1. Half-Metallic Single Crystal CrO2 Films
(JHU MRSEC)
Spintronic effects & devices depend directly on spin polarization P
Density of states
FM metal
0 < P < 1
NM metal
P = 0
Half Metal
P = 1
(e.g., Cu) (e.g., Co) the ultimate

2. Spintronic effects & devices
high R
low R
GMR
Spin-valve GMR read-head
MRAM
high R
low R
TMR

3. 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

4. Single Crystal [100] CrO2 Films by CVD
Point Contact
Andreev Reflection
In ballistic (Sharvin) limit
l > 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, (R) (2001).

5. 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