Edith Cowan University
Research Online
ECU Presentations
2011
Nano-engineered high-performance magnetooptic garnet materials
Mohammad Nur-E-Alam
Edith Cowan University, m.nur-e-alam@ecu.edu.au
Mikhail Vasiliev
Edith Cowan University, m.vasiliev@ecu.edu.au
Viacheslav Kotov
Institute of Radio Engineering and Electronics, Russian Academy of Sciences
Kamal Alameh
Edith Cowan University, k.alameh@ecu.edu.au
Presented at the 2011 International Conference on Materials for Advanced Technologies (ICMAT), 26th June-1st July, 2011, Suntec, Singapore.
This Presentation is posted at Research Online.
http://ro.ecu.edu.au/ecupres/8
Nano-engineered high-performance
magneto-optic garnet materials
Mohammad Nur-E-Alam1, Mikhail Vasiliev1, Viacheslav Kotov2
and Kamal Alameh1
1Electron
Science Research Institute, Edith Cowan University, 270 Joondalup Dr,
Joondalup, WA 6027, Australia
2Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 11
Mohovaya St, Moscow 125009, Russia
OUTLINE
• Introduction
 Introduction to Bismuth- and rare-earth-substituted iron garnets and
application examples
• Material synthesis and characterization
 RF magnetron sputtering technology
 Conventional oven annealing for crystallizing the amorphous layers
• Thin-film engineered garnet materials, properties &
applications
 (Bi, Dy)3(Fe, Ga)5O12 and
 (Bi, Lu)3(Fe, Al)5O12
Introduction to Rare Earth Iron garnets
Rare-earth iron garnets: R3Fe5O12 where R is a rare earth atom
• Commonly known garnet materials are:
Yttrium Iron garnet (YIG = Y3Fe5O12),
Gadolinium Gallium garnet (GGG= Gd3Ga5O12) and
Bismuth Iron garnet (BIG = Bi3Fe5O12 )
Crystal structure of
magnetic garnets
• The two very important subclasses of garnets for use in magneto-optic (MO) applications
are described by:
(Bi, Dy)3(Fe, Ga)5O12 and
(Bi, Lu)3(Fe, Al)5O12
- Bismuth-substituted rare-earth iron garnets doped with Ga or Al, of importance due to
the strong Faraday effect and a large variety of possible properties adjustable through
• Still considered to be the best transparent MO material for
material composition
non-reciprocal optical components
 magnetic recording media
 magnetic field sensors
MO imaging media
MO planar waveguides
magnetically-tunable photonic crystal structures
Background theory: Faraday effect
Magneto-optical phenomenon = interaction between light and magnetic field
β=VBd
β = Faraday rotation angle
V = Verdet constant
d = material thickness
MO material
For thin-film materials, we use
specific Faraday rotation:
θF [ °/µm] = β / d
(at B = Bsat)
Extraordinary magneto-optical properties of Bi-substituted iron garnets first
reported in 1969 (C. F. Buhrer, J. Appl. Phys. 40(11), 4500–4502, 1969).
• Highest specific Faraday rotation in the visible and near-IR regions (of all
semi-transparent dielectric materials)
Thin film materials synthesis & characterization
Optical
characterization
MO characterization
Magnetic and
microstructural
characterization
RF Magnetron sputtering
(a common method & very
suitable for integratedoptics devices)
Our system at ESRI, ECU
• The parameters of importance are: film thickness, absorption spectra, specific
Faraday rotation, coercive force, switching field, saturation field, and
magnetization direction
• Optimization of magnetic properties is crucial for the development of new
functional materials and for many emerging technologies in integrated optics and
photonics
MO thin films & process parameters
Photographs of a correctly annealed garnet-Bi2O3 nanocomposite thin film and
of two other nanocomposite films of similar type, but over-annealed
• Amorphous films: High optical absorption + no magnetism ⇒ Zero
Faraday rotation
• Crystallized films: Low optical loss + magnetization ⇒ High MO
figures of merit are possible
Q [°] = 2 * |ΘF| [°/µm] / α [µm-1]
The optimized annealing regimes for highly Bi-substituted garnet
materials are strongly dependent on the film composition
Transmission(%)
Absorption coefficient (cm-1)
Bi2Dy1Fe5-xGaxO12 : Bi2O3 thin film materials and
engineering of their optical properties
Wavelength (nm)
Wavelength (nm)
• The parameters of importance are: absorption coefficient and specific Faraday rotation
spectra. Co-deposition from a garnet-stoichiometric target + Bi2O3 target reduces absorption
significantly (M. Vasiliev, M. N. Alam et al, Opt. Express 17(22), 19519–19535, 2009).
• Correctly annealed films with optimized Bi2O3 content also show increased Faraday rotation
(M. Vasiliev, M. Nur-E-Alam, K. Alameh et al, J. Phys. D Appl. Phys. 44(7), 075002, 2011).
Bi2Dy1Fe5-xGaxO12 : Bi2O3 thin film materials and
their properties – Faraday rotation
Specific
remnant
magnetization
SpecificFaraday
Faraday rotation
rotation, atat
remnant
magnetisation
(deg/ (deg/
µ m) µm)
11
GGG \ Bi2Dy1Fe4Ga1O12, specific Faraday rotation measured in thin (150 nm)
films
532, 10.12
10
532, 9.8
GGG \ Bi2Dy1Fe4Ga1O12, specific Faraday rotation measured in thick (> 500
nm) films
9
8
Material’s phase
content depends on
the process
parameters
Composite 300 W Bi2Dy1Fe4Ga1O12 + 90 W Bi2O3 layers on GGG measured specific Faraday rotation data points in films with t > 500 nm
7
Composite 200 W Bi2Dy1Fe4.3Ga0.7O12 + 25 W Bi2O3 layers on GGG measured specific Faraday rotation data points in films with t > 500 nm
6
MO Figure of Merit,
GGG \ Bi2Dy1Fe4.3Ga0.7O12, specific Faraday rotation data points measured
in thick (> 500 nm) films
5
Q = 2 * |ΘF| / A;
ΘF = 0.1 – 10 °/µm;
4
A = 0.01 – (> 7000) cm-1
532, 4
3
We achieved:
635, 2.6
2
Q (green) ≈ 30°
670, 1.9
635, 1.66
670, 1.54
780, 0.89
Q (red) ≈ 50°
1
780, 0.67
635, 1.1
670, 0.79
780, 0.47
0
500
Optical properties of
garnet layers depend
significantly on the
material phase
520
540
560
580
600
620
640
660
680
700
720
Wavelength (nm)
Wavelength
(nm)
740
760
780
800
820
Q (1550 nm range) is
expected to be > 1000
Crystal structure properties of Bi2Dy1Fe5-xGaxO12
thin film materials
1600
(420)
1400
Intensity (arb. units)
1200
(422)
Fe3O4
(642)
1000
Bi2Dy1Fe4Ga1O12: Bi2O3 composite film on glass, annealed at 580 °C
(211)
800
(400)
Fe3O4
(640)
(444)
(842)
(800)
(220)
600
Bi2Dy1Fe4.3Ga0.7O12: Bi2O3 composite film on glass, annealed at 560 °C
(321)
400
Fe3O4
(521)
200
Bi2Dy1Fe4Ga1O12 film on glass, annealed at 620 °C
0
10
20
30
40
50
60
70
2Θ (degs)
Stronger garnet-phase reflection peaks and weaker iron oxide peaks observed in
high-performance oxide-mixed composites
•Garnet phase with bcc cubic lattice type
• Crystal lattice parameters have been calculated from XRD data
• Average grain size 37 nm (agrees with TEM imaging results)
80
Magnetic properties of Bi2Dy1Fe5-xGaxO12 thin film
materials
10
Downwards from "+" saturation
Upwards from "-" saturation
8
Return path to memory state from point at 1580 Oe
Coercive force
(1.25 kOe)
Faraday rotation (deg/mm)
6
Return path to memory state from point at 910 Oe
back to near demagnetized state and into virgin
magnetization loop
Return path to memory state from point at 582 Oe
4
2
0
-3000
-2000
-1000
0
1000
2000
-2
-4
-6
-8
-10
Magnetic field (He)
• Control over the magnetic hysteresis loop properties of garnet layers – an
area of our ongoing research; crucial for the design of integrated optic
devices using Faraday effect
• Multiple remnant magnetization levels demonstrated in films with
perpendicular magnetization (M. Nur-E-Alam, M. Vasiliev, and K. Alameh, Opt.
Quantum Electron. 41(9), 661–669, 2009).
3000
Bi1.8Lu1.2Fe3.6Al1.4O12 Magneto-soft thin films
• Low absorption
coefficients observed
Error due to all sources
• High specific Faraday rotation
 5.9 deg/µm at 532 nm
 1.6 deg/µm at 635 nm
 1.07 deg/µm at 660 nm
• Measured MO quality
factors (2ΘF/A)
13.9° (±1.6°) at 532 nm
15.7° (±2°) at 635 nm
12.7° (±0.7°) at 660 nm
RF sputtered Bi1.8Lu1.2Fe3.6Al1.4O12 magnetically-soft thin films are
very attractive for different magneto-optic applications and for
designing novel magnetically-controlled photonic components
Faraday-effect hysteresis loops
Faraday rotation (deg/mm)
Faraday
rotation (deg/µm)
Garnet layer on GGG, deposited
@ 250 C
-500
Garnet layer on GGG, deposited
@ 680 C
6
Hc = (45 ± 5) Oe
Hsat ~350 Oe
5
4
Hc = (10 ± 2) Oe
Hsat ~200 Oe
3
2
1
0
-400
-300
-200
-100
-1
0
100
200
300
400
500
-2
-3
-4
• Strong substrate dependency
of coercive force observed
• Hc ~ 45 Oe for the films on
GGG substrates deposited at
250 °C and Hc below 10 Oe
obtained in films deposited at
high substrate temperatures
(680 °C).
•Measured Faraday-effect
magnetic field sensitivity at
532 nm: > 100 °/(cm·Oe)
-5
-6
Magnetic field
(Oe) (Oe)
Magnetic
field
Hysteresis loop of Bi1.8Lu1.2Fe3.6Al1.4O12 MO
films deposited onto (GGG) substrates
•Low coercive force ⇒ lower
external magnetic field
required to control light
through polarisation
Magnetic domain structures: polarization microscopy
(a)
(b)
20 µm
Substrate T=250° C
Substrate T=680° C
 Domain structures observed in the absence of external magnetic fields using
transmission-mode polarization microscopy
 Regular maze-type domains were observed in sputtered Bi1.8Lu1.2Fe3.6Al1.4O12 films
deposited onto GGG at (a) 250 °C and (b) 680 °C substrate temperature
 Films deposited at high T(sub) are almost domain-free ⇒ almost in-plane magnetization
Good crystalline quality, low coercive force values and high magnetic sensitivity
achieved in our magnetically-soft garnet materials which are attractive for the
development of reconfigurable nanophotonic devices and garnet waveguides
Bi1.8Lu1.2Fe3.6Al1.4O12 : Bi2O3 nanocomposites and
engineering of the material properties
(BiLu)3(FeAl)5O12 + 4.5 vol% Bi2O3
annealed for 3 hrs @ 620 °C
Composition type
(BiLu)3(FeAl)5O12 + 4.5 vol% Bi2O3
annealed for 20 hrs @ 615 °C
34.5
20.85
25.6
18.03
(BiLu)3(FeAl)5O12 + 4.5 vol% Bi2O3
annealed for 5 hrs @ 615 °C
22.17
(BiLu)3(FeAl)5O12 + 4.5 vol% Bi2O3
annealed for 10 hrs @ 610 °C
22.1
(BiLu)3(FeAl)5O12 + 4.5 vol% Bi2O3
annealed for 5 hrs @ 610 °C
42.8
50.2
The effects of
adjusting the garnet
stoichiometry by cosputtering extra Bi2O3
have been studied;
significantly improved
material properties
were achieved
27.5
20.6
 High Faraday rotations
11.9
observed
635 nm MO figure of merit
15.7
 Very low absorption
Bi1.8Lu1.2Fe3.6Al1.4O12
532 nm MO figure of merit
13.9
deposited at T sub = 250 °C,
coefficients measured
annealed for 1 hr @ 650 °C
(below 1000 cm-1 at
0
20
40
60
635 nm).
MO figure of merit (degrees)
 High MO figures of
merit measured at
MO figures of merit measured in garnet and garnet-oxide
635 nm (more than
composite films of type Bi1.8Lu1.2Fe3.6Al1.4O12 : Bi2O3
50°)
Bi1.8Lu1.2Fe
3.6Al1.4O12 C
Substrate
T=250°
deposited at T sub = 680 °C,
annealed for 3 hrs @ 630 °C
42.8
Improved optical transparency achieved in nanocomposites
Left: 650 nm-thick film of Bi1.8Lu1.2Fe3.6Al1.4O12
on a Gd3Ga5O12 (GGG) substrate;
Right: 1150 nm-thick film of
(Bi1.8Lu1.2Fe3.6Al1.4O12 + 20 vol.% co-sputtered
Bi2O3) on a GGG substrate - both films are asdeposited
Annealed (crystallized) films:
Left: 1030 nm-thick
(Bi2Dy1Fe4Ga1O12 +24 vol.%
Bi2O3) on glass;
Right: 1080 nm-thick
Bi2Dy1Fe4.3Ga0.7O12 on GGG.
Surface morphology and magnetic properties of
Bi1.8Lu1.2Fe3.6Al1.4O12 : Bi2O3 nanocomposite thin films
2D image of garnet-oxide composite film
Substrate T=250° C
3D image of garnet-oxide composite film
 Comparatively lower coercive
force has been achieved for
nanocomposite oxide-mixed films
 Nano-crystalline structure of
garnet materials has been
observed
Applications of MO garnet films
The garnet and garnet-oxide thin film materials possess an excellent combination of optical,
magnetic and MO properties.
Suitable for use in a wide range of emerging application areas
• Nano-structured magnetic photonic crystals (MPC) for
magneto-optic polarization controllers in a wide angular
range (up to ± ΘFmax)
• Ultrafast spatial or temporal modulators of light intensity
• Non-reciprocal waveguide components
• Dielectric permanent magnets with adjustable magnetic
field landscapes over the film surface
• Nano-engineered high-contrast magnetic field sensors
and visualisers
• Potential applications in biology (cell manipulation)
100 µm
X 1000
Magnetic lattices for trapping ultra-cold atoms
High resolution images of
magnetic data tracks have been
acquired using visible and UV
polarisation microscopy
Asymmetrical 2D magnetic lattice formed
using a film of Bi2Dy1Fe4Ga1O12 sputtered
onto a Si substrate (A. Abdelrahman et al,
Phys. Rev. A 82(1), 012320, 2010).
Ultra-fast spatial light
modulators and image
recognition systems
CONCLUSION
 Bi-substituted MO garnet thin-film materials (both
magnetically-soft and hard) with excellent optical and
record-high MO quality have been demonstrated
 Sputter-deposition and oven annealing processes
required for the manufacture of high-quality garnet films
have been studied and the process parameters were
optimized
 The combination of material properties achieved is of
interest for the development of different emerging types
of reconfigurable nano-photonic devices
 Our research work will be continued to further optimize
the material properties and demonstrate the potential of
garnets in a range of new applications
Thank you
Electron Science Research Institute, Edith Cowan University