Magnetic and Fermi surface properties of CePd₅Al₂ and PrPd₅Al₂

We succeeded in growing single crystals of the antiferromagnet CePd ₅Al₂ 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 PrPd₅Al ₂. In both compounds, the B02 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 PrPd₅Al ₂ 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 H_c2 for H ∥ [100] in the pressure-induced superconductor CePd₅Al ₂ is larger than that for H ∥ [001]: -dH_c2/dT = 100 kOe/K for H ∥ [100], and -dH_c2/dT = 18 kOe/K for H ∥ [001] at the superconducting transition temperature T_sc = 0:9 K. This anisotropy in H_c2 is also highly different from that of NpPd ₅Al₂, suggesting that superconductivity is closely correlated with magnetism.