Transcript SIMSERIDES EXMATEC04 POSTER

Temperature dependent magnetization and magnetic phases of
conduction-band dilute-magnetic-semiconductor quantum wells with non-step-like density of states
1,2
Constantinos Simserides
1
2
University of Athens, Physics Department, Solid State Section, Athens, Greece
Leibniz Institute for Neurobiology, Special Lab for Non-Invasive Brain Imaging, Magdeburg, Germany
SUMMARY
Density of States (DOS)
We study the magnetization and the magnetic phases of
*
m A
● the DOS deviates from the
II-VI-based n-doped non-magnetic-semiconductor (NMS) /
n
(

)


(


E
)
famous step-like (B→0) form.
i
,

2
narrow to wide dilute-magnetic-semiconductor (DMS) /
i ,
2
n-doped NMS quantum wells under in-plane magnetic field.
Not
only
the
general
shape
of
the
DOS
varies
,
but
this
effect
is
also
quantitative.
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.
• for any type of interplay between spatial and magnetic confinement

in-plane
n(  ) 
e.g. n-doped DMS
magnetic field
ZnSe / Zn1-x-yCdxMnySe / ZnSe
conduction band, narrow to wide,
QWs
DMS QWs
*
A 2m
2  2
2


 
i,


dkx
 (   Ei , ( k x ))
  Ei , ( k x )
Enhanced electron spin-splitting, Uoσ
*
U o
*
g m

 c  yN 0 J sp d SBS (  )    
2me
spin-spin exchange interaction
between
s- or p- conduction band electrons
and
d- electrons of Μn+2 cations
proportional to the cyclotron gap

g Mn  B SB  J sp d S
ndown  nup
2
k BT
Low temperatures.
Higher temperatures.
spin-splitting maximum,
~ 1/3 of conduction band offset
spin-splitting decreases
enhanced contribution of spin-up electrons
Feedback mechanism due to ndown(r) - nup(r).
RESULTS AND DISCUSSION
Dispersion, Density of States, Free Energy
Density of States diverges significantly
ideal step-like 2DEG form
L = 10 nm
(spatial confinement dominates)
~ parabolic spin subbands
A single behavior of
increase B 
Internal Energy
more flat dispersion 
Free Energy
few % DOS increase
Entropy
L = 30 nm
(drastic dispersion modification)
 severe changes
from
to physical properties:
Magnetic Phases, Spin Polarization
 
• spin-subband populations
N s ,down  N s ,up
Ns
Spin polarization tuned by varying
temperature and magnetic field.
• internal energy, U
• free energy, F
Spin-subband dispersion
and
• Shannon entropy, S
DOS
• magnetization, M
Magnetization
narrow L = 10 nm, almost parabolic dispersion
Spin-subband Populations
Free Energy
L = 30 nm
Internal energy
Entropy
considerable fluctuation of M
(if vigorous competition between
spatial and magnetic confinement)
L = 10 nm : almost parabolic dispersion
+ Depopulation of
higher spin-subband
L = 60 nm
(~ spin-down bilayer system)
L = 30 nm : strong competition between
spatial and magnetic confinement
Spin-subband dispersion
and
DOS
L = 60 nm : ~ spin-down bilayer system
L = 60 nm, ~ bilayer system
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.
L = 60 nm
Spin-subband Populations
Free Energy
Internal Energy
Entropy
♫
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 …
Bibliography
+ Depopulation of
higher spin-subband
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