Terahertz spectroscopy of AuFe spin glasses
- PDF / 289,647 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 4 Downloads / 229 Views
ORDER, AND PHASE TRANSITIONS IN CONDENSED SYSTEMS
Terahertz Spectroscopy of AuFe Spin Glasses A. S. Prokhorova, V. B. Anzina, D. A. Vitukhnovskiœa, E. S. Zhukovaa, I. E. Spektora, B. P. Gorshunova,*, S. Vongtragoolb, M. B. S. Hesselberthb, J. Aartsb, G. J. Nieuwenhuysb, M. Dummc, D. Faltermeierc, S. Kaiserc, S. Yasinc, M. Dresselc, and N. Drichkoc,d a
Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow, 119991 Russia b Kamerlingh-Onnes Laboratory, Leiden University, 2300 RA, Leiden, The Netherlands c Physikalisches Institut 1, Universität Stuttgart, D-70550 Stuttgart, Germany d Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia * e-mail: [email protected] Received July 11, 2006
Abstract—The electrodynamic response of spin glasses (in the form of thin AuFe films) in the terahertz frequency range has been studied using backward-wave oscillator (BWO) spectroscopy (10–40 cm–1) and optical ellipsometry (5000–33000 cm–1) techniques at temperatures from 5 to 295 K. The room-temperature dynamic conductivity spectra of AuFe films are typical of metals and can be described within the framework of the Drude theory of conduction by free charge carriers. Changes in the microscopic parameters of charge carriers in AuFe films with increasing iron content, which are related to additional scattering of carriers on the impurity magnetic moments, have been studied on the quantitative level, including the carrier relaxation frequency and characteristic time, plasma frequency, and conductivity. It is established that the spin-glass phase at a temperature of ~5 K exhibits dispersion of the conductivity in the frequency range 10–40 cm–1, which can be related to the appearance of a mobility gap in the subsystem of free electrons involved in the RKKY interaction between magnetic centers (Fe atoms). PACS numbers: 75.50.Lk, 78.66.-w, 78.30.Er DOI: 10.1134/S1063776106120065
1. INTRODUCTION The properties of spin glasses and the phenomena taking place in such systems are among the most important issues in modern solid state physics [1–3]. It is commonly believed that spin glasses in fact represent solids in a new magnetic state, the properties of which are both of basic importance and of considerable interest for practical applications. Spin glasses possess a number of special properties which distinguish them from other magnetic materials. The most pronounced manifestations of this specificity are (i) the presence of a sharp break at the freeze point (Tf) in the temperature dependence of the magnetic susceptibility and (ii) a strong dependence of the shape and position of this break on the probing magnetic field. Indeed, as the magnitude and frequency of the probing field increase, the break becomes less sharp and Tf grows (see, e.g., [4]). The imaginary part of the magnetic susceptibility is small at temperatures above Tf and exhibits a broad maximum below Tf . The break in the susceptibility is indicative of the possible phase transition to a spinglass state. At the same ti
Data Loading...
