Alfred Lee

Magnetic force microscopy of epitaxial magnetite films through the Verwey transition

Magnetic force microscopy was performed on 300 nm thick magnetite films grown epitaxially on MgO (001) at temperatures ranging from well below to well above the Verwey transition temperature, TV. Frequency shift images were acquired at different locations on the sample as temperature was increased through the Verwey transition. The magnetic domain features are persistent at all temperatures, which indicates that the domains are pinned across the phase transition, probably due to antiphase boundaries. An enhancement of magnetic contrast below TV indicates the moments tilt out of the plane below TV, which is corroborated by superconducting quantum interference device magnetometry.

Focused ion beam deposition of Co71Cr17Pt12 and Ni80Fe20 on tips for magnetic force microscopy

We demonstrate that a focused ion beam can deposit magnetic coatings on cantilevers used for atomic force microscopy, thereby producing a sensor for magnetic force microscopy. This technique is highly versatile, allowing the convenient deposition of complex or expensive materials, such as Co71Cr17Pt12. A second material chosen for this demonstration was the permalloy (Ni80Fe20). We show magnetic images acquired with these cantilevers to illustrate their excellent properties and the differences between coatings. In principle, multilayer coatings could be easily made with this technique.

Simple electronics for inertial and Pan-type piezoelectric positioners used in scanning probe microscopes

We describe a new type of circuit designed for driving piezoelectric positioners that rely on the stick-slip phenomenon. The circuit can be used for inertial positioners that have only one piezoelectric element (or multiple elements that are moved simultaneously) or for designs using a sequential movement of independent piezoelectric elements. A relay switches the piezoelectric elements between a high voltage source and ground, thus creating a fast voltage step followed by a slow ramp produced by the exponential discharging of the piezoelectric elements through a series resistor. A timing cascade is generated by having each relay power the next relay in the sequence. This design is simple and inexpensive. While it was developed for scanning probe microscopes, it may be useful for any piezoelectric motor based on a fast jump followed by a slow relaxation.