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


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


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.


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:


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


PAC methodhfB

coincidence

hfN

L Bgm Magnetic interaction:

Electric quadrupole interaction: )12(4

IIeQVzz

Q


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


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


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%


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

0.06

0.08

0.10

-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

0.02

0.04

0.06

0.08

0.10

-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

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


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


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


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]


Zn O

Temperature dependence of the magnetic hyperfine field at 111 Cd in ZnO doped with Co.

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