Neutron scattering studies on URu₂Si₂

Abstract

This paper aims to review some of the neutron scattering studies performed on URu₂Si₂ in Grenoble. This compound has been studied for a quarter of century because of a so-called hidden-order ground state visible by most of the bulk experiments but almost invisible by microscopic probes like neutrons, muons NMR or X-ray. We stress on some aspects that were not addressed previously. Firstly, the comparison of the cell parameters in the 1-2-2 systems seems to point that the magnetic properties of URu₂Si₂ are leading by an U⁴⁺ electronic state. Secondly, a compilation of the different studies of the tiny antiferromagnetic moment indicates that the tiny antiferromagnetic moment has a constant value which may indicate that it is not necessarily extrinsic. We also present the last development on the magnetic form factor measurement in which the magnetic density rotates when entering in the hidden-order state. To end, the thermal dependence of the two most intense magnetic excitations at Q₀ = (1,0,0) and Q₁ = (0.6,0,0) seems to indicate two different origins or processes for these excitations.

Keywords:

• heavy-fermion
• hidden-order
• URu₂Si₂

Acknowledgements

We thank D. Aoki, E. Ressouche, R. Ballou, J. Flouquet, J.P. Sanchez and J.P. Brison for helpful discussions.

Notes

1 In the Ref. [47], we used the damped harmonic oscillator plus a quasi-elastic functions contribution instead of the damped magnetic excitation function.

2 A high-quality single crystal of with a rod shape of 8 mm high and 4 mm diameter with as vertical axis, grown by the Czochralski method in tetra-arc furnace, already used for the inelastic neutron scattering measurements at the wave-vector was installed on the thermal triple-axis IN22 CEA-CRG at ILL. The spectrometer was set up in its polarized configuration. The experiment was performed with a fixed final energies of 14.7 meV (). The beam was polarized by a Heusler monochromator vertically focusing and analysed in energy, and polarization by a Heusler analyser vertically and horizontally focusing. The flipping ratio was around 17 and the energy resolution was 0.95 meV. No collimation was installed. The background was reduced by slits placed before and after the sample. The inelastic scans were performed with Q parallel to the -axis in the non-spin-flip channel which provides all the necessary information (See Table C1 in Appendix 3). The intensities of the scans were corrected of monitor error due to harmonic wavelength neutron contamination. The difference of scans gives the dynamical magnetic response (not corrected of the Bose factor) with, for example, the transverse susceptibility and the longitudinal susceptibility.

4 The Dirac’s function: .

Part of this work was supported by Euromagnet II via the EU under Contract No. RII3-CT-2004-506239, ERC starting grant (NewHeavyFermion) and French ANR projects (CORMAT, SINUS, MAGFINS).