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AM: Magnetismus

AM 18: Postersitzung Fürstenberghaus

AM 18.43: Poster

Wednesday, March 19, 1997, 14:30–17:30, F"u

Magnetic and Transport Properties of   (La/Nd)_2/3(Ca/Sr)_1/3 MnO_3−δ at low temperatures — •W. Schnelle¹, A. Poddar¹, P. Murgaraj¹, L. Haupt², P. Mandal², K. Bärner², and E. Gmelin¹ — ¹Max-Planck-Institut für Festkörperforschung, Heisenberstr. 1, D-70569 Stuttgart — ²IV. Physikal. Institut, Universität Göttingen, Bunsenstr. 11-15, D-37073 Göttingen

Oxygen deficient giant magnetoresistance (GMR) compounds show a complex magnetic structure which changes drastically with temperature and magnetic field. In particular, we investigated the order-order and order-disorder transitions (150K and 250K) through specific heat capacity, Hall effect, magnetoresistivity and magnetisation measurements. An anomaly near the order-order transition is a common signature in all the above stated experiments. The transition entropy derived from the peak in the heat capacity is ≈ 0.4 R ln2. Hall data indicate that at low temperatures mobile carriers are holes while the magnitude of the Hall voltage decreases with rising temperature. Surprisingly, around 220K the Hall voltage changes its sign. This may be due to a change in the dominant carrier type from hole type to electron type. This is consistent with the reported sign change in the thermoelectric power results. Magnetisation measurements show a canted type of antiferromagnetic structure at low temperatures, consistent with the reported neutron diffraction studies.