My research is in magnetism. Most of my work now is in magnetic alloys, and how you can control the magnetic and resistive properties of materials by changing the concentrations of the elements in the alloy. For example, combining just two magnetic elements, Ni and Fe in different ways, you can get a variety of different properties. One well known alloy with 35% Ni and 65% Fe is called Invar. Invar is known for having very little thermal expansion. Changing to about 80% Ni and 20% Fe results in the most used material in magnetoelectronics, permalloy.  The thermal stability of Invar is missing, but permalloy has:
  1. high magnetic permeability, which means it responds to an applied magnetic field
  2. low coercivity, so it is easy to change the direction of magnetization
  3. nearly zero magnetostriction. Most materials will change their shape when the magnetization changes. That is why transformers “hum.” The AC current is changing the magnetization of the transformer core, and the material in the core is changing size/shape slightly. Permalloy has minimal shape change.
 
The interesting magnetic properties of permalloy make it a good choice for magnetic devices like computer hard drive reading heads.
In one study, we changed the concentration of Fe and Cr in a Ni host. We looked at the photoelectrons that were emitted after shining high intensity synchrotron radiation on them. The figure on the right shows the electron intensity at the Fermi-level for the ∑1 band. The two peaks, labeled with up and down arrows represent the majority and minority spin electrons respectively. The fact that the minority spin electron peak broadens significantly with increasing Fe indicates that the mean free path for these electrons is shortened, in other words these spins are scattered preferentially. A dopant of Cr, on the other hand, simply kills the magnetic moment, as shown by the decreasing spacing between the two peaks. Neither of the spins is preferentially scattered.The mechanism that causes these changes is still under investigation.
In an experiment done during the summer of 2007, I took a summer undergraduate research student to the synchrotron to do Magnetic Circular Dichroism (MCD) on alloys of Ni and Mn. MCD provides element-specific information about the magnetic moment of the sample, so we expect to get a better feel for how the atoms of the host and dopant interact magnetically.Those results are still being analyzed by my student as an independent research project along with our collaborators at Penn State.
On campus at Elon, where I don’t have access to synchrotron radiation, I can make magnetic measurements using the Magneto-Optic Kerr Effect (MOKE). Two students built and programmed the system with me as research projects.