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We investigated the heat controlled magnetic anisotropy (HCMA) in magnetic tunnel junctions with various junction sizes. We evaluated the HCMA from perpendicular magnetic anisotropy under a direct current voltage measured by the spin-torque diode technique. The maximum HCMA magnitude of 5.4 μJ (Wm)−1 was observed, and the HCMA increased with increasing diameter. Our results can be explained by a simple heat dissipation model and suggest that the in-plane heat current affects HCMA.

We propose the use of artificial spin ice (ASI) for reservoir computing and evaluate its performance from simulation results. Our ASI reservoir is formed by 72 magnets arranged in a honeycomb lattice and the temperature is 0 K. A pseudo-random binary sequence is sent to the reservoir and its status is updated by external magnetic fields. Short-term memory capacity of 3.5 and nonlinear computational capacity of 2.9 are achieved when the strength of the magnetic fields is near the switching field of the magnets. The performance can be optimized by tuning the aspect ratios of the magnets.

A single-crystal multilayer consisting of Fe, cobalt phthalocyanine (CoPc), and MgO was grown on an fcc-MgO(001) substrate. The reflection high-energy diffraction observation showed that the ultrathin fcc-MgO(001) film could be grown on bcc-Fe(001)/CoPc when the thickness of CoPc was less than 0.7 nm (about two molecular layers). A tunnel junction with a bcc-Fe(001)/CoPc/fcc-MgO(001)/bcc-Fe(001) layer achieved a tunnel magnetoresistance of about 20% and an electric field endurance of more than 1 V/nm at room temperature. The novel multilayer in the present study will enable us to advance the frontiers of molecular spintronics.

The voltage-controlled magnetic anisotropy of ferromagnetic metals may offer potential applications of nonvolatile memories with ultralow power consumption. For achieving ultrafast recording and long-time endurance, voltage-induced effects without undesirable lattice distortions should be ensured. In this study, in-situ extended X-ray absorption fine structure analysis of an Fe/Pt/MgO junction demonstrated the unaltered interfacial atomic structure, in which the radial distances between the Pt and the neighboring Fe, Pt, O, and Mg atoms changed by less than ±0.01 A under electric fields of ±0.18 V/nm. Therefore, the anisotropy change is driven by a purely electronic mechanism without lattice deformation or atomic relaxation.