First-Order Transition in the Itinerant Ferromagnet CoS1.9Se0.1
Undoped CoS2 is an isotropic itinerant ferromagnet with a continuous or nearly continuous phase transition at TC = 122 K. In the doped CoS1.9Se0.1 system, the Curie temperature is lowered to TC = 90 K, and the transition becomes clearly first order in nature. In particular we find a discontinuous evolution of the spin dynamics as well as strong time relaxation in the ferromagnetic Bragg intensity and small-angle neutron scattering in the vicinity of the ferromagnetic transition. In the ordered state the long-wavelength spin excitations were found to be conventional ferromagnetic spin waves with negligible spin-wave gap (<0.04 meV), indicating that this system is also an excellent isotropic (soft) ferromagnet. In a wide temperature range up to 0.9TC, the spin-wave stiffness D(T) follows the prediction of the two-magnon interaction theory, D(T) = D(0)(1 - AT5/2), with D(0) = 131.7 ± 2.8 meV Å 2. The stiffness, however, does not collapse as T → TC from below. Instead a quasielastic central peak abruptly develops in the excitation spectrum, quite similar to results found in the colossal magnetoresistance oxides such as (La-Ca)MnO3.
T. J. Sato et al., "First-Order Transition in the Itinerant Ferromagnet CoS1.9Se0.1," Physical Review B - Condensed Matter and Materials Physics, vol. 68, no. 21, pp. 2144111-2144118, American Physical Society (APS), Dec 2003.
The definitive version is available at http://dx.doi.org/10.1103/PhysRevB.68.214411
Keywords and Phrases
Calcium; Cobalt; Ferromagnetic Material; Lanthanum; Manganese Derivative; Selenium; Sulfur; Chemical Modification; Magnetism; Mathematical Analysis; Molecular Interaction; Phase Transition; Temperature
International Standard Serial Number (ISSN)
Article - Journal
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