An apparatus includes circuits and a module configured to determine an external magnetic field based on a parameter of each circuit. Each circuit includes an array of magnetic tunnel junctions partitioned into subarrays. The magnetic tunnel junctions in each subarray are arranged in rows, the magnetic tunnel junctions in each row are connected in series, and the rows are connected in parallel. The subarrays are connected in series. Each magnetic tunnel junction includes a storage layer having a storage magnetization and a sense layer having a sense magnetization. Each magnetic tunnel junction is configured such that the sense magnetization and impedance of each magnetic tunnel junction vary in response to an external magnetic field. The parameter of each circuit varies based on a combined impedance of the multiple magnetic tunnel junctions. The module is implemented in at least one of a memory or a processing device.