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We consider electron transport in a nearly half-metallic ferromagnet, in which the minority spin electrons close to the band edge at the Fermi energy are Anderson-localized due to disorder. For the case of spin-flip scattering of the conduction electrons due to the absorption and emission of magnons, the Boltzmann equation is exactly soluble to the linear order. From this solution we calculate the temperature dependence of the resistivity due to single magnon processes at sufficiently low temperature, namely $k_BTll D/L^2$, where $L$ is the Anderson localization length and $D$ is the magnon stiffness. And depending on the details of the minority spin density of states at the Fermi level, we find a $T^{1.5}$ or $T^{2}$ scaling behavior for resistivity. Relevance to the doped perovskite manganite systems is discussed.
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We measured the Raman spectra of ferromagnetic nearly half metal CoS2 in a broad temperature range. All five Raman active modes Ag, Eg, Tg(1), Tg(2) and Tg(3) were observed. The magnetic ordering is indicated by a change of the temperature dependences of the frequency and the line width of Ag and T g(2) modes at the Curie point. The temperature dependence of the frequencies and linewidths of the Ag, Eg, Tg(1), T g(2) modes in the paramagnetic phase can be described in the framework of the Klemens approach. Hardening of the Tg(2), Tg(1) and A g modes on cooling can be unambiguously seen in the ferromagnetic phase. The linewidths of Tg(2) and Ag modes behave a natural way at low exciting laser power (decrease with decreasing temperature) in the ferromagnetic phase. At high exciting laser power the corresponding linewidths increase at temperature decreasing below the Curie temperature. Then as can be seen the line width of Ag mode reaches a maxima at about 80K. This intriging feature probably signifies a specific channel of the optical phonon decay in the ferromagnetic phase of CoS2. Tentative explanations of some of the observed effects are given, taking into account the nearly half metallic nature of CoS2.
We study spin-scattering asymmetry at the interface of two ferromagnets (FMs) based on a half-metallic Co$_{2}$Fe$_{0.4}$Mn$_{0.6}$Si (CFMS)/CoFe interface. First-principles ballistic transport calculations based on Landauer formula for (001)-CoFe/CFMS/CoFe indicate strong spin-dependent conductance at the CFMS/CoFe interface, suggesting large interface spin-scattering asymmetry coefficient ($gamma$). Fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo spin-valve (PSV) devices involving CoFe/CFMS/Ag/CFMS/CoFe structures exhibit an enhancement in magnetoresistance output owing to the formation of the CFMS/CoFe interface at room temperature (RT). This is well reproduced qualitatively by a simulation based on a generalized two-current series-resistor model with taking the presence of $gamma$ at the CFMS/CoFe interface, half-metallicity of CFMS, and combinations of terminated atoms at the interfaces in the CPP-GMR PSV structure. We show direct evidence for large $gamma$ at a half-metallic FM/FM interface and its impact on CPP-GMR effect even at RT.
The phenomenology of magnetic damping is of critical importance for devices that seek to exploit the electronic spin degree of freedom since damping strongly affects the energy required and speed at which a device can operate. However, theory has struggled to quantitatively predict the damping, even in common ferromagnetic materials. This presents a challenge for a broad range of applications in spintronics and spin-orbitronics that depend on materials and structures with ultra-low damping. Such systems enable many experimental investigations that further our theoretical understanding of numerous magnetic phenomena such as damping and spin-transport mediated by chirality and the Rashba effect. Despite this requirement, it is believed that achieving ultra-low damping in metallic ferromagnets is limited due to the scattering of magnons by the conduction electrons. However, we report on a binary alloy of Co and Fe that overcomes this obstacle and exhibits a damping parameter approaching 0.0001, which is comparable to values reported only for ferrimagnetic insulators. We explain this phenomenon by a unique feature of the bandstructure in this system: The density of states exhibits a sharp minimum at the Fermi level at the same alloy concentration at which the minimum in the magnetic damping is found. This discovery provides both a significant fundamental understanding of damping mechanisms as well as a test of theoretical predictions.
Using density functional theory we have performed theoretical investigations of the electronic properties of a free-standing one-dimensional organometallic vanadium-benzene wire. This system represents the limiting case of multi-decker V_n(C6H6)_{n+1} clusters which can be synthesized. We predict that the ground state of the wire is a 100% spin-polarized ferromagnet (half-metal). Its density of states is metallic at the Fermi energy for the minority electrons and shows a semiconductor gap for the majority electrons. We found that the half-metallic behavior is conserved up to 12%, longitudinal elongation of the wire. However, under further stretching, the system exhibits a transition to a high-spin ferromagnetic state that is accompanied by an abrupt jump of the magnetic moment and a gain of exchange energy.
textit{Ab-initio} calculations based on density functional theory (DFT) are performed to study the structural, electronic, and magnetic properties of two-dimensional (2D) free-standing honeycomb CrAs. We show that CrAs has low buckled stable structure. Magnetic CrAs has larger buckling than non-magnetic CrAs. 2D-CrAs is a ferromagnetic semiconductor for lattice constant $a leq 3.71$AA, and above this lattice constant CrAs is a half-metal ferromagnet. 2D-CrAs is shown to be half-metal ferromagnetic with magnetic moment of 3.0$mu_{rm{B}}$ per unit cell, at equilibrium structure. The $d_{z}^{2}$ orbital of $e_{g}$ band is completely empty in the spin-down state whereas it is almost occupied in the spin-up state, and the magnetic moment in the $e_{g}$ band is mainly dominated by the $d_{z}^{2}$ orbital of Cr. The $d_{zx}/d_{zy}$ and $d_{xy}$ orbitals of $t_{2g}$ band are partially occupied in the spin-up state and behaves as metal whereas they are insulator in the spin-down state. Phonon calculations confirm the thermodynamic stability of 2D-CrAs. The ferromagnetic (FM) and antiferromagnetic (AFM) interaction between the Cr atoms reveal that the FM state is more stable than the AFM state of 2D-CrAs.
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