A Mossbauer effect study of the magnetic phase diagram and spin wave excitations in the antiferromagnet Cs2FeCl5.H2O
Year: 1987
Type: article
Abstract: Mossbauer spectra of Cs 2 FeCl 5 .H 2 O, an antiferromagnet with T N =6.75K, in applied magnetic fields have enabled the magnetic phase diagram to be determined. At the spin-flop field of B SF approximately=1.3 T the spins are observed to re-orient from the a to the c axis suddenly, as expected for a first-order transition, although no hysteresis was detected. By contrast the transitions to the paramagnetic state are continuous, being completed at B c 0 approximately=13 T at 0K with the field required perpendicular to the a axis being slightly larger than for fields applied along the a axis. The saturation value for the magnetic hyperfine field B HF is (52.0+or-0.5)T. At 4.2K, B HF varied with applied magnetic field showing minimum values at B SF and B c . This arises because this temperature is sufficiently close to T N for the sublattice magnetisation to be affected by the applied field, and may be accounted for by spin wave theory. For small fields along the magnetic (a) axis spin waves are excited and B HF decreases, while for B perpendicular to the a axis fluctuations are suppressed and B HF increases. The fluctuations are largest at the transition fields B SF and B c which explains the observed minima in B HF . Fairly good agreement is found with spin wave theory with values B E =6.5 T and B A =0.2 T for the exchange and anisotropy fields respectively. The quadrupole splitting is very small at 290K increasing to a constant value of 0.30 mm s -1 between 77K and T N , suggesting a change in crystal structure.
Authors: J A Johnson, C E Johnson, M F Thomas
Institution: University of Liverpool
Language: English
Subfield: Condensed Matter Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2076587840