The βNMR facility at TRIUMF:

new tools for Materials Science at the nanoscale

W.A. MacFarlane1, G.D. Morris2

1Chemistry Department, University of British Columbia, Vancouver

2TRIUMF, Vancouver

ACS Boston, FRIB Symposium, Aug 24, 2010

TRIUMF

UBC

2 km

Whistler

123 km

Downtown

Vancouver

http://www.triumf.ca/ 12 km

Outline

1. TRIUMF βNMR/βNQR facility

2.Why use βNMR to study materials ?

3.A few examples:

a. magnetic proximity effects in metalsb. spin injection, dilute magnetic semiconductorsc. interface properties of high Tc superconductors

1. The βNMR Method

high energy radiation is

easy to detect

use them to elucidate

physical, chemical and biological processes

Radiotracers

Positron

Emission

Tomography

Parity Violation

ß emission iscorrelated withthe spin directionof the decayingnucleus,

violating mirrorsymmetry

Lee and Yang 1957

8Li 8Be + e- + ne

Spin=2, Q=+31 mbg =6.3 MHz/T<A>=-1/3 t= 1.2s

q

13 MeV

N(E)

E

Asymmetric Nuclear b-decay of 8Li

Isotopes for bNMR at ISAC

Isotope Spin τ1/2 g b-Decay Estimated

(MHz/T) Asymmetry Rate (s-1)

8Li 2 0.8 6.3 0.33 108

11Be 1/2 13.8 22 ~0.3 107

15O 1/2 122 10.8 0.66 108

19O 5/2 26.9 4.6 0.71 108

17Ne 1/2 0.1 0.33 106

require: light, short-lived,high asymmetry

H0

Backward

Forward

βNMResonance

H1cos(ωt)

18895 18900 18905 18910-0.30

-0.25

-0.20

-0.15

-0.10

Asy

mm

etry

Frequency (kHz)

w0

two polarizations

Bloc

w0 = gH0

H0

Backward

Forward

1 / T1time

0 2 4 6 8 10-0.20

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

Asy

mm

etry

Time (s)

Beam on

For 0.5s

Pd Foil

T = 293 K

B0 ~ 140 G

ELi = 30 keV

T1 ~ 1.65 s

βNMR Measurement of the Spin Lattice Relaxation Rate

nb: error bars

grow as exp(t/τ)

data for the

two polarizations

TRIUMF Implementation

seeβNMR: Morris et al., Phys. Rev. Lett. 93, 157601 (2004). βNQR: Salman et al., Phys. Rev. B 70, 104404 (2004).facility: Kiefl et al., Physica B 326, 189 (2003).polarizer: Levy et al., NIMB 204, 689 (2003).

ISAC Production Target

500 MeV

Proton Beam

Foils:

Ta

SiC

ZrCExtracted ion beam ~30 keV

To

Isotope

Separator

×

M. Dombsky/TRIUMF

for Li+: surface ionization

βNMR

βNQR

Titan

Osaka

ISAC Low Energy Area

Optical Polarizer

Circularly Polarized Laser

Li+ ion beam

D1 in Li: 671 nm

Polarization of 8Li Nuclei in 4.1 T

0 100 200 300

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1N

ucle

ar

Po

lari

za

tio

n

Temperature (K)

Thermal Equilibrium Value

Optical Polarized Value

Spin Polarized 8Li+

Polarizer

βNQR

Spectrometer

βNMR Spectrometer

Fast Kicker (2005) allows semi-simultaneous operation

βNMR Spectrometer

9 TeslaNMRMagnet

Loading a sample into the high-field βNMR spectrometer

Load Lock

10-9 torr

Cryostat drives into solenoid bore (9 Tesla)

Gold Foil

Hap

ke/

TR

IUM

F

βNQR Spectrometer

8 mm

8Li at 5 keV

beam stoppedin scintillator,imaged with CCD

βNQR sample ladder

βNMR Cleanroom

Uses:

- Sample handling

- UHV cryostat

maintenance

R. Abasalti

1996

Mössbauer

Perturbed Angular Correlations

Muon Spin Rotation SRβNMR

…

Nuclear Techniques to

Study the Solid State

2. Why use βNMR

to study materials?

Solid Interfaces

A B

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

atomicresolution

Deceleration of the Ion Beam

Beam

Energy

30.4 keV

range in the probe ions: depth resolution!

Relation to Fundamental Properties

HM = -= i

)0,0( = AShift:

0

02

1

),()(

1

w

w qqAkT

T q

Relaxation:

Magnetic Susceptibility

Moriya Expression

In the RF (μeV to zero)

can be multicomponentand/or inhomogeneous

also: quadrupolar effects, diamagnetic shielding, ...

3. Examples

Magnetic Proximity Effect

Fe Ag

MetallicFerromagnet

NonmagneticMetal

M

?

Depth Resolved βNMR in Magnetic Multilayers

• Ag/Fe epitaxial heterostructures

• T.A. Keeler et al., Phys. Rev. B 77, 144429 (2008)

25820 25830 25840 25850 25860

Frequency [kHz]

4nm Gold (20 monolayers)

80nm Silver

2nm Iron

GaAs

2 μg!

e.g. Magnetic Proximity Effect

Fe Ag

MetallicFerromagnet

NonmagneticMetal

M

Using implanted 8Li ßNMR,

aymptotic behaviour of the envelope ~ r -2

Keeler et al. Phys. Rev. B 77, 144429 (2008)

Towards Spin Injection

Fe n-GaAsAu

20ML 14ML

magnetized

V

spin injectionSchottky Barrier

- +- +- +

Access to the Schottky Barrier Region

Q. Song

electrostaticpotentialwithin GaAs

implantationprofilesfrom SRIM

Avoiding the Schottky Barrier

with

Dilute Magnetic Semiconductors:

GaAs:Mn

Q. Song

Dilute Magnetic Semiconductors

dilute local (atomic) magnetic momentsMn2+ S = 5/2

a backgroundof free carriers(holes)

Mn doped GaAs

Mn acceptor (STM)

Yakunin et al. PRL 92, 216806 (04)Substitutional (Ga): Acceptor

Interstitial: Double Donor

Ga1-xMnxAs is not stable in bulk

180 nm Ga0.95Mn0.05As / GaAs

Sharp Substrate

Line

Depth Dependence at 50 K (< TC)

broad, negatively shifted line,fast spin relaxation from theMn doped layer

Q. Song et al., Physica B (2009)

unpublished data removed here

Time Reversal Symmetry

Breaking Superconductivity?

H. Saadaoui

AgYBa2Cu3O7

15 nm

d-wave

superconductor

110

5 nm ?

small spontaneous magnetic fields

ProximalDetection

Surface Effects in d wave SC

H // film

Search for broken time reversal

symmetry near the surface of

<110> YBa2Cu3O7 (Urbana

Tc=86.7K) (Hassan Saadaoui)

Beam energy 2 keV

<110> YBa2Cu3O7 film

from L.H. Greene

Competition

Low

Energy

Muon

Facility

at PSI

http://lmu.web.psi.ch/

low energy via moderation, reacceleration

CollaborationR.F. Kiefl (UBC, Phys), K.H. Chow (Alberta, Phys) S.R. Dunsiger (TU

Munich), Z. Yamani (NRC-CINS, Chalk River), E. Morenzoni, Z.

Salman (PSI)

Students: T. Parolin, H. Saadaoui, M.D. Hossain, Q. Song, A. Mansour,

D. Wang, M. Smadella, T. Keeler, I . Fan, and many undergrads

TRIUMF: G.D. Morris, C.D.P. Levy, M.R. Pearson, A. Hatakeyama

(Tokyo), S. Daviel, R. Poutissou, D. Arseneau, R. Baartman, M. Olivo,

S.R. Kreitzman

SAMPLES:L.H. Greene (Urbana), T. Hibma, S. Hak (Groningen), B.

Heinrich (SFU), Y. Maeno (Kyoto), P. Fournier (Sherbrooke), J.Y.T. Wei

(Toronto), J.W. Brill (Kentucky), J. Chakhalian (MPI-Stuttgart,

Arkansas), G. Condorelli, R. Sessoli (Florence), C. Ferdeghini (Genoa),

J.K. Furdyna (Notre Dame), K.M. Yu (LBL), N.J.C. Ingle (UBC), R.

Liang, D.A. Bonn, W.N. Hardy (UBC), E. Katz (Beer Sheva), F. Fujara

(TU Darmstadt), R. Neumann (GSI), T. Tiedje (UBC, UVic)

End

more info:bnmr.triumf.ca