Design and construction of a magnetic force microscope

A magnetic force microscope (MFM) is a special type of scanning force microscope which measures the stray field above a ferromagnetic sample with the help of a ferromagnetic cantilever. The aim of this project was to design and build a MFM head and interface it with a commercial scanning probe electronics controller with the help of an appropriate force sensor. The MFM head and the force sensor were to be designed to work at low temperatures (down to 4 K) and in high vacuum. During this work, a magnetic force microscope (MFM) head was designed. Its design is symmetrical and modular. Two dimensional views were prepared to ensure proper geometry and alignment for the various modules. Based on these views, individual parts in the various modules were manufactured and combined for the final assembly of the head. This MFM head has many essential and advanced features which were incorporated during the design process. Our MFM head has an outside diameter of 5 cm and thus has a low thermal mass. The head operates inside a 100 cm long vacuum can which is kept in a cold bath inside a superinsulated dewar. Other features of this MFM head include thermal compensation of the important parts, flexibility to use commercial MFM cantilevers and a large scan range compared to the previous designs. Some of the anticipated system specifications are: 1) room temperature scanning range of 175?? 175 ??m, 2) low temperature scanning range between 35-50 ??m, 3) smallest detectable magnetic force in the range of one pN and 4) smallest detectable magnetic force gradient in the range of 10-3 to 10 -5 N/m. This MFM head was interfaced to a commercial scanning probe electronics apparatus by designing a fiber-optic interferometer as the sensor for the detection of the cantilever deflection. The fiber-optic sensor also has features of its own such as stability, compactness and low susceptibility to noise because of all-fiber construction. With this MFM head, we hope to image many magnetic samples which were previously impossible to image at Texas A&M.