Longitudinal resonance for thin film ferromagnets with random anisotropy
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2018 American Physical Society. At the microscopic level, individual spins in ferromagnets with random anisotropy tip transversely with distinct local angles relative to the magnetization M - . When driven by an rf field along the equilibrium M - 0, which changes dM=M0dM - , the transverse tippings rotate about M - 0, corresponding to a new macroscopic collective angle about M - 0. The coupling of dM and leads to a new longitudinal mode that in bulk has a frequency that is largely independent of field H. A longitudinal mode has been observed in thin films of ferromagnets with random anisotropy, but its frequency is H dependent; for H at angle to the film normal and fixed resonator frequency f, Hcos was constant to angles of 80, with H saturating for larger angles. When the demagnetization field is included the theory yields such an H vs for <80, thus providing evidence for the predicted angle . However, lower frequency resonators are needed to manifest the predicted macroscopic anisotropy energy.