Temperature dependence of the magnetic hyperfine field at 111 Cd in ZnO doped with Co.
description
Transcript of Temperature dependence of the magnetic hyperfine field at 111 Cd in ZnO doped with Co.
HFI /NQI 2010 – CERN, Geneva A. W. Carbonari
Temperature dependence of the magnetic hyperfine field at 111Cd in ZnO
doped with Co.
A. W. Carbonari, M. E. Mercurio, M. R. Cordeiro, and R. N. Saxena
IPEN - Instituto de Pesquisas Energéticas e Nucleares São Paulo - Brasil
Hyperfine Interactions Laboratory
HFI /NQI 2010 – CERN, Geneva A. W. Carbonari
Introduction
Thomas Dietl , et al. Science 287, 1019 (2000) – calculated that ZnO doped with 5% of Mn would present TC above room temperature.
Yuji Matsumoto, et al. Science 291, 854 (2001) – measured magnetization in TiO2doped with 7% Co. Results showed TC > 400 K and saturated magnetization = 0.32 mB
Semiconductor oxides doped with 3d ions are good candidates to produceDiluted magnetic semiconductor (DMS) material for spintronics
ZnO, In2O3, TiO2, SnO2, SnO, etc. are wide band-gap semiconductor oxides, which have been reported to show ferromagnetic ordering when doped with transition metal elements
HFI /NQI 2010 – CERN, Geneva A. W. Carbonari
Introduction
Almost all papers which have reported the occurrence of ferromagnetism in ZnO doped with different transition elements observed it by magnetization measurements.
Several papers have, however, reported that samples of ZnO doped with transition metal elements do not show magnetism.
Magnetic ordering observed:
• Only in nano-structured thin films,
• not in bulk samples,• only in small fraction of samples
(2% to 3%)• It is likely due to defects (oxygen
vacancies).
Magnetic ordering not observed:
• magnetism could come from impurities in samples,
• defects in samples are difficult ot control.
HFI /NQI 2010 – CERN, Geneva A. W. Carbonari
Introduction
An investigation of doped ZnO samples using a very sensitive local technique would help to understand the occurrence of magnetism in these materials.
In this work perturbed angular correlation (PAC) technique was used to investigate the electric quadrupole interactions during preparation of ZnO samples doped with Co as well as to study the temperature dependence of the magnetic hyperfine field (Bhf) in one of them.
Bad samples show magnetism
Good samples don’t show magnetism
Latest explanation about this controversy is that:
HFI /NQI 2010 – CERN, Geneva A. W. Carbonari
PAC methodPAC measures the time dependence of the g-ray emission pattern. This evolution in time is caused by hyperfine interactions
The angular distribution of the emission pattern is given by the correlation function
W(q,t) = 1 + A22G22(t)P2(cosq)
Hyperfine interactions cause a precession of the emission pattern described by the perturbation factor
HFI /NQI 2010 – CERN, Geneva A. W. Carbonari
PAC methodhfB
coincidence
hfN
L Bgm Magnetic interaction:
Electric quadrupole interaction: )12(4
IIeQVzz
Q
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Experimental
Sample preparation:
Zn(1-X)Co(X)O (Powder)
Zn (99.9999%) dissolved in HNO3
Mixed aqueoussolution
Gel
xerogel
Co(99.9999%) dissolved inHNO3
Sol. heatedand
stirred citric acid
+Ethylene
glycol
111InCl3
350 oC
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0 100 200 300 400-0.05
0.00
0.05
0.10-0.05
0.00
0.05
0.10-0.05
0.00
0.05
0.10
time(ns)
Commercial ZnO
Sol-gel ZnO
-R(t)
Sol-gel Zn0.95Co0.05O
0 100 200 300 400
0.00
0.05
0.10
Time (ns)
ZnO (Commercial)
0.00
0.05
0.10
-R(t)
ZnO (HCl)
0.00
0.05
0.10
ZnO (HNO3)
0.00
0.05
0.10
ZnO (H2SO
4)
0 100 200 300 400
0.00
0.05
0.10
0.00
0.05
0.00
0.05
0.00
0.05
0.10
Time (ns)
ZnO (5%Co) Tm= 77K
-R(t)
ZnO (5%Co) Tm= 295K
ZnO (1%Co) Tm= 295K
ZnO Tm= 295K
ResultsTwelve samples of pure ZnO: < v Q > = 31.9(3)
MHzseveral samples of ZnO doped with different concentrations of Co, Mn, Cu:
v Q ~ 32(4) MHz
HFI /NQI 2010 – CERN, Geneva A. W. Carbonari
1 2 30.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
fract
ion
ResultsZnO doped with 10% of Co
0 50 100 150 200 250 300 350-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
-R(t)
t (ns)
Tann = 350 ºC
1 - Xerogel: after first annealing at 350 oC
0 50 100 150 200 250 300 350-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Tann = 500 ºC
-R(t)
t (ns)
3 - pellet: annealing at 500 oC in N2
0 50 100 150 200 250 300 350-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Tann = 500 ºC
-R(t)
t (ns)
2 - annealing at 500 oC in flowing N2
nQ1 = 31 MHz, h1 = 0.3, d1 = 9%, f1 = 8%
nQ2 = 150 MHz, h1 = 0.2, d1 = 7%, f1 = 12.5%
nQ3 = 190 MHz, h1 = 0, d1 = 58%, f1 = 79.6%
HFI /NQI 2010 – CERN, Geneva A. W. Carbonari
0 50 100 150 200 250 300 350-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.00
0.02
0.04
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-0.02
0.00
0.02
0.04
0.06
0.08
0.10
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
1000 K
t(s)
950 K-R(t)
900 K
775 K
0 50 100 150 200 250 300 350-0.02
0.00
0.02
0.04
0.06
0.08
0.10
-0.02
0.00
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-0.02
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0.10
-0.02
0.00
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0.10
t (s)
1175 K
-R(t)
1100K
1075 K
1025 K
Results
Sample sealed in a quartz ampoule at 2 x 10–2 mbar
200 400 600 800 1000 12000.0
0.1
0.2
0.3
0.7
0.8
0.9
1.0
1.1
fract
ion
temperature (K)
32 MHz
151 MHz
broad-distribution nQ Sample measured at different temperaturesfrom ~500 oC to ~900 oC
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0 100 200 300 400-0.04
0.00
0.04
0.08
0.12295 K (after cooling)
-R(t)
t(s)
0 100 200 300 400-0.04
0.00
0.04
0.08
0.12
-R(t)
t(s)
295 K (before cooling)
0 100 200 300 400-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
0.20
t(s)
290 K-R(t)
50 K
0 50 100 150 200 250 300 3500.0
0.5
1.0
1.5
2.0
2.5
Bhf [
T ]
T [ K ]
Resultsquartz ampoule was broken: sample measured at room temperature
Sample measured from 50 K to 295 K
• Bhf ~ 2T• First order transition• Unusual magnetic behavior
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30 40 50 60 70 80 90 100
-1000
0
1000
2000
3000
4000
5000
6000
7000
Inte
nsity
(a.u
.)
2q(Deg.)
Zn0.9Co0.1O
Sample quality checked be X-ray diffractomertry, SEM and EDS
Good bulk sample showing magnetism!
Results
HFI /NQI 2010 – CERN, Geneva A. W. Carbonari
0 100 200 300-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
-R(t)
t(s)
1025 K
0 100 200 300 400-0.04
0.00
0.04
0.08
0.12
-R(t)
t(s)
295 K (before cooling)
ConclusionKey to understand the occurrence of magnetism:
Explanation of the probe environment corresponding to nQ = 151 MHz
In2O3 ? nQ1 = 155 MHz h = 0 (29%) nQ2 = 119 MHz h = 0.71 (71%)[S. Habenicht et al. Z. Phyz. B101(1996)187]
Co2O3 ? nQ = 146 MHz h = 0.15 [Z. Inglot et al. J. Phys.:condens. Matt. 3(1991)2137]TN = 40 K
CoO ? nQ = 0 TN = 298 K Bhf (4K) = 17.7 T[H. H. Rinneberg, D. A.Shyrley, Phys. Rev. 13(1976)2138]
In – VOX ? nQ = 185 MHz h = 0.1 in ZnO + Zn [S. Deubler et al., Nucl. Instrum. Meth. B63(1992)223]
In near interstitial Zn ? nQ = 170 MHz h = 0.12 in ZnO + Zn [R. Wang et al., J. Solid State Chem. 122(1996)166]
HFI /NQI 2010 – CERN, Geneva A. W. Carbonari
Zn O