Magnetic and Fermi surface properties of CePd5Al2 and PrPd5Al2

We succeeded in growing single crystals of the antiferromagnet CePd5Al2 and the paramagnet PrPd5Al2 with a tetragonal crystal structure by the Bridgman method, and studied the magnetic and Fermi surface properties by measuring the electrical resistivity, magnetic susceptibility, magnetization, specific heat, and de Haas-van Alphen (dHvA) oscillation. We constructed the crystalline electric field (CEF) scheme from the experimentally observed anisotropic magnetic susceptibility and magnetization of CePd5Al2 and PrPd5Al2. In both compounds, the B20 value in the CEF parameters is negative and large, implying that the magnetic easy axis is the [001] direction. The present magnetism of CePd5Al2 and PrPd5Al2 is highly different from that of the heavy fermion superconductor NpPd5Al2 with the magnetic easy axis of the [100] direction. From the dHvA experiment for CePd5Al2 and PrPd5Al2, we observed a few dHvA branches, which correspond to nearly cylindrical band-32 hole and band-33 electron Fermi surfaces of the non-4f reference LaPd5Al2. Reflecting the anisotropy of effective masses based on the nearly cylindrical Fermi surfaces along the tetragonal [001] direction, the upper critical field Hc2 for H parallel [100] in the pressure-induced superconductor CePd5Al2 is larger than that for H parallel [001]: -dHc2/dT=100 kOe/K for H parallel [100], and -dHc2/dT=18 kOe/K for H parallel [001] at the superconducting transition temperature Tsc=0.9 K. This anisotropy in Hc2 is also highly different from that of NpPd5Al2, suggesting that superconductivity is closely correlated with magnetism. (author)