Post on 08-Jan-2016
description
Magnetization and magnetic phases of conduction-band dilute-magnetic-semiconductor quantum wells with non-step-like density of states
Constantinos Simserides 1,2
1 University of Athens, Physics Department, Solid State Section, Athens, Greece 2 Leibniz Institute for Neurobiology, Special Lab for Non-Invasive Brain Imaging, Magdeburg, Germany
Density of States (DOS)
,i ,i )E(Am
)(n*
22
● the DOS deviates from the famous step-like (B→0) form.
Not only the general shape of the DOS varies , but this effect is also quantitative.
• for any type of interplay between spatial and magnetic confinement
,i x,i
x,ix
*
)k(E
))k(E(dk
mA)(n
222
2
RESULTS AND DISCUSSION
Density of States diverges significantly from ideal step-like 2DEG form
severe changes to physical properties:
• spin-subband populations
• internal energy, U
• free energy, F
• Shannon entropy, S
• magnetization, M
~ parabolic spin subbands
increase B
more flat dispersion
few % DOS increase
A single behavior of
Internal Energy
Free Energy
Entropy
L = 10 nm (spatial confinement dominates)
L = 30 nm(drastic dispersion modification) Spin-subband dispersion and DOS
Spin-subband Populations Internal energyFree Energy Entropy
L = 30 nm
+ Depopulation of higher spin-subband
L = 60 nm(~ spin-down bilayer system)
Spin-subband dispersion and DOS
L = 60 nm Spin-subband Populations Internal EnergyFree Energy Entropy
+ Depopulation of higher spin-subband
Bibliography[1] H. Ohno, J. Magn. Magn. Mater. 272-276, 1 (2004); J. Crystal Growth 251, 285 (2003). [5] S. P. Hong, K. S. Yi, J. J. Quinn, Phys. Rev. B 61, 13745 (2000). [9] H. W. Hölscher, A. Nöthe and Ch. Uihlein, Phys. Rev. B 31, 2379 (1985). [2] M. Syed, G. L. Yang, J. K. Furdyna, et al, Phys. Rev. B 66, 075213 (2002). [6] H. J. Kim and K. S. Yi, Phys. Rev. B 65, 193310 (2002). [10] B. Lee, T. Jungwirth, A. H. MacDonald, Phys. Rev. B 61, 15606 (2000).[3] S. Lee, M. Dobrowolska, J. K. Furdyna, and L. R. Ram-Mohan, Phys. Rev. B 61, 2120 (2000). [7] C. Simserides, Physica E 21, 956 (2004). [11] L. Brey and F. Guinea, Phys. Rev. Lett. 85, 2384 (2000).[4] C. Simserides, J. Comput. Electron. 2, 459 (2003); Phys. Rev. B 69, 113302 (2004). [8] H. Venghaus, Phys. Rev. B 19, 3071 (1979).
Epilogue - Outlook
☺ Magnetization of conduction-band, narrow to wide NMS/DMS/NMS structures with in-plane B.
☺ If strong competition (spatial vs. magnetic) confinement impressive fluctuation of M.
☺ Spin polarization tuned by varying T and B.
♫ In this poster we have approximated ndown(r) – nup(r) by (Ns,down - Ns,up) / L …
♫ A more orderly study of the magnetic phases will be hopefully presented …
Dispersion, Density of States, Free Energy
considerable fluctuation of M(if vigorous competition between spatial and magnetic confinement)
L = 10 nm : almost parabolic dispersion
L = 30 nm : strong competition between spatial and magnetic confinement
L = 60 nm : ~ spin-down bilayer system
Magnetization
Enhanced electron spin-splitting, Uoσ
Low temperatures.
spin-splitting maximum,~ 1/3 of conduction band offset
Higher temperatures.
spin-splitting decreases enhanced contribution of spin-up electrons
Feedback mechanism due to ndown(r) - nup(r).
)(SBJyNm
mgU Sdspc
e
**
o 02
Tk
nnSJSBg
B
updowndspBMn 2
spin-spin exchange interaction between
s- or p- conduction band electrons and
d- electrons of Μn+2 cations
proportional to the cyclotron gap
Spin polarization tuned by varying temperature and magnetic field.s
up,sdown,s
N
NN
narrow L = 10 nm, almost parabolic dispersion
Magnetic Phases, Spin Polarization
L = 60 nm, ~ bilayer system
in-plane
magnetic field
SUMMARYWe study the magnetization and the magnetic phases of
II-VI-based n-doped non-magnetic-semiconductor (NMS) / narrow to wide dilute-magnetic-semiconductor (DMS) /
n-doped NMS quantum wells under in-plane magnetic field.The parallel magnetic field is used as a tool, in order to achieve
non-step-like density of states in these -appropriate for conduction-band spintronics- structures.
conduction band, narrow to wide, DMS QWs
e.g. n-doped DMS ZnSe / Zn1-x-yCdxMnySe / ZnSe QWs