AVS 46th International Symposium
    Magnetic Interfaces and Nanostructures Technical Group Thursday Sessions
       Session MI+NS-ThA

Paper MI+NS-ThA1
Cryogenic Magnetic Force Microscopy Instrumentation

Thursday, October 28, 1999, 2:00 pm, Room 618/619

Session: Magnetic Imaging
Presenter: M. Roseman, McGill University, Canada
Authors: M. Roseman, McGill University, Canada
P. Grutter, McGill University, Canada
Correspondent: Click to Email
We describe our cryogenic magnetic force microscope, operating between 4 and 300 Kelvin. The instrument is designed to fit within a 3" diameter bore of an 8 Tesla magnet. Cooling is achieved through the use of He exchange gas, which is pumped out prior to imaging in order to provide a vacuum of better than 10@super -5@ mbar during operation. The instrument uses a fibre optic interferometer to measure cantilever deflections. Through the use of a phase lock loop, this interferometric signal allows for the tracking of the cantilever resonant frequency with a resolution of 0.25 Hz in a 100 Hz measurement bandwidth. Our cantilevers are commercially available, made of single crystal silicon coated with a magnetic film, and routinely exhibit Q-factors of greater than 100,000 at 4 Kelvin. Piezoelectric-based clamping linear positioners, with step sizes of 50 nm (at 77 Kelvin) and capable of operation in high magnetic fields, perform in-situ tip and fibre approaches. As an effective means of vibration isolation, we suspend the microscope from a soft bellows. Comprised of 70 convolutions, the bellows damps out vibrations by more than an order of magnitude, effectively isolating the microscope from the surrounding environment, including pump vibrations and liquid helium boil-off. Particular attention has been paid to optimizing the signal to noise ratio through a systematic study of various noise sources, with the intent of achieving a thermally limited sensitivity.