Transcript ppt

Dr. A. R. Koymen
New Physics in Magnetic Nanolayers
Sputtering System
SQUID
Artificial Ferrimagnets
& Compensation Temperature
T < Tcomp
Gd
Fe
Gd
Magnetic Moment [arb units]
H→
1.0
Tcomp
Gd
Fe
0.0
0
Fe
T > Tcomp
0.5
100
200
300
Temperature [K]
400
Gd
Fe
Thermal Hysteresis (Bow-tie)
Magnetic Moment [emu]
Magnetic Superheating and Supercooling
0.00025
(Co 2nm/Gd 2nm)8
0.00020
Co
Gd
0.00015
0.00010
0.00005
100 Oe
0.00000
-0.00005
-0.00010
0
50
100
150
200
250
300
Temperature [K]
E   H (t1m1 cos 1  t 2 m2 cos  2 )  Jm1m2 cos( 2  1 )  t1m1 H a cos 2 1
S. Demirtas, M. R. Hossu, R. E. Camley, H. C. Mireles and A. R. Koymen, accepted for publication in
Phys. Rev. B
TM and RE response to temperature
Gd
0.0016
0.0012
Co
0.0008
0.0004
0.0000
0
50 100 150 200 250 300
Temperature [K]
Coercivity (HC) [Oe]
Magnetic Moment [emu]
350
300
250
Gd
200
150
100
Co
50
0
-50
0
50
100
150
200
250
Temperature [K]
Different response of the sublattices to temperature is
the key for thermal hysteresis
300
Thermal Hysteresis vs Hext
Theory
Experiment
Ha = 20 G
H
0.0001
Gd
a) 50 Oe
1.0
Co
0.5
0.0000
0.0
(Co 2nm/Gd 2nm)8
-0.0002
0.0002
0.0001
b) 100 Oe
-0.0001
0.0002
0.0001
c) 200 Oe
0.0000
0.0002
0.0001
d) 400 Oe
0.0000
0
50
100
150
200
Temperature [K]
250
300
-0.5
Magnetic Moment [arb units]
Magnetic Moment [emu]
-0.0001
0.0000
H = 50 Oe
-1.0
H = 100 Oe
0.5
0.0
-0.5
0.8
0.6
0.4
0.2
0.0
-0.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
0
H = 200 Oe
H = 400 Oe
50
[Co 2nm/Gd 2nm]8
100 150 200 250 300
Temperature [K]
Co/Tb Multilayer
Maria Hossu and A. R. Koymen, accepted for publication in Journal of Applied Physics
0.0012
0.0010
Magnetic Moment
0.0008
0.0006
0.0004
0.0002
3000 Oe
0.0000
0
50
100
150
T [K]
200
250
300
CoGd Alloys (experiment vs theory)
S. Demirtas, R. Camley and A. R. Koymen, accepted for publication in Applied Physics
Letters
H
a) 100 Oe
Gd
0.0001
0.04
0.02 a) 100 Oe
0.00
-0.02
Co
Magnetic Moment (arb units)
Magnetic Moment [emu]
0.0000
0.00010
0.00005
b) 200 Oe
0.00000
0.00012
0.00008
0.00004
c) 400 Oe
0.00000
0.00015
0.00010
0.04
0.02
0.00 b) 200 Oe
-0.02
0.04
0.02
c) 400 Oe
0.00
0.04
0.02
0.00005
d) 800 Oe
0.00000
0
100
0.00
200
300
Temperature [K]
400
0
d) 800 Oe
100
200
300
Temperature [K]
400
Magnetic Recording (toy model)
Magnetic
Moment
Gd
Co
1-state
RT
Temperature
0-state
Zero field
Cooling curve
• Positive magnetic field
• Selective
(writes one type of data)
• Symmetric and tunable
• Amorphous
• Fe, Co, Gd, Tb
(perpendicular/longitudinal)
• Stable at small sizes (AF
coupled)
• High areal density
• Grain size? seed layer?
Ongoing Research
• Maria Hossu(Ph.D. student)
• Manufacture multilayers that have out of
plane anisotropy (use new X-ray machine)
• Mustafa Arikan (Ph.D. student)
Discover new magnetic semiconductors for
device applications (GaTbAs, GaGdAs)
Interface domains
Co81Gd19 30nm/Ag 2nm/Co83Gd17 30nm
0.0004
0.0004
100 Oe
0.00020
200 Oe
0.0003
Magnetic Moment [emu]
0.0003
0.0002
0.0002
0.0001
Magnetic Moment [emu]
0.0000
0.0001
-0.0001
0
100
200
300
400
0
100
200
400
0.0004
0.0004
600 Oe
0.0003
0.0003
0.0002
0.0002
0.0001
0.0001
100
200
300
1200 Oe
0.00016
100
100
200
300
2500 Oe
0.00018
0.00014
400
0.00024
Tcomp2
Tcomp1
150
200
250
300
Temperature [K]
400
0.00020
2500 Oe
0.00021
0.00016
0.00015
0.00014
150
200
250
300
•
5000 Oe
0.00018
0.00018
100
300
CoGd/Ag/CoGd
0.00012
100
Temperature [K]
150
200
250
300
•
Switching of the hard layers
creates interface domains
Hard-soft change relaxes
interface domains
Multiple thermal hysteresis – Co/Gd
Magnetic Moment [emu]
(Co 40/Gd 80)4
0.0004
0.0003
75 Oe
0.0002
0.0001
0.0000
200
250
300
350
Temperature [K]
400
0.0004
(Co 40/Gd 80)4
0.0003
0.0002
0.0001
200 Oe
0.0004
0.0003
0.0002
0.0001
400 Oe
200
250
300
350
400
Temperature [K]
0.0003
Magnetic Moment [emu]
Magnetic Moment [emu]
0.0005
(Co 40/Gd 80)4
0.0002
0.0001
260 K
0.0000
-0.0001
-0.0002
-0.0003
-2000
-1000
0
1000
Magnetic Field [Oe]
2000
Decoupling of the hysteresis
loop can create
tunable thermal hysteresis