Oscillating voltage dependence of high-frequency impedance in magnetic tunneling junctions

Oscillating voltage (V_Os), which depends on the frequency dependence of the magnetoimpedance (MI) effect, was applied to study a magnetic tunneling junction (MTJ) of Ru(5 nm)/Cu(10 nm)/Ru(5 nm)/IrMn(10 nm)/CoFeB(4 nm)/Al₂ O₃/CoFeB(4 nm)/Ru(5 nm) at frequencies up to 40 MHz. The MI ratio decreased as the V_Os was increased. The MI ratio turned from positive to negative at a certain frequency. An equivalent circuit model was employed to analyze the results. The fact that MTJ can be regarded as the composition of a resistance component and two sets of parallel resistance (R) and capacitance (C) components in series has been utilized to describe the individual impedance contribution from the lead of cross pattern, barrier, and interface. The resistance (R_barrier) and capacitance (C _barrier) of the barrier effect are functions of V_Os. The R_barrier decreases as the V_Os, increases, However, C _barrier behaves the opposite way. The tendency is for interfacial resistance R_interface and interfacial capacitance C _interface to have opposite results with increasing V_Os. This work provides a detailed investigation of high-frequency transport behavior subjected to V _Os, especially useful for MTJ characterization.