The inadequacy of applied-field Mossbauer spectroscopy as a means of proving the existence of speromagnetism

Abstract

The authors reply to the suggestion that a two-sublattice collinear spin model employed by them to analyse applied-field Mossbauer spectra of various insulators yields impossibly large values for the uniaxial anisotropy constant and should therefore be disregarded in favour of a model of speromagnetism. The authors note that the value of the anisotropy constant obtained for antiferromagnetic goethite ( alpha -FeOOH) using the collinear model, K1 approximately=3*105 J m-3, is constant with both spin-flop measurements on bulk goethite and with independent theoretical calculations. The anisotropy constants of samples of the disordered iron oxyhydroxide feroxyhite ( delta '-FeOOH), obtained with the collinear model, may be as high as approximately 10*105 J m-3. The anisotropy constants of three reputedly speromagnetic insulators, calculated using the collinear model, fall within this range, and are therefore not impossibly large. The authors reaffirm that there remains a fundamental misconception in the belief that applied-field Mossbauer spectroscopy may be employed to distinguish between speromagnetism and antiferromagnetism in randomly aligned particles and disordered materials.