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MA: Magnetismus

MA 27: Spinstrukturen und magnetische Phasenüberg
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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 Tsurkan^1,2, 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 T^3/2-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.