Regensburg 1998 – wissenschaftliches Programm

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AM: Magnetismus

AM 11: Postersitzung

AM 11.58: Poster

Dienstag, 24. März 1998, 16:15–20:00, B

Investigation of Physical Properties of CMR Perovskite Manganates — •Y. Xu, A. Müller, A. Drechsler, V. Dworak, W. Guan, and U. Hartmann — Experimentalphysik, Universität des Saarlandes, D-66041 Saarbrücken

We have successfully prepared the perovskite manganates
La_0.67Ca_0.33MnO₃, La_0.67Ba_0.33MnO₃, and La_0.67Sr_0.33MnO₃. XRD revealed all samples being single perovskite phase. Magnetization measurements show that all samples are ferromagnetic with high Curie temperature close to room-temperature. Magnetoresistance values were deduced from resistivity measurements at various magnetic fields up to 8 T. The grain size ranges from a few ten nm to a few µm demonstrated by SEM. Polishing the sample surface creates some relatively flat areas of ∼ µm on the crystals. This offers the possibility of local MFM investigations. With a magnetic CoCrPt tip even without an external field, the magnetic image contrast is very clear below T_C. Under a field of 23 mT parallel and 45 mT perpendicular to the surface of La_0.67Sr_0.33MnO₃ sample, the magnetic image contrast increases considerably. Similar results were obtained for La_0.67Ba_0.33MnO₃. However, for La_0.67Ca_0.33MnO₃ at room temperature (above T_C) there is no contrast in the magnetic image in zero field and even under a field of up to 50 mT. Our measurements in particular show the possibility to study the magnetic structure in the crystals by MFM.