Time-Dependent Neutron Depolarization: A Novel Method in Magnetic Materials Research

Abstract

Due to its magnetic moment the neutron is sensitive to the presence and/or variation of magnetic fields along its trajectory. Already fourty years ago it was shown /1/ that from the change of the polarization degree of a neutron beam on transmission through ferromagnetic samples information can be gained about the quantity δ_av B² _s, where δ_av is the mean size of the domains and B_s is their spontaneous magnetic induction. In the past this neutron depolarization technique has prooved to be useful not only in studying ferromagnetic domain structures /2–6/ but also for the investigation of magnetic critical phenomena /7,8/ and even of the mixed state of type II superconductors /9/. Of particular importance for the progress of the method has been the introduction of three-dimensional polarization analysis by Rekveldt /6/, which for ferromagnets allows to determine separately both the mean size and induction of the domains as well as the mean square direction cosines of the domain inductions with respect to the direction of the mean magnetization of the irradiated volume of the sample. Even correlations between neighbouring domain orientations and correlations between domain dimensions and magnetizations can be detected by this generalized technique /10/.