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Half-Metallic Single Crystal CrO2 Films

(JHU MRSEC)Spintronic effects & devices depend directly on spin polarization P

EF

NM metal P = 0

EF

FM metal 0 < P < 1

E F

Half Metal P = 1

P N (EF ) N (EF )

N (EF ) N (EF )Density of states

(e.g., Cu) (e.g., Co) the ultimate

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high R

low R Spin-valve GMR read-head

Spintronic effects & devices

GMR

high R

low R

TMR

word / sense lines

MRAM

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Half Metallic FerromagnetsThe ultimate spin-polarized material

•A single spin band

•100% spin polarized

•Integer magnetic moment/unit cellM = µB (nmajority - nminority)

nmajority + nminority = integernmajority = integer

nmajority - nminority = integer

CrO2 (2 µB/unit cell)

Band structure of CrO2

Crystal lattice of CrO2

a

bc

Cr

O

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Single Crystal [100] CrO2 Films by CVD

Point ContactAndreev Reflection

• In ballistic (Sharvin) limitl > a

Mean free path contact size

CrO2 (P = 98.4%) is half metallic !

Ji, Strijkers, Yang, Chien, Byers, Anguelouch, Xiao, and Gupta, Phys. Rev. Lett. 86, 5585 (2001).Anguelouch, Gupta, Xiao, Abraham, Ji, Ingvarsson, and Chien, Phys. Rev. B 64, 180408(R) (2001).

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Significance of Half-Metallic Ferromagnets

Ultimate magnetic tunnel junctions: infinite TMR

Conducting Insulating

Perfect spin injector for semiconductors and metals

Physics of a single spin band