Cryogenic capability added to NIST's pulsed inductive microwave magnetometer. (General Developments).

NIST's recently developed Pulsed Inductive Microwave Magnetometer (P1MM) has now been enhanced with variable temperature capability. The new instrument can measure the magnetodynamic response of magnetically soft, thin-film materials at temperatures from 25 K to 325 K. In addition, the CryoPIMM has been augmented with high-field magnets that can apply dc bias fields up to 45 mT, permitting the study of materials with high anisotropy, such as single-crystal films of iron and nickel.

Built at NIST-Boulder, the CryoPIMM will be a powerful new tool to investigate the fundamental origins of precessional damping in thin metallic films. Most magnetic materials with a high permeability also exhibit under-damped response when driven with rf fields. The origin of the oscillatory response stems from the gyromagnetic properties inherent in all ferromagnets. The magnetic moment of the electron is fundamentally coupled to the quantum mechanical spin angular momentum: when a torque is applied to the magnetization, the intrinsic response of the electron moment is precession, much like how a gyroscope precesses under the influence of the Earth's gravitational field. However, in sharp contrast to a mechanical gyroscope, the angular momentum of the electron spin precesses at megahertz to gigahertz frequencies. In the absence of any coupling between the electron spins and the rest of the crystal environment, the precession would continue indefinitely. In reality, the spins are coupled to the atomic lattic e such that the precession is eventually damped. Nevertheless, the resulting oscillations of the magnetic moment can be deleterious in practical applications, such as magnetic data storage. For example, the data rate in commercial disk drives is now approaching I Gbit/s. Disk drive engineers must be careful to avoid effects stemming from gyromagnetic precession at these frequencies. Most importantly, there is a need to determine sources of damping, with the goal of controlling the damping as a material design parameter.

There are multiple conflicting theories for damping in metallic thin films. One is "magnon-electron scattering" or "sd-exchange." This theory predicts a strong temperature dependence in the range of 4 K to 100 K. Observation of a temperature dependence in the damping would be strong confirming evidence for the sd-exchange theory.

CONTACT: Tom Silva, [phone]; [e-mail].