Neutron Scattering Measurements of the Staggered Magnetization of an Antiferromagnetic Epitaxial Thin Film FeF₂

Abstract

Elastic neutron scattering measurements performed at the NIST reactor have been used to measure the staggered magnetization near the transition temperature in a thin antiferromagnetic epitaxial film of FeF₂ of thickness 0.8μm and diameter 1cm grown on a diamagnetic (001) ZnF₂ substrate by MBE. The use of a thin film permits extinction-free Bragg intensities, something which has proven impossible in bulk crystals. The growth techniques yield sufficient crystal quality to observed resolution limited magnetic Bragg scattering peaks and to approach the transition within a reduced temperature of t = 0.003. The structure quality of this sample has been characterized using X-ray double crystal diffraction with a measured rocking curve lin ewidth of less than 30 arc sec. The sample thickness, while small enough to eliminate extinction, is sufficiently large to assure three-dimensional Ising model critical behavior. We indeed observe critical behavior consistent with theoretical predictions. The success of the thin film experiments demonstrates the possibilities of extinction-free Bragg scattering measurements in a variety of antiferromagnetic materials, including multilayered systems.