Magnetoelastic Coupling and Delta-E Effect in Magnetoelectric Torsion Mode Resonators

Magnetoelectric resonators have been studied for the detection of small amplitude and low frequency magnetic fields via the delta-E effect, mainly in fundamental bending or bulk resonance modes. Here, we present an experimental and theoretical investigation of magnetoelectric thin-film cantilevers that can be operated in bending modes (BMs) and torsion modes (TMs) as a magnetic field sensor. A magnetoelastic macrospin model is combined with an electromechanical finite element model and a general description of the delta-E effect of all stiffness tensor components C-ij is derived. Simulations confirm quantitatively that the delta-E effect of the C-66 component has the promising potential of significantly increasing the magnetic sensitivity and the maximum normalized frequency change Delta f(r). However, the electrical excitation of TMs remains challenging and is found to significantly diminish the gain in sensitivity. Experiments reveal the dependency of the sensitivity and Delta f(r) of TMs on the mode number, which differs fundamentally from BMs and is well explained by our model. Because the contribution of C-11 to the TMs increases with the mode number, the first-order TM yields the highest magnetic sensitivity. Overall, general insights are gained for the design of high-sensitivity delta-E effect sensors, as well as for frequency tunable devices based on the delta-E effect.