SGER: Adiabatic Magnetization Transport in Metals at the Nanoscale

Howard University, Washington DC

Investigators

Abstract

TECHNICAL: This is an SGER project focused on energy/entropy transport in nanostructured conductors. PI plans to investigate electronic transmission through constrictions, under ballistic conditions and with an applied non-homogeneous magnetic field, of charge carriers that have orbital and spin degrees of freedom. Heat removed at contacts that can potentially be used for cooling/power generation, would be evaluated by measuring the Seebeck coefficient. The project is inspired by the thermodynamic process of adiabatic demagnetization that is the basis of a successful cooling technology and the process that PI aims to demonstrate can be denominated 'adiabatic demagnetization in a wire'. The project is experimental. The nanostructures are made of bismuth, antimony, and their alloys because these semimetals exhibit low intrinsic dissipation. To fabricate the samples, PI will employ a high pressure, high-temperature injection technique that uses nanochannel dielectrics as a template structure to fabricate dense and massive composites consisting of arrays or networks of bismuth constrictions with controllable diameters in the range of 100 nm to 1 um. These materials are organized in devices, featuring a source of inhomogeneous field, which will also be fabricated. Measurements of the energy/entropy transport will be performed in these devices. Estimates show great prospects. PI's theoretical model of energy/entropy transport, that considers both phonon and electron mean-free-paths, show that transfer peaks for nanostructure characteristic sizes of around 500 nm. The estimated efficiency is close to the Carnot efficiency at low temperatures (4 kelvin). By using materials that have extraordinarily long electronic mean free paths (namely bismuth) shaped into nanosize structures of characteristic sizes smaller than the mean free path the project explores, in solid state materials, electronic phenomena traditionally observed in vacuum electronics. The project also aims to impact the field of magnetism in nanostructures, that is closely related to the field of spintronics because the mechanisms of transfer of magnetic polarization will be explored. NON-TECHNICAL: The research impacts the field of solid-state thermal-to-electric conversion, thermoelectrics and thermoionics. These processes involve neither mechanical parts that wear down nor fluorocarbons that damage the environment and solid state coolers and generators can be miniaturized for use in miniature sensors and actuators. This project includes a strong educational component, emphasizing the participation of undergraduate students in the research program. Howard University, graduates more African-American students than any other college in the nation. Howard is noted for excellence in undergraduate and graduate education. The research program will offer both undergraduate and graduate students opportunities to participate in a diverse range of scientific activities.