Condensed Matter Special Seminar: "Magnetic Phase Transitions in Nanoscale Materials."
(sign-up)Casey W. Miller, Rochester Institute of Technology
Physics - Condensed Matter
The precise fabrication of magnetic heterostructures can lead to novel physical properties when well known materials are confined in one or more dimensions, or are placed in proximity to dissimilar materials. An excellent example of this is the 2007 Nobel Prize winning phenomenon of giant magnetoresistance, which is displayed by precisely engineered magnetic multilayers. My laboratory employs the tools of nanoscience to investigate magnetism in nanoscale materials, with particular attention to magnetic phase transitions. We grow structures to investigate magnetic phase transitions and related phenomena, such as the magnetocaloric effect-a thermodynamic phenomenon being explored for refrigeration technologies. While this effect has been well studied in the bulk, it remains mostly unexplored at the nanoscale. A combination of high quality film growth, magnetometry, and magnetic depth profiling with polarized neutron beams shows that nanostructuring leads to a distribution of exchange energies that reduce the magnetocaloric effect. To explore this in more detail, we have created and measured 100nm thick magnetic films comprised of a linear gradient of exchange energies . This “artificially inhomogeneous” structure enables us exciting control over the magnetic structure, including the ability to continuously tune the magnetic depth profile with both field and temperature.
 “Spatial Evolution of the Ferromagnetic Phase Transition in an Exchange Graded Film,” B. J. Kirby, H. F. Belliveau, D. D. Belyea, P. A. Kienzle, A. J. Grutter, P. Riego, A. Berger, and Casey W. Miller, Phys. Rev. Lett. 116, 047203 (2016).
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