Depth dependent spin dynamics of canonical spin glass films: A low-energy muon spin rotation study

We have performed depth dependent muon spin rotation/relaxation studies of the dynamics of single layer films of {\it Au}Fe and {\it Cu}Mn spin glasses as a function of thickness and of its behavior as a function of distance from the vacuum interface (5-70 nm). A significant reduction in the muon spin relaxation rate as a function of temperature with respect to the bulk material is observed when the muons are stopped near (5-10 nm) the surface of the sample. A similar reduction is observed for the whole sample if the thickness is reduced to e.g. 20 nm and less. This reflects an increased impurity spin dynamics (incomplete freezing) close to the surface although the freezing temperature is only modestly affected by the dimensional reduction

Asymmetric Lineshape due to Inhomogeneous Broadening of the Crystal-Field Transitions in Mn12ac Single Crystals

The lineshape of crystal-field transitions in single crystals of Mn12ac molecular magnets is determined by the magnetic history. The absorption lines are symmetric and Gaussian for the non-magnetized state obtained by zero-field cooling (zfc). In the magnetized state which is reached when the sample is cooled in a magnetic field (fc), however, they are asymmetric even in the absence of an external magnetic field. These observations are quantitatively explained by inhomogeneous symmetrical (Gaussian) broadening of the crystal-field transitions combined with a contribution of off-diagonal components of the magnetic susceptibility to the effective magnetic permeability.Comment: 4 pages, 3 figure

Stoichiometry determination of VOx thin films by O-18-RBS spectrometry

This paper reports on the stoichiometry determination of epitaxially grown vanadium monoxide (VOx) thin films on MgO(100) substrates. The epitaxial growth was confirmed by RHEED, LEED and XRD techniques. The oxygen content of VOx thin films, as a function of oxygen flux, was determined using Rutherford backscattering spectrometry. The 18O isotope was used for film growth, in order to distinguish between the oxygen of film and substrate. The upper and lower stoichiometry limit found are consistent with the ones known for bulk material

High-frequency magnetic spectroscopy on the molecular magnetic cluster V-15

Vongtragool S, Gorshunov B, Mukhin AA, van Slageren J, Dressel M, Müller A. High-frequency magnetic spectroscopy on the molecular magnetic cluster V-15. PHYSICAL CHEMISTRY CHEMICAL PHYSICS. 2003;5(13):2778-2782.A novel type of high-frequency magnetic resonance spectroscopy was used to investigate magnetic excitations of the molecular magnetic cluster V-15 in the frequency range from 1.5 cm(-1) to 10 cm(-1), at low temperatures, between 2.5 K and 30 K. In the optical transmission spectra, we observed absorption lines over a wide range of magnetic fields up to 6.5 T, which correspond to the Zeeman splitting of the low-lying spin states. Our frequency-domain technique, and advanced data analysis allow accurate determination of the principal values of the anisotropic g tensor, and other mode parameters, even for powder samples. The g values were obtained as gparallel toc = 1.981 +/- 0.003 and g(perpendicular toc) = 1.953 +/- 0.003, while the intrinsic linewidth was found to be Deltanu = 0.02 - 0.035 cm(-1) ( 210 - 370 Oe). The temperature dependence of Deltamu, the mode contribution to the magnetic permeability, is in good agreement with theory

Frequency-domain magnetic resonance spectroscopy of molecular magnetic materials

van Slageren J, Vongtragool S, Gorshunov B, et al. Frequency-domain magnetic resonance spectroscopy of molecular magnetic materials. PHYSICAL CHEMISTRY CHEMICAL PHYSICS. 2003;5(18):3837-3843.A brief review is presented of a novel method of high-frequency magnetic resonance spectroscopy, which sweeps the frequency at a fixed magnetic field, including zero field. We describe the main features of this frequency-domain spectrometer which works in the spectral range from 30 GHz to 1.5 THz and at magnetic fields up to 8 T; the temperature can be as low as 0.4 K. The versatility of this technique is demonstrated by means of a number of examples from the field of molecular magnetism

Charge Localization due to RKKY Interaction in the Spin Glass AuFe

PACS. 75.50.Lk – Spin glasses and other random magnets. PACS. 71.55.Jv – Disordered structures; amorphous and glassy solids. PACS. 72.15.Rn – Localization effects (Anderson or weak localization). Abstract. – Measurements of electrodynamic response of of spin glass AuFe films in comparison with pure gold films are performed at frequencies from 0.3 THz (10 cm −1) up to 1000 THz (33000 cm −1) using different spectroscopic methods. At room temperatures the spectra of pure gold and of AuFe are typically metallic with the scattering rate of carriers in AuFe being significantly enlarged due to scattering on localized magnetic moments of Fe ions. In the spin-glass phase of AuFe at T = 5 K a pseudogap in the conductivity spectrum is detected with the magnitude close to the Ruderman-Kittel-Kasuya-Yosida (RKKY) energy for AuFe: ∆RKKY ≈ 2.2 meV. The origin of the pseudogap is associated with partial localization of electrons which mediate the RKKY interaction between localized magnetic Fe centers. Introduction. – Phenomena in spin glasses represent one of the central topics of modern solid state physics; they are of fundamental interest and also have a variety of possible applications [1]. The spin-glass state is realized in intermetallic alloys, for instance, when ions of