CORRELATION BETWEEN STRUCTURAL AND MAGNETOELASTIC PROPERTIES IN SPUTTERED NI-RICH NI100-XYX ALLOYS

After a rapid recall of the available results concerning the magnetic properties of crystalline and amorphous Ni100-xYx alloys, we attempt to explain the dependence on the Y content of the magnetoelastic properties in sputtered Ni-rich Ni100-xYx compounds (0 < x < 10). According to previous and generalized data resulting from the analysis of Franck and Kasper crystalline and glassy phases, the total Radial Distribution Function (RDF) of Ni90.5Y9.5 is decomposed into partial RDF's. The estimated coordination number of Y atoms, as a function of x, allows us to correlate the observed critical value x(c) = 5 both with the amorphization of the alloy and the change of sign of the spontaneous magnetostriction lambda-s. At the highest Y content, Ni100-xYx may be viewed as a dilute solution of Y in a "pure amorphous Ni structure" where the local order is of icosahedral symmetry. This amorphous state results in positive values of lambda-s. At low x (x < 5) the preponderant octahedral local order is responsible for negative values of lambda-s and suggests a local atomic arrangement similar to the one observed in fcc Ni. These two kinds of local order allow us to interprete the variations of (lambda-s/sigma-s2)T = 0 as a function of the amount of yttrium.