-The high-field anomaly in antiferromagnetic heavy-fermion U (Pt0.95Pd0,05)3 has been investigated by means of magnetisation measurements up to 18 T. The metamagnetic-like transition (at -12 T at T = 1.3 K, for a field in the basal plane) was found to be present up to 15 K, i.e. a temperature well above the NBel temperature (TN = 5.8 K) . The data taken on a single-crystalline sample, yield a magnetic anisotropy in the basal plane. The magnetic phase diagram is presented. Recently, it has become clear that antiferromagnetic spin-fluctuations (AFSF) play an important role in the low-temperature properties of most (if not all) of the heavy-fermion compounds. In the case of UPt3 it was first illustrated that the greater part of the transport, thermal and magnetic properties could be ascribed to strong (anti-)ferromagnetic spinfluctuations [I]. Alloying studies [2] and inelastic neutron-scattering experiments [3] have demonstrated that the spin fluctuations are predominantly of antiferromagnetic (AF) chaiacter. Furthermore, it has been shown that the AF correlations (confined to the basal plane for hexagonal UPt3) collapse by applying a large magnetic field, in particular when the component of the field in the basal plane achieves a value of 20 T. This was evidenced by the observation of a metamagnetic-like transition [4] (the differential susceptibility, Xdiff, peaks at B, = 20 T) and a maximum in the magnetoresistance [5] for the same field value. Subsequent magnetostriction measurements (B < 24 T) are consistent herewith [6]. On alloying UPt3 with Pd, B,, decreases, indicating a weakening of the AF coupling. Magnetisation measurements at T = 4.2 K on polycrystalline samples [2] reveal that B, shifts towards lower fields (w 16 T and 11 T for 2 % and 5 % Pd, resp.). For a 15 % Pd compound the anomaly is not observed. On the other hand, specific-heat measurements [2] have shown that long-range AF order occurs in the concentration range 2-10 % Pd, with a maximum TN of 5.8 K near 5 % Pd. Neutron-diffraction experiments [7] on a 5 % Pd compound yield an AF propagation vector along the baxis. The ordered moment amounts to 0.6 ~ B / U atom. (d = 3 mm) by means of spark erosion. Magnetisation measurements have been performed at the SNCI in Grenoble, using a conventional extraction method in a Bitter magnet (B < 18 T) . Data were gathered for fields along the aand bdirections in the hexagonal plane ( b i a ) . Hereto, the sample was oriented by means of X-rays and glued onto the sample holder. The uncertainty in the orientation of the sample amounts to 2'. In figure 1 we show the magnetisation curves, M (B) , and X d i a (B) for the aand baxis at 1.3 K and 4.2 K. Apparently, the M (B) curves become much steeper on cooling from 4.2 K t o 1.3 K, whereas B, In order to study the relation between the occurrence of AFSF and long-range AF order, we have performed magnetisation measurements on a singlecrystalline U (Pto.95Pdo.05)~ sample, in fields up to 18 T, well above and below TN. The U(Pto.95Pd0.05)~ sample was prepared by the Czochralski technique, and shaped into a sphere Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19888343 C8 762 JOURNAL DE PHYSIQUE increases from 10.1 to 12.6 T and from 9.8 to 11.8 T, for the aand baxis, respectively. Furthermore, a sizeable anisotropy in the basal plane appears. The temperature dependence (1.3 5 T 5 20.1 K ) of the M (B) curves for the baxis (Fig. 2) reveals that the anomaly is still present above TN = 5.8 K, but weakens and disappears above 15 K. The inflection points are found at 11.3, 11.2 and 10.5 T at temperatures of 7.5, 10 and 15 K, respectively. The temperature dependence of the initial susceptibility as derived from figure 2 is in good agreement with earlier low-field data for a different sample (B < 1.3 T) [8]. Comparing the data for B // a at 4.2 K with the data obtained in the Amsterdam High Field Installation 181, we notice an excellent agreement.

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@inproceedings{Visser2017HIGHFIELDMO, title={HIGH-FIELD MAGNETISATION OF HEAVY-FERMION U (Pt0.95Pd0.05)3}, author={Albert Visser and Mary V Sprang and A . A . Menovsky and Jochem Franse}, year={2017} }