We have measured the detailed dependence of the oscillation frequencies, linewidths, and output powers of spin-transfer nanocontact oscillators as functions of applied field strength, bias current, and angle of the applied magnetic field. For fields applied only moderately out of the plane of the film, the evolution of these properties is continuous. However, for fields applied more strongly out of plane they exhibit discontinuous evolution in both current and applied field. These

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... s typically correlate with changes in the device resistance, changes in device output power, and a broadening of their spectral linewidths. However, away from these discontinuities, the oscillator output powers are larger and the linewidths narrower when compared to geometries having the fields applied at smaller angles. Our measurements suggest that the discontinuous evolution of the frequency with current and applied field results from an abrupt change in the precessional mode of the free layer.