STATIC POLARIZATION ECHOES IN METAL POWDERS

Overview & Synopsis

Static polarization echoes with long time storage in metal powders placed in steady magnetic field have been studied. The echo amplitudes were found to be unstable when the surrounding He gas pressures were less than 10 Pa, whereas they were stabilized by introducing a small amount of He gas of ≥ 100 Pa at 4.2 K. The phenomenon can be understood if the process involves the macroscopic reorientation of individual particles and if the mechanical rotation of the individual particles is stabilized by the increase in interparticle friction due to the presence of He gas molecules on the particles. A particular base axis of the rotation is proposed to be specified by an anisotropic magnetic dipole caused by electric currents associated with the mechanical oscillation of particles.