This study investigates magnetic layer structures suitable for devices measuring mechanical responses such as stress, strain and pressure. The sensors are based either on giant magnetoresistiance (GMR) structures or on magnetic tunneling junctions (MTJ's) both intentionally prepared with highly magnetostrictive free layer materials. Results for magnetostrictive Fe<sub>50</sub>Co<sub>50</sub> materials or amorphous Co- or Fe-based alloys serving as sensing (or “free”) layers are discussed in view of possible applications. In general, gauge factors in the range of 300-600 have been obtained for strain sensors based on MTJ's, whereas gauge factors of 2-4 are typical for metal based thin film, and 40-180 for piezoresistive strain gauges.
We demonstrate micromechanical detection of ferromagnetic resonance (FMR) in thin magnetic films. FMR spectroscopy is performed on nanometer scale samples integrated with a micromachined silicon cantilever. We present several techniques by which the FMR signal is coupled to a mechanical response of the cantilever. Cantilevers with low spring constants and high mechanical Q are essential for these measurements. Sub-nanometer displacements of the cantilever are detected using a laser beam-bounce system typical of many atomic force microscopes (AFM). The high sensitivities achieved by integrating the sample with the detector allow magnetic measurements on samples with total magnetic moments smaller than detectable with conventional magnetometers. Metrology applications for micromachined magnetometers include ultra-thin film material characterization, magnetic field microscopy, microwave field imaging, and deposition process monitors.