Voltage control of magnetocrystalline anisotropy in ferromagnetic-semiconductor-piezoelectric hybrid structures

We demonstrate voltage control of the magnetic anisotropy of a (Ga,Mn)As device bonded to a piezoelectric transducer. The application of a uniaxial strain leads to a large reorientation of the magnetic easy axis, which is detected by anisotropic magnetoresistance measurements. Calculations based on the mean-field kinetic-exchange model of (Ga,Mn)As provide a microscopic understanding of the measured effect. The reported smooth voltage control of the uniaxial in-plane anisotropy, electrically induced magnetization switching, and detection of unconventional crystalline components of the anisotropic magnetoresistance illustrate the generic utility of our multiferroic system in providing device functionalities and in the research of micromagnetic and magnetotransport phenomena in diluted magnetic semiconductors.

Figure 1

(Color) [(a) and (b)] The longitudinal resistances $R_{xx}$ and [(c) and (d)] the transverse resistances $R_{xy}$ as a function of magnetic field at angle $\theta$. The curves with $\theta$ close to an easy axis ($30°$ at $-150\text{V}$ and $80°$ at $+150\text{V}$) are relatively flat as a function of field, indicating small rotation of the angle of the magnetization. $T=50\text{K}$.

Figure 2

(Color) (a) The microscopic $E\left(\widehat{M}\right)$ curves for the three piezovoltages. $\varphi$ is the angle of the magnetization with respect to the Hall bar. (b) The longitudinal AMR from theory calculations with a nonsaturating magnetic field of 20 mT rotated clockwise and anticlockwise in the plane of the film. Arrows show the direction of rotation in the hysteretic region. The inset shows the same for a field of 40mT. (c) The experimental AMR curves with a field of 40 mT rotated clockwise and anticlockwise in the plane of the film. ${\rho }_{av}$ is the ${\rho }_{xx}$ averaged over $360°$ in the low-field regime. $\theta$ is the angle of the magnetic field with respect to the Hall bar. $T=50\text{K}$.

Figure 3

(Color) (a) Low-field magnetic hysteresis curve at $+150\text{V}$. The field is swept from saturating negative field at $165°$ to the position shown by the black arrow. Then (b) the piezovoltage is swept, inducing a rotation of the angle of the magnetization indicated by the red arrows. Numbered arrows represent the order and direction of the voltage sweeps. $T=30\text{K}$.

Figure 4

(Color) The change in the longitudinal $\Delta {\rho }_{xx}/{\rho }_{av}$ and the transverse $\Delta {\rho }_{xy}/{\rho }_{av}$ components of the AMR for piezovoltages of $\pm 150\text{V}$. For clarity, the $y$ axis is offset for each curve so that the minimum is at zero.