Design and commissioning of a high magnetic field muon spin relaxation spectrometer at the ISIS pulsed neutron and muon source

Abstract

Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. The high magnetic field (HiFi) muon instrument at the ISIS pulsed neutron and muon source is a state-of-the-art spectrometer designed to provide applied magnetic fields up to 5 T for muon studies of condensed matter and molecular systems. The spectrometer is optimised for time-differential muon spin relaxation studies at a pulsed muon source. We describe the challenges involved in its design and construction, detailing, in particular, the magnet and detector performance. Commissioning experiments have been conducted and the results are presented to demonstrate the scientific capabilities of the new instrument.

Studies of a Large Odd‐Numbered Odd‐Electron Metal Ring: Inelastic Neutron Scattering and Muon Spin Relaxation Spectroscopy of Cr8Mn

“…Indeed, the peak is larger than the expected variation in background in this field range. If we interpret the data in this way then, assuming linear variation of A ( t =0) either side of the crossing, we estimate this occurs with a centre at B cross =3.73(5) T. Since we expect a minimum in the asymmetry as a function of the applied field, in correspondence of the level crossing,22 superimposing this minimum on the increase in A ( t ) caused by the field‐dependent change in α would then result in the behaviour we observe. Assuming this model, then a subtraction of an estimated background contribution (grey line, bottom‐right inset, Figure 9) leads to the resonance shown in the upper panel of the right inset, Figure 9, which has a full width half maximum of around 0.5 T. The precise width of a resonance derived in this way is highly dependent on the model used to fit the background, but is generally much larger than that expected for a pure level crossing involving states of different symmetries.…”

The new high field photoexcitation muon spectrometer at the ISIS pulsed neutron and muon source

“…The HiFi spectrometer is built around the 5T superconducting split pair magnet (and fast-sweep z-axis coils up to 40 mT as well as 15 mT x-and y-axis transverse coils) with a room temperature internal bore along the beam axis, which contains the detectors and four transverse ports (sides, top, and bottom). 21 These ports form a "cruciform" which is usually pumped and provides an insulating vacuum for cryostats. As shown in Fig.…”

“…20 One of the spectrometers, HiFi, can apply a magnetic field on a sample up to 5 T, and is optimized for time-differential muon spin relaxation studies. 21 Such high field is especially useful in the avoided level-crossing (ALC) resonance technique, which probes the Mu energy states by scanning and finding a field where two Mu levels cross over. [2][3][4]22 At the specific field the muon spin is depolarized either because 1) the muon polarization is transferred to neighboring nuclear spins due to quantum mechanically coupled states (so-called ∆ 0 transition), or 2) the muon spin flips due to its precession around the symmetry axis of Mu (this ∆ 1 transition is usually only observable in solids).…”

“…The target jig has also been imaged with the low-light CCD camera used for observing the muon beam spot. 21 Once the beam path is defined, two iris diaphragms aligned to the DL beam are positioned far apart on the optical table. The real laser beam is then aligned to the irises, and normally follows the pre-defined beam path down to the sample.…”

Quantum-critical spin dynamics in a Tomonaga-Luttinger liquid studied with muon-spin relaxation

“…The reason for this were limitations in the high-field/low-temperature capabilities of existing μ + SR instruments and the difficulty of such experiments. The commissioning of the worldwide-unique HiFi instrument at ISIS, U.K. [11] now enables μ + SR to probe spin dynamics in longitudinal fields up to 5 T at 20 mK. The longitudinal (field parallel to initial muon spin) configuration is necessary for probing spin dynamics.…”