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Register a new userGrowth and properties of ferromagnetic In(1-x)Mn(x)Sb alloys
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We discuss a new narrow-gap ferromagnetic (FM) semiconductor alloy, In(1-x)Mn(x)Sb, and its growth by low-temperature molecular-beam epitaxy. The magnetic properties were investigated by direct magnetization measurements, electrical transport, magnetic circular dichroism, and the magneto-optical Kerr effect. These data clearly indicate that In(1-x)Mn(x)Sb possesses all the attributes of a system with carrier-mediated FM interactions, including well-defined hysteresis loops, a cusp in the temperature dependence of the resistivity, strong negative magnetoresistance, and a large anomalous Hall effect. The Curie temperatures in samples investigated thus far range up to 8.5 K, which are consistent with a mean-field-theory simulation of the carrier-induced ferromagnetism based on the 8-band effective band-orbital method.
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A narrow-gap ferromagnetic In(1-x)Mn(x)Sb semiconductor alloy was successfully grown by low-temperature molecular beam epitaxy on CdTe/GaAs hybrid substrates. Ferromagnetic order in In(1-x)Mn(x)Sb was unambiguously established by the observation of clear hysteresis loops both in direct magnetization measurements and in the anomalous Hall effect, with Curie temperatures T_C ranging up to 8.5 K. The observed values of T_C agree well with the existing models of carrier-induced ferromagnetism.
It is shown that a temperature window between the Curie temperatures of martensite and austenite phases around the room temperature can be obtained by a vacancy-tuning strategy in Mn-poor Mn1-xCoGe alloys (0 <= x <= 0.050). Based on this, a martensitic transformation from paramagnetic austenite to ferromagnetic martensite with a large magnetization difference can be realized in this window. This gives rise to a magnetic-field-induced martensitic transformation and a large magnetocaloric effect in the Mn1-xCoGe system. The decrease of the transformation temperature and of the thermal hysteresis of the transformation, as well as the stable Curie temperatures of martensite and austenite, are discussed on the basis of the Mn-poor Co-vacancy structure and the corresponding valence-electron concentration.
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.
Epitaxial thin films of the substitutionally alloyed half-Heusler series CoTi$_{1-x}$Fe$_x$Sb were grown by molecular beam epitaxy on InAlAs/InP(001) substrates for concentrations 0.0$leq$x$leq$1.0. The influence of Fe on the structural, electronic, and magnetic properties was studied and compared to that expected from density functional theory. The films are epitaxial and single crystalline, as measured by reflection high-energy electron diffraction and X-ray diffraction. Using in-situ X-ray photoelectron spectroscopy, only small changes in the valence band are detected for x$leq$0.5. For films with x$geq$0.05, ferromagnetism is observed in SQUID magnetometry with a saturation magnetization that scales linearly with Fe content. A dramatic decrease in the magnetic moment per formula unit occurs when the Fe is substitutionally alloyed on the Co site indicating a strong dependence on the magnetic moment with site occupancy. A crossover from both in-plane and out-of-plane magnetic moments to only in-plane moment occurs for higher concentrations of Fe. Ferromagnetic resonance indicates a transition from weak to strong interaction with a reduction in inhomogeneous broadening as Fe content is increased. Temperature-dependent transport reveals a semiconductor to metal transition with thermally activated behavior for x$leq$0.5. Anomalous Hall effect and large negative magnetoresistance (up to -18.5% at 100 kOe for x=0.3) are observed for higher Fe content films. Evidence of superparamagnetism for x=0.3 and x=0.2 suggests for moderate levels of Fe, demixing of the CoTi$_{1-x}$Fe$_x$Sb films into Fe rich and Fe deficient regions may be present. Atom probe tomography is used to examine the Fe distribution in a x=0.3 film. Statistical analysis reveals a nonhomogeneous distribution of Fe atoms throughout the film, which is used to explain the observed magnetic and electrical behavior.
The discovery of high thermoelectric performance in n-type polycrystalline Mg3(Sb,Bi)2 based Zintl compounds has ignited intensive research interest. However, some fundamental questions concerning the anisotropic transport properties and the origin of intrinsically low thermal conductivity are still elusive, requiring the investigation of single crystals. In this work, high-quality p-type Mg3Sb2 and Mg3Bi2 single crystals have been grown by using a self-flux method. The electrical resistivity r{ho} of Mg3Bi2 single crystal displays an anisotropy with r{ho} in-plane twice larger than out-of-plane. The low-temperature heat capacity and lattice thermal conductivity of Mg3Sb2 and Mg3Bi2 single crystals have been investigated by using the Debye-Callaway model, from which the existence of low-lying vibration mode could be concluded. Large Gruneisen parameters and strong anharmonicity are found responsible for the intrinsically low thermal conductivity. Moreover, grain boundary scattering does not contribute significantly to suppress the lattice thermal conductivity of polycrystalline Mg3Sb2. Our results provide insights into the intrinsic transport properties of Mg3X2 and could pave a way to realize enhanced thermoelectric performance in single-crystalline Mg3X2-based Zintl compounds.
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