Magnetic behavior of metastable fcc Fe-Cu after thermal treatments

Abstract

A ferromagnetic and supersaturated fcc Fe5lCu49 solid solution has been obtained by mechanical alloying. After subsequent thermal treatments the fcc phase undergoes a spinodal decomposition which finally, at 780 K, yields a mixture of fcc and bcc phases. In this work, a systematic magnetic study is carried out on samples at diferent decomposition states in order to determine the process of transformation into the stable phases. We observe a 20% maximum diminution on the magnetic moment with increasing temperatures of the thermal treatment. The Mossbauer spectrum taken at 8 K shows that 20% of the Fe atoms are in a nonferromagnetic state. On the other hand, upon heating up to 723 K the roomtemperature coercive field increases dramatically to 640 Oe, and after cooling down to 10 K it decreases to 270 Oe. Deviations from the T law in the temperature dependence of the magnetization have been observed. This behavior is explained by fluctuations in composition due to the spinodal decomposition, which lead to fluctuations of the magnetic order parameters, i.e. , magnetic moment and Curie temperature.

Near-neighbor mixing and bond dilation in mechanically alloyed Cu-Fe

“…%. 15,25,26,32,33 This technique offers an alternative to rapidquenching techniques to form metastable alloys of elements which are immiscible under equilibrium conditions. Uenishi et al 18 report that the lattice parameter of bcc and fcc HEBM Cu-Fe alloys increase near linearly with increasing concentration of the dilute element, i.e., Cu in bcc Fe and Fe in fcc Cu, reaching a maximum for Cu 50 Fe 50 .…”

“…15,[22][23][24][25][26] In those studies, the degree of chemical and structural shortrange order was indirectly measured using magnetic measurements, x-ray diffraction, and/or thermal analysis. In an earlier study, Harris et 30 sample which had been milled for 20 h, but not in the Ag-based samples, even after 200 h of milling.…”

Microstructure and magnetism of nanoparticles withγ-Fecore surrounded byα-Feand iron oxide shells

“…Up to now, this ␥-Fe phase was observed in small iron precipitates embedded in a Cu matrix, 38 in FeCu mechanically alloyed compounds, 39,40 in the synthesis of carbon nanotubes, [41][42][43][44][45][46][47][48] or in Fe-NPs and thin films but confined down to a few monolayers of thickness. [49][50][51][52][53][54][55] The magnetism of ␥-Fe phase depends strongly on the Fe-Fe interatomic distances 56 although both the morphology of the sample and the particle size could play an important role.…”

Synthesis of multicomponent metallic layers during impulse plasma deposition

“…These kinds of alloys can be precursors for a granular mixture of immiscible elements from which giant magnetoresistance can be derived [8]. As reported by Crespo et al [32,33], the supersaturated and metastable fcc phases undergo a spinodal decomposition, which Phase boundaries obtained by: (A) equilibrium phase boundary at room temperature [11], (B) liquid quenching [14,15], (C) vapor deposition [19], (D) electrodeposition [16,18], (E) sputtering on cryogenic substrates [20], (F) mechanical alloying [23][24][25], and (G) the IPD method (this work).…”

“…Thus, equilibrium in the solid state is characterized by a twophase structure. The immiscible Fe-Cu alloys have been an object of interest of many research groups, and they are well-known and widely studied in the literature [12][13][14][15][16][17][18][19][20][21][22][23][24][25][31][32][33][34]. Therefore, in this work the Fe-Cu system is regarded as a good model to study the formation of non-equilibrium phases.…”