152 research outputs found
Orientation and temperature dependence of domain wall properties in FePt
An investigation of the orientation and temperature dependence of domain wall properties in FePt is presented. The authors use a microscopic, atomic model for the magnetic interactions within an effective, classical spin Hamiltonian constructed on the basis of spin-density functional calculations. They find a significant dependence of the domain wall width as well as the domain wall energy on the orientation of the wall with respect to the crystal lattice. Investigating the temperature dependence, they demonstrate the existence of elliptical domain walls in FePt at room temperature. The consequences of their findings for a micromagnetic continuum theory are discussed. (c) 2007 American Institute of Physics
Intrinsic spin orbit torque in a single domain nanomagnet
We present theoretical studies of the intrinsic spin orbit torque (SOT) in a
single domain ferromagnetic layer with Rashba spin-orbit coupling (SOC) using
the non-equilibrium Green's function formalism for a model Hamiltonian. We find
that, to the first order in SOC, the intrinsic SOT has only the field-like
torque symmetry and can be interpreted as the longitudinal spin current induced
by the charge current and Rashba field. We analyze the results in terms of the
material related parameters of the electronic structure, such as band filling,
band width, exchange splitting, as well as the Rashba SOC strength. On the
basis of these numerical and analytical results, we discuss the magnitude and
sign of SOT. Our results show that the different sign of SOT in identical
ferromagnetic layers with different supporting layers, e.g. Co/Pt and Co/Ta,
could be attributed to electrostatic doping of the ferromagnetic layer by the
support.Comment: 10 pages, 2 figure
Moving toward an atomistic reader model
With the move to recording densities up to and beyond 1 Tb/in/sup 2/, the size of read elements is continually reducing as a requirement of the scaling process. The expectation is for read elements containing magnetic films as thin as 1.5 nm, in which finite size effects, and factors such as interface mixing might be expected to become of increasing importance. Here, we review the limitations of the current (micromagnetic) approach to the theoretical modeling of thin films and develop an atomistic multiscale model capable of investigating the magnetic properties at the atomic level. Finite-size effects are found to be significant, suggesting the need for models beyond the micromagnetic approach to support the development of future read sensors
Multiscale modeling of magnetic materials: Temperature dependence of the exchange stiffness
For finite-temperature micromagnetic simulations the knowledge of the temperature dependence of the exchange stiffness plays a central role. We use two approaches for the calculation of the thermodynamic exchange parameter from spin models: (i) based on the domain-wall energy and (ii) based on the spin-wave dispersion. The corresponding analytical and numerical approaches are introduced and compared. A general theory for the temperature dependence and scaling of the exchange stiffness is developed using the classical spectral density method. The low-temperature exchange stiffness A is found to scale with magnetization as m(1.66) for systems on a simple cubic lattice and as m(1.76) for an FePt Hamiltonian parametrized through ab initio calculations. The additional reduction in the scaling exponent, as compared to the mean-field theory (A similar to m(2)), comes from the nonlinear spin-wave effects
Resonant electronic states and I-V curves of Fe/MgO/Fe(100) tunnel junctions
The bias dependence of the tunnel magnetoresistance (TMR) of Fe/MgO/Fe tunnel
junctions is investigated theoretically with a fully self-consistent scheme
that combines the non-equilibrium Green's functions method with density
functional theory. At voltages smaller than 20 mVolt the I-V characteristics
and the TMR are dominated by resonant transport through narrow interface states
in the minority spin-band. In the parallel configuration this contribution is
quenched by a voltage comparable to the energy width of the interface state,
whereas it persists at all voltages in the anti-parallel configuration. At
higher bias the transport is mainly determined by the relative positions of the
band-edges in the two Fe electrodes, which causes a decrease of the
TMR
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