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.
@article{arxiv.1603.00933,
title = {Frequency driven inversion of tunnel magnetoimpedance in magnetic tunnel junctions},
author = {Subir Parui and Mário Ribeiro and Ainhoa Atxabal and Amilcar Bedoya-Pinto and Xiangnan Sun and Roger Llopis and Fèlix Casanova and Luis E. Hueso},
journal= {arXiv preprint arXiv:1603.00933},
year = {2017}
}