For distribution - thanks

[CM ICTP - Trieste]

CONDENSED MATTER SECTION

INFORMAL SEMINAR



Tuesday, 11 September   -    11:00 a.m.


Lecture Room 'C' -  Main Bldg. - terrace level



QU Fanyao   ( Concordia University, Canada )

"Nanomagnetism and spin dependent transport through diluted magnetic 
quantum dots"

Abstract

Meticulous control of the coupling between spins is essential to the 
use of magnetic nanostructures in spintronics and quantum information 
devices.   Such spin coupling has been studied in bulk ferromagnets, 
thin films,  clusters, nanotubes, one dimensional monatomic metal 
chains.  With the development of lithography and scanning tunneling 
microscope (STM)  techniques, magnetic manipulations can even be 
realized in quantum dots  (QDs), single atoms and molecules. In this 
talk, I will present a theory of magnetic exchange interactions and 
carrier mediated spin-spin interaction between Mn2+ ions in quantum 
dots containing electrons and magnetic ions.  We find the interaction 
between the electron and Mn ion to depend strongly on the number of 
electrons.  It can be switched off for closed shell configurations and 
maximized for partially filled shells.  The Mn-Mn interaction also 
depends strongly on the number of electrons.  For closed electronic 
shells we derive the effective RKKY interaction.  For partially filled 
shells, finite electron spin polarizes Mn2+ ions via many-electron 
magneto-polaron effect, leading to effective carrier mediated 
ferromagnetic spin-spin interactions.  We also explore the possibility 
of tailoring magnetism by controlling the confining potential,  
particle numbers, temperature, and strength of the Coulomb 
interactions.   It is found that the interplay of strong Coulomb 
interactions and quantum confinement leads to enhanced inhomogeneous 
magnetization which persists at higher temperatures than in the 
noninteracting case.  The temperature of the onset of magnetization can 
be controlled by changing the number of particles as well as by 
modifying the quantum confinement and the strength of the Coulomb 
interactions.  Finally, I will show how these remarkably magnetic 
properties are manifested in the electrical behavior of a single 
electron transistor.