Magnetic Behavior in Nanoscale Magnetic Heterostructures

Pennsylvania State Univ University Park, University Park PA

Investigators

Abstract

This condensed matter physics project focuses on the measurement and understanding of factors that determine the range of spin ordering in metallic magnets. The fundamental measure of spin ordering is the spin-spin correlation length, L. For example, the critical temperature, Tc, for magnetic ordering depends on the strength, i. e. range, of the interactions between individual spins. This material parameter is often unknown, so that the critical temperatures at which magnets lose their strength cannot be predicted with certainty. The parameter L also determines how Tc decreases as the dimensions of a magnet are reduced. Tc goes precipitously to zero in the nanoscale regime when the dimensions of the magnet approach L. Plotting and fitting experimental curves of Tc as a function of the thickness of nanoscale thin films provides a measure of the intrinsic spin-spin coupling length, L. The experimental plots also reveal the onset of quantum 'finite-size' effects as the thickness approaches a few nanometers. The correlation length L also determines the coupling between thin magnetic layers in magnetic heterostructures. The coupling strength between spins can be 'tuned' to different values by carefully alloying different magnetic elements. The research program will investigate these effects in ultrathin layers and heterostructures of different coupled magnetic materials as a function of material composition. The results are of importance to the future development of magnetic recording and magnetic memory devices as the dimensions approach the nanoscale. The technology is 'cutting edge' so that the program will serve to train a new generation of scientists in this high technology field and prepare them for careers in academe, industry and government. This research focuses on measuring and understanding those factors that determine the range of magnetic coupling between magnetic moments in magnets. This parameter, the spin-spin correlation length, is a fundamental quantity that determines how the magnetism decays to zero with increasing temperature. This parameter is unknown so that the critical temperatures at which magnets lose their strength cannot be predicted with certainty. This parameter also determines how the critical temperature decreases as the dimensions of a magnet is reduced, going precipitously to zero in the nanoscale regime when the dimensions approach that of this unknown length parameter. A new discovery reveals that by plotting and fitting experimental curves of this parameter as a function of the thickness of nanoscale thin films provides a measure of this parameter. The coupling between thin magnetic layers in magnetic heterostructures is also a consequence of this same parameter. This coupling strength can be 'tuned' to different values by carefully alloying different magnetic elements. The research program will investigate these effects in ultrathin layers and heterostructures of different coupled magnetic materials as a function of nanoscale thickness and material composition. The results are of importance to the future development of magnetic recording and magnetic memory devices as the dimensions approach the nanoscale. The technology is 'cutting edge' so that the program will serve to educate a new generation of scientists in a rapidly evolving, high technology field.