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Etude expérimentale et théorique de la relaxation des moments magnétiques dans un verre de spin Ising

Abstract : We study dynamical properties of the metallic Ising spin glass compound FexTiS2 where iron atoms are intercalated in a layered structure. SQUID static magnetization as well as structural characterizations measurements (powder method, Rietveld refinement) are presented so as to understand the complex phase diagram of this alloy. We study the form of the spin relaxation function. One of the interests of working with such an anisotropic material is to be close to models used by theorists and numerical simulations. This ones, for temperatures below Tg and for T = Tg, shows an algebraic behavior of the relaxation function. With the aim of giving an insight into the dynamics above Tg, muon depolarization (mSR) (for x = 2, 3 and 5 %) and neutron spin echo (NSE) (x = 20 and 36 %) experiments are carried out. These two spectroscopy techniques together give access to a time window extending approximately from nanosecond to microsecond. Both reveal quasi-static character and a quite slow spin dynamics, but in the case of mSR, the shape of the dynamical spin-spin autocorrelation function q(t) is indirectly determined with the help of a new depolarization model. Analysis of our experimental spectra are conducted by the comparisons with curves drawn from numerical calculus based on this model and by fits using assumptions for q(t). The results are coherent with q(t) taking an Ogielski form and the thermal variations of the microscopic parameters agree well with simulations of 3D Ising spin systems. We note qualitative differences of dynamics between this quasi Ising compound and Heisenberg alloys such as AuFex and AgMnx. For this last one, observation of the spectra clearly indicates a quasi-algebraic spin relaxation.
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Contributor : Fatih Gulener <>
Submitted on : Wednesday, November 27, 2002 - 10:28:33 PM
Last modification on : Wednesday, April 17, 2019 - 1:19:12 AM
Long-term archiving on: : Tuesday, September 11, 2012 - 6:15:22 PM

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Fatih Gulener. Etude expérimentale et théorique de la relaxation des moments magnétiques dans un verre de spin Ising. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 2001. Français. ⟨tel-00001917⟩

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