h. p. gunnlaugsson /r. sielemann, 57 mn mössbauer collaboration at isolde/cern

H. P. Gunnlaugsson/R. Sielemann,

57Mn Mössbauer collaboration at ISOLDE/CERN

Magnetism in Iron Implanted Oxides: A Status Report

Århus: H. P. Gunnlaugsson, G. Weyer CERN: K. JohnstonMilan: R. Mantovan, M. FanciulliReykjavík: T. E. Mølholt, S. Ólafsson, H. P. GíslasonSouth Africa: D. Naidoo, K. Baruth-Ram, H. Masenda, W. Dlamini, W. N. SibandaLeuven: G. LangoucheBerlin: R. SielemannJapan: Y. Yutaka, Y. Kobahashi

57Mn Mössbauer collaboration at ISOLDE/CERN

Magnetism in Iron Implanted Oxides: A Status Report

Motivation (Magnetism in TM doped oxides)

Physical/technical introduction (CERN Mössbauer)

Experimental spectra Mn/Fe in ZnO and others

Ordered Magnetism versus Paramagnetism

Conclusion

Magnetic inventory

vacancy

TM

Transition metal probe

Metals alloys

componds

Dilute magnets

Defect magnetis

m

0

200

400

600

800

1000

1200

1400

1600

0 0.5 1 1.5 2

Spins/atoms

TC o

r T

N (

K)

Ferromagnetism

Minimum needed

Room temperature

Diluted magneticsemiconductors

57Fe emission Mössbauer spectroscopy

57Fe

57MFe (T½ = 98 ns)14.4 keV, I = 3/2

I = 1/2

57Co (T½ = 271 d)57**Fe (T½ = 8 ns)57Mn (T½ = 1.5 min)

EC

Coulombexcited-

ER = 40 eV

~ 10-9 eV

Mössbauer spectroscopy at ISOLDE/CERNProton Booster

Synchrotron

1.4 GeV p+

UC2 target

LaserSelective ionization of Mn and Sn

Accelerationto 60 keVImplantation

chamber

Mass separation

Mössbauer drive system and detector

~6108 At. s-1

Highlights:-Low concentrations of probe atoms (~10-4 At.%)

-Valence state of Fe

-Site symmetry

-Magnetic interactions

Implantation of 57Mn

III-V semiconductors

See poster presented by Hilary Masenda (PS3-24)

-5 -4 -3 -2 -1 0 1 2 3 4 5

Velocity (mm/s)

Rel

ativ

e em

issi

on (

arb.

uni

ts) GaAs

426 K

300 K

-Damage site-Substitutional Fe-Fe-V complexes

No 6-line magnetic pattern!

-12 -9 -6 -3 0 3 6 9 12

Velocity (mm/s)

Em

issi

on (

arb.

uni

t)

B ext = 0 Tq = 60o

ZnO without external magnetic field

H. P. Gunnlaugsson et al., APL, 2010 (accepted)

ZnO temperature series

-10 -7.5 -5 -2.5 0 2.5 5 7.5 10-10 -7.5 -5 -2.5 0 2.5 5 7.5 10

Rel

ativ

e em

issi

on (

arb.

uni

ts)

Velocity (mm/s)

450 K

433 K

370 K

366 K

339 K

300 K

837 K

795 K

664 K

579 K

522 K

494 K

See talk given by T. Mølholt after this talk

1.0

1.5

2.0

2.5

3.0

-12 -8 -4 0 4 8 12

Velocity (mm/s)

Rel

ativ

e em

issi

on Al2O3

T = 300 K

Other oxides:

See poster presented by H. P. Gunnalugsson (PS3-23)

See talk given by T. Mølholt after this talk and (PS3-22)

-12 -8 -4 0 4 8 12

Velocity (mm/s)

Rel

ativ

e em

issi

on

77 KFeS FeIFeD

Other oxides:

MgOT = 77 K

Mössbauer spectroscopy of magnetic materials

Single line resonance detector

57Mn (T½ = 1.5 min)

57*Fe 14.4 keVT½ = 98 nsI = 3/2

57Fe I = 1/2

mI

3/2

1/2-1/2-3/2

1/2

-1/2

Bhf·g3/2·mI

Bhf·g1/2·mI

mI = 0, ±1

BµB IgH NNˆˆ

Ferromagnetism (S = 5/2 good quantum number)

Bext

SampleMössbauer

Spectrum

Relative lineratios

Individual line ratios depend on the angle between Bext and

3 4 1 1 4 33 0 1 1 0 3

mI = 0

Temperatue dependent magnetic order

Bhf

Spins

Mössbauerspectra

Magnetic hyperfine field

TC or TN

T

-T Bhf

- No line broadening

Cold Hot

Slow paramagnetic relaxations

IJ

HHFI

3dLattice · charge, · phonons

Spins · nuclear- · electron-

Coupled(C) to:

electron spin

Lattice vibrations

Fe2+ (3d6)5D4

Fe3+ (3d5)6S5/2

ml

-2-1012

ml

-2-1012

Spin lattice relaxations

Sa ~ Sb

S ~ S

ss

Hdd orHex

)exp(

12

12 EE

HH exddss

Spin-spin relaxations

Conditions for static Bhf

C ≥ L (Nucl. Larmor time)C ≥ N (lifetime of Mössbauer state) Bhf not T dependent Otherwise broadened

Broadening in MS if >~0.1 at.%

Mössbauer spectra of paramagnetic Fe3+

Needs electron spin operators!

...ˆˆˆˆˆ NQIHFIEZICF HHHHH

±1/2±3/2

±5/2

6S5/2

+5/2

+3/2

+1/2

-1/2

-3/2

-5/2

Bext

Few K

SSHCFˆˆˆ D SµH BEZI

ˆˆ gB

Low B

SIH HFIˆˆˆ A

Plays a role. Combined electronic and nuclear states

High B (> 0.3 T)

Kramer doublets give sextets with

Bhf |SZ|

-12 -8 -4 0 4 8 12

Velocity (mm/s)

±5/2

±3/2

±1/2

Sum

High B (> 0.3 T)

Kramer doublets give sextets with

Bhf |SZ|

-12 -8 -4 0 4 8 12

Velocity (mm/s)

±5/2

±3/2

±1/2

Sum

Paramagnetism (slow relaxation)

Bext

Sample

Individual line ratios depend on the angle between Bext and

SZ = ±5/2

SZ = ±3/2

SZ = ±1/2

mI = 0 from SZ = ±3/2

ZnO at RT in Bext = 0.6 T

Sextet originating from Kramer doublets clearly observed

No relaxation at RT?

H. P. Gunnlaugsson et al., APL, 2010 (accepted)

Slow paramagnetic relaxations at RT plausible?

Temperature (K)

109

108

107

106

105

104

103

102

101100 102 103

Spi

n re

laxa

tion

rat

e (s

-1)

T1 data from

Tribollet et al.,(2008)

Broadening in MS

Does defect magnetism exist?

In ZnO, implanted Mn/Fe Fe3+ shows slow paramagnetic relaxations

-> No spin-spin relaxations with defects

<- Theory overestimates range of magnetism from isolated defects (Zunger et al., 2010), data misinterpretated and precipitation not documented (Potzger et al., 2008+)

Is defect or dilute magnetism myth?

Defect magnetism exists!

-10 -5 0 5 10-10 -5 0 5 10

Velocity (mm/s)

Rel

ativ

e em

issi

on (

arb.

uni

ts)

10 -10

Poly-crystalline

(iii)

HOPG (ii)

HOPG (i)14 K

40 K

100 K

200 K

25 K

295 K

Sext D2D1

S1

D2D1

S1

-Implantation of 57**Fe into Graphite

-Sextet (Fe2+) observed at 14 K

-Reduced Bhf at 40 K (not a static Bhf)

Sieleman et al., PRL, 2007

Conclusions/summary-Implanted Mn/Fe ions in oxides lead to TM in various charge states and lattice sites

-Fe as 3+ state has extremely long relaxation time and displays static (para)-magnetic spectra. Most extreme case Fe in ZnO.

-Application of external magnetic field decouples perturbing fields and yields spectrum looking like an effective magnetic field.

-Identification of defect related magnetism by Mössbauer spectroscopy has been observed at very low temperatures in graphite.

Thank you

IS443 summer 2009 missing K. Johnston, M. Fanciulli,

K. Baruth-Ram, Y. Kobahashi