Tunnel magnetodielectric effect: Theory and experiment

The recently discovered tunnel magnetodielectric (TMD) effect-the magnetic field-induced increase in the dielectric permittivity (epsilon & PRIME;) of nanogranular composites caused by the spin-dependent quantum mechanical charge tunneling-is of interest for both the scientific value that combines the fields of magnetoelectric and spintronics and multifunctional device applications. However, little is known about how large the maximum dielectric change delta epsilon'/epsilon' can achieve and why the delta epsilon'/epsilon' variations obey the dependence of square of normalized magnetization (m(2)), which are critically important for searching and designing materials with higher delta epsilon'/epsilon'. Here, we perform approximate theoretical derivation and reveal that the maximum delta epsilon'/epsilon' can be estimated using intrinsic tunneling spin polarization (P-T) and extrinsic normalized magnetization (m), that is, delta epsilon'/epsilon' = 2P(T)(2)m(2). This formulation allows predicting over 200% of theoretical limit for m = 1 and accounts for the observed m(2) dependence of delta epsilon'/epsilon' for a given P-T. We experimentally demonstrate that x-dependence of delta epsilon'/epsilon' in (CoxFe100-x)-MgF2 films is phenomenologically consistent with this formulation. This work is pivotal to the design of ultra-highly tunable magnetoelectric applications of the TMD effect at room temperature. (C) 2022 Author(s).