The Reconstructive Crystal Structure and the Exchange Energy
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0966-T10-20
The Reconstructive Crystal Structure and the Exchange Energy Ahmad Yazdani, Reza Osati Araghi, and Farid Arya Tarbiat Modares University, Tehran, Iran
ABSTRACT In order to describe the role of temperature variation on suppress of broad range of magnetic transition, the effect of annealing on different samples of a Gd-based intermetallic compound (i.e., Gd2Au) is investigated. The X-ray, AC and D.C susceptibility and electrical resistivity measurements for different annealed samples revealed that: (i) A great exchange dispersion is observed in A.C susceptibility (ii) This unstable exchange can be stabilized at certain annealing temperature, where the short rang unstable Ferromagnetic (F.M) breaks down or even changes to an Antiferromagnetic (AF.M) stable state. (iii) The DC susceptibility shows a spin-glass like transition temperature at TN= 61 K, above which the compound exhibits a completely paramagnetic (P.M) behavior and is field independent. (iv) the iso-thermal magnetization does not follow the field induced transition (F.I.T) and behaves completely paramagnet which is independent of the field up to the highest available fields. The electrical resistivity measurement shows: a) A pronounced sharp bend at TN=61 K is manifested in ρ(T). b)some strong peak of X-ray pattern change into double adjacent lines in some intervals of low temperatures
INTRODUCTION Beside the contradictory results reported on magnetic behavior of the isostructure of Gd2Au (Gd2Al) [1,2],some contradiction are also exist in the results concerning the magnetic ordering of Gd2Au [3,4,5].It is not clear whether non Curie ñ Weiss law with AF.M state at TN= 61K (in low field)[3] or the CñW law ìθpî in high field with F.M state at TC=161K > θp=125K [4] are dominant characteristics of this system where the broad high shouldering transition temperature is strongly field dependent. It seems that despite the wealth of experimental data, the microscopic origins of unusual double magnetic transition are not yet understood. However, to explain the role of exchange fluctuations as an important factor in such system [6,7], we need to visualize the role and identity of c.e that is affected by exchange interaction, since the latter between localized 4f is mediated by conduction electron[8]. Though in the case of Gd, it is shown that 5d states form a shoulder at the Fermi level [9]. In this discussion we show that Gd2Au compounds exhibit an intrinsic antiferromagnetic behavior at a certain temperature(i.e., TN=61K, where a cusp appears) above which all internal magnetic fields as fluctuated local field are vanished at certain annealed temperature. This is an interesting result since unlike the previous studies [4,5] that claim an unstable magnetic behavior for Gd2Au compounds we show a stable antiferromagnetic state for a particular annealing process. However, the heat treatment process is
applied in terms of the fluctuation and distribution of exchange around the definite local field. This process stabilizes the system by two spin-lattice rel
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