Complex transport and magnetism of the ternary boride YbPt₅B₂

Abstract

Novel ternary platinum borides YbPt5B2 and LuPt5B2 have been synthesized by arc melting of constituent elements and subsequent annealing at 1020 K. The unit cell of YbPt5B2 [YbPt5B2 type, monoclinic space group C2/m, a=15.4982(6) Å, b= 5.5288(3) Å, c= 5.5600(3) Å, β= 105.367(3)∘, single-crystal x-ray diffraction data] is composed of two structural fragments alternating along the a axis and extending infinitively along the b axis: (i) columns of face-fused, boron-filled, and empty edge-connected trigonal metal prisms, and (ii) zigzag chains of B-filled trigonal prisms connected by common edges. LuPt5B2 was found to be isotypic (Rietveld refinement of powder x-ray diffraction data). YbPt5B2 exhibits two magnetic phase transitions at Tmag1∼ 8 K and Tmag2∼ 4 K as deduced from specific heat, magnetostriction, electric resistivity, and magnetization data. The Kadowaki-Woods ratio of 1.22×10−5μΩcm(molK/mJ)2 classifies YbPt5B2 as a heavy fermion system. A magnetic phase diagram was established, using magnetostriction and magnetoresistance data. Nonmagnetic LuPt5B2 is characterized by a simple metallic behavior.