Magnetic order of CePdAl under pressure-neutron diffraction study

The heavy-fermion compound CePdAl adopting the hexagonal ZrNiAl type of structure (space group P-62m) orders at ambient pressure antiferromagnetically below 2.7 K with an incommensurate propagation vector q=(0.5 0 τ), τ≅0.35. Two, of the three Ce atoms in the hexagonal unit cell carry magnetic moment of about 1.6-1.8 μ_B, while the remaining one remains frustrated down to at least 35 mK. The application of hydrostatic pressure leads to a suppression of the long-range magnetic order above the critical pressure P_c. The results of neutron diffraction experiments under pressure suggest a value of P_c=0.75 (5) GPa as compared with 0.95 GPa determined from the bulk measurements. At pressures lower than P_c, the magnetic structure of CePdAl seems to be quite robust with a very little temperature-dependent propagation vector and unusual dependence of the magnetic moment. The P-T phase diagram has been constructed.