Dresden 2003 – wissenschaftliches Programm
MA 27.11: Vortrag
Donnerstag, 27. März 2003, 17:45–18:00, HSZ/405
Specific heat of Cr-based thiospinels — •Veronika Fritsch1, Hans-Albrecht Krug von Nidda1, Joachim Hemberger1, Vladimir Tsurkan1,2, Reinhard Tidecks1, and Alois Loidl1 — 1Institut für Physik, Universität Augsburg, Universitätsstraße 1, D-86159 Augsburg — 2Institute of Applied Physics, Academy of Science of Moldova, Academiei 5, MD-2028, Chisinau
The Cr-based thiospinels A2+Cr23+S42− with A = Cd, Mn or Fe are crystallizing in the cubic normal spinel structure. The specific heat was measured on single crystals, which were grown by chemical transport, in the temperature range between 2.3 and 30 K in magnetic fields up to 10 T by a quasi-adiabatic method. CdCr2S4 is a ferromagnetic insulator, due to the ferromagnetic Cr-sublattice (Cr: 3d3, S = 3/2) and a non-magnetic Cd2+ ion. MnCr2S4 (Mn: 3d5, S = 5/2) and FeCr2S4 (Fe: 3d6, S = 2) at low temperatures are ferrimagnetic insulators. Due to the interactions within the Mn- respectively Fe-sublattice and their coupling to the ferromagnetic Cr-sublattice the magnetic structure is more complex. This is also reflected in the specific heat. In CdCr2S4 typical ferromagnetic behaviour was found with a T3/2-law and an exponential decay at low temperatures. In MnCr2S4 the entropy is strongly enhanced by applying an external magnetic field. Obviously a magnetic field induces disorder in the system. In contrast in FeCr2S4, which exhibits a strong magnetocrystalline anisotropy, the specific heat is determined by the orbital degrees of freedom and remains nearly unchanged by an external magnetic field.