MAGNETIC ORDERING OF PUBI
A neutron diffraction study of a single crystal of PuBi has been performed. In zero magnetic field PuBi orders antiferromagnetically below T-N = 57 +- 1 K. The magnetic ordering is characterized by a wave vector k = /OOk/ and a longitudinal polarization: m--k // k. k is independent of temperature (k - 0.22 - 0.002 r-in, down to 1.5 K.) This absence of temperature dependence suggests commensurate nature of the ordering which is also documented by the presence of third order harmonics. The magnetic structure can be represented by a long period square wave slightly different from a (4+4-) sequence of ferromagnetic (001) planes. The application of a magnetic field along the /100/ axis induces no change of the antiferromagnetic structure up to a transition to the paramagnetic saturated state. The critical field is rather large. This study allows some comments on the plutonium monopnictides. PuP, PuAs, PuSb and PuBi the magnetic moments are quenched along /001/ directions by a strong anisotropy. The Pu**3+ magnetic moment value is nearly constant among the monopnictide serie. The ordering temperature decreases with increasing atomic separation, the magnetic ordering goes from ferromagnetism (PuP, PuAs, PuSb) to antiferromagnetism (PuSb, PuBi). However the wave vector is rather small in the incommensurate high temperature phase of PuSb (k = 0.13 at T-N) and in PuBi (k - 0.233) indicating that the exchange interactions vary slowly along the serie of Pu monopnictides and keep a strongly anisotropic character.
Bibliographic Reference: 16EMES JOURNEES DES ACTINIDES, GRAINAU/GARMISCH- PARTENKIRCHEN (GERMANY), APRIL 28-30, 1986 WRITE TO CEC LUXEMBOURG, DG XIII/A2, POB 1907 MENTIONING PAPER E 32859 ORA
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Record Number: 1989125011600 / Last updated on: 1987-01-01
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