A note on magnon life-time in itinerant electron ferromagnetic alloys

A model of a binary ferromagnetic alloy A_1?cB_c is discussed in terms of a single band Hubbard type hamiltonian. It is shown by summing up contribution of single-site scattering to all orders, that the inverse life time of long-wavelength magnons due to disorder scattering is proportional to q⁵ and, in the limit c ? 1, to the concentration c.     

sd-Exchange electron spin resonance in a ferromagnetic metal

The possibility of resonance absorption in the terahertz range caused by the sd-exchange interaction at the incidence of an electromagnetic wave on a ferromagnetic metal has been predicted. The absorption coefficient has been calculated. It has been shown that the resonance frequency is determined by the magnetization of a ferromagnet and the absorption coefficient additionally depends on the orientation of the magnetization with respect to the plane of polarization of the wave.     

The ferromagnetic transition temperature of dilute Pd-Co,Pd-Fe and Pd-Mn alloys

Results of resistivity measurements on dilute Pd-Mn alloys with concentrations from 0.15 at .% to 0.7 at .% are discussed. A calculation of the transition temperature of Pd-Co, Pd-Fe and Pd-Mn alloys with concentrations between 0.05 at .% and 3 at .% is presented and compared with the available experimental data.     

Mössbauer effect studies of spin disturbances in dilute ferromagnetic alloys

¹¹⁹Sn Mössbauer effect studies of dilute Pt Fe, Pd Fe and Ni Fe alloys are reported. For Pt Fe an oscillatory spatial dependence of the spin-polarization about the Fe atoms is observed. The range increases with increasing temperature. For Pd Fe and Ni Fe the host properties are masked by the magnetic disturbances induced by the tin probe atoms.     

Renormalization of spin polarised itinerant electron bands in the normal state of a model ferromagnetic superconductor

This paper studies the normal state properties of itinerant electrons in a toy model,which is constructed according to the model for coexisting ferromagnetism and superconductivity proposed by Suhl [Suhl H 2001 Phys.Rev.Lett.87 167007].In this theory with ferromagnetic ordering based on localized spins,the exchange interaction J between conduction electrons and localized spin is taken as the pairing glue for s-wave superconductivity.It shows that this J term will first renormalize the normal state single conduction electron structures substantially.It finds dramatically enhanced or suppressed magnetization of itinerant electrons for positive or negative J.Singlet Cooper pairing can be ruled out due to strong spin polarisation in the J > 0 case while a narrow window for s-wave superconductivity is opened around some ferromagnetic J.     

Nuclear spin ferromagnetic phase transition in an interacting two dimensional electron gas

Electrons in a two-dimensional semiconducting heterostructure interact with nuclear spins via the hyperfine interaction. Using a a Kondo lattice formulation of the electron-nuclear-spin interaction, we show that the nuclear-spin system within an interacting two-dimensional electron gas undergoes a ferromagnetic phase transition at finite temperatures. We find that electron-electron interactions and non-Fermi liquid behavior substantially enhance the nuclear-spin Curie temperature into the mK range with decreasing electron density.     

Effects of spin fluctuations in itinerant electron ferromagnets

Effects of spin fluctuations on the paramagnetic spin susceptibility, magnetization and specific heat are calculated in gaussian statistics as a power series of k_BT. The results are applied to nickel and iron. It is shown that in effect spin fluctuations reduce the molecular field coefficient above the Curie temperature.     

Ferromagnetic transition in one-dimensional itinerant electron systems

We use bosonization to derive the effective field theory that properly describes ferromagnetic transition in one-dimensional itinerant electron systems. The resultant theory is shown to have dynamical exponent z = 2 at tree level and upper critical dimension dc = 2. Thus one dimension is below the upper critical dimension of the theory, and the critical behavior of the transition is controlled by an interacting fixed point, which we study via epsilon expansion. Comparisons will be made with the Hertz-Millis theory, which describes the ferromagnetic transition in higher dimensions.     

Theoretical study of spin waves in the itinerant ferromagnetic state of MnAs

The dynamic susceptibility is studied for the ferromagnetic state of MnAs on the basis of the itinerant electron theory. The spin waves exist throughout the entire Brillouin zone and the existence of an optical spin-wave branch is predicted.     

On the electrical resistivity of noble based transition metal dilute alloys

We apply the CPA expression of the electrical conductivity to the case of Au-based alloys containing 3d and 4d transition impurities. In this approach, a s-diagonal disorder larger for the 3d case than for the 4d one can explain the measured differences in resistivity between these two cases.     

Nonequilibrium quantum phase transition in itinerant electron systems

We study the effect of the voltage bias on the ferromagnetic phase transition in a one-dimensional itinerant electron system. The applied voltage drives the system into a nonequilibrium steady state with a nonzero electric current. The bias changes the universality class of the second order ferromagnetic transition. While the equilibrium transition belongs to the universality class of the uniaxial ferroelectric, we find the mean-field behavior near the nonequilibrium critical point.     

A discontinuous transition to ferromagnetic phase in a two-band itinerant ferromagnet

Conditions for the onset of ferromagnetism in a discontinuous way are given for a model system composed of a band and an atomic level located in the middle of the band. Such model reflects the system of two strongly hybridized bands of equal width. The presence of a linear term in the total magnetization for the ground state energy is demonstrated. At a discontinuous transition the Stoner criterion is not fulfilled [i.e. (U + J)?(μ) < 1]. Both mixed-valent and integral-valent ferromagnetic states are possible. The detailed calculations are done on the basis of rectangular density of states for the band electrons.     

Spin waves in dilute ferromagnetic alloys of Pd-Fe type

The concentration dependence of spin waves stiffness coefficient in Pd-Fe alloys is calculated. Our results are in a good agreement with experimental results.     

Thermoelectric spin diffusion in a ferromagnetic metal

We present a semiclassical theory of spin diffusion in a ferromagnetic metal subject to a temperature gradient. Spin-flip scattering can generate pure thermal spin currents by short-circuiting spin channels while suppressing spin accumulations. A thermally induced spin density is locally generated when the energy dependence of the density of states is spin polarized.     

The electron spin-density space distribution in ferromagnetic Heusler alloys

The hyperfine magnetic fields on Mn⁵⁵, Co⁵⁹, Al²⁷ and Si²⁹ were measured by the spinecho technique in several systems of Heusler alloys. The concentration dependence of local magnetic moments of Mn and Co ions in different lattice positions was determined and the space distribution of delocalized electron spin-density was analyzed. The hyperfine fields on spelements were calculated using the main theoretical models.     

铁磁非铁磁夹层中电子自旋波的传输及应用

建立了有限对一维铁磁性和非磁性层交错组成的周期系统, 应用布洛赫自旋波量子理论, 研究了该系统的基本性质及电子波函数散射特征对交错层数量依赖的关系. 研究发现: 在系统中电子波函数可表示为无限周期系统中转换矩阵特征向量的叠加或类布洛赫函数, 解此函数可得到任意层数系统的单色波散射的精确解. 在此基础上, 导出了电子波函数在周期系统中反射系数和透射系数对能量的依赖关系. 对光谱窗口的计算发现其势能和宽度几乎与全反射区域一样. 该系统由于高能量的传输和在电子自旋方向上对交换能的依赖而可能用于自旋滤波器. 关键词： 磁性多层膜 铁磁性和非磁性结构 电子散射 电子自旋滤波器     

The Curie temperature of dilute ferromagnetic alloys near the percolation threshold

Upper limit for the Curie temperature T_c(x) of the dilute Heisenberg ferromagnet near percolation threshold is derived. Qualitative arguments are put forward that this limit gives a correct dependence of T_c on the concentration of magnetic atoms x.     

Localization transitions for nuclear spin waves in ferromagnetic alloys

We investigate the possible localization of nuclear spin waves associated with the minority constituent of a binary ferromagnetic alloy. NMR methods for observing the transition and the time scale of propagating spin waves are suggested.     

Positive muon spin depolarization in quenched aluminium dilute alloys

Aluminum dilute alloys (Al-0.047 at% Mg, Al-0.052 at% Cu and Al-0.051 at% Si) were quenched from 600 and 450C. The positive muon behavior in the quenched alloys has been studied. Three peaks (Peak I, II and III) are found. Peak I is due to the trapping and detrapping of positive muons at single impurity atoms. The muon spin depolarization rate at the trap in Peak I was found to be 0.36sec^–1. Peak II is connected to impurity clusters. Peak III is the trapping of muons at quenched-in vacancies. The depolarization rate at the trapping site was found to be 0.2sec^–1. The activation energy of the trapping rate was found to be 25 meV. As the quenched-in vacancies annealed out, the trapping rates decreased to near zero.