Neutron scattering studies of magnetic semiconductor thin films and superlattices. T. M. Giebultowicz 1 and Henryk Kępa 2,1 1. Dept. of Physics, Oregon State university, Corvallis, OR,USA 2. Institute of Experimental Physics, Warsaw University, Poland Subtitle:
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Neutron scattering studies of magneticsemiconductor thin films and superlattices
T. M. Giebultowicz1and Henryk Kępa2,1
1. Dept. of Physics, Oregon State university, Corvallis, OR,USA
2. Institute of Experimental Physics, Warsaw University, Poland
Doing neutron scattering in Oregon?
Magnetic semiconductors - historical remark: MOTHER NATUREmade them almost exclusivelyantiferromagnetic!
When we started our research long time ago, we had no other choice
than to study
Antiferromagnetic / NonmagneticSuperlattices (e.g., EuTe/PbTe)
AFM Bragg reflection
bulk TN = 9.6 K
EuTe 3-m epilayer
NIST Center for Neutron Research NG1reflectometer
= 4.75 Ǻ
New epitaxial systems:
Curie temperatures for
strongly p-type alloys
with 5% Mn.
Year 2000: We find Dr. A. Sipatov from
Ukraine, who grows very interesting
EuS/PbS and EuS/YbSe superlattices!
EuS – Heisenberg ferromagnet TC = 16.6 K (bulk), Eg=1.5 eV
PbS – narrow-gap (Eg=0.3 eV) semiconductor (n≈ 1017 cm-3)
YbSe – wide-gap (Eg=1.6 eV) semiconductor (semiinsulator)
all NaCl-type structure with lattice constants:
(lattice mismatch ≈ 0.5%)
number of repetitions
Unpolarized neutron reflectivity experiments on
the EuS/PbS system
(NG-1 reflectometer, NIST Center for Neutron Research)
Interlayer exchange coupling mediated by valence band electrons
J.Blinowski & P.Kacman, Phys. Rev. B 64 (2001) 045302.
P.Sankowski & P.Kacman, Acta Phys. Polon. A 103 (2003) 621
Advantages of using polarized neutrons…
FM domains in Ga(Mn)As/GaAs superlattices
Here are data from a Ga(Mn)As/GaAs superlattice
(6% of Mn) obtained using an unpolarized beam:
Polarized neutron beam experiments – the principles
Atomic spins S and the applied magnetic
field H lie in the x-z reflecting planes.
External field H and the neutron
polarization P are parallel to z-axis
Parallel to H projections of S non-spin-flip (NSF) scattering
Perpendicular ones purely magnetic spin-flip (SF)
Polarized neutron reflectivity profiles for the
EuS/YbSe (46/20) Å.
in-plane  axis horizontal
EuS/PbS (30/4) Å - polarization analysis of the 1-st AFM SL Bragg peak
Polarized neutrons and the in-plane magnetic anisotropy in EuS/PbS & EuS/YbSe
EuS/PbS superlattices on (111)BaF2
Polarized neutron reflectivity studies
…. etc., where:
is the angle of rotation of the sample about Q
Neutron polarization analysis
For saturated sampleα=90º