Regensburg 1998 – scientific programme
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TT: Tiefe Temperaturen
TT 21: Postersitzung III: Spin-Peierls-Systeme, Metall-Isolator-Übergang, Lokalisierung; SL: Theorie; Quantenflüssigkeiten und -kristalle; Amorphe Materialien, Tunnelsysteme; Borcarbide, Fullerene, konventionelle SL; SL dünner Filme; Experimentiertechniken
TT 21.27: Poster
Thursday, March 26, 1998, 15:00–18:30, D
The Magnetic Phase Diagram of pure PrBa2Cu3O7−δ Single Crystals — •W. Schnelle, S. Uma, and E. Gmelin — Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart
The antiferromagnetic ordering of Pr-ions in twinned single crystals of PrBa2Cu3O7−δ free from all detrimental impurities is investigated by specific heat measurements for 2.2<T<40 K both in warming and in cooling. Magnetic fields up to 16 T parallel and perpendicular to the c-axis are applied. A sharp peak at TNPr = 16.6 K marks the Pr-paramagnetic-antiferromagnetic transition. In addition, a first-order transition displaying a hysteresis (at 13.4 K in warming; ≈ 11 K in cooling), indicating a change of the magnetic stucture of the Pr subsystem occurs. The two antiferromagnetic phases are confirmed by dc-susceptibility, thermal expansion in a capacitance dilatometer, and neutron scattering measurements [1]. The field dependent behaviour of the phase transitions is strongly anisotropic. While the antiferromagnetism is suppressed for H ∥ c in a field of 16 T, for H ⊥ c the specific heat peak at TNPr splits. The specific heat cp(T) at high fields and the magnetic entropy of Rln3 give evidence for a 3+ valence state of the Pr-ions. Based on our measurements we present a magnetic phase diagrams H vs. T for both field directions in pure PrBa2Cu3O7−δ.
[1] S. Uma et al. Submitted to J. Phys. C, November 1997