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AM: Magnetismus

AM 9: Poster: Magnetowid. (1-17), Dü. Schichten (18-34), Oberfl
ächenmag. (35,36), Mikr. Methoden (37-45), Mikromag. (46-58), Phasenüberg. (59-77), Spektroskop. (78-91), Nanokr.Mat.(92-96), Anisotrop. (97-101), Schmelzen(102-104),Sonst/postdeadl.(105-109)

AM 9.75: Poster

Dienstag, 27. März 2001, 14:45–19:00, Foyer S 3

Magnetic and thermodynamic properties of antiferromagnetically ordering geometrically frustrated spinels — •Walter Schnelle — MPI für Chemische Physik fester Stoffe, Dresden, Germany

The normal cubic spinels MgCr₂O₄ and ZnCr₂O₄ exhibit strong geometrical frustration for antiferromagnetic (AFM) interactions of the Cr³⁺. Data of specific heat capacity and magnetic susceptibility of a polycrystalline sample of MgCr₂O₄ and of single crystals of ZnCr₂O₄ show long-range AFM ordering at T_N ≈ 12.5 K, indicated by sharp drops in χ(T). At T_N large first-order peaks in c_p(T) are found, which are not influenced by fields up to 140 kOe. χ(T) displays a maximum at 34.2(4) K (Mg) / 45.8(4) K (Zn). The results are discussed in the context of a model for magnetic frustration in tetrahedral lattices. The question wether the full magnetic entropy of 2 R ln4 is set free is investigated. From a comparison of the calorimetrically determined entropy with a value derived from a reaction equilibrium it is found that there is no significant residual entropy in MgCr₂O₄, in contrast to “spin-ice”-pyrochlores.