Neutron depolarization in reentrant spin glasses Ni1−xMnx

Publisher Website
Google Scholar
Abstract
Polarization analysis of the transmitted beam was performed using a pulsed neutron source in a reentrant spin‐glass (RSG) system Ni1−xMnx, for a concentration range (0.23≤x≤0.28) encompassing the critical concentration. The same samples were previously used to determine the magnetic phase diagram by magnetization measurements. The polarization P was measured as a function of temperature (15≤T≤300 K), neutron wavelength (3≤λ≤10 Å) and applied field (7 Oe≤H≤125 Oe). Unlike other RSG systems, P measured in a 7 Oe field decreases at all temperatures below the Curie temperature even for the samples close to the critical concentration. The wavelength dependence of the polarization indicates the existence of magnetic domains whose size δ decreases with increasing x from a few tenths of micrometers at x=0.23 to a few thousands of angströms at x=0.25. No depolarization occurs for x>0.25. As shown for x=0.23, the irreversibilities of the polarization, which depends on the cooling conditions, indicate that the domain arrangement freezes at low temperature. Clearly, in NiMn, the drop of the susceptibility at low temperature does not result from a decrease of the size or magnetization of the domains but from a slowing down of their mobility.