Broadband ferromagnetic resonance spectrometer. (News Briefs).

NIST researchers have constructed a broadband spectrometer for measurements of ferromagnetic resonance (FMR) in magnetic thin films from 1 GHz to 26 GHz. Like electron paramagnetic resonance and nuclear magnetic resonance, FMR involves precession of the magnetization around an equilibrium direction, but motion of the magnetization is heavily influenced by the large magnetization that is characteristic of ferromagnets. Measurements of the resonance condition as a function of applied field direction are valuable for determining magnetic anisotropy energies and coupling between magnetic layers in multilayer structures such as the spin valves that are used as the active elements of read heads in modern disk drives.

The resonance line width includes the effects of both inhomogeneities and intrinsic damping. The extrinsic line width is an important indicator of film quality, and the intrinsic damping, which governs the magnetic relaxation rate, is projected to become increasingly important for the development of fast magnetic memory (MRAM) and GHz-rate disk drives. In disk drives, the relaxation rate is important for high data rate operation of the read head and for writing, both in the writer and in the media. In addition, the damping mechanisms that couple the magnetism to the thermal bath also drive the magnetic fluctuations that characterize the superparamagnetic limit of storage density.

The broad frequency range and the angular control provided by this new spectrometer allows thorough testing of line width and damping models that are needed to separate the inhomogeneous and intrinsic contributions to the measured resonance line width. Initial measurements using the new spectrometer have been made on films with intentionally created defects and nominally uniform films.

CONTACT: Bob McMichael, (301.) 975-5121; [e-mail].