Skyrmion generation and perpendicular magnetic anisotropy modification in Heusler alloy ultrathin films

<p><b>This thesis explores the magnetic properties of Heusler alloy thin films for spintronics applications. The skyrmion generation under different externalstimulation was focused in MgO/Mn2CoAl/Pd ultrathin films and the anomalous Hall effect of Co2MnGa thin films.</b></p> <p>The perpendicularly magnetized MgO/Mn2CoAl/Pd ultrathin films were firstly optimised by changing the thickness of Pd layer so that the effective magnetic anisotropy can be tuned and various magnetic textures can be obtained for different purposes. Based on the understanding of Pd dependence of magnetic properties, The skyrmion generation by applying an in-plane magnetic field was investigated to fine tune the effective magnetic anisotropy. Further the fractal analysis was used to describe the evolution of the magnetic states and categorise the formation of skyrmions. </p> <p>Then skyrmion generation by ionic liquid gating has been investigated in this trilayer. Both non-volatile and volatile skyrmions can be generated by applying a range of voltage sequences. The potential mechanisms, magneto-ionic and electrostatic charge effects, have been discussed as well.</p> <p>Finally, the thickness dependence of Co2MnGa thin films was studied. This material can be used as a spin-orbit generator for manipulating skyrmions. A large anomalous Hall angle (AHA) was demonstrated in Co2MnGa thin films (20 - 50 nm) showing a AHA ~11.4% at low temperature and ~9.7% at room temperature, which can be ascribed to the nontrivial topology of the band structure with large intrinsic Berry curvature. However, the anomalous Hall angle decreases significantly with thicknesses below 20 nm, which band structure calculations confirm is due to the reduction of the majority spin contribution to the Berry curvature.</p>

Skyrmion generation and perpendicular magnetic anisotropy modification in Heusler alloy ultrathin films

<p><b>This thesis explores the magnetic properties of Heusler alloy thin films for spintronics applications. The skyrmion generation under different externalstimulation was focused in MgO/Mn2CoAl/Pd ultrathin films and the anomalous Hall effect of Co2MnGa thin films.</b></p> <p>The perpendicularly magnetized MgO/Mn2CoAl/Pd ultrathin films were firstly optimised by changing the thickness of Pd layer so that the effective magnetic anisotropy can be tuned and various magnetic textures can be obtained for different purposes. Based on the understanding of Pd dependence of magnetic properties, The skyrmion generation by applying an in-plane magnetic field was investigated to fine tune the effective magnetic anisotropy. Further the fractal analysis was used to describe the evolution of the magnetic states and categorise the formation of skyrmions. </p> <p>Then skyrmion generation by ionic liquid gating has been investigated in this trilayer. Both non-volatile and volatile skyrmions can be generated by applying a range of voltage sequences. The potential mechanisms, magneto-ionic and electrostatic charge effects, have been discussed as well.</p> <p>Finally, the thickness dependence of Co2MnGa thin films was studied. This material can be used as a spin-orbit generator for manipulating skyrmions. A large anomalous Hall angle (AHA) was demonstrated in Co2MnGa thin films (20 - 50 nm) showing a AHA ~11.4% at low temperature and ~9.7% at room temperature, which can be ascribed to the nontrivial topology of the band structure with large intrinsic Berry curvature. However, the anomalous Hall angle decreases significantly with thicknesses below 20 nm, which band structure calculations confirm is due to the reduction of the majority spin contribution to the Berry curvature.</p>

Linear chains of nanomagnets: engineering the effective magnetic anisotropy

Tunable effective magnetic anisotropy is achieved by engineering the thickness and lattice arrangement of linear chains of nanomagnets.

Influence of aluminum substitution on the fi eld of effective magnetic anisotropy and the degree of magnetic texture of anisotropic polycrystalline hexagonal ferrites of barium and strontium for substrates of microstrip devices of microwave electronics

In this paper, the effect of Al3+ ions substitutions on the value of the effective magnetic anisotropy field НАeff and the degree of magnetic texture f of the anisotropic polycrystalline hexagonal barium and strontium ferrites were studied. The samples were obtained by the ceramic technology method and the texture was formed by pressing in a magnetic field. The sample preparation technology presented in detail. The batches of barium hexaferrites were synthesized with the concentration of Al3+ ions: 0.9; 1.4; 2.5 and 2.6 formula units while strontium hexaferrites had Al3+ concentration of 0.1 formula units. It has been shown that by this technology barium and strontium hexaferrites with high value of (in range of 19—35 kOe) and with f = 80—83% could be obtained. The achieved values of НАeff and f could be sufficient for the production of substrates for microstrip microwave devices in millimeter−wave region.For the first time a raise in the degree of magnetic texture of polycrystalline barium hexaferrites with an increase of concentration of Al3+ ions were detected; a slight (5.5—5.8%) magnetic texture of isotropic strontium hexaferrites was also detected. The achieved results discussed in detail. For studied hexaferrites the mechanism of magnetic texture formation during the process of synthesis is proposed.