Angular Dependence Of Torque Research Articles

Spin-Transfer Torques Generated by the Anomalous Hall Effect and Anisotropic Magnetoresistance

Spin-orbit coupling is a well-studied means to change the orientation of a spin, and thus flip a logic bit in a spintronic device. The authors offer an advance by showing how the anomalous Hall effect and the anisotropic magnetoresistance, both discovered in the 19th century, can be used like the spin Hall effect to generate spin-orbit torques. This approach provides greater control over the angular dependence of torque than existing methods, and can switch perpendicularly magnetized samples, or move domain walls efficiently.

Angular dependence of electromagnetic torque in a bulk high-temperature superconductor

The angular dependence of the magnetic torque has been measured in cubic shaped YBaCuO samples. The bulk sample was prepared by a seeded-melt growth process in which a small NdBaCuO seed was used to induce domain growth of YBaCuO. The sample had cubic shape so that its edges coincided with basic crystallographic directions. The measurements were conducted in static and dynamic modes. Under static mode, the angular dependencies of the torque have been obtained in a series of zero field cooled magnetic hysteresis measurements. Between each measurement at a specific angle, the sample was warmed up above critical temperature. Under dynamic mode, the magnetic field was increased up to a certain point and then the sample was turned around its axis continuously. It was found that the static torque was a sinusoidal function of the double angle between the external field and one of basic directions of the crystal structure. It also exhibited prominent anisotropy in relation to the crystal structure of the high-temperature superconductor. The dynamic torque-angle relation is not only a result of the anisotropic structure of the superconductor but also a result of the strong intrinsic pinning of this material. Based on Kogan’s theory for the anisotropic superconductors and the Bean model approach, a physical model has been developed to describe the angular dependence of the magnetic torque.

Models of Vortices in Anisotropic Superconductors

The line energy of a single magnetic vortex at an arbitrary direction in an anisotropic superconductor is evaluated in three different phenomenological models, the anisotropic London model, the anisotropic Ginzburg–Landau model, and the Lawrence–Doniach model. The vortex line energy in the anisotropic London model can be solved by Fourier transformation, but the core cutoff is not present in the model. Using the Klemm–Clem transformations of the free energy and vortex coordinates in the anisotropic Ginzburg–Landau model, a theorem relating the shape of the effective core cross-section in the anisotropic London model to that in the anisotropic Ginzburg–Landau model is presented. This theorem allows the anisotropic London model to be used in the entire regime $H_{c1} \leq H \ll H_{c2} $, regardless of the anisotropy and field direction. The resulting lower critical field $H_{c1} ( \theta _H )$ can exhibit a discontinuity, a kink, or be monotonic in its angular dependence. In addition, the transformations are applied to the case of a core cross-section of a single vortex in the Lawrence–Doniach model, and the angular dependence of the magnetic torque is calculated. The torque exhibits the expected dimensional crossover, having an angular dependence which reduces to that for an anisotropic Ginzburg–Landau superconductor very near to $T_c $, and to that for a lattice of coupled, parallel Josephson junctions well below the dimensional crossover temperature $T^ * $. In the vicinity of $T^ * $, however, dramatic oscillations in the angular dependence of the torque are predicted.

Improvement of corrosion resistance of GdTbFe by metal coatings

For an application of rare earth (RE) transition metal (TM) alloys for erasable optical recording the corrosion sensitivity has to be limited in order to obtain long-term stability. The use of thin RE-TM films as a storage medium needs a top coating to avoid strong surface-induced change of intrinsic material properties due to oxidation. This paper presents annealing experiments of GdTbFe films in air within the temperature range of 65 to 160 °c. The GdTbFe films of 40 and 80 nm thickness were coated with Al,Cr,CrNi and Cu coatings of 50 and 200 nm thickness, respectively. The values of coercivity and the angular dependence of torque were measured in the initial state right after the preparation of samples. These values were compared with the results of the annealed films. The angular dependence of torque and the corresponding oxygen depth profiles (SIMS) show different results for the coated and non-coated samples. Coatings of Cr or Al having 20 or 50 nm thickness both are suitable being an excellent barrier against the diffusion of oxygen into the magnetic layer.

On the magnetothermodynamical behaviour of Er3+ and Dy3+ ions in calcium fluoride

The parameters characterising thermal properties, namely Schottky specific heat and associated anomaly in the temperature range 10–750 K, and magnetic properties, namely, principal and mean magnetic susceptibilities, effective magnetic moment, anisotropy and angular dependence of torque in the temperature range 10–400 K have been derived with the help of crystal field studies for the Er3+:CaF2 and Dy3+:CaF2 systems.