Fabrication and characterization of ferromagnetic tips for magnetic resonance force microscopy
Creators:Steward, Ross A.
Advisor:Hammel, Peter C.
Clymer, Bradley D.
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Electrical and Computer Engineering Honors Theses; 2008
This thesis deals with the custom fabrication of micron scale rare-earth ferromagnetic tips for use in magnetic resonance force microscopy (MRFM) experiments. Magnetic resonance force microscopy is a three dimensional subsurface imaging technique with the potential for atomic scale sensitivity and resolution. Tips are fabricated here by gluing particles as small as 1 μm to end of atomic force microscopy (AFM) cantilevers and milling the particles to a desired size and shape by sputtering material off using a focused beam of gallium ions. Particle gluing followed by focused ion beam (FIB) milling is shown here to be a promising and, so far, somewhat effective technique for fabricating optimal ferromagnetic tips for certain MRFM experiments. Fabrication results displaying ferromagnetic tips possessing sharp points with radii smaller than 50 nm are presented here. One of the major problems that has been encountered when FIB milling small particles is a loss in coercivity, sometimes from around 10,000 Gauss to less than 100 Gauss. Although indications lead to the conclusion that ion beam related damage is the cause of this decrease in coercivity, this assertion has not yet been proven. Based on the results of simulations and previous research it is believed that the loss of coercivity is related to particle heating caused by ion beam exposure, rather than direct damage caused by impinging ions from the beam or secondary recoil atoms knocked loose by the beam. This loss in coercivity is one of several different sources of variability that leads to inconsistent fabrication results. Room temperature cantilever magnetometry is shown here to be an extremely sensitive, time efficient, and economical technique for determining certain magnetic properties of the tip including magnetic moment, hysteresis loop, and anisotropy. Results are presented here from measurements on magnetic tips micron scale dimensions and moments as small as 10^(-13) J/T. Calculations described here show the theoretical sensitivity limit of the room temperature magnetometer to be as high as 4 x 10^(-17) J/T using commercially available AFM cantilevers.
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