Two-dimensional Easy-plane Ferromagnet Research Articles

Temperature dependence of spin waves in Rb2CrCl4: a two-dimensional easy-plane ferromagnet

Using inelastic neutron scattering techniques, the temperature dependence of spin waves propagating in the two-dimensional easy-plane ionic ferromagnet Rb2CrCl4 have been measured between 5.3 and 62.7K at three wavevectors in the ( zeta zeta 0) direction: with zeta =0.1, 0.25 and 0.4, and at one wavevector in the ( zeta 00) direction: zeta =0.15. At all wavevectors discrete spin waves are observed to persist above the Curie temperature, Tc approximately 53K. As the temperature increases from 5.3K it is found that the low-energy, long-wavelength, spin waves renormalise more rapidly than those at higher energy. The system should provide a good test of recent theories of spin wave renormalisation.

Magnetic susceptibility and optical spectra of the organic-intercalated two-dimensional ferromagnets bis(monomethylammonium)- and bis(monoethylammonium) tetrachlorochromate(II)

The title compounds have been prepared and characterised by chemical analysis and X-ray diffraction. By magmetic-susceptibility and magnetisation measurements they are shown to order ferromagnetically at Tc= 58 ± 2 and 55 ± 2 K respectively. Up to ca. 0.7 Tc the magnetisation M(T) obeys the equation 1 –[M(T)/M(0)]=CTγ where γ= 1.5 ± 0.1. The optical spectra of both compounds contain sharp absorption bands at 533 and 626 nm, assigned as quintet–triplet ligand-field transitions. Up to 0.9 Tc their intensities vary with temperature as T2, as predicted for ‘hot’ exciton–magnon combination bands in a two-dimensional easy-plane ferromagnet.

Neutron scattering study of the magnetism of Rb2CrCl4, a two-dimensional easy-plane ferromagnet

The crystal and magnetic structure, and the temperature variation of the moment, of Rb2CrCl4 have been investigated using neutron diffraction. The Cr2+, S = 2, spins order ferromagnetically at Tc = 57 ± 2 K. At 4.2 K they lie perpendicular to the tetragonal axis with a moment of 3.7 ± 0.4 μB/ion. As the temperature is raised the moment falls rapidly in a manner characteristics of a two-dimensional easy-plane ferromagnet.