Complex transport and magnetism of the ternary boride YbPt5B2

Novel ternary platinum borides ${\mathrm{YbPt}}_{5}{\mathrm{B}}_{2}$ and ${\mathrm{LuPt}}_{5}{\mathrm{B}}_{2}$ have been synthesized by arc melting of constituent elements and subsequent annealing at 1020 K. The unit cell of ${\mathrm{YbPt}}_{5}{\mathrm{B}}_{2} {[\mathrm{YbPt}}_{5}{\mathrm{B}}_{2}$ type, monoclinic space group $C2/m, a=15.4982(6)\phantom{\rule{0.28em}{0ex}}\AA{}, b=5.5288(3)\phantom{\rule{0.28em}{0ex}}\AA{}, c=5.5600(3)\phantom{\rule{0.28em}{0ex}}\AA{}, \ensuremath{\beta}=105.367{(3)}^{\ensuremath{\circ}}$, 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. ${\mathrm{LuPt}}_{5}{\mathrm{B}}_{2}$ was found to be isotypic (Rietveld refinement of powder x-ray diffraction data). ${\mathrm{YbPt}}_{5}{\mathrm{B}}_{2}$ exhibits two magnetic phase transitions at ${T}_{\mathrm{mag}1}\ensuremath{\sim}8\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{mag}2}\ensuremath{\sim}4\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ as deduced from specific heat, magnetostriction, electric resistivity, and magnetization data. The Kadowaki-Woods ratio of $1.22\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.28em}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{cm}{(\mathrm{mol}\phantom{\rule{0.28em}{0ex}}\mathrm{K}/\mathrm{mJ})}^{2}$ classifies ${\mathrm{YbPt}}_{5}{\mathrm{B}}_{2}$ as a heavy fermion system. A magnetic phase diagram was established, using magnetostriction and magnetoresistance data. Nonmagnetic ${\mathrm{LuPt}}_{5}{\mathrm{B}}_{2}$ is characterized by a simple metallic behavior.