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Muon spin rotation spectroscopy on a UNiGa single crystal

Van der Waals-Zeeman Laboratory, UniL'ersity of Amsterdam, 1018 XE, Amsterdam, The Netherlands; Department of Metal Physics, Charles Unit~ersity; The Czech Republic; Institute of Particle Physics, ETH Ziirich, CH-5232, Villigen PSI, Switzerland; Hahn-Meitner Institute, BENSC, D-14109, Berlin 39, Germany
Journal of Magnetism and Magnetic Materials (Impact Factor: 1.83). 01/1995; DOI: 10.1016/0304-8853(94)00884-1

ABSTRACT UNiGa orders antiferromagnetically (AF) below 39 K with four different AF phases appearing with decreasing temperature. These phases are reflected in taSR spectra by different sets of frequencies. In paramagnetic range three different Knight shift signals were detected. The results can be explained assuming three different stopping sites. UNiGa is one of the UTX compounds crystallizing in the hexagonal ZrNiAI structure and consists of U-Ni and Ni-Ga layers alternating along the c-axis. The huge uniax-ial magnetic anisotropy in UNiGa is caused by strong 5f-electron bonding within the U-Ni planes and the con-siderable U 5f-orbital moments [1]. This mechanism locks the U magnetic moments along the c-axis (a negligible induced magnetization on the Ni sites is expected). The bonding anisotropy results in a strong ferromagnetic cou-pling of U magnetic moments within U-Ni planes. The interlayer coupling is weaker and yields the stacking se-quence of + or -oriented moments along the c-axis which can be changed easily. A single crystal of UNiGa was grown in FOM-ALMOS at the University of Amsterdam by a modified Czrochalski technique from a stoichiometric melt. A small portion of resulting single-crystalline sample was checked by means of X-ray Laue diffraction and by micro-probe analysis and was found to be stoichiometric and single crystalline within the experimental error. For IxSR spectroscopy studies, plates oriented perpendicular to the c-axis with thickness of 0.4 mm were spark eroded and mounted on a silver sample holder covering about 300 mm 2 in total. The txSR studies were performed on the General Pur-pose Surface-Muon Spectrometer arM3 at the Paul Scher-rer Institute. The recorded depolarization functions could be described by combining several exponential functions and were thus characterized by initial asymmetries, damp-ing rates and characteristic frequencies.

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