Subject 9 Magnetic Nanostructures

Subject 9 Magnetic Nanostructures - Revised syllabus Week...

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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 (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
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Subject 9 Magnetic Nanostructures Examples: magnetic data storage giant magneto-resistance (GMR) exchange bias spin valve read heads magnetic tunnel junctions
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First, some basic concepts in magnetism
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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 = 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 = + = + = + = in a material When a material magnetizes
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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
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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
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This note was uploaded on 03/30/2010 for the course EN 510.422 taught by Professor Dr.evanma during the Spring '10 term at Johns Hopkins.

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Subject 9 Magnetic Nanostructures - Revised syllabus Week...

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