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Register a new userAnalytic treatment of the precessional (ballistic) contribution to the conventional magnetic switching
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Authors
Ya. B. Bazaliy
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We consider a switching of the magnetic moment with an easy axis anisotropy from an up to a down direction under the influence of an external magnetic field. The driving field is applied parallel to the easy axis and is continuously swept from a positive to a negative value. In addition, a small constant perpendicular bias field is present. It is shown that while the driving field switches the moment in a conventional way, the perpendicular field creates an admixture of the precessional (ballistic) switching that speeds up the switching process. Precessional contribution produces a non-monotonic dependence of the switching time on the field sweep time with a minimum at a particular sweep time value. We derive an analytic expressions for the optimal point, and for the entire dependence of the switching time on the field sweep time. Our approximation is valid in a wide parameter range and can be used to engineer and optimize of the magnetic memory devices.
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We consider a magnetic moment with an easy axis anisotropy energy, switched by an external field applied along this axis. Additional small, time-independent bias field is applied perpendicular to the axis. It is found that the magnets switching time is a non-monotonic function of the rate at which the field is swept from up to down. Switching time exhibits a minimum at a particular optimal sweep time. This unusual behavior is explained by the admixture of a ballistic (precessional) rotation of the moment caused by the perpendicular bias field in the presence of a variable switching field. We derive analytic expressions for the optimal switching time, and for the entire dependence of the switching time on the field sweep time. The existence of the optimal field sweep time has important implications for the optimization of magnetic memory devices.
Voltage-induced magnetization dynamics in a conically magnetized free layer with an elliptic cylinder shape is theoretically studied on the basis of the macrospin model. It is found that an application of voltage pulse can induce the precessional switching of magnetization even at zero-bias magnetic field, which is of substantial importance for device applications such as voltage-controlled nonvolatile memory. Analytical expressions of the conditions for precessional switching are derived.
Cross-control of a material property - manipulation of a physical quantity (e.g., magnetisation) by a nonconjugate field (e.g., electrical field) - is a challenge in fundamental science and also important for technological device applications. It has been demonstrated that magnetic properties can be controlled by electrical and optical stimuli in various magnets. Here we find that heat-treatment allows the control over two competing magnetic phases in the Mn-doped polar semiconductor GeTe. The onset temperatures $T_{rm c}$ of ferromagnetism vary at low Mn concentrations by a factor of five to six with a maximum $T_{rm c} approx 180$ K, depending on the selected phase. Analyses in terms of synchrotron x-ray diffraction and energy dispersive x-ray spectroscopy indicate a possible segregation of the Mn ions, which is responsible for the high-$T_{rm c}$ phase. More importantly, we demonstrate that the two states can be switched back and forth repeatedly from either phase by changing the heat-treatment of a sample, thereby confirming magnetic phase-change- memory functionality.
We test whether current-induced magnetization switching due to spin-transfer-torque in ferromagnetic/non-magnetic/ferromagnetic (F/N/F) trilayers changes significantly when scattering within the N-metal layers is changed from ballistic to diffusive. Here ballistic corresponds to a ratio r = lambda/t greater than or equal to 3 for a Cu spacer layer, and diffusive to r = lambda/t less than or equal to 0.4 for a CuGe alloy spacer layer, where lambda is the mean-free-path in the N-layer of fixed thickness t = 10 nm. The average switching currents for the alloy spacer layer are only modestly larger than those for Cu. The best available model predicts a much greater sensitivity of the switching currents to diffuse scattering in the spacer layer than we see.
We measured the low temperature specific heat of a sputtered $(Fe_{23AA}/Cr_{12AA})_{33}$ magnetic multilayer, as well as separate $1000AA$ thick Fe and Cr films. Magnetoresistance and magnetization measurements on the multilayer demonstrated antiparallel coupling between the Fe layers. Using microcalorimeters made in our group, we measured the specific heat for $4<T<30 K$ and in magnetic fields up to $8 T$ for the multilayer. The low temperature electronic specific heat coefficient of the multilayer in the temperature range $4<T<14 K$ is $gamma_{ML}=8.4 mJ/K^{2}g-at$. This is significantly larger than that measured for the Fe or Cr films (5.4 and $3.5 mJ/K^{2}mol$ respectively). No magnetic field dependence of $gamma_{ML}$ was observed up to $8 T$. These results can be explained by a softening of the phonon modes observed in the same data and the presence of an Fe-Cr alloy phase at the interfaces.
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