This document summarizes the fabrication of patterned ferromagnetic shape memory thin films. It discusses two routes for micropatterning Ni-Mn-Ga thin films using self-assembled polystyrene spheres and reactive ion etching. Route 1 uses a Si sacrificial layer deposited at 500°C, while Route 2 produces arrays of Ni-Mn-Ga antidots at room temperature followed by annealing at 500°C. Characterization shows the patterned films via Route 2 exhibit ferromagnetism up to 100°C and a spread martensitic transformation, demonstrating their functional properties. Route 1 showed promise but requires further optimization.

1. FABRICATION OF PATTERNED
FERROMAGNETIC SHAPE
MEMORY THIN FILMS
Pablo Álvarez-Alonso
1

2. Group of Magnetism and Magnetic Materials
I
http://gmmmt.net
Objetives: New magnetic materials: from preparation and characterization to
applications.
Research lines:
Magnetoelasticity
Magnetoimpedance and magnetoresistance
Magnetocaloric materials
Nanopatterned magnetic materials
2 Ferromagnetic Shape Memory Alloys

3. BCMaterials
II
http://www.bcmaterials.net/
Objetives: Functional Materials with advanced Mechanical, Thermal, Electric, Magnetic,
and Optical properties- from basic aspects to applications.
Research lines:
Ferromagnetic Shape Memory Alloys
Smart Polymers and composites
Hybrid multiferroics (magnetoelectric) materials
Active (smart) materials
Materials for Energy
Materials for Sensors and Bio-Sensors.
Materials for Particle accelerators
Advanced functional materials
Magnetic Nanoparticles-Biomedical and Industrial Applications.
Magnetic Nanostructures
Nanopatterned magnetic materials
3

4. OUTLINE
1. INTRODUCTION
2. ANTIDOTS FABRICATION
2.1 High temperature method
2.2 Low temperature method
3. RESULTS
3.1 Microstructure
3.2 Phase transitions
3.3 Magnetic properties
4. CONCLUSIONS
4

5. INTRODUCTION
1
MINIATURIZATION
Driving force of technological and social change
Moor’s law: the number of transistors in a circuit doubles each two years
MEMS (Micro-Electro-Mechanic System)
* Inkjet-printer cartridges
* Accelerometers
* Micromirrors
* Microtransmissions
* Chemical, pressure, and flow
sensors
* Microactuators
Multifunctional materials
 Weight-efficient
 Volume-efficient performance flexibility
 Less maintenance
5

6. INTRODUCTION
1
Magnetic Shape memory Alloys
Martensitic
transformation
(1st order)
 Direct (A M)
 Indirect (M A)
Changes in shape
SMA (T)
MSMA (T,H)
Variant Equivalent structures with
different orientations
Magnetic field-induced strain
(MFIS) in Ni-Mn-Ga
1-10% Single crystal Sensors and Actuators!
<0.01% Polycrystalline (suppression of the twin-boundaries
motion)
6

7. INTRODUCTION
1
Ni-Mn-Ga micropillars
[3]
Ni-Mn-Ga microfibers
[2]
Ni-Mn-Ga grain size ~ Characteristic sample
size
Increase of the free space Increase of the MFIS
Fabrication of Ni–Mn–Ga nanostructures is a challenging
[1] M. Chmielus et al., Nat. Mater. 8 (2009) 854 - 855
[2] N. Scheerbaum et al., Acta Mater. 55 (2007) 2707
[3] M. Reinhold et al., J. Appl. Phys. 106 (2009) 053906
[4] M. Schmitt et al., Microelectron. Eng. 98 (2012) 536–
539
task
Ni-Mn-Ga foams
[1]
Ni-Mn-Ga cantilevers
[4]
7

8. ANTIDOTS FABRICATION
2
Nanospheres lithography
 Fast (parallel) fabrication
process
 Large areas (~1cm2)
 Low cost technique
APPROACHES
Mix of “Bottom-up” and “Top-down” techniques
* Sputtering
* Self-assembled spheres
(polystyrene, latex,
silica,…)
* Reactive Ion Etching
4 main stages:
a) Deposit of the spheres (monolayer)
b) Reduction of the spheres
c) Metal deposition
d) Removal of the spheres
8

9. ANTIDOTS FABRICATION
2
COMMON STEPS
Substrate: Si (100)
PS spheres recipe [1]
Polymerization
Reflux at 60ºC /
18h
N2
Atmosphere
Milli-Q water
+
Dry in vacuum
oven (12h)
Ingredients:
 2g of S (estyrene) monomer
 0.04g of AIBN (azobisisobutironitrile) initiator
 0.1g of PVP (polivynilpyrrolidone) stabilizer
 20g of methanol dissolvent
[1] J. Lee et al., J. Colloid Interface Sci. 298 (2006)
663–671
Directions:
Centrifuged
20 mm
9

10. ANTIDOTS FABRICATION
2
Drop-coating [1]
COMMON STEPS
 Large-scale monolayered particle mask
 High hexagonal order
 Short preparation time
4 stages:
 Deposit a drop
PS-5% + DI-95%
Vol DI = Vol Ethanol
 Glass with DI water
 Consolidation
Triton 2%
 Liftoff
0.5cm
[1] J. Rybczynski et al., Colloids Surf. Physicochem. Eng. Asp. 219 (2003)
1–6
10

11. ANTIDOTS FABRICATION
2
PS reduction: Reactive-Ion Etching
RIE
Ions and Radicals
Conditions for the dry etch
Gases
Flow
(sccm)
ICP/RF
(W)
Pressure
(Torr)
Temperature
(oC)
Time
(min)
PS sphere
reduction
O2 12
0/100 0.1 10 3
Ar 5
Physical etch
Chemical (selective) etch
COMMON STEPS
11

12. ANTIDOTS FABRICATION
2.1
Conditions for the dry etch
ROUTE 1
Gases
Flow
(sccm)
ICP/RF
(W)
Pressure
(Torr)
Temperature
(oC)
Time
(min)
SiO2 SF6 30 150/150 0.1 10 0.3
Si CHF3 10 0/50 0.02 10 15
 PS spheres removal with a dissolvent
(Tetrahidrofurane, THF)
12

13. ANTIDOTS FABRICATION
2.1
Magnetron DC Sputtering
ROUTE 1
Sputtering conditions
Ar pressure
(mbar)
Power
(W)
DTarget-Substrate
(cm)
Temperature
(ºC)
Time
(min)
2.6·10-2 150 9 500 5
Ni-Mn-Ga Thickness≈250nm
13

14. ANTIDOTS FABRICATION
2.1 ROUTE 1
Si wet etching
Potassium hydroxide (KOH) Si and SiO2 etchant
KOH (20%) [1]
Si (100) SiO2
KOH 20% 60-100ºC / 1-10min
[1] H. Seidel et al., J. Electrochem. Soc. 137 (1990) 3612-3632
14

15. ANTIDOTS FABRICATION
2.2
Sputtering conditions
PS melting point≈100ºC
ROUTE 2
 Dissolvent
(THF)
Enhance the structural order
degree [1]
Infrared furnace (P = 10-5 torr)
Goal
 500ºC / 4h
 800ºC / 1h
[1] V.A. Chernenko et al., Mater. Trans. 47 (2006) 619
Ar pressure
(mbar)
Power
(W)
DTarget-Substrate
(cm)
Temperature
(ºC)
Time
(min)
2.6·10-2 150 9 RT 10
Ni-Mn-Ga
Thickness≈500nm
15

16. 2.2
ANTIDOTS FABRICATION
Unpatterned films
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
40
20
0
-20
-40
Deposited at 500ºC
Deposited at RT
Annealed at 500ºC
Annealed at 800ºC
M (Am2/Kg)
m
0
H (T)
T = 0ºC
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Pre-heated substrate Higher atomic ordering degree
m
0
H=10mT
Formation of Ni agglomerates
Annealing at 500ºC Enhancement of the
magnetic properties
(RT)
Ms =46 Am2/Kg
Ms =13 Am2/Kg
ROUTE 2
16
0 100 200 300 400
-0.2
Unpatterned film annealed at 800oC
M(Am2/Kg)
Temperature (ºC)

17. 10μm
3.1
RESULTS
MICROSTRUCTURE
30μm
Mean diameter: 1.35 μm
St. Deviation: 0.04 μm
Mean diameter: 1.00 μm
St. deviation: 0.06 μm
After RIE
Drop-Coating
* PS diameter
homogeneity * Large
domains size
17

18. 3.1
RESULTS
Elements % at
Ni 48 ± 1
Mn 32 ± 1
Ga 20 ± 1
Height of the Si dots
AFM
~250 nm-thick Ni-Mn-Ga Film
* Sidewall deposition of Si dots
* Large Ni-Mn-Ga crystalline grains
ROUTE 1 (High temperature)
18

19. ROUTE 1 (High temperature)
100ºC
Wet
Etching
KOH
(20%)
Partial Si removal
Film removed
in <3 min
60ºC
3.1
RESULTS
Colapse of
Ni-Mn-Ga layer
19

20. 3.1
RESULTS
Mean diameter: 1.16 μm
St. Deviation 0.07 μm
Continuous film
(RT)
Patterned film
(RT)
Elements % at % at
Ni 49 ± 1 50 ± 1
Mn 27 ± 1 27 ± 1
Ga 24 ± 1 23 ± 1
Similar mean composition but inhomogeneity ~1-2μm
Room temperature
500ºC / 4h
ROUTE 2 (Room temperature)
~500 nm-thick Ni-Mn-Ga
patterned and continuous
films
* Small crystalline size
* Slight increase of the grain
size
* Deformation of the antidots
20

21. 3.2
RESULTS
VSM and Four-probe
method
0.030
0.025
0.020
Resistencie ()
30
20
10
0
M (Am2/Kg)
1
m0H = 10mT
0.016
0.014
0.012
0.010
0.008
Resistencie ()
6
4
2
0
m0H = 10mT
M (Am2/Kg)
2
-100 -50 0 50 100 150
0.030
0.025
0.020
0.015
Resistencie ()
Temperature (ºC)
1.0
0.8
0.6
0.4
0.2
0.0
m0H = 10mT
M/Ms
3
PHASE TRANSITIONS
1. Unpatterned Ni-Mn-Ga film deposited at 500ºC
2. Unpatterned Ni-Mn-Ga film annealed at 500ºC
3. Patterned Ni-Mn-Ga film annealed at 500ºC
Route 2
Sharp decrease of magnetization TC ≈100ºC
TM≈ -50/25 ºC
TC ≈50ºC.
No martensitic transformation Crystal
disorder
Multiple drops of the magnetization TC ≈100ºC
TM <-30ºC
1
.
2
.
3
.
21

22. 3.2
RESULTS
1.0
0.5
0.0
-0.5
-1.0
Ni-Mn-Ga antidots (Route 2)
T = 50ºC
T= -173ºC
-1.0 -0.5 0.0 0.5 1.0
M/Ms
m
0
H (T)
MAGNETIC PROPERTIES
Unpatterned Ni-Mn-Ga film (deposited at 500ºC)
1.0
0.5
0.0
-0.5
-1.0
T = 50ºC
T = -173ºC
-1.0 -0.5 0.0 0.5 1.0
M/Ms
m
0
H (T)
Martensite Higher anisotropy Larger coercive field HC
Sample μ0Hc (mT) at -173ºC μ0Hc (mT) at 50ºC μ0ΔHc (mT)
Unpatterned film
deposited at 500ºC
120 49 71
Patterned film
annealed at 500ºC/4h
84 17 67
22

23. 4
CONCLUSIONS
1 Two ways for Ni-Mn-Ga thin-films micropatterning have been
developed by using self-assembled polystyrene spheres and
reactive ion etching.
 Route 1: Si sacrificial layer to deposit Ni-Mn-Ga at 500ºC.
 Route 2: Large area of 2D-arrays of Ni-Mn-Ga antidots at room
temperature and subsequent annealing in a high-vacuum furnace
at 500ºC for 4 hours.
2 Route 1 proved to be promising (optimization is need)
3 Antidots synthesized by Route 2 present functional characteristics:
Ferromagnetisms (TC~100ºC) and a spread martensitic
transformation. 23