Scientific highlight May 2007
First experiments with 7T cryomagnet
W. Hutchison, G. A. Stewart (UNSW), D. Goossens(ANU), K. Nishimura (Toyama U.), A. J. Studer and M. Avdeev (ANSTO)
In-situ neutron diffraction studies on samples under external magnetic field allow a direct link to be established between bulk the magnetic response measured with a magnetometer and changes in the magnetic structure on an atomic level. Recently a vertical field cryomagnet has been aquired reaching a filed as high as 7.2T at temperatures as low as 4.2K. This has opened the door to a completely new class of experiments at OPAL reactor.
A previous powder neutron-diffraction study [1] established that TbNiAl4 is a linear antiferromagnet in the lowest-temperature phase in zero magnetic field, and has an incommensurate structure in an intermediate-temperature phase. The first aim was to explore the intermediate-phase structure in the magnetic field manifold. Magnetisation measuremen
ts on single crystals have indicated that TbNiAl4 has an intermediate moment state between ~4.5 and 9 T at low temperatures and is paramagnetic with full moment above 9 T. Neutron diffraction data were collected at ~5 K and at various magnetic fields up to 6 T. Preliminary results shown in Fig 2 suggest the ferromagnetic moments to be developing along the b axis, this being consistent with a higher susceptibility in that direction. The magnetic phase is commensurate at all fields. Detailed quantitative analysis of magnetic structure is in progress.
[1] W. D. Hutchison, D. J. Goossens, K. Nishimura, K. Mori, Y. Isikawa and A. J. Studer, J. Magn. Magn. Mater. 301, 352 (2006).