Probing Interfacial Friction and Dissipation in Granular Gold­ Nickel Alloys with a Quartz Crystal Oscillator in an External Magnetic Field

We present here a quartz crystal microbalance study of two-phase gold nickel alloys whose internal granular properties are probed by exposure to a fluctuating external magnetic field. The work is motivated by prior studies demonstrating that granular two-phase materials exhibited lower friction and wear than solid solution alloys with identical compositions [1]. In particular, we report a ``flexing'' effect which appears when an external magnetic field is applied, and is manifested as a decrease in the magnitude of oscillation amplitude that is synchronized with the applied field; the effect is not seen on the complimentary solid solution samples. The effect is consistent with internal interfacial friction between nickel and gold grains, indicating a degree of freedom which may decrease friction even in the absence of an external magnetic field. This is supported through analysis of energy dissipation in the system, using the Butterworth­-Van Dyke equivalent circuit model [2]. Data and interpretation are also presented that rule out alternate explanations such as giant magnetoresistance [3] and/or other resistive phenomenon within the film.\\[4pt] [1] L. Pan, Ph.D. Thesis, NCSU (2011).\\[0pt] [2] R. Cernosek et al, IEEE Transactions ­ Ultrasonics, 45 (5) 1998\\[0pt] [3] J. Xiao et al., PRL 68 (25) 1992