Disorder effects in alloys are usually modeled by averaging various supercell calculations considering different positions of the alloy atoms. This approach, however, is only possible as long as the portion of the individual components of the alloy is sufficiently large. Herein, we present anab initiostudy considering the lithium insertion material Li1-x[Ni0.33Co0.33Mn0.33]O2as model system to demonstrate the power of the coherent potential approximation within the Korringa-Kohn-Rostoker Green's function method. This approach enables the description of disorder effects within alloy systems of any composition. It is applied in this study to describe the (de-)intercalation of arbitrary amounts of lithium from the cathode active material. Moreover, we highlight that using either fully optimized structures or experimental lattice parameters and atomic positions both lead to comparable results. Our findings suggest that this approach is also suitable for modeling the electronic structure of state-of-the-art materials such as high-nickel alloys.

In our proof-of-principle study we examine the influence of skyrmions on magnetoresistive transport. In particular, we show that magnetic tunnel junctions are a technologically appealing and promising way for electrical detection of noncollinear magnetic structures. The calculated effect is shown to originate from scattering between different k states and cannot be identified through densities of states alone. Our results suggest that the detection efficiency strongly depends on the utilized materials.

Voltage-controlled magnetic anisotropy (VCMA) enables high-speed magnetization switching [1]. It has been found that VCMA can be increased by inserting heavy metal (e.g. Pt) [2]. Clarifying the mechanism is important for larger VCMA. In this study, we measured tunnel spectra of Fe-Pt-MgO-Fe tunnel junctions and observed the change in density of state (DOS) depending on Pt thickness. The film stack, MgO (5 nm)|V (30 nm)|Fe (0.57 nm)|Pt (0~0.4 nm)|MgO (1.4 nm)|Fe (10 nm)|Au (5 nm) was deposited on an MgO(001) substrate by molecular beam epitaxy method. Figure 1 is color mappings representing the dI/dV spectrum as a function of the Pt thickness and bias voltage. Black dots in Fig. 1 shows peak points of differential conductance (dI/dV) which are shifted by inserting Pt. The peak points shift on Fermi energy at Pt thickness 0.2 nm (1 ML) as shown by black circle. Figure 2 is first principles calculation of DOS for the Δ1 band of V (5 ML)|Fe (4 ML)|Pt (0 or 1 ML)|MgO (5 ML). The blue and red line represents the DOS with and without the Pt 1 ML insertion, respectively. Comparing to first principles calculation in Fig. 2, we found interfacial resonant states appear at the Fermi level in the majority-spin DOS of V|Fe|Pt|MgO. It suggests that the surface resonant state affects magnetic anisotropy energy and its voltage control. This research was supported by KAKENHI (No. JP26103002) and ImPACT program.

Shinji Miwa, Junji Fujimoto, Philipp Risius, Kohei Nawaoka, Minori Goto, and Yoshishige Suzuki Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan Center for Spintronics Research Network, Osaka University, Toyonaka, Osaka 560-8531, Japan Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan (Received 12 February 2017; revised manuscript received 7 June 2017; published 26 July 2017)