Magnetic properties of nanostructured ball-milled Fe and Fe₅₀Co₅₀alloy

Abstract

Nanostructured Fe and Fe 50 Co 50 powders were prepared by high-energy ball milling. Microstructural and magnetic properties changes with milling time were followed by x-ray diffraction, differential scanning calorimetry and vibrating sample magnetometry. The nonequilibrium microstructure originates from a grain size reduction to about 12 nm and the introduction of internal strain up to 1.5% (root-mean-square strain). The occurrence of disorder in the ball-milled powders is evidenced by the broad exothermic reaction during the heating of ball-milled samples, the variation of lattice parameters and the increase of the saturation magnetization during the first 3 h of milling for Fe and continuously for the Fe 50 Co 50 powder mixture. According to both the reduction of Fe Curie temperature, T c , and the increase of the phase transformation T α→γ , the paramagnetic temperature domain of nanostructured bcc α-Fe is extended by about 50 • C. The Fe 50 Co 50 nanostructured powder behaves as a soft ferromagnet with low values of both the coercive field and the squareness ratio M r /M s .

Thermal Stability of the Nanostructured Powder Mixtures Prepared by Mechanical Alloying

“…Figure 6. Evolution of the Curie temperature and the lattice parameter of the Fe powders as a function of milling time [7]. decreased by about 10 K from that of coarse-grained Gd while the magnetic transition is broader [49].…”

“…[1]. A broad range of alloys, solid solutions, intermetallics and composites have been prepared in the nanocrystalline, quasicrystalline or amorphous state [2][3][4][5][6][7][8][9][10]. A significant increase in solubility limit has been reported in many mechanically alloyed systems [11,12].…”

Comparison of disorder induced by annealing and quench and by ball‐milling in B2 FeCo

“…Iron-cobalt based alloys exhibit interesting magnetic properties, with high Curie temperatures, high saturation magnetization, high permeability and low losses [1,5]. In the Slater-Pauling curve of bulk magnetization versus Co concentration, the maximum magnetization occurs at about 30 at.% of Co [3].…”

“…Highenergy ball-milling can promote the formation of amorphous phases, nanostructured materials, and crystalline metastable phases [4,5]. Mechanical processing techniques produce a high density of defects, vacancies, grain boundaries and ultra-fine to nanosized grains [1,4,5].…”

“…The high density of defects, especially vacancies and grain boundaries, enhance the kinetics of ordering, enabling studies at low temperatures and practical times. Many studies were and are still devoted to mechanical alloying of iron-rich Fe-Co alloys (see among others [1,[5][6][7]). Our aim is to study order-disorder transformations in pseudo-binary Fe (1-x)/2 Co (1-x)/2 M x prepared by mechanical alloying, where M is an element which has a limited solubility in FeCo and x is typically less than 0.2.…”