Cartoon of a spin valve: Current flows - nseresearch.orgspintronics_nseg.pdf · 20 nm 1 µm...
1
Nonmagnetic NC STATE UNIVERSITY Center Focus: the CMS is exploring the utility of switchable/bistable paramagnetic molecules as interfacial “spin filters” to enhance and to gate injection and detection of spin polarized electrons from/to magnetic electrodes. • Iron spin crossover compounds form stable films by evaporation • Transport measurements across the spin crossover transition show a change in conductance in agreement with calculations • High-spin Fe II conducts better than low-spin Fe II STM Images of the first two layers on Au(111) High Spin Low Spin SQUID Magnetometry Theoretical I-V: AFM of 60 nm Film: Experimental I-V: 1 nm 20 nm 1 μm Dimerization by π interactions in monolayer similar to crystal structure 77 K (Low-Spin) 300 K (High-Spin) These results demonstrate that spin crossover complexes form the basis for a new type of molecular device as supported by theory. • Differential conductance exhibits ‘resonances’ below tautomeric transition • Low temperature resonances switched off by light •The resonances are peaks/dips in d 2 I/dV 2 () and are switched-off by light (red traces in (a) and (b)), thus returning to the high temperature behavior (orange traces at 150K). (c) Theoretical density of states plot that confirms the difference in minority and majority spin density conducive to the measured spin-valve effect. (d) Spin valve effect in permalloy/VT molecule/Co trilayer structure – tunneling magnetoresistance (TMR = (R AP -R P )/R P ) at two temperatures. Au Au/Ti Co II O N O t-Bu O O N t-Bu t-Bu t-Bu CN CN Device These results demonstrate that valence tautomers form the basis for a new type of molecular photoswitch device. Co III O N O t-Bu O O N t-Bu t-Bu t-Bu CN CN (d) (a) (b) 78-Light OFF 78-Light ON 120 T(K) 150–Light OFF 110 90 78 -0.2 0.0 0.2 0.4 -0.4 -0.2 0.0 0.2 0.4 -0.4 Potential (Volts) Potential (Volts) (c) Energy (eV) -5 -4 -3 -2 -1 0 1 2 3 4 UP Spin Down Spin Theory DOS (arbit. Units) -0.5 0 0.5 1.0 TMR (%) 1.5 1.0 -0.5 0.0 0.5 Field (kOe) 290K 77K Cartoon of a spin valve: Current flows between magnetic electrodes only when magnetic moments are alighned parallel 1.0 0.5 -1.0 Current (μA) Low Spin High Spin 10 -10 0 6 2 -2 -6 Potential (Volts) Potential (Volts) 0.0 1.0 -0.6 0.6 -1.0 -0.2 -0.5 0.2 Current (μA) 30 0 10 20 -10 -20 -30
Transcript of Cartoon of a spin valve: Current flows - nseresearch.orgspintronics_nseg.pdf · 20 nm 1 µm...
Nonmagnetic
NC STATE UNIVERSITY!
Center Focus: the CMS is exploring the utility of switchable/bistable paramagnetic molecules as interfacial “spin filters” to enhance and to gate injection and detection of spin polarized electrons from/to magnetic electrodes.
• Iron spin crossover compounds form stable films by evaporation • Transport measurements across the spin crossover transition show a change in conductance in agreement with calculations
• High-spin FeII conducts better than low-spin FeII
STM Images of the first two layers on Au(111)
High Spin
Low Spin
SQUID Magnetometry
Theoretical I-V:
AFM of 60 nm Film: Experimental I-V:
1 nm
20 nm
1 µm
Dimerization by π interactions in
monolayer similar to crystal
structure
77 K (Low-Spin)
300 K (High-Spin)
These results demonstrate that spin crossover complexes form the basis for a new type of molecular device as supported by theory.
• Differential conductance exhibits ‘resonances’ below tautomeric transition
• Low temperature resonances switched off by light
• The resonances are peaks/dips in d2I/dV2 () and are switched-off by light (red traces in (a) and (b)), thus returning to the high temperature behavior (orange traces at 150K). (c) Theoretical density of states plot that confirms the difference in minority and majority spin density conducive to the measured spin-valve effect. (d) Spin valve effect in permalloy/VT molecule/Co trilayer structure – tunneling magnetoresistance (TMR = (RAP-RP)/RP) at two temperatures.
Au Au/Ti
CoIIONO
t-BuOO
N
t-But-Bu
t-Bu
CN
CN
Device
These results demonstrate that valence tautomers form the basis for a new type of molecular
photoswitch device.
CoIIIONO
t-BuOO
N
t-But-Bu
t-Bu
CN
CN
(d)
(a) (b)
78-Light OFF 78-Light ON
120
T(K) 150–Light OFF
110 90 78
-0.2 0.0 0.2 0.4 -0.4 -0.2 0.0 0.2 0.4 -0.4
Potential (Volts) Potential (Volts)
(c)
Energy (eV) -5 -4 -3 -2 -1 0 1 2 3 4
UP Spin Down Spin
Theory
DO
S (a
rbit.
Uni
ts)
-1.0 -0.5 0 0.5 1.0
TMR
(%)
1.5
1.0
-0.5
0.0
0.5
Field (kOe)
290K 77K
Cartoon of a spin valve: Current flows between magnetic electrodes only when magnetic moments are alighned parallel
1.0 0.5 -1.0
Cur
rent
(µA
)
Low Spin High Spin
10
-10
0 6
2 -2
-6
Potential (Volts)
Potential (Volts)
0.0
1.0 -0.6 0.6 -1.0 -0.2
-0.5
0.2
Cur
rent
(µA
) 30
0
10
20
-10
-20
-30
