Construction of a Low Temperature Capable Frequency-Modulation Magnetic Resonance Force Microscope*

We constructed a low temperature capable frequency-modulation magnetic resonance force microscope (FM-MRFM) and applied to detecting electron spin resonance signals from tiny DPPH particles with ease in control and thereby improved signal-to-noise ratio. The electronics was composed of a spin-polarization modulator, a cantilever-oscillation feedback gain controller, and a phase-locked loop (PLL) FM demodulator. The controller kept the cantilever oscillating at its resonance frequency by positively feeding back to a piezo-actuator the gain-controlled drive signal phase shifted by 90 degrees with respect to the cantilever oscillation in the PLL circuit. The modulator generated waveforms to modulate the strength or frequency of radio-frequency field in phase with the drive signal. The whole setup enabled to sense as readily as spins resonate by tracking the cantilever resonance frequency without breakdown in fastidious conditions. We will discuss the details and features of our microscope and furthermore ongoing MRFM results.