Neutron Diffraction Studied in Magnetism 1947-67
Neutron diffraction is the most powerful of modern tools for the determination of the arrangement of atomic magnetic moments in solids. At Brookhaven the method has been developed and used to characterize the magnetic structures of a wide variety of metals and compounds, and to relate them to existing theories of magnetism as well as to observed physical properties.
The Néel model of ferrimagnetism, in which oppositely-directed magnetic substructures give rise to a resultant ferromagnetic moment, has been established in great detail for a number of compounds crystallizing with the spinel structure.
In the case of antiferromagnetism, the role of the anion in determining magnetic spin arrangements has been elucidated in studies of a variety of oxides, sulfides, and related compounds. These studies have strongly supported the concept that indirect exchange interactions operate through metal-anion-metal bonds.
Research at Brookhaven has produced the first application of magnetic, or time-reversal, symmetry to the characterization of ordered spin arrangements in solids.
The investigation of metallic chromium at BNL resulted in the discovery, also made simultaneously at Saclay and the University of Tokyo, of stable magnetic states in which classical magnetic structures are modulated in direction, magnitude, or both. This modulation now appears to be a commonly occurring phenomenon and has been studied here in materials of widely different chemical structure.
The investigation of chromium-substituted calcium ferrite has led to the discovery that two distinct magnetic phases can coexist at equilibrium in the solid state.
Magnetic structure determination at Brookhaven, combined with physical measurements performed elsewhere, has established that dysprosium aluminum garnet is a close physical realization of the Ising antiferromagnet. Neutron critical scattering measurements, which reflect the cooperative behavior of the spin system close to the transition temperature, have confirmed many of the theoretical predictions for the Ising model
L. Corliss, J. Hastings, and F. G. Brockman, "A Neutron Diffraction Study of
Magnesium Ferrite," Phys. Rev. 90, 1013 (1953).
Last Modified: June 28, 2012