Funded by the National Science Foundation
Nano + Magnetism
'Nanostructured' (NS) describes materials with length scales from 1-100 nm. This class of materials may include small particles, multilayered and thin film materials, or bulk materials with nanometer-sized grains. NS materials often have unique electrical, chemical, structural and magnetic properties, with potential applications including: information storage, color imaging, bioprocessing, magnetic refrigeration and ferrofluids.
All of these materials have the common property that a significant fraction (up to 50%) of the sample volume is composed of grain boundaries and interfaces, collectively called the 'interphase'. The magnetic properties are dominated by the presence of the interphase, the role of the interphase in interparticle coupling, and the disorder inherent in nanostructures. Most real systems exhibit contributions from both coupling and reduced size.
Our interest in disordered magnetism focuses on non-equilbirum phases, the interaction of two-phase systems, and spin glass behavior. For an overview of our work, see our paper Role of Disorder in the Magnetic Properties of Mechanically Milled Nanostructured Alloys
Magnetic Rare Earths
Much of our work focuses on understanding the properties of magnetic rare earths, such as Gd and Tb. These materials are interesting because in their nanostructured form, they exhibit modified ferromagnetic behavior and glassy behavior at lower temperatures. Since it is unlikely that such concentrated materials would be true spin glasses, we are fabricating samples with different physical properties (grain size, strain, etc.) and trying to understand the origin of the magnetically glassy behavior.
Inert Gas Condensation
Samples are made using inert-gas condensation. This allows us to control the particle size and particle size distribution. A glovebox fitted with a CF flange allows us to transfer samples without exposure to air.
Laves Phase Materials
Laves-phase materials such as GdX2 where X is a metal such as Al, Ir or Pt, maintain their crystal structure but become progressively disordered when mechanically milled. Because the disorder can be changed progressively, the effects of the disorder can be tracked.