Low temperature phase transitions and magnetic structure of PrB6

Specific heat, thermal expansion and electrical resistivity measurements on PrB6 single crystals show that there are two low temperature phase transitions at 6.9 and 4.2 deg K, respectively, the latter temperature varying somewhat among different crystals. Neutron diffraction measurements were made on both single and polycrystalline samples of PrB6. The neutron data indicate a spontaneous incommensurate magnetic ordering at 6.9 deg K with Q = (0.23, 0.23, 0.5) 2 pi /ao. At 4.2 deg K a commensurate magnetic phase is seen with Q = (0.25, 0.25, 0.5) 2 pi /ao coexisting with the incommensurate phase. At 1.74 deg K, only the commensurate phase remains. A model is proposed for the commensurate antiferromagnetic structure and a profile analysis based on that model yields a magnetic moment of 1.77 Bohr magnetons per praseodymium ion at 1.74 deg K. 10 ref.--AA