A HIGH RESOLUTION HARD X-RAY DIFFRACTOMETER AND ITS APPLICATION TO THE STUDY OF MAGNETIC PHASE TRANSITIONS

Klaus-Dieter Liß (1), Agnes Royer (1), Tapan Chatterji (2)

(1) European Synchrotron Radiation Facility, B.P. 220  F-38043 Grenoble Cedex
(2) Institut Max von Laue - Paul Langevin, B.P. 156,  F-38042 Grenoble Cedex
e-mail: liss@esrf.fr
 

The high resolution triple axis diffractometer at the high energy beamline ID15A at ESRF is presented. X-ray energies around 100 keV allow to investigate bulk material of heavier element composition. The high resolution of 5·10^-7 transverse and 5·10^-6 longitudinal is demonstrated on a perfect silicon sample with a regular pattern of deep pores etched into one of its surfaces. Using the right scattering strategy this reveals a large number of satellites in a reciprocal space map [1]. Non-perfect samples up to a certain mosaic spread can be accessed straight forward by the high longitudinal resolution and has been applied to investigate thermal expansion of a series of materials. Spin ordering couples through magnetoelastic effects to the lattice parameter revealing expansion anomalies in the anti-ferromagnet EuAs₃ or even a change of space group at the anti-ferromagnetic phase transition in MnS₂ [2]. The anormal thermal expansion of the newly discovered inorganic Spin-Peierls system a'-NaV₂O₅ has been compared to the temperature dependence of the intensity of the 3/2 1/2 15/4 superstructure reflection below the phase transition temperature T_SP and a simple extrapolation gives the critical exponent of the second order transition [3].
 

References:

[1] K.-D. Liss, A. Royer, T. Tschentscher, P. Suortti, A. P. Williams, "On high resolution reciprocal space mapping with a triple crystal diffractometer for high energy X-rays"  Journal of Synchrotron Radiation, (1998). 5: p. 82-89.

[2] T. Chattopadhyay, K.-D. Liss, T. Tschentscher, "Anomalous thermal expansion due to magnetism in EuAs₃ and MnS₂", in "ESRF highlights". (1997), p. 19. or
http://www.esrf.fr/exp_facilities/id15a/science/expansion_1997/expansion.html

[3] T. Chatterji, K.-D. Liß, G. J. McIntyre, M. Weiden, R. Hauptmann, C. Geibel, "Has NaV₂O₅ a spin-Peierls ground state?"  Physical Review Letters, (1998). submitted.
 

The figure presents the temperature variation in a'-NaV2O5 in lattice spacing Dd/d along [005]. The inset on the right bottom shows the log-log plot of normalized strain e/e0 against reduced temperature t in the critical regime. The inset on the left top shows a plot of strain Dd/d along [005] at different temperatures below TSP against the integrated intensity of the 3/2,1/2,15/4 superlattice reflection which is the square of the order parameter .