Muons and magnets

Abstract:

We report the results of a muon spin rotation study on electron-doped chromium sulfides, Cr2S3-x, with 0≤x≤0.08. Two muon-spin precession frequencies are observed in each sample, corresponding to two distinct stopping sites. We show that even a small amount of electron doping, induced by sulfur deficiency, causes a drastic change in the magnetic properties. © 2005 The American Physical Society.

Abstract:

We present numerical calculations of a tight-binding model applied to a finite square lattice in the presence of a perpendicular magnetic field. The persistent current associated with each eigenstate is calculated, the chirality of which is determined by whether the eigenstate exists within the bulk or localised to the edges of the lattice. This treatment allows us to extract oscillations in the magnetization, which are analogous to de Haas-van Alphen oscillations. We consider the influence of short range disorder and long range potential modulations on these systems.

Abstract:

We report millimetre-wave electron spin resonance (ESR) measurements on single crystals of the high-spin molecules Cr-10(OMe)(20)(O2CCMe3)(10) and Cr12O9(OH)(3)(O2CCMe3)(15) within a temperature range of 1.4 K to 50 K and in magnetic fields of up to 5 Tesla. In our experiments it is possible to vary the orientation of the magnetic field with respect to the crystal axes, and thus to study the ESR lineshapes as a function of both temperature and angle. Our results confirm that Cr-10(OMe)(20)(O2CCMe3)(10) behaves as a single-molecule magnet with S = 15 and D = -0.03 K, while Cr12O9(OH)(3)(O2CCMe3)(15) has S = 6 and D similar to 0.1 K. A comparison of the experimental spectra with numerical simulations gives good agreement at low temperatures. At higher temperatures, we observe a narrowing of the ESR spectrum that is not explained by simple models.

Abstract:

Spin-polarized muons can be implanted in various molecular magnetic materials in order to measure static and dynamic magnetic field distributions at a local level. The positively-charged muon is an unstable, radioactive particle which has spin-1/2, a lifetime of 2.2 mu s, about one-ninth of the proton mass and a magnetic moment of approximately 1/200 mu(B). Both pulsed and continuous beams of muons can be produced with almost 100% spin polarization and significant intensity at various accelerator facilities. The subsequent decay of the muon into a positron allows the extraction of the muon-spin autocorrelation function which can be related to the magnetic field distribution inside a sample. This experimental technique has found particular application to the problem of hydrogen in semiconductors, as well as the study of the vortex lattice in both high-temperature and organic superconductors. Nevertheless, it has been most widely employed in the field of magnetism. We describe how our experiments using spin-polarized muons have been used to provide information about organic ferromagnets, molecular magnets, spin-chains and single molecule magnets.