This study aims to fabricate a voltage-tuneable magneto resistive sensor with the ability to measure small magnetic field signals in three dimensions. Sensing direction in magneto resistive sensors is linked to the magnetization of reference layer. Materials like CoFe1, CoFeB2 and Heusler alloys3 are good choices as reference layers due to their adjustable magnetic anisotropies. Here, using ionic liquid gating (ILG), we observed that magnetic anisotropy of reference layer CoFeB is switchable in MgO(1.5nm)/CoFeB(1.6nm)/W(0.5nm) stack. We used ionic liquid N, N-diethyl-N-methyl N-(2-methoxyethyl) ammonium bis (trifluoromethylsulfonyl) imide (DEME TFSI) (IoLiTec) for applying the gate voltage (VG) ranging between ±3.5V. Using the magneto-optical Kerr effect, we have investigated the change of anisotropy using different gate voltages. We found that magnetic anisotropy switches from out-of-plane (virgin state) to in-plane upon the application of +3.5V, whereas removal of applied voltage +3.5V or application of -3.5V, switches magnetic anisotropy back to out-of-plane, demonstrating the switching behaviour of the stack is reversible and repeatable. Moreover, we observed that out-of-plane to in-plane anisotropy switching time is higher (~45 sec) compared to in-plane to out-of-plane switching time (~25 sec). Hence, a stack having stronger out-of-plane and switchable anisotropy is ideal to use in voltage tuneable magneto resistive sensors.
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