Crystal growth, structure, and physical properties ofLn(Cu,Al)12 (Ln = Y, Ce, Pr, Sm,and Yb) and Ln(Cu,Ga)12 (Ln = Y, Gd–Er, and Yb)

Abstract

Single crystals of Ln(Cu,Al)12 and Ln(Cu,Ga)12 compounds (Ln = Y, Ce–Nd, Sm, Gd–Ho,and Yb for Al and Ln = Y, Gd–Er, Yb for Ga) have been grown by flux-growth methods and characterizedby means of single-crystal x-ray diffraction, complemented with microprobeanalysis, magnetic susceptibility, resistivity and heat capacity measurements.Ln(Cu,Ga)12 andLn(Cu,Al)12 ofthe ThMn12 structure type crystallize in the tetragonalI4/mmm space group withlattice parameters a∼8.59 Å and c∼5.15 Å and a∼8.75 Å and c∼5.13 Å for Ga and Al containing compounds, respectively. For aluminium containingcompounds, magnetic susceptibility data show Curie–Weiss paramagnetism inthe Ce and Pr analogues down to 50 K with no magnetic ordering down to 3 K,whereas the Yb analogue shows a temperature-independent Pauli paramagnetism.Sm(Cu,Al)12 ordersantiferromagnetically at TN∼5 K and interestingly exhibits Curie–Weiss behaviour down to 10 K with noVan Vleck contribution to the susceptibility. Specific heat data show thatCe(Cu,Al)12 is a heavy fermionantiferromagnet with TN∼2 K and with an electronic specific heat coefficientγ0 as large as390 mJ K2 mol−1. In addition, this isthe first report of Pr(Cu,Al)12 and Sm(Cu,Al)12 showing anenhanced mass (∼80 and 120 mJ K2 mol−1). For Ga containing analogues, magnetic susceptibility data also show the expectedCurie–Weiss behaviour from Gd to Er, with the Yb analogue being once again a Pauliparamagnet. The antiferromagnetic transition temperatures range over 12.5, 13.5, 6.7, and3.4 K for Gd, Tb, Dy, and Er. Metallic behaviour is observed down to 3 K for all Ga and Alanalogues. A large positive magnetoresistance up to 150% at 9 T is also observed forDy(Cu,Ga)12. The structure, magnetic, and transport properties of these compounds will bediscussed.