Magnetooptics in Spin Glasses

Abstract

Magnetooptics we used successfully to deduce the static and dynamic magnetic properties of insulating spin glasses. The Faraday rotation stands as the only available technique to perform dynamical measurements of the magnetization over a very wide time range or of the susceptibility over an extended frequency range. Very recently, Faraday rotation measurements of the phase 1ag of the a.c. susceptibi1itY,with respect to the .modu1ated fie1d~have been sUccessfully used to give the first evidence of a transition at finite temperature in the 3d spin glass Eu 4SrO 6S [I]. In this paper, we report on the first dynamic studies of a 2d-Ising insulating spin g2ass :' Fe O 3MgO C1 2 . The in-phase (X~) and out of phase (X~) comRonents of the susceptibility were measured at low' temperature in the frequency range 1.5 <V<B x 10 Hz. Our results are consistent with a phase transition at T = 0, announced by an extended critical slowing down up to T = 4 K. We also report on the relaxation of the thermoremanent magnetization in the 3 x 10-4 -2 x 10 2 s time range. Results well agree with previous simu1ations in 2d-Ising spin glasses and support the above conclusions.

Static and dynamic evidence for a transition at Tc = 0 in the Ising spin glass Fe0.3Mg0.7Cl2

“…For example the field cooled magnétisation does not reach as flat a plateau as in CuMn but it conserves a slight negative slope in terms of the temperature and remains strongly dependent on the cooling rate [1] . Also, our first dynamic data, obtained from Faraday rotation experiments in the frequency range 1.5-80000 Hz [2,3] , showed that the low temperature slope of x" depends more on frequency than is usual. Furthermore we pointed out that the dynamic critical behaviour was unconventional, not characteristic of a 3d Ising spin glass, but more relevant of 2d Ising spin glasses and we were able to conclude from this study that we had with this system the first example of a spin glass transition occurring at Te = 0.…”

“…In our former a.c. susceptibility study [2,3], we mainly considered the temperature Tf, related to the onset of irreversibilities, where tge = IX" /XI had a constant small value (10-2 ), and assuming that tge = wr/2r [13], we deduced the correspondance between Tf and the characteristic relaxation time T of the system : T(Tf) = 0.01/w. Because of the scatter on the measurement of x" at the lowest frequencies, we have used in the present paper the r(T) dependence obtained from the analysis of the breakaway point between xfj and xeq , as suggested by Carré et aL [14].…”

Analytical expression of the magneto-optical Kerr effect and Brillouin light scattering intensity arising from dynamic magnetization

“…Within this article, we present the analytical dependence of the TR-MOKE and BLS signals for several types of spin-wave modes. Such calculations can serve either for separation of MOKE and BLS signals from a single ferromagnetic (FM) material in a stack of FM layers [16][17][18][19], or for the quantitative determination of the energy carried by each spin-wave mode.…”

Dynamic evidence for a 2d - 3d crossover in the Ising spin glass Fe0.35Mg0.65Br2

“…The second series of experiments has been performed using a magneto-optical method derivated from the Faraday effect [5,11]. The sample used is one of the pieces constituting the stacked sample considered above.…”