Fig. 7
From: Resonant torsion magnetometry in anisotropic quantum materials
Cantilever resonance. a Frequency scans through the normal mode resonance at room temperature and in air. The in-phase and out-of-phase voltages are shown in blue and red, respectively. b The Lorentzian at resonance can be observed as a circle when plotted in the complex plane. Off resonance, the background voltage VBG is measured. Approaching the resonance corresponds to tracing the circle in a counter-clockwise direction starting from VBG. The resonant frequency is observed at V(ωo). The positions Z1, Z2, and Z3 in the complex plane are different possible positions of the reference point (zero voltage) from which the phase can be measured with the PLL. Depending upon the drive voltage and the capacitance compensation, the circle can be shifted to encompass, lie outside, or lie on the border of the phase reference. The effect this has on the phase swing at resonance is discussed in the text. Distortions of the circle, which are not observed in our measurements with drive voltages below 100 mV, are an indication of the nonlinear response regime of the lever
