Structural and magnetic study of nanostructured (Fe79Mn21)80Cu20 alloy synthesized by ball milling

M. MIZRAHI; A. F. CABRERA; S. J. STEWART; H. TROIANI; S. M. COTES; J. DESIMONI

Centro Atómico Constituyentes, CNEA, Gral. San Martín, Prov. Bs. As., Argentina

Congreso; At the frontiers of Condensed Matter II, Magnetism, Magnetic Materials and their Applications; 2004

Centro Atómico Constituyentes, CNEA, Argentina

Iron-Mn based alloys show considerable promise for technological applications. Its physical properties can be modified by the incorporation of miscible or immiscible alloying atoms such as Si or Cu. Since the high-energy ball milling technique allows synthesizing phases far from the equilibrium and very defective nanostructures, our research project is devoted to the study of nanoparticles obtained by this process in the Fe-Mn and Fe-Mn-X (with X=Si, Cu) systems. In particular, the present work is focused in the (Fesubs{79}Mnsubs{21})subs{80}Cusubs{20} composition. Accurate amounts of elemental Fe, Mn, Cu powders were high-energy-ball-milled during 15 hours using a vibratory miller. The sample characterization was performed by X-ray diffraction and transmission electron microscopy (TEM). The magnetic behavior of the particles was analyzed by means of Mössbauer spectroscopy, dc-magnetization and ac-susceptibility measurements. X-ray diffractograms revealed that it{fcc} is the prevailing phase, although a tiny amount of the it{bcc} phase is also present. A dispersion of nanoparticle sizes was detected using TEM. The dark field technique revealed that isolated nanoparticles are constituted by smaller regions (average size 10 nm) with different crystalline orientation among them. The thermal dependence of both the magnetization and susceptibility data were interpreted in relation to the present phases and the influence of the particle size distribution. The Mössbauer spectra were fitted to a component belonging to the antiferromagnetic it{fcc} phase, in addition to a paramagnetic signal. The thermal evolution of these spectra showed that the ordering of the antiferromagnetic greek{g}-FeMn phase occurs at about 180 K, while the other component remains in a paramagnetic state even at the lowest temperature achieved. The influence of the nanostructured and disordered nature of the present phases on the magnetic behaviour is discussed.