Ferromagnetic resonance of micrometer-sized samples

Submicrometer-sized slotline and coplanar waveguide devices were used for ferromagnetic resonance (FMR) measurement on submicrometer-sized magnetic fine particles. FMR measurements were taken on individual magnetic disks, having diameters ranging from 50 to 1 μm, using either a slotline–coplanar waveguide (CPW) junction device or a coplanar waveguide transmission line junction device. The magnetic samples were etched from a 105 nm thick amorphous Fe80B15Si5 film on a quartz substrate. Absorption modes, which were measured with the submicrometer-sized slotline CPW, followed the Kittel magnetic resonance model for frequencies from 1 to 20 GHz for the 1 μm diam disk. By detecting the second harmonic of the lock-in amplifier’s reference signal, we have measured disk samples as small as 1 μm in diameter. We estimated that the sensitivity is of the order of 3×109 spins, almost four orders of magnitude better than the sensitivity of a standard electron paramagnetic resonance system.