Spintronics Abstract CrVTiAl Tunnel Junctions Spin Filter Materials
Graduate Category: Physical and Life Sciences Degree Seeking: PhD Abstract ID# 1803
Spintronics: Next Generation Electronics 1Department
Michelle E.
of Physics, Northeastern University;
2 Jamer ,
2NIST
1 Buda ,
1 Lane ,
3,4 McDonald ,
Gianina Christopher Ian 1 3,4 1 Arun Bansil , Laura H. Lewis and Don Heiman
Brian
Bernardo
1 Barbiellini ,
Center for Neutron Research, NIST, Gaithersburg, MD; 3Department of Chemical Engineering, Northeastern University; 4Department of Mechanical and Industrial Engineering, Northeastern University
Abstract
Tunnel Junctions
Present-day electronics rely almost exclusively on the charge of electrons. However, by utilizing the intrinsic magnetic moment of the electron, which arises from its angular momentum or “spin”, spintronic devices can be produced that are smaller and more versatile than traditional electronic devices. Spin Filter Materials (SFMs) utilized in a tunnel-junction are ideal for producing the next generation of spintronic devices
Introduction: Spintronics
CrVTiAl
• Insulating barrier between metallic contacts
CrVTiAl synthesized via arc melting • Annealed at 1000 °C for 1 week
– Arrow shows magnet direction
and quenched in water
• Current produced through Quantum Tunneling
• Measured a = 6.136 ± 0.005 Å
• Magnetic Tunnel Junctions (MTJs) used in hard drive read-heads
• Near zero moment (m = 0.002 µB)
• Resistivity shows semiconducting carriers (ΔE = 0.16 eV) Spin Down Spin Up
1
• Used currently in memory applications
Energy (eV)
Spin Filter Materials (SFMs)
– Electron spin produces magnetic field
• Semiconductor with spin-dependent band gaps
– Hard Drive read heads, magnetic RAM Electron spin
• Requires spin polarized materials (shown below) • Present materials are ferromagnetic, producing harmful fringing fields that interfere with neighboring components • We seek nonmagnetic spin-polarized semiconductors
• Used as tunneling barrier to produce spin-polarized current – SFM sandwiched between metallic layer (below)
220
0.65 eV 0.36 eV EF
200
160
X WK
L UW
L K UX
0
100
200 300 T (K)
400
500
(Left) Predicted band structure has 0.36 eV gap for spin up and 0.65 eV gap for spin down electrons. (Right) Resistivity deviates from linear metallic behavor due to semiconductor-like states (ΔE = 0.16 eV).
• Near 100% spin polarization from EuSe
Conclusion
• Large magnetic moments (large fringing fields)
Schematic densities of states for spin-polarized materials. The material’s magnetic structure interacts with the electrons, causing each spin to behave differently. This can be exploited to produce current of only one spin direction
240
-1
Past work on EuX (X = O, S, Se)
CrVTiAl is an ideal candidate to overcome these limitations. Predictions give: • ΔEG =0.29 eV • Zero magnetic moment • TC =2200 K
Data Expected Metallic Behavior Fit with semiconducting carriers
180
• Tunneling current decreases exponentially with increasing barrier height (see below) – The spin with the smaller gap tunnels easier – Effectively filters out spin with larger gap
• TC below 70 K – Too low for applications
Crystal structure for CrVTiAl
(predicted a = 6.20 Å)
• Spintronics manipulates electron spin direction
• Allows for lower power consumption
3 Lejeune ,
(·cm)
Gregory M.
1 Stephen ,
• Current
•
Spin-filter materials provide a convenient path to spinpolarized currents CrVTiAl is a promising candidate for applications – Low, temperature-independent moment – Semiconducting states
References 1. G. M. Stephen et al. App. Phys. Lett. 109, 242401 (2016). 2. I. Galanakis et al. J. Phys. Condens. Matter 26, 86003 (2014) 3. J.S. Moodera et al. J. Phys. Condens. Matter 19, 165202 (2007)
Spintronics: Next Generation Electronics 1Department
Michelle E.
of Physics, Northeastern University;
2 Jamer ,
2NIST
1 Buda ,
1 Lane ,
3,4 McDonald ,
Gianina Christopher Ian 1 3,4 1 Arun Bansil , Laura H. Lewis and Don Heiman
Brian
Bernardo
1 Barbiellini ,
Center for Neutron Research, NIST, Gaithersburg, MD; 3Department of Chemical Engineering, Northeastern University; 4Department of Mechanical and Industrial Engineering, Northeastern University
Abstract
Tunnel Junctions
Present-day electronics rely almost exclusively on the charge of electrons. However, by utilizing the intrinsic magnetic moment of the electron, which arises from its angular momentum or “spin”, spintronic devices can be produced that are smaller and more versatile than traditional electronic devices. Spin Filter Materials (SFMs) utilized in a tunnel-junction are ideal for producing the next generation of spintronic devices
Introduction: Spintronics
CrVTiAl
• Insulating barrier between metallic contacts
CrVTiAl synthesized via arc melting • Annealed at 1000 °C for 1 week
– Arrow shows magnet direction
and quenched in water
• Current produced through Quantum Tunneling
• Measured a = 6.136 ± 0.005 Å
• Magnetic Tunnel Junctions (MTJs) used in hard drive read-heads
• Near zero moment (m = 0.002 µB)
• Resistivity shows semiconducting carriers (ΔE = 0.16 eV) Spin Down Spin Up
1
• Used currently in memory applications
Energy (eV)
Spin Filter Materials (SFMs)
– Electron spin produces magnetic field
• Semiconductor with spin-dependent band gaps
– Hard Drive read heads, magnetic RAM Electron spin
• Requires spin polarized materials (shown below) • Present materials are ferromagnetic, producing harmful fringing fields that interfere with neighboring components • We seek nonmagnetic spin-polarized semiconductors
• Used as tunneling barrier to produce spin-polarized current – SFM sandwiched between metallic layer (below)
220
0.65 eV 0.36 eV EF
200
160
X WK
L UW
L K UX
0
100
200 300 T (K)
400
500
(Left) Predicted band structure has 0.36 eV gap for spin up and 0.65 eV gap for spin down electrons. (Right) Resistivity deviates from linear metallic behavor due to semiconductor-like states (ΔE = 0.16 eV).
• Near 100% spin polarization from EuSe
Conclusion
• Large magnetic moments (large fringing fields)
Schematic densities of states for spin-polarized materials. The material’s magnetic structure interacts with the electrons, causing each spin to behave differently. This can be exploited to produce current of only one spin direction
240
-1
Past work on EuX (X = O, S, Se)
CrVTiAl is an ideal candidate to overcome these limitations. Predictions give: • ΔEG =0.29 eV • Zero magnetic moment • TC =2200 K
Data Expected Metallic Behavior Fit with semiconducting carriers
180
• Tunneling current decreases exponentially with increasing barrier height (see below) – The spin with the smaller gap tunnels easier – Effectively filters out spin with larger gap
• TC below 70 K – Too low for applications
Crystal structure for CrVTiAl
(predicted a = 6.20 Å)
• Spintronics manipulates electron spin direction
• Allows for lower power consumption
3 Lejeune ,
(·cm)
Gregory M.
1 Stephen ,
• Current
•
Spin-filter materials provide a convenient path to spinpolarized currents CrVTiAl is a promising candidate for applications – Low, temperature-independent moment – Semiconducting states
References 1. G. M. Stephen et al. App. Phys. Lett. 109, 242401 (2016). 2. I. Galanakis et al. J. Phys. Condens. Matter 26, 86003 (2014) 3. J.S. Moodera et al. J. Phys. Condens. Matter 19, 165202 (2007)
