HalfMetallic Single Crystal CrO2 Films

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Half-Metallic Single Crystal CrO2 Films (JHU
MRSEC)
Spintronic effects devices depend directly on
spin polarization P
(e.g., Cu) (e.g., Co) the ultimate
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Spintronic effects devices
GMR
Spin-valve GMR read-head
MRAM
TMR
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Half Metallic Ferromagnets The ultimate
spin-polarized material
Band structure of CrO2

• A single spin band
• 100 spin polarized

• Integer magnetic moment/unit cell
• M µB (nmajority - nminority)
• nmajority nminority integer
• nmajority integer
• ? nmajority - nminority integer
• CrO2 (2 µB/unit cell)

Crystal lattice of CrO2
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Single Crystal 100 CrO2 Films by CVD
Point Contact Andreev Reflection

• In ballistic (Sharvin) limit
• l gt 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