Frequency driven inversion of tunnel magnetoimpedance in magnetic tunnel junctions

TL;DR

This paper reports a frequency-dependent reversal of tunnel magnetoimpedance in magnetic tunnel junctions, revealing new insights into high-frequency spin transport and interface effects.

Contribution

It demonstrates a frequency-driven sign reversal of tunnel magnetoimpedance and uncovers a positive tunnel magnetocapacitance, advancing understanding of high-frequency spin phenomena in MTJs.

Findings

Magnetoimpedance reverses sign at certain frequencies.

Positive tunnel magnetocapacitance observed.

Capacitive coupling explains the frequency effects.

Abstract

Magnetic tunnel junctions (MTJs) are basic building blocks for devices such as magnetic random access memories (MRAMs). The relevance for modern computation of non-volatile high-frequency memories makes ac-transport measurements of MTJs crucial for exploring this regime. Here we demonstrate a frequency-mediated effect in which the tunnel magnetoimpedance reverses its sign in a classical Co/Al{_2}O{_3}/NiFe MTJ, whereas we only observe a gradual decrease of tunnel magnetophase. Such effects are explained by the capacitive coupling of a parallel resistor and capacitor in the equivalent circuit model of the MTJ. Furthermore, we report a positive tunnel magnetocapacitance effect, suggesting the presence of a spin-capacitance at the two ferromagnet/tunnel-barrier interfaces. Our results are important for understanding spin transport phenomena at the high frequency regime, in which the spin-polarized charge accumulation at the two interfaces plays a crucial role.