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排序方式: 共有120条查询结果,搜索用时 468 毫秒
91.
Yukari Fujioka Johannes Frantti Christopher Rouleau Alexander Puretzky Zheng Gai Nickolay Lavrik Andreas Herklotz Ilia Ivanov Harry Meyer 《Annalen der Physik》2019,531(11)
Insulating uniaxial room‐temperature ferromagnets are a prerequisite for commonplace spin wave‐based devices, the obstacle in contemporary ferromagnets being the coupling of ferromagnetism with large conductivity. It is shown that the uniaxial A1 + 2xTi4+1 ? xO3 (ATO), A = Ni2+,Co2+, and 0.6 < x ≤ 1, thin films are electrically insulating ferromagnets already at room temperature. The octahedra network of the ATO and the corundum and ilmenite structures are the same yet different octahedra‐filling proved to be a route to switch from the antiferromagnetic to ferromagnetic regime. Octahedra can continuously be filled up to x = 1, or vacated (?0.24 < x < 0) in the ATO structure. TiO‐layers, which separate the ferromagnetic (Ni,Co)O‐layers and intermediate the antiferromagnetic coupling between the ferromagnetic layers in the NiTiO3 and CoTiO3 ilmenites, can continuously be replaced by (Ni,Co)O‐layers to convert the ATO‐films to ferromagnetic insulator with abundant direct cation interactions. 相似文献
92.
Muktish Acharyya 《Phase Transitions》2018,91(8):793-810
The dynamical responses of XY ferromagnet driven by linearly polarised propagating and standing magnetic field wave have been studied by Monte Carlo simulation in three dimensions. In the case of propagating magnetic field wave (with specified amplitude, frequency and the wavelength), the low temperature dynamical mode is a propagating spin wave and the system becomes structureless (or random) in the high temperature. A dynamical symmetry breaking phase transition is observed at a finite (non-zero) temperature. This symmetry breaking is confirmed by studying the statistical distribution of the angle of the spin vector. The dynamic non-equilibrium transition temperature was found to decrease as the amplitude of the propagating magnetic field wave increased. A comprehensive phase boundary is drawn in the plane formed by temperature and amplitude of propagating field wave. The phase boundary was observed to shrink (in the low temperature side) for longer wavelength of the propagating magnetic wave. In the case of standing magnetic field wave, the low temperature excitation is a standing spin wave which becomes structureless (or random) in the high temperature. Here also, like the case of propagating magnetic wave, a dynamical symmetry breaking non-equilibrium phase transition was observed. A comprehensive phase boundary was drawn. Unlike the case of propagating magnetic wave, the phase boundary does not show any systematic variation with the wavelength of the standing magnetic field wave. In the limit of vanishingly small amplitude of the field, the phase boundaries approach the recent Monte Carlo estimate of equilibrium transition temperature. 相似文献
93.
Coexistence of ferromagnetism and superconductivity in normal mental/superconductor/ferromagnet structures
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<正>We extend the Blonder,Tinkham and Klapwijk theory to the study of the inverse proximity effects in the normal mental/superconductor/ferromagnet structures.In the superconducting film,there are the gapless superconductivity and the spin-dependent density of states both within and without the energy gap.It indicates an appearance of the inverse-proximity-effect-induced ferromagnetism and a coexistence of ferromagnetism and superconductivity near the interface.The influence of exchange energy in the ferromagnet and barrier strength at the superconductor/ferromagnet interface on the inverse proximity effects is discussed. 相似文献
94.
First Principle Study on the Magnetic and Electric Properties of Wurtzite Cr-phosphides and Cr-sulphides: Several Half-metallic Ferromagnets
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The geometrical structures of wurtzite CrX (X=As, Sb, O, Se, and Te) were optimized, then their electric and magnetic properties were investigated by the ˉrst-principle calculations within the generalized gradient approximation for the exchange-correlation functional based on the density functional theory. These Cr-phosphides and Cr-sulphides were predicted to be half-metallic ferromagnets whose spin-polarization at the Fermi level is absolutely 100%.The molecular magnetic moments of Cr-phosphides and Cr-sulphides are 3.00 and 4.00 μB, which arise mainly from Cr-ions, respectively. There is ferromagnetic coupling in both Cr-phosphides and Cr-sulphides. The Curie temperatures of Cr-sulphides and Cr-phosphides are high. The electronic structures of Cr-ions are a21g↑↓t41u↑↓t11u e2g↑in Cr-phosphides and a21g↑↓t41u↑↓t11u↑t32g↑in Cr-sulphides, respectively. 相似文献
95.
Tunneling planer Hall (TPH) effect in Ni81 Fe19/Al2O3/NixFe1−x trilayer junction is different from general planer Hall effect in single-layer film or two-layer junction. This effect concerns
the spin-polarized transport, so that the TPH voltage depends on the angle between magnetic vectors of two ferromagnetic layers.
The TPH effect is reported to be influenced by composition and magnetic properties of FM layers and the thickness of the insulating
layer. 相似文献
96.
Combining the two-site cluster approximation with the discretized path-integral representation (DPIR) and Suzuki-Trotter formalism, the critical properties of anisotropic Heisenberg ferromagnet with a crystal field are studied. We find that the tricritical point can appear in the case of negative crystal field. And the exchange anisotropy not only reduces the critical temperature and tricritical point, but also makes re-entrant phenomena instead of the existence of the tricritical point when the exchange anisotropic parameter is larger than a critical value. 相似文献
97.
Li Jiabo 《高等学校化学研究》1991,7(3):181-183
Nowadays the studies of organize ferromagnets have been becoming a very attractive area of material science in both theoretical and experimental aspects. A major theoretical problem on design of OFM is to estimate the effective exchange integrals(J) between radical sites. However, most of theoretical work was on hypothetical hydrocarbons, which were impracticable in the synthesis. The recent breakthrough in the synthesis of OFM turns the theorist's attention to some more realistic models such as those 相似文献
98.
DONG Zheng-Chao 《理论物理通讯》2004,41(5):775-780
The tunneling spectroscopy and shot noise in ferromagnet/insulator/triplet-superconductor (FM/I/triplet-SC) structures are studied by taking into account the roughness interfacial barrier and exchange splitting in the FM. For the triplet-SC of
Sr2RuO4,
we consider two-dimensional f-wave order parameter symmetries having nodes within the RuO2
plane, which reasonably describe both thermodynamic and thermal conductivity data. It is shown that the ferromagnetic exchange splitting gives rise to a decrease in the differential
conductance, the average current, and the shot noise power, while the noise power-to-current ratio is increased; the interface roughness is found to lead to a decrease in the differential
conductance and the average current, and an increase in the noise power-to-current ratio. 相似文献
99.
Properties of semi-infinite (S=1) Heisenberg ferromagnet with biquadratic exchange were studied in terms of surface exchange (=IS/I) and biquadratic coupling (a). It was shown that a strict correlation exists, depending on , between the type of surface spin waves (acoustic or optical) and the mean-field (MF) critical temperature, bulk (Tc) and surface TcS>Tc (for
). Within the framework of the Landau–Ginsburg theory for semi-infinite simple cubic ferromagnet, a detailed study is presented of the critical behaviour of the system, in particular in the vicinity of the tricritical point which is the consequence of the biquadratic interaction. It is shown that tricritical exponents satisfy exactly the scaling relations for d=3. The analysis of the spin–spin correlation function within the framework of the same theory, shows that there occurs the critical magnetic scattering of low-energy electrons (LEED) from the surface in the case
, when the ordering temperature TcS is approached from above (from paramagnetic phase). In the opposite case,
, there occurs no surface critical scattering. It was also shown that in the vicinity of the tricritical point, the biquadratic interaction increases the range of validity of the MF approximation. 相似文献
100.
CHEN Yuan XIANG Ying HU Ai-Yuan 《理论物理通讯》2008,49(5):1349-1352
Longitudinal susceptibility of the spin-1/2 low-dimensional Heisenberg ferromagnet in a magnetic field, is
studied by the Green's function method within the random phase
approximation. The static and dynamic longitudinal susceptibilities
are calculated in the low- and high-field regions. Power laws for
the position and height of the static susceptibility maximum are
shown not to support the predictions of Landau theory. 相似文献