Narrowing Effect of Dipole Forces on Inhomogeneously Broadened Lines

Abstract

Under the proper circumstances dipole forces can decrease an inhomogeneous broadening of a magnetic resonance line. The necessary condition is that the magnetization of the material be very much greater than the inhomogeneity, and is therefore most easily observed in ferromagnetic materials. Experiments are described in which this narrowing effect was observed in manganese ferrite and yttrium iron garnet. The theory of this effect is discussed for the two cases in which the spatial period of the inhomogeneity is large compared to atomic distances and either (I) short compared to sample size or (II) comparable to sample size. Applications to line broadening in paramagnets and polycrystalline ferrites, and to the low-temperature peak in single crystals of yttrium iron garnet and manganese ferrites, are discussed.