{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Subject 9 Magnetic Nanostructures

Subject 9 Magnetic Nanostructures - Revised syllabus Week(2...

Info iconThis preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
Week (2 meetings/wk) Contents (wk starting 1/25) Introduction ; Characterizing nanoscale structures (2/1) Processing I : Microfabrication, IC and IC compatible; Thermodynamics : effects of small systems (2/8) Blizzard of 2010 (2/15) Nanoporous materials : Au fuel cell and catalysis (Erlebacher); Processing II : Nanoparticles (Searson) (2/22) Kinetics , surface diffusion, surface smoothing. Mechanical properties of nanostructured materials (3/1) Electronic properties and devices (3/8) Nano in fluids (Cammarata); Bio nanosystems & properties (Mao) (3/15) Spring vacation (3/22) Nanostructures and devices for optical properties (3/29) Magnetic nanostructures/properties; Nanoscale reactive multilayers (4/5) Student project presentations start (title due March 24 ) All homework sets due April 8 (4/12) Student project presentations (4/19) Student project presentations (4/26) Student project presentations (5/3) Student project presentations Revised syllabus
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Subject 9 Magnetic Nanostructures Examples: magnetic data storage giant magneto-resistance (GMR) exchange bias spin valve read heads magnetic tunnel junctions
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 4
First, some basic concepts in magnetism
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
M H χ = χ - susceptibility M - magnetization H - applied magnetic field μ - permeability μ o for free space (=1 unitless in cgs 4 π x10 -7 Vs/Am) μ r - relative permeability B - magnetic induction (Wb/m 2 or Tesla) = H+4 π M Gauss in cgs o B H μ = Magnetic moments on atoms due to: electron spins (spin angular momentum; quantum number s ) orbital motion (orbital angular momentum, quantum number l ) change in orbital motion in a magnetic field M 0 = number of atoms per unit volume ( n ) x atomic magnetic moment ( m ) M 0 - magnetization at zero applied magnetic field (H = 0) M 0 (10 6 A m -1 ) T C (K) Fe 1.71 1043 Co 1.42 1388 Ni 0.48 634 permalloy (NiFe) 0.86 in free space ( ) ( ) (1 ) o o o o r B H M H H H H μ μ χ μ χ μ μ = + = + = + = in a material When a material magnetizes
Background image of page 6
Diamagnetic χ -10 -5 Orbiting e- accelerates in applied H, creating very weak M that opposes H Spin moments all cancel out, rendering them non-magnetic Cu, Ag, Au, Bi, Be Superconductors (perfect diamagnetism, B=0 inside) χ -1 Paramagnetic (see next slide) χ 10 -3 - 10 -5 Incomplete cancellation of spin, but random Weak M parallel to applied magnetic field, when atomic moments aligned by field, the total χ is small as it is easily randomized by the T around. Al, Pt, Mn, Ti Ferromagnetic χ 50 - 10,000 Due to exchange interaction, spins in atomic moments talk and coordinate, forming domains Domain moments aligned parallel to applied magnetic field, difficult to be randomized until T c Fe, Co, Ni, rare earth metals and their alloys Response to a Magnetic Field
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
E F E F N(E) H=0 N(E) N(E) N(E) H>0 E E μ mH 0 Paramagnetic Materials M H No net magnetic moment at H = 0 With H, net spin up, but weak, mostly still random H gone, M gone due to randomization by T o r H μ μ
Background image of page 8
Coupling between unpaired electrons in solids E ex = -2J E S 1 ·S 2 E ex - energy J E - exchange interaction S - spin anglular momentum J < 0 E ex > 0 for S 1 ( ) and S 2 ( ) E ex < 0 for S 1 ( ) and S 2 ( ) ↑↓ coupling favored antiferromagnetic materials J > 0 E ex > 0 for S 1
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 10
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}