Electric-Field Induced Reversible Switching of the Magnetic Easy Axis in Co/BiFeO3 on SrTiO3
Tieren Gao, Xiaohang NMN Zhang, William D. Ratcliff, Shingo Maruyama, Makoto Murakami, Anbusathaiah Varatharajan, Zahra Yamani, Peijie Chen, Ke Wang, Huairuo NMN Zhang, Robert D. Shull, Leonid A. Bendersky, John NMN Unguris, R. Ramesh, Ramamoorthy Ramesh, I. Takeuchi
We demonstrate reversible electric-field-induced switching of the magnetic state of the Co layer in Co/BiFeO3 (BFO) (001) thin film heterostructures fabricated on (001) SrTiO3 substrates. The angular dependence of the coercivity and the remanent magnetization of the Co layer indicates that its easy axis reversibly switches back and forth 45 ° between the (100)/(110) crystallographic directions as a result of alternating application of positive and negative voltage pulses between the patterned top Co electrode layer and the (001) SrRuO3 layer on which the ferroelectric BFO is epitaxially grown. A mechanism based on the intrinsic magnetoelectric coupling in multiferroic BFO involving projection of the antiferromagnetic G-type domain is used to explain the observation. We have also measured the exact canting angle of the G-type domain in strained BFO films for the first time using neutron diffraction. To explore applications of the electric-field-tunable magnetic easy axis in electronic devices, we have fabricated BFO-based spin-valve devices with a GMR ratio as large as 4% at room temperature.