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

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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 characterized by means of single-crystal x-ray diffraction, complemented with microprobe analysis, magnetic susceptibility, resistivity and heat capacity measurements. Ln(Cu,Ga)12 and Ln(Cu,Al)12 of the ThMn12 structure type crystallize in the tetragonal I4/mmm space group with lattice parameters a∼8.59 and c∼5.15 and a∼8.75and c∼5.13 for Ga and Al containing compounds, respectively. For aluminium containing compounds, magnetic susceptibility data show Curie-Weiss paramagnetism in the Ce and Pr analogues down to 50K with no magnetic ordering down to 3K, whereas the Yb analogue shows a temperature-independent Pauli paramagnetism. Sm(Cu,Al)12 orders antiferromagnetically at TN∼5K and interestingly exhibits Curie-Weiss behaviour down to 10K with no Van Vleck contribution to the susceptibility. Specific heat data show that Ce(Cu,Al)12 is a heavy fermion antiferromagnet with TN∼2K and with an electronic specific heat coefficient γ0 as large as 390mJK2mol-1. In addition, this is the first report of Pr(Cu,Al)12 and Sm(Cu,Al)12 showing an enhanced mass (∼80 and 120mJK2mol-1). For Ga containing analogues, magnetic susceptibility data also show the expected Curie-Weiss behaviour from Gd to Er, with the Yb analogue being once again a Pauli paramagnet. The antiferromagnetic transition temperatures range over 12.5, 13.5, 6.7, and 3.4K for Gd, Tb, Dy, and Er. Metallic behaviour is observed down to 3K for all Ga and Al analogues. A large positive magnetoresistance up to 150% at 9T is also observed for Dy(Cu,Ga)12. The structure, magnetic, and transport properties of these compounds will be discussed. © 2010 IOP Publishing Ltd.

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Journal of Physics Condensed Matter

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