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Register a new userHeteroepitaxial growth of tetragonal Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ (0 $leqslant$ x $leqslant$ 1.2) Heusler films with perpendicular magnetic anisotropy
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This work reports on the structural and magnetic properties of Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ Heusler films with different Fe content x (0 $leqslant$ x $leqslant$ 1.2). The films were deposited heteroepitaxially on MgO single crystal substrates, by magnetron sputtering. Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ films with the thickness of 35 nm were crystallized in tetragonal D0$_{22}$ structure with (001) preferred orientation. Tunable magnetic properties were achieved by changing the Fe content x. Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ thins films exhibit high uniaxial anisotropy Ku $geqslant$ 1.4 MJ/m3, coercivity from 0.95 to 0.3 T and saturation magnetization from 290 to 570 kA/m. The film with Mn$_{1.6}$Fe$_{1.1}$Ga$_{1.3}$ composition shows high Ku of 1.47 MJ/m3 and energy product ${(BH)_{max}}$ of 37 kJ/m3, at room temperature. These findings demonstrate that Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ films have promising properties for mid-range permanent magnet and spintronic applications.
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We report thermoelectric properties of Ir$_{1-x}$Rh$_x$Te$_2$ ($0 leqslant x leqslant 0.3$) alloy series where superconductivity at low temperatures emerges as the high-temperature structural transition ($T_s$) is suppressed. The isovalent ionic substitution of Rh into Ir has different effects on physical properties when compared to the anionic substitution of Se into Te, in which the structural transition is more stable with Se substitution. Rh substitution results in a slight reduction of lattice parameters and in an increase of number of carriers per unit cell. Weak-coupled BCS superconductivity in Ir$_{0.8}$Rh$_{0.2}$Te$_2$ that emerges at low temperature ($T_c^{zero}$ = 2.45 K) is most likely driven by electron-phonon coupling rather than dimer fluctuations mediated pairing.
In this work we report the appearence of a large perpendicular magnetic anisotropy (PMA) in Fe$_{1-x}$Ga$_x$ thin films grown onto ZnSe/GaAs(100). This arising anisotropy is related to the tetragonal metastable phase in as-grown samples recently reported [M. Eddrief {it et al.}, Phys. Rev. B {bf 84}, 161410 (2011)]. By means of ferromagnetic resonance studies we measured PMA values up to $sim$ 5$times$10$^5$ J/m$^3$. PMA vanishes when the cubic structure is recovered upon annealing at 300$^{circ}$C. Despite the important values of the magnetoelastic constants measured via the cantilever method, the consequent magnetoelastic contribution to PMA is not enough to explain the observed anisotropy values in the distorted state. {it Ab initio} calculations show that the chemical ordering plays a crucial role in the appearance of PMA. Through a phenomenological model we are able to explain that an excess of next nearest neighbour Ga pairs (B$_2$-like ordering) along the perpendicular direction arises as the source of PMA in Fe$_{1-x}$Ga$_x$ thin films.
The static and dynamic magnetic properties of tetragonally distorted Mn--Ga based alloys were investigated. Static properties are determined in magnetic fields up to 6.5~T using SQUID magnetometry. For the pure Mn$_{1.6}$Ga film, the saturation magnetisation is 0.36~MA/m and the coercivity is 0.29~T. Partial substitution of Mn by Co results in Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$. The saturation magnetisation of those films drops to 0.2~MA/m and the coercivity is increased to 1~T. Time-resolved magneto-optical Kerr effect (TR-MOKE) is used to probe the high-frequency dynamics of Mn--Ga. The ferromagnetic resonance frequency extrapolated to zero-field is found to be 125~GHz with a Gilbert damping, $alpha$, of 0.019. The anisotropy field is determined from both SQUID and TR-MOKE to be 4.5~T, corresponding to an effective anisotropy density of 0.81~MJ/m$^3$. Given the large anisotropy field of the Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ film, pulsed magnetic fields up to 60~T are used to determine the field strength required to saturate the film in the plane. For this, the extraordinary Hall effect was employed as a probe of the local magnetisation. By integrating the reconstructed in--plane magnetisation curve, the effective anisotropy energy density for Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ is determined to be 1.23~MJ/m$^3$.
We report the observation of anomalies in the longitudinal magnetoresistance of tensile-strained (Ga,Mn)As epilayers with perpendicular magnetic anisotropy. Magnetoresistance measurements carried out in the planar geometry (magnetic field parallel to the current density) reveal spikes that are antisymmetric with respect to the direction of the magnetic field. These anomalies always occur during magnetization reversal, as indicated by a simultaneous change in sign of the anomalous Hall effect. The data suggest that the antisymmetric anomalies originate in anomalous Hall effect contributions to the longitudinal resistance when domain walls are located between the voltage probes. This interpretation is reinforced by carrying out angular sweeps of $vec{H}$, revealing an antisymmetric dependence on the helicity of the field sweep.
The composition dependence of the structural, magnetic, and transport properties of epitaxially grown Mn-Co-Ga films were investigated. The crystal structure was observed to change from tetragonal to cubic as the Co content was increased. In terms of the dependence of saturation magnetization on the Co content, relatively small value was obtained for the Mn$_{2.3}$Co$_{0.4}$Ga$_{1.3}$ film at a large {it K}$_textrm u$ value of 9.2 Merg/cm$^3$. Electrical resistivity of Mn-Co-Ga films was larger than that of pure Mn-Ga film. The maximum value of the resistivity was 490 $muOmega$cm for Mn$_{2.2}$Co$_{0.6}$Ga$_{1.2}$ film. The high resistivity of Mn-Co-Ga might be due to the presence of localized electron states in the films due to chemical disordering caused by the Co substitution.
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