgPdSn type) with some amount of disorder and has a saturation magnetization of 3.7 Bohrs magneton/f.u.. and Curie temperature of 620 K. The saturation magnetization is found to follow the Slater-Pauling behavior, one of the prerequisites for SGS. Nearly temperature-independent carrier concentration and electrical conductivity is observed from 5 to 300 K. An anomalous Hall coefficient of 162 S/cm is obtained at 5 K. Point contact Andreev reflection data has yielded the current spin polarization value of 0.64, which is found to be robust against the structural disorder. All these properties are quite promising for the spintronic applications such as spin injection and can bridge a gap between the contrasting behavior of half-metallic ferromagnets and semiconductors.
We report the evolution of magnetic moment as well as magnetic anisotropy with crystalline order in Co$_2$MnSi thin films grown on $(100)$ MgO by pulsed laser deposition. The films become more ordered as the annealing temperature ($T_A$) increases from 400 to 600 $^0$C. The extent of emph{L}$2_1$ ordering in the films annealed at 600 $^0$C is $approx 96%$. The static magnetization measurements by vibrating sample magnetometry shows a maximum moment of 4.95 $mu_B$ per formula unit with low coercivity ($H_C$ $approx$ 65 Oe) in the films annealed at 600 $^0$C. A rigorous analysis of the azimuthal and polar angle dependent ferromagnetic resonance (FMR) measured at several temperatures allows determination of various anisotropy fields relevant to our system as a function of $T_A$. Finally, we have evaluated the exchange stiffness constant down to 100 K using spin wave modes in FMR spectra. We have also estimated the exchange energies as well as stiffness constant by varying the lattice parameter emph{ab-initio} using the Korringa-Kohn-Rostoker method.
Half Metal Magnets are of great interest in the field of spintronics because of their potential full spin-polarization at the Fermi level and low magnetization damping. The high Curie temperature and predicted 0.7eV minority spin gap make the Heusler alloy Co2MnSi very promising for applications.We investigated the half-metallic magnetic character of this alloy 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 the Fermi level and a minority spin state is observed at the Fermi level. We show that a minority spin gap at the Fermi energy can nevertheless be recovered either by changing the stoichiometry of the alloy or by covering the surface by Mn, MnSi or MgO. This results in extremely small damping coefficients reaching values as low as 7x 10-4.
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