Spin dynamics inFe2O3−TeO2glass: Experimental evidence for an amorphous oxide spin glass

Abstract

We have examined spin dynamics including magnetic aging and memory effects as well as critical slowing down for 20Fe 2 O 3 · 80TeO 2 ͑mol %͒ glass. Scaling analysis on critical slowing down reveals that the present glass exhibits a critical behavior as observed in a prototype of spin glasses. Aging and memory effects peculiar to spin glasses have been observed in the magnetically ordered phase of the present glass. These experimental results strongly confirm that the 20Fe 2 O 3 · 80TeO 2 glass is converted into a spin glass phase at a very low temperature. It is thought that a disordered structure of the oxide glass gives rise to randomness and frustration in the magnetic structure, leading to the spin glass phase transition.Spin glass has attracted considerable attention since its experimental discovery, 1 as many vigorous investigations have been carried out to clarify its curious magnetic structure and phase transition. The spin glass system is also a matter of interest from the viewpoint of its analogy to many complex systems, such as associative memory in the brain. 2 One of the most interesting phenomena observed in spin glasses involves spin dynamics. Magnetic moments are frozen in such a way that the direction of each of the magnetic moments is randomly oriented in a spin glass below its transition temperature, and it takes an infinite time to reach a thermodynamic equilibrium state. Experimental, theoretical, and numerical approaches have been performed for clarification of the spin dynamics peculiar to spin glass phase, such as critical slowing down and aging phenomena involving rejuvenation and memory effects. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Amorphous solids derived from ionic compounds, such as oxide and fluoride glasses, bearing a large amount of magnetic ions can be categorized into a lattice in which a disordered distribution of magnetic moments is dominant. There are some reports as to magnetic properties of the oxide and fluoride glasses. Temperature dependence of field-cooled and zero-field-cooled susceptibilities indicates that these glasses exhibit magnetic transitions like those of spin glasses or superparamagnets. For instance, in 1975, just three years after the discovery of a canonical spin glass of Au-Fe alloys, Verhelst et al. found that oxide glasses in a CoO-Al 2 O 3 -SiO 2 system manifest spin glass-like transitions. 19 Assuming the presence of magnetic clusters, they applied a simple superparamagnetic model to the magnetic transition observed in temperature variation of zero-field-cooled susceptibility. For this glass system, the relaxation process of remanent magnetization below the transition temperature was explored by Rechenberg et al. 20 They measured the time dependence of remanent magnetization after the external field was turned off for a field-cooled sample and analyzed the experimental results in terms of the superparamagneic model in which a distribution of anisotropy energy for the superparamagnetic clusters was assumed. Renard et al. examined t...

Magnetic properties of disordered oxides with iron and manganese ions

“…Hence, the superparamagnetic or cluster spin glass-like behaviour may affect the magnetic transition. To clarify thoroughly the mechanism of magnetic transition observed for Fe 2 O 3 -TeO 2 glasses, further measurements such as temperature dependence of non-linear susceptibility are required as described below, although our recent study of spin dynamics on the Fe 2 O 3 -TeO 2 glass with 20 mol% of Fe 2 O 3 undoubtedly confirms that the glass becomes a spin glass phase at very low temperatures [20]. Fig.…”

Preparation and magnetic properties of amorphous EuTiO3 thin films

“…Spin glass (SG)-like magnetic transition of oxide and fluoride glasses has been extensively investigated so far [1][2][3][4][5][6]. In most insulating oxide and fluoride glasses, short-range antiferromagnetic (AFM) superexchange interactions via anions are dominant, as demonstrated by the negative values of Weiss temperature (θ W ) [4][5][6].…”

Spin dynamics in oxide glass of Fe2O3–Bi2O3–B2O3 system

“…In particular, there are few experiments concerning spin dynamics of magnetically ordered phases. Recently we have demonstrated that 20Fe 2 O 3 Á 80TeO 2 (mol%) glass exhibits the spin dynamics involving magnetic aging and memory effects as well as critical slowing down as observed in archetypal spin glasses [8]. In the present investigation, we have carried out experiments relevant to the magnetic aging and memory effects in magnetically ordered phase of 32Fe 2 O 3 Á 48Bi 2 O 3 Á 20B 2 O 3 (mol%) glass prepared by using a conventional melt-quenching method.…”

“…Below spin glass transition temperature, magnetic moments are frozen in such a manner that the direction of each of the magnetic moments is randomly oriented, but it takes an infinite time to reach a thermodynamic equilibrium state. Experimental, theoretical, and numerical approaches have been carried out to clarify the spin dynamics in the spin glass phase such as magnetic aging phenomena involving rejuvenation and memory effects [3][4][5][6][7][8], although these phenomena are not completely understood yet.Amorphous phases of ionic compounds such as oxide and fluoride glasses containing a large amount of magnetic ions are a prototype of a solid in which magnetic moments are randomly distributed. Several investigators reported that oxide glasses containing a large amount of magnetic ions show magnetic transitions as observed in spin glasses or superparamagnets [9][10][11].…”

“…Below spin glass transition temperature, magnetic moments are frozen in such a manner that the direction of each of the magnetic moments is randomly oriented, but it takes an infinite time to reach a thermodynamic equilibrium state. Experimental, theoretical, and numerical approaches have been carried out to clarify the spin dynamics in the spin glass phase such as magnetic aging phenomena involving rejuvenation and memory effects [3][4][5][6][7][8], although these phenomena are not completely understood yet.…”