Magnetic field strength and orientation effects on co-fe discontinuous multilayers close to percolation

Received 1 August 2010; revised manuscript received 16 September 2010; published 21 October 2010 Magnetization and magnetoresistance in function of the magnitude and orientation of applied magnetic field were studied in Co-Fe discontinuous multilayers close to their structural percolation. The high pulsed magnetic fields up to 33 T were used in the 120–310 K temperature range. Comparison between longitudinal and transverse with respect to the film plane field configurations was made in the low-field and high-field regimes in order to clarify the nature of the measured negative magnetoresistance. Coexistence of two distinct magnetic fractions, superparamagnetic SPM, consisting of small spherical Co-Fe granules and superferromagnetic SFM, by bigger Co-Fe clusters, was established in this system. These fractions were shown to have different relevance for the system magnetization and magnetotransport. While the magnetization is almost completely up to 97% defined by the SFM contribution and practically independent of temperature in this range, the magnetoresistance experiences a crossover from a regime dominated by Langevin correlations suppressed with temperature between neighbor SPM and SFM moments at low fields, to that dominated by spin scattering enhanced with temperature of charge carriers within SFM clusters at high fields. Also, the demagnetizing effects, sensitive to the field orientation, were found to essentially define the low-field behavior and characteristic crossover field.