Spin wave based weak magnetic field measurement at room temperature using magnonic crystal

Abstract

We describe a weak magnetic field sensor operating at room temperature based on the magnonic crystal (MC). MC consisting of periodic stripes of cobalt (Co) and permalloy (Py) in one dimension is studied. The magnonic bandgaps are calculated by solving the eigenvalue problem of the Landau–Lifshitz equation using the finite element method. Magnonic bandgap frequency shifts depend upon the external magnetic field and this phenomenon is utilized for magnetic field sensing. The sensitivity characteristics of MCs with dispersion spectra in the gigahertz (GHz) frequency range are studied. It is found that the sensor’s performance gets enhanced for smaller thickness and larger periodicity. The sensitivity reaches a magnitude as large as 66.0 GHz T−1 for 10 nm thickness and 1 μm periodicity. Our analysis indicates that a limit of detection (LOD) of the order of 10−11 T can be achieved for all the geometric configurations considered in the 0–1 T range. The results are explained in terms of corresponding fundamental concepts and phenomena. Further, our simulation results show that the typical gap (e.g. 1 nm) between Co and Py stripes does not significantly affect the sensitivity of the sensor. The results also indicate that any small variation (e.g. 1 nm) in MC thickness may lead to reasonable variation in sensitivity magnitudes. Moreover, the proposed sensor’s performance is significantly superior (in terms of sensitivity, LOD, miniaturization, and material, etc) to the currently available state-of-the-art magnetometers.