Nuclear magnetic ordering

Abstract

Because of the smallness of dipolar interactions between nuclear spins in diamagnetic solids, temperatures of the order of 10-6 K or less are required to produce nuclear magnetic ordering. In our study, we cool only the nuclear spins in a two-step process. The spins are first polarized in high field by the 'solid effect’ to an equivalent temperature of a few mdeg and then demagnetized in the rotating frame, which lowers their temperature below 10-6K. Experiments have been so far mostly limited to magnetic resonance measurements on the F spins in CaF2. The parallel and perpendicular susceptibilities exhibit a behaviour characteristic of antiferromagnetism. Results on perpendicular susceptibility and critical field are in quantitative agreement with an extension of the Weiss field theory. Neutron diffraction experiments on CaF2 and magnetic ordering studies on LiF are in progress. © 1972, Walter de Gruyter. All rights reserved.