Münster 1999 – scientific programme
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TT: Tiefe Temperaturen
TT 10: Non-Fermi-Liquid Verhalten in Heavy Fermions
TT 10.7: Talk
Tuesday, March 23, 1999, 16:00–16:15, F3
Pressure dependence of the transition to magnetic order in ZrZn2 — •C. Pfleiderer1, M. Uhlarz1, H. v. Löhneysen1, S. Hayden2, and G. G. Lonzarich3 — 1Physikalisches Institut, Universität Karlsruhe, Engesserstr. 7, D-76128 Karlsruhe, Germany — 2H. H. Willis Physics Laboratory, University of Bristol, Bristol BS8 ITL, UK — 3Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK
The development of a spontaneous moment at low T in weakly ferromagnetic materials may be inferred from the temperature dependence of the low-field susceptibility or high-field magnetic isotherms, respectively. We report here on the consistency of these methods in determining the pressure dependence of Tc in three samples of the Laves phase ZrZn2 with residual resistance ratios ρ(300 K)/ρ(4.2 K) = 21, 23 and 80. Careful comparison of the field cooled (fc) and zero field cooled (zfc) DC susceptibility was carried out by means of a low field squid magnetometer (residual background field <10−2 G) and a non-magnetic miniature clamp cell at pressures up to 18 kbar. Magnetic isotherms, on the other hand, were measured in a 5 T squid magnetometer at ambient pressure and a 7 T extraction magnetometer at high pressure, respectively. For the samples with RRR = 21 and 23 we observe large inconsistencies of the values of Tc as inferred from the zfc and fc T dependence and the magnetic isotherms, contrasting heavily the consistent properties of the sample with RRR = 80. Our measurements clarify the nature of inconsistencies of Tc(p) of ZrZn2 discussed in the literature, highlighting the role of impurites and disorder in obscuring the observation of the intrinsic dependence of Tc(p).