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Register a new userMagnetic anisotropy of polycrystalline high-temperature ferromagnetic Mn$_x$Si$_{1-x}$ ($xapprox0.5$) alloy films
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A set of thin film Mn$_x$Si$_{1-x}$ alloy samples with different manganese concentration x = 0.44 - 0.63 grown by the pulsed laser deposition (PLD) method onto the Al$_2$O$_3$(0001) substrate was investigated in the temperature range 4 - 300 K using ferromagnetic resonance (FMR) measurements in the wide range of frequencies (f = 7 - 60 GHz) and magnetic fields (H = 0 - 30 kOe). For samples with x = 0.52 - 0.55, FMR data show clear evidence of ferromagnetism with high Curie temperatures T$_text{C}$ ~ 300 K. These samples demonstrate complex and unusual character of magnetic anisotropy described in the frame of phenomenological model as a combination of the essential second order easy plane anisotropy contribution and the additional forth order uniaxial anisotropy contribution with easy direction normal to the film plane. We explain the obtained results by a polycrystalline (mosaic) structure of the films caused by the film-substrate lattice mismatch. The existence of extra strains at the crystallite boundaries leads to an essential inhomogeneous magnetic anisotropy in the film plane.
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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.
We present the studies of structural, electrical, and magnetic properties of bulk Cd$_{1textrm{-}x}$Mn$_{x}$GeAs$_{2}$ crystals with low Mn content, $x$, varying from 0 to 0.037. The studied samples have excellent crystallographic quality indicated by the presence of diffraction patterns never before observed experimentally for this compound. The electrical transport in our samples is dominated by thermal activation of conducting holes from the impurity states to the valence band with activation energy of about 200$;$meV. The defect states acting as ionic scattering centers with concentration in the range from 6 to 15$times$10$^{17}$$;$cm$^{-3}$ are observed. The effective Mn content in our samples, $bar{x}_{theta}$, determined from fit of the susceptibility data to the Curie-Weiss law, is very close to the average chemical content, $x$. It indicates that the Mn ions are distributed randomly, substituting the Cd sites in the host CdGeAs$_{2}$ lattice. We observe a negative Curie-Weiss temperature, $|theta|$$,$$leq$$,$3.1$;$K, increasing as a function of $x$. This indicates the significance of the short-range interactions between the Mn ions.
We present an experimental study for polycrystalline samples of the diluted magnetic semiconductor Mn(x)Ga(1-x)N (x<0.04) in order to address some of the existing controversial issues. Different techniques were used to characterize the electronic, magnetic, and structural properties of the samples, and inelastic neutron scattering was employed to determine the magnetic excitations associated with Mn monomers and dimers. Our main conclusions are as follows: (i) The valence of the Mn ions is 2+. (ii) The Mn(2+) ions experience a substantial single-ion axial anisotropy with parameter D=0.027(3) meV. (iii) Nearest-neighbor Mn(2+) ions are coupled antiferromagnetically. The exchange parameter J= 0.140(7) meV is independent of the Mn content x, i.e., there is no evidence for hole-induced modifications of J towards a potentially high Curie temperature postulated in the literature.
We present a comprehensive and systematic magnetization and ac susceptibility study of Mn$_{1-x}$Fe$_{x}$Si over an extensive range of ten Fe concentrations between $x$ = 0 - 0.32. With increasing Fe substitution, the critical temperature decreases but the magnetic phase diagrams remain qualitatively unaltered for $x$ $leq$ $x^*$ $approx$ 0.11 with clear boundaries between the helical, conical, and skyrmion lattice phase as well as an enhanced precursor phase. A notably different behavior sets in for $x$ $=$ 0.11, 0.13 and 0.14, where certain characteristics of helimagnetic correlations persist, but without clear phase boundaries. Although a qualitative change already sets in at $x^*$, the transition temperature and spontaneous magnetization vanish only at $x_C$ = 0.17 where also the average magnetic interactions change sign. Although the Curie-Weiss temperature reaches -12~K for $x$ = 0.32, no signature of long-range magnetic order is found down to the lowest temperature, indicating a possible significant role for quantum fluctuations in these systems.
The composition-dependent behavior of the Dzyaloshinskii-Moriya interaction (DMI), the spin-orbit torque (SOT), as well as anomalous and spin Hall conductivities of Mn$_{1-x}$Fe$_x$Ge alloys have been investigated by first-principles calculations using the relativistic multiple scattering Korringa-Kohn-Rostoker (KKR) formalism. The $D_{rm xx}$ component of the DMI exhibits a strong dependence on the Fe concentration, changing sign at $x approx 0.85$ in line with previous theoretical calculations as well as with experimental results demonstrating the change of spin helicity at $x approx 0.8$. A corresponding behavior with a sign change at $x approx 0.5$ is predicted also for the Fermi sea contribution to the SOT, as this is closely related to the DMI. In the case of anomalous and spin Hall effects it is shown that the calculated Fermi sea contributions are rather small and the composition-dependent behavior of these effects are determined mainly by the electronic states at the Fermi level. The spin-orbit-induced scattering mechanisms responsible for both these effects suggest a common origin of the minimum of the AHE and the sign change of the SHE conductivities.
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