Slide 1
Juliana Marques Ramos1,2German Thesis Advisor: Reiner Vianden2,
Brazilian Thesis Advisor: Artur Wilson Carbonari1
Collaborators: Joo Guilherme Martins Correia, Rafael S de
Freitasand ISOLDE collaboration Carrier Mobility and Magnetic
Interactions in TiO21Instituto de Pesquiss Energticas e Nucleares,
So Paulo University, Brazil2Helmholtz-Instituts fr Strahlen- und
Kernphysik, Bonn University, Germany
1Non volatility +Current control trough spin- Increase density
of information stored per unit area and the speed of data
processing;- Reduces energy consumption;[1] FERT, A. Review of
Modern Physics, v. 80 n.4, 1517, 2008.[2] MOLNAR, V. S.; READ, D.
New materials for semiconductor spin-electronics.Proceedings of the
IEEE. v.91, p.715-726, 2003.[3] WOLF, S. A.;et. al.Spintronics: A
Spin-Based Electronics Vision for the Future.Science,v. 294,
p-1488-1495, 2001.Current control trough spin + Optic properties-
The combination of the two materials in a single chip would
function of various devices: - Gather logic, communication skills,
collective storage and detection [1]. To magnetic semiconductorsThe
control of spin-dependent phenomena in semiconductors can lead to
devices such as spin light-emitting diodes (spin-LEDs), spin field
effect transistors (spin-FETs) e spin qubits for quantic computers
[2, 3]. MotivationFrom magnetic metals...
2Fe dopingCandidate as DMS [1] Defects produced by the
dopingCandidate as DMS [1,2]Related works[1] J. M. D. Coey, M.
Venkatesan and C. B. Fitzgerald, Nature Materials, 4 (2005)
173.
[2] S. K. S. Patel, S. Kurian, N. S. Gajbhiye, AIP Advances, 2
(2012) 012107.RTFM
The absence of any sextet in fit-derived Mssbauer spectraclearly
showed that the ferromagnetic componentin the samples is not due to
metallic iron and iron oxide."3Results
Presence of magnetizations saturation as a function of the
field; Presence of the hysteresis curve M (H); Low coercive field
(applications which require switching) Significant remanent
magnetization (non volatile behavior)4Results
Rapid increase of the magnetization at a certain critical
temperature; Subtle anomaly near 50 K; The magnetization of a
paramagnet also increases when we decreasethe temperature.
5Considerations- Value of coercive field (low) and remanence.-
Macroscopic measurements provide only indications of a possible
existenceof FM long-range order (not to be confused with FM
correlations that occurseven at high temperature). - To be sure of
ferromagnetic long-range ordering- Origin of FM: existence of
clusters?
carry out neutron diffraction and observe magnetic diffraction
peaks.PAC Spectroscopy
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Coincidence
Magnetic interaction:Quadrupole interaction:
6
PAC Results: TiO2 + 3% FeProbe nuclei diffused!Sample has still
a lot of defects!Vzz ~ 6 x 1021 V/m2 Site 1: ~ 0.2 Site 2: ~
0.8Site 1: ~ 3 % Site 2: ~ 25 % Site 1: f ~ 40 % Site 2: f ~ 60
%
PAC Results: TiO2 + 3% FeSite 1Site 2Vzz = 6 x 1021 V/m2Vzz = 7
x 1021 V/m2 = 0.28 (0.01) = 0.71 (0.01) = 4 % (0.05) = 20 % (0.08)f
= 23 % (2)f = 77 % (7)L = 1,74 (0.13) Mrad/s B = 0,115 TL = 13,6
(1.1) Mrad/s B = 0,925 T13 K27 KSite 1Site 2Vzz = 6 x 1021 V/m2Vzz
= 7 x 1021 V/m2 = 0.27 (0.01) = 0.7 (0.01) = 2 % (0.01) = 15 %
(0.1)f = 22 % (2.1)f = 80 % (6)L = 1,74 (0.11) Mrad/s B = 0,115 TL
= 13,76 (1.01) Mrad/s B = 0,945 T70 K: (too weak)/no magnetic
ordering
PAC Results: TiO2
IS 481 PAC Results: TiO2 111mCd
PAC Results: TiO2 181Hf
After the EC decay of the 111In and the following Auger process,
the 111Cd atom is in a highly unstable charged state. In
semiconductor oxides, depending on the electronic and structural
properties of the impurityhost system, the 111Cd probe can trap
some electron holes for a time long enough (in the order of ns) to
reach the sensitive intermediate state of the 111Cd nuclei.
In the time interval of the PAC coincidence detection,
transitions between different charge states out of the equilibrium
can occur producing a time-dependent EFG at the 111Cd site.
SummaryRoom temperature ferromagnetismTwo electric quadrupole
interactionsWeak magnetism: not applicable in spintronic!Time
dependent EFG at 111Cd site
Future WorkX-ray absorption fine structure (EXAFS)
measurementsNeutron diffraction: long-range ferromagnetic
ordering?To be sure of ferromagnetic long-range ordering we will
carry out neutron diffraction and observed magnetic diffraction
peaks.
Looking for a Post Doc position
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Reactor team!
Dr. Reiner Vianden
Me! Mr. Marius Arenz IS481: Poster SectionDr. Patrick
KesslerThank you! Obrigada! Danke sehr!15
