Anisotropic magnetoresistance (AMR) effect has been systematically investigated in various Heusler compounds Co₂MnZ and Co₂FeZ (Z = Al, Si, Ge, and Ga) epitaxial films and quantitatively summarized against the total valence electron number N_V. It was found that the sign of AMR ratio is negative when N_V is between 28.2 and 30.3, and turns positive when N_V becomes below 28.2 and above 30.3, indicating that the Fermi level (E_F) overlaps with the valence or conduction band edges of half-metallic gap at N_V ∼ 28.2 or 30.3, respectively. We also find out that the magnitude of negative AMR ratio gradually increases with shifting of E_F away from the gap edges, and there is a clear positive correlation between the magnitude of negative AMR ratio and magnetoresistive output of the giant magnetoresistive devices using the Heusler compounds. This indicates that AMR can be used as a facile way to optimize a composition of half-metallic Heusler compounds having a high spin-polarization at room temperature.

Current-induced domain wall motion in TbFeCo wires with perpendicular magnetic anisotropy has been directly observed by Kerr microscope. The moving direction of domain wall is opposite to the current direction, which is in agreement with the spin torque transfer theory. The critical current density found in TbFeCo is lower than 10⁷ A/cm², which is an order smaller than in other metallic materials reported so far. In addition, the critical current density gets increased with the increase of the pinning potential in TbFeCo thin film, which is also consistent with the theoretical prediction for a pinning dominant mechanism.

We have investigated the structure and magnetoresistance of current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo spin valves (PSVs) using Co₂Mn(Ga_0.25Ge_0.75) (CMGG) Heusler alloy ferromagnetic layers annealed at different temperatures. Relatively large ΔRA of 6.1 mΩμm² and MR ratio of 40.2% were obtained in the CPP-PSV annealed at 400 °C. Annealing at higher than 400 °C led to a significant deterioration of MR outputs. Detailed structure analysis using transmission electron microscopy, three-dimensional atom probe, and synchrotron x-ray diffraction showed that the degradation of MR in the over-annealed sample was due to the increase of DO₃ disorder in the CMGG layer, while the layered structure of the film is fully preserved.

The surface magnetism of Fe(001) was studied in an atomic layer-by-layer fashion by using the in situ iron-57 probe layer method with a synchrotron Mössbauer source. The observed internal hyperfine field $H_{\mathrm{int}}$ exhibits a marked decrease at the surface and an oscillatory behavior with increasing depth in the individual upper four layers below the surface. The calculated layer-depth dependencies of the effective hyperfine field $|H_{\mathrm{eff}}|$, isomer shift $\delta$, and quadrupole shift $2ϵ$ agree well with the observed experimental parameters. These results provide the first experimental evidence for the magnetic Friedel oscillations, which penetrate several layers from the Fe(001) surface.

The near-future ultra-high-density magnetic recording with an assist recording technology requires a substantial evolution of the read-head technology. A read sensor with a small sensor resistance-area product (RA), a large magnetoresistance ratio (Δ R/R), and a thin total sensor thickness is required for the low bit error rate and high-spatial resolution of reading. We developed current-perpendicular-to-plane giant magnetoresistance sensors using highly spin-polarized Heusler alloy ferromagnetic layers with the spin polarization of the conducting electron β ~ 0.8. A reasonably large Δ R/R up to 14% was obtained by a practical bottom-pinned spin-valve structure with a conventional metallic spacer layer of an Ag₉₀n₁₀ (AgSn) alloy. By replacing the spacer layer with a conductive oxide-based AgSn/InZnO bilayer, a large Δ R/R up to 32% was realized at RA value of ~ 0.1 Ω · μm², which is optimal for the read sensor application. A large voltage output up to 6 mV was obtained for a sensor utilization of ~ 33% at a bias voltage of 100 mV.