Regensburg 2000 – wissenschaftliches Programm
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AM: Magnetismus
AM 8: Magnetische Phasenübergänge in drei- und niederdimensionalen Strukturen
AM 8.5: Vortrag
Montag, 27. März 2000, 16:45–17:00, H22
Antiferromagnetic order in the geometrically frustrated chromium spinel MgCr2O4 — •W. Schnelle — Max-Planck-Institut für Chemische Physik fester Stoffe, Dresden, Germany
Magnesiochromite MgCr2O4 is a cubic spinel exhibiting antiferromagnetic (afm) order. The Cr3+-ions with S=3/2 reside on the spinel B-site and form a structure leading to geometrical frustration for afm exchange interactions. The low-temperature structure, the specific heat capacity, the isothermal magnetization, and the susceptibility of a high-density polycrystalline sample of MgCr2O4 have been determined. High-temperature susceptibility data indicate a strong afm interaction of the Cr-ions. Long-range magnetic ordering is found at 12.55 K indicated by a huge peak in specific heat capacity and a sharp drop in magnetic susceptibility. The phase transition is of first order and shows a temperature hysteresis. However, no structural change or discontinuous behaviour of the cubic lattice parameter is found at the temperature of the phase transition. The determination of the magnetic heat capacity reveals a broad contribution with a shape similar to a Schottky anomaly well above the phase transition. The total magnetic entropy is 2 · Rln4, as expected. The magnetic specific heat and the susceptibility is discussed in the context of strong geometrical frustration and short-range correlations.