Low temperature phase transitions and magnetic structure of PrB6

Abstract Specific heat, thermal expansion and electrical resistivity measurements on PrB 6 single crystals show that there are two low temperature phase transitions at 6.9 K and 4.2 K, respectively, the latter temperature varying somewhat among different crystals. Neutron diffraction measurements were made on both single and polycrystalline samples of PrB 6 . The neutron data indicate a spontaneous incommensurate magnetic ordering at 6.9 K with Q = (0.23, 0.23, 0.5) 2 π / a o . At 4.2 K a commensurate magnetic phase is seen with Q = (0.25, 0.25, 0.5) 2 π / a o coexisting with the incommensurate phase At 1.74 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 K.