Electric control of magnetization via control of carriers' spectrum anisotropy

The current state of information technology accentuates dichotomy between processing and storage of information, with logical operations performed by charge-based devices and non-volatile memory based on magnetic materials. The major obstacle for a wider use o f magnetic materials for information processing is the lack of efficient control of magnetization. Reorientation of magnetic domains is conventionally perform ed by no n-local external magnetic fields or by externally polarized currents [1–3]. Efficiency of the latter approach is greatly enhanced in materials where ferromagnetism is carrier-mediated [4]. In the latter case anisotropy of carrier s' spectrum is transferred into the magnetic anisotropy of magnetic ions. For example, in magnetic semiconductor (Ga,Mn)As magnetic Mn ions haved configuration and their total orb ital moment is zero. Therefore, magnetic an isotropy originates from the spin-related anisotropy of the holes spectrum. This anisotropy is strain-dependent [5] and, as we show in this work, can be controlled electrostatically in multi-ferroic strain-coupled devices. In addition, in strained crystalline materials without the center of i nversion there is a coupling between spin and kinetic momentum of carriers (spin-orbit interactions), wh ich results in finite polarization and anisotropic modification of hole spectrum in the presence of current [5–7]. In this work we demonstrated two types of magnetization control: in device A uniaxial strain is applied by a strain-coupled piezoelectric material and magnetization direction is controlled by electrostatic voltages; in device B magnetization is controlled by spin-orbit effective field generated intrinsically by non-polarized dc current. In both cases we report reversible manipulation of magnetization direction, which demonstrates a direct implementation of a nonvolatile memory cell.