TRISP is a high-resolution neutron spectrometer combining the three axes and neutron resonance spin echo (NRSE) techniques. The design of TRISP is optimized for the study of intrinsic linewidths of elementary excitations (phonons, magnons) with an energy resolution in the µeV region over a broad range of momentum and energy transfers. Compared to conventional three axes spectrometers (TAS), this corresponds to an improvement of the energy resolution of one to two orders of magnitude.
TRISP also incorporates the Larmor diffraction (LD) technique, which allows to measure lattice spacings with a relative resolution Δd/d = 1.5 · 10-6, i.e. one to two orders of magnitude better than conventional neutron or X-ray diffraction. Absolute d-values can be determined by calibrating the instrument against an Si standard. The main applications of LD include thermal expansion under pressure and low or high temperature, and distributions of lattice constants (second order stresses). LD thus is unique in a parameter region, where standard methods such as dilatometry fail.
- Measurement of the intrinsic linewidths of phonons (fig. 2, see gallery)
- Measurement of the instrinsic linewidths spin excitations (fig. 3).
- Larmor diffraction is used to determine thermal expansion and second order stresses under pressure and at low or high temperature (fig 4).
Besides the standard FRM II sample environment a dedicated dilution cryostat with a base temperature of 6 mK is available.
- thermal beam tube SR5
polarizing supermirror bender
1.3 Å-1 < ki < 7.0 Å-1
- Velocity selector
Astrium type, as higher order wavelengths filter
- PG (002) or (004)
variable focussing horizontal and vertical
- PG (002)
variable horizontal focussing
- Heusler (111) (polarized neutrons)
variable horizontal focussing
- Resonance spin echo, enclosed by mu-metal magnetic screen.
Dr. Thomas Keller
Prof. Dr. Bernhard Keimer
Linewidth of a dispersive excitation
Figure 1: Measurement of the linewidth of a dispersive excitation at TRISP: The TAS background spectrometer defines a resolution ellipsoid in the (q, ω)-space (blue ellipse), the spin-echo enhances the energy resolution within the resolution ellipsoid. Tuning of the spin-echo resolution (red line) to the group velocity of excitations is achieved by rotating the RF spin flip coils. A detailed analysis of the resolution properties is given by K. Habicht et al., J. Appl. Cryst. 36, 1307 (2003).
Linewidths of transverse acoustic phonons
Figure 2: Linewidths of transverse acoustic phonons along q = (ξ, ξ , 0) in Pb at selected temperatures. Several anomalies are visible, which are not predicted by state-of-the-art ab initio calculations (gray symbols). (P. Aynajian et al., Science 319, 1510 (2008)).
Intrinsic magnon linewidth
Figure 3: Intrinsic magnon linewidth Γ in antiferromagnetic MnF2 at temperatures ranging from 15 to 40 K, as a function of q. We have plotted [Γ (T, q) – Γ (3 K, q)], where Γ (3 K, q) is given in the inset. (S. Bayrakci et al., Science 312, 1927 (2006))
Temperature dependence of magnetic and electronic contributions
Figure 4: Temperature dependence of magnetic and electronic contributions, a2, of the lattice constant of MnSi at various pressures measured by Larmor-diffraction. The inset displays changes of the lattice constant at ambient pressure versus T2 as normalized to a0 = 4.58Å. The relative resolution is Δd/d=1.5×10-6 (C. Pfleiderer et al, Science 316, 1510, (2008)).