Antiferromagnetic correlations in Fe-Cu granular alloys: The role of the surface structure

Fe precipitates in a Cu-fcc matrix, prepared using the Bridgeman method and with an average composition of Cu97Fe3, displayed the coexistence of ferro magnetism (FM), spin glass-like (SGL) behavior and antiferromagnetic (AFM) correlations. The two former contributions may be attributed, respectively, to the segregation of FM, alpha-Fe-bcc precipitates and to the few Fe spin s distributed in the matrix. The annealing procedures increased the FM cont ribution and, as particle growth and phase segregation took place, the SGL behavior progressively disappeared. Results from high resolution transmissi on electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), and electron energy-loss spectroscopy (EELS) suggest that the AFM correlations are due to the alpha-Fe particles that show a surface layer of a few nanom eters in thickness, of either FeO and/or gamma-Fe-fcc. XPS and EELS measure ments confirm the presence of FeO; however, the latter is only tentatively suggested by the HRTEM analysis of the particle/matrix interfaces. (C) 2000 American Institute of Physics. [S0021-8979(00)08106-8].