G P Gupta

Applied magnetic field Mössbauer studies of the quasi one-dimensional system AFeS2:A = K, Rb, Cs

Abstract Mossbauer measurements of single crystal and quasi single crystal samples of AFeS 2 compounds show no evidence for any variation of the hyperfine field with applied fields up to 10.0 T. This is consistent with what would be expected in a quasi one-dimensional system with relatively high anisotropy, and does not preclude a contribution to the anomalously low value of the saturation hyperfine field from zero point spin reduction effects.

One-dimensional antiferromagnetism in N2H6FeF5: A Mossbauer spectroscopic study

Mossbauer measurements on polycrystalline N2H6FeF5 show that it exhibits a low Neel temperature, a low saturation value of the hyperfine field and a variation of the hyperfine field with the orientation of the applied field. These are all typical characteristics of a one-dimensional antiferromagnetic system.

Zero-point spin reduction in the one-dimensional antiferromagnet K2FeF5

Mossbauer spectra of K2FeF5 show that it undergoes an ordering to an antiferromagnetic state at 11.2+or-0.5K. An anomalously low value (41.0+or-0.5T) of the saturation hyperfine field for a high-spin ferric ion is observed. This is interpreted as resulting from zero-point spin reduction.

Temperature variation of the field-dependent spin reduction in the one-dimensional antiferromagnets: K2FeF5 and Rb2FeF5

Mossbauer spectra of single crystals of K2FeF5 and Rb2FeF5 show that, in accordance with spin-wave theory, the spin reduction resulting from the application of an external magnetic field, which is enhanced in one-dimensional antiferromagnets, decreases significantly when the temperature is lowered. In addition, the value of the critical field for spin flopping in K2FeF5 is reduced on lowering the temperature.

A Mössbauer study of the variation of hyperfine field with applied field in Cs2FeCl5·H2O

Abstract Mossbauer results on Cs 2 FeCl 5 ·H 2 O measured the Neel temperature, (6.75 ± 0.5) K, and saturation hyperfine field, (52.0 ± 0.05) T. Fields applied parallel to the magnetic easy axis produced spin flop at B sf = (1.5 ± 0.1) T ) amd a spin-flop to paramagnetic transition at an estimated B c = (10.0 ± 0.2) T. The field dependence of hyperfine field is discussed in terms of magnetic excitations.

Applied-field-dependent magnetisation curves of the one-dimensional antiferromagnet K2FeF5 (Mossbauer spectra)

Mossbauer spectroscopic measurements of hyperfine fields have been used to obtain information on the magnetisation curves of single crystals of K2FeF5 in the presence of applied magnetic fields in the antiferromagnetic region below the Neel temperature. In zero applied field the magnetisation curve is of the expected form but with an anomalously low value of the saturation hyperfine field. With fields applied perpendicular to the magnetic easy axis the magnetisation curve is raised with respect to that in zero field but remains essentially parallel to it. For fields applied parallel to the magnetic easy axis the magnetisation curve is lowered compared with that in zero field with the effect decreasing with decreasing temperature so that the curves converge as absolute zero is approached.

Magnetic and electric-field gradient axes in the one-dimensional antiferromagnet K2FeF5

Mossbauer spectra obtained from single crystals of the one-dimensional antiferromagnet K2FeF5 show that the spins are initially aligned along the b axis, perpendicular to the chains of (FeF6)3- octahedra which run along the a axis. With an applied field along the b axis the spins reorientate (flop) to lie in the a-c plane between the a and c axes. The principal axis of the electric field gradient is in the a-b plane at an angle of 42+or-5 degrees to the b axis.

Mössbauer studies of the one-dimensional antiferromagnetic systems: A2FeF5

Abstract Mossbauer measurements on A 2 FeF 5 (A 2 = K 2 , Rb 2 or N 2 H 6 ) show low Neel temperatures, low saturated values of the hyperfine field and a temperature dependent variation of the hyperfine field with applied field. These are all typical characteristics of one-dimensional antiferromagnetic systems, and are consistent with the predictions of spin-wave theory.

Soliton broadening observed in the Mössbauer spectra of the one-dimensional antiferromagnet K2FeF5

Abstract At temperatures above the Neel temperature considerable line broadening is observed in the Mossbauer spectra of single crystal samples of K 2 FeF 5 obtained with certain external applied magnetic fields. The temperature dependence of the excess linewidth shows the exponential behaviour which is characteristic of the presence of solitons.