Spin Waves Spin Waves Spin Waves Inelastic electron scattering - - PowerPoint PPT Presentation

Spin Waves

Spin Waves

Spin Waves

• Q|| = K|| = k||

f sin(θ0- θ) - k|| i sin(θ)

h = Ei - Ef W(110) Fe

[110] [110] [001] _

θ0 θ

ki kf

M

Q h

Inelastic electron scattering – SPEELS

3000 6000 100 200 1000 2000 3000

Intensity [counts/s] Diff Difference [counts/s] Energy Loss [meV]

Difference I = I - I

I I

K = 0.6 Å-1 E = 20 meV E = 4 eV 2 ML Fe/W(110) @ RT

Photocathode- preparation Sample preparation

• LEED
• MOKE
• Auger

SPEEL- spectrometer

• H. Ibach, D. Bruchmann, R. Vollmer,
• M. Etzkorn, P. S. Anil Kumar and J. Kirschner,
• Rev. Sci. Instrum., 74 (2003) 4089.

Analyzer Channeltron

circularly polarized light

180°-Monochromator 90°-Monochromator

GaAs- photocathode Polarization P = 0.75 ± 0.1

The SPEEL – Spectrometer

SPEELS – fundamental example

I

100 200 300 400 500 0.00 0.05 0.10

I

Energy loss (meV) Normalized intensity

spin wave excitation

Stoner-continuum

8 ML Co on Cu(001)

• R. Vollmer (†), M. Etzkorn, P. S. Anil Kumar, H. Ibach, J. Kirschner,
• Phys. Rev. Lett. 91, 147201 (2003).

K = 0.87 Å-1 E = 40 meV E = 6.7 eV

• 2
• 1

1 2 100 200 300 400

Wave vector (Å )

• 1

Spin wave energy (meV)

   X X X K K X 

SPEELS data neutron data

neutron data: R. N. Sinclair and B. N. Brockhouse, Phys. Rev. 120, 1638 (1960).

50 100 150 200 250 300

• 1.8 -1.5 -1.2 -0.9 -0.6 -0.3

0.0 0.3 0.6 0.9 1.2 1.5 1.8

25 50 75 100

FWHM (meV)

5 10 15 20

Difference (103c/s)

Wave vector(A

• 1)

Spin wave energy (meV)

Spin wave dispersion for the 2 ML Fe/W(110) film

Dbulk= 280 meVÅ2

 H _ H _ _ h = DQ

2(1 - Q 2)

D = 180 meVÅ2 ß = 0.256

NNH model for 2 ML Fe h = 12 JS [1 - cos(Qa0/2)]

• W. X. Tang, Y. Zhang, I. Tudosa, J. Prokop, M. Etzkorn, J. Kirschner, Phys. Rev. Lett. 99, 087202 (2007).

E = 20 meV E = 4 eV E = 25 meV E = 6.25 eV For Q > 1.1 Å-1

Brillouin light scattering (BLS) process

= inelastic scattering of photons from spin waves

sc = L

spectrum of scattered light

   q q q

SC L

 

Spin wave frequency Frequensy shift [GHz] anti-Stokes Stokes BLS-Intensity [Counts]

proportional to the spin wave intensity  2

Brillouin light scattering spectrometer

high-resolution interferometry with high contrast for measurements of acoustic phonons and spin waves

Courtesy of J. Hamrle, TU Kaiserslautern

Space and time resolved BLS

• O. Büttner et al., PRB 61, 11576 (2000)

spatial resolution: 30 µm (300nm) time resolution: 1.7 ns dynamic range: >60 dB

Brillouin light scattering spectrometer

Sketches of mechanical stage and mirror mount for the FP1 rigid mirror are reproduced from John Sandercock’s 1993 manual.

Tandem Fabry-Perot Interferometer

Spin waves in a magnetic film

Heusler compound Co2Cr1-xFexAl: Magnetic properties determined by BLS

• 30
• 20
• 10

10 20 30 500 1000 1500 2000 2500 3000 3500

CCFA/Cr 80 Oe H || [110] BLS intensity [a.u.] frequency [GHz]

Brillouin light scattering spectrum

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 4 6 8 10 12 14 16 18 20 22 24 26

BLS frequency [GHz] H [kOe]

Mesurement of perpendicular magnetization gradient

• 30
• 20
• 10

10 20 30 500 1000 1500 2000 2500 3000 3500

CCFA/Cr 80 Oe H || [110] BLS intensity [a.u.] frequency [GHz]

Courtesy of J. Hamrle, TU Kaiserslautern

by fit to model found: A=0.480.4 erg/cm3 (for bcc Fe: A=2.0 erg/cm3)

45 90 135 180 225 270 315 360 14.4 14.8 15.2 15.6 16.0

experimental data numerical fit

sample orientation [deg] B L S frequency [GH z]

Al(1.3nm)/Co2MnSi(30nm)/Cr(40nm)/MgO(100):

350 375 400 425 450 475 500 0,0 0,2 0,4 0,6 0,8 1,0

• K

1 [10 5 erg/cm 3]

annealing temperature [°C]

volume anisotropy constant K drops down by a factor of 10 B2 L21 K1=–9104 erg/cm3

Heusler compound Co2MnSi: anisotropy and structural transition

Courtesy of J. Hamrle, TU Kaiserslautern