Optical Writing of Magnetic Properties by Remanent Photostriction

We present an optically induced remanent photostriction in ${\mathrm{BiFeO}}_3$, resulting from the photovoltaic effect, which is used to modify the ferromagnetism of Ni film in a hybrid ${\mathrm{BiFeO}}_3/\mathrm{Ni}$ structure. The 75% change in coercivity in the Ni film is achieved via optical and nonvolatile control. This photoferromagnetic effect can be reversed by static or ac electric depolarization of ${\mathrm{BiFeO}}_3$. Hence, the strain dependent changes in magnetic properties are written optically, and erased electrically. Light-mediated straintronics is therefore a possible approach for low-power multistate control of magnetic elements relevant for memory and spintronic applications.

Figure 1

(a) The remanent polarization state created by 30 sec UV light. (b) Corresponding photocurrent. (c) Remanent photostriction detected by measuring the resistance of the Ni film (d) and by static x-ray diffraction of BFO (e).

Figure 2

(a) Schematics of the experiment. (b) Room-temperature ferromagnetic loops of an 11 nm thick Ni film on top of a BFO single crystal before (1) and after (2) excitation by 404 nm light (fluence $250\mathrm{J}{\mathrm{cm}}^{-2}$). The initial $M(H)$ loop (1) can be recovered (3) by an electric pulse (c) that corresponds to the ferroelastic coercive force $E_c$ as represented by an example sketch (d) [46].