Scanning Hall Probe Microscopy (SHPM) using Quartz Crystal AFM Feedback

Scanning Hall Probe Microscopy (SHPM)[1] is a quantitative and non-invasive technique for imaging localized surface magnetic field fluctuations such as ferromagnetic domains with high spatial and magnetic field resolution of $\sim $50nm {\&} 7mG/(Hz)$^{0.5}$ at room temperature. In the SHPM technique, Scanning Tunneling Microscope(STM)[1] or Atomic Force Microscope(AFM)[2] feedback is usually used for bringing the Hall sensor into close proximity of the sample. In the latter, the Hall probe has to be integrated with an AFM cantilever in a complicated microfabrication process. In this work, we have eliminated the difficult cantilever-Hall probe integration process; a Hall sensor is simply glued at the end of a 32,768 Hz Quartz crystal, which is used as force sensor. The sensor assembly is dithered at the resonance frequency and the quartz force sensor output is detected with a Lock-in. SHPM electronics is modified to detect AFM topography and the phase, along with the magnetic field image. NIST MIRS ( Hard Disk ) sample is imaged with the Quartz Crystal AFM feedback and the performance is found to be comparable with the SHPM using STM feedback. Quartz Crystal AFM feedback offers a very simple sensor fabrication and operation in SHPM. This method eliminates the necessity of conducting samples for SHPM. [1] A. Oral \textit{et. al.} Appl. Phys. Lett., 69, 1324 (1996) [2] A.J. Brook \textit{et. al.} Appl. Phys. Lett. 82, 3538 (2003)