Composition dependent properties of Ni 2 MnGa based ferromagnetic shape memory alloys Qing-Miao Hu...

Composition dependent properties of Ni2MnGa based ferromagnetic shape memory

alloys

Qing-Miao Hu

Institute of Metal Research, Chinese Academy of Sciences

Wenhua Road 72, Shenyang 110016, China

Workshop on Atomic-Scale Challenges in Advanced Materials:

Defects in MaterialsTurku, Finland

August 22-23, 2013

Co-workers

Dr. Hu-Bin LuoInstitute of Metal Research, Chinese Academy of Sciences

Dr. Chun-Mei LiInstitute of Metal Research, Chinese Academy of Sciences

Royal Institute of Technology/Uppsala University , Sweden

Prof. Rui YangInstitute of Metal Research, Chinese Academy of Sciences

Prof. Börje JohanssonRoyal Institute of Technology/Uppsala University , Sweden

Prof. Levente VitosRoyal Institute of Technology/Uppsala University , Sweden

Outline

Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability

Summary

Background and MotivationGeneral

Mn: 3.86, Ni: <0.3, Ga: 0.00

Magnetic Transition:

Ferromagnetic Paramagnetic

Ni2MnGa: Heusler Alloys

c/a = 1

Structure Transition:

Cubic L21 Austinite

Orthorhombic Martensite

Reversible: Shape Memory Effect

c/a >1

c/a <1

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202 K 376 K

Coupling between the structure and magnetic transitions leads to some unique properties:

•Giant magnetocaloric effect; •Magnetostriction; •Magnetoresistance.

Potential applications: •Magnetic refrigeration;•Magnetostrictive

transducers;•etc.


Perfect Ni2MnGa

How to control composition to achieve desirable TM? Can we find some easy predictors to connect composition and TM?

Khovaylo, et al., Phys. Rev. B 72, 224408 (2005)


Tsuchiya, et al., ISIJ International 46, 1283 (2006)

Fe doped Ni2MnGa

1. Number of valence electrons per atom (e/a) and TM

Chernenko, et al., Acat Mater. 50, 53 (2002)

Background and MotivationPredictors for the composition dependence of TM

2. c/a ratio of martensite and TM

Lanska, et al., J. Appl. Phys 95, 8074 (2004)


3. Energy difference between austinite and martensite (E) and TM

Chen, et al., Appl. Phys. Lett. 89, 231921 (2006)


Bungaro and Rabe, Phys. Rev. B, 2003

cdcdT

10

dT

dc

T

1

Ren and Otsuka, Mater Sci Forum (2000)

NiTi SMA： Larger C of the austenite corresponding to lower TM.

4. Elastic modulus Cand TM?


Background and MotivationPhase stability: Structure of modulated martensite

The modulated structure is very complex: shear: changing c/a; shuffle: wave-like movement of atoms on [110]

Alloying effect on the modulated structure?

a

a



Outline


Summary

MethodEMTO-CPA

First-principles method based on density functional theory

Basis Sets: Exact muffin-tin orbitials (EMTO), spdf

Exchange-correlation functional: GGA-PBE

Coherent potential approximation for the random distribution of alloying atoms.

Outline


Summary

Geometry of Ni2MnGa projected to (001) plane

Ga

Mn

Ni

Ni2MnGa

Ni2-xMnGa1+x

Indirect site-occupancy

MnNi

GaMn

GaNi

Direct site-occupancy

Results and DiscussionSite-occupancy in Ni2MnGa based alloys

Off-stoichiometric: Indrect: Ga-rich Ni-deficient alloys, forming

GaMn and MnNi.

Phys. Rev. B 79, 144112 (2009); 84, 024206 (2011)

Results and DiscussionSite-occupancy in Ni2MnGa based alloys

Free energy of different site-occupancy configurations

Fe/Co/Cu doped:Indirect: Fe-doped Ga-deficient alloys

Co-doped Mn- or Ga-deficient alloysCu always take direct site-occupancy

Outline


Summary

Results and DiscussionElastic modulus and TM

7.0 7.2 7.4 7.6 7.8

141

144

147

150

153

156

7.0 7.2 7.4 7.6 7.8

10

15

20

90

95

100

105

Bulk

Mod

ulu

s (G

Pa)

e/ a

She

ar M

odul

us (

GP

a)

C44

C

e/ a

9 12 15 18

0

100

200

300

400

500

600

TM (K

)

C7.35 7.50 7.65 7.80

0

100

200

300

400

500

600

TM (

K)

e/ a

Off-stoichiometric Ni2MnGa

Phys. Rev. B 79, 144112 (2009)

Fe/Co/Cu doped Ni2MnGa

7.4 7.5 7.6 7.7 7.8 7.9

2

4

6

8

10

Ni2+x

MnGaCux

Ni2Mn

1-xGaCu

x

Ni2MnGa

1-xCu

x

Ni2+x

MnGaCox

Ni2Mn

1-xGaCo

x

Ni2MnGa

1-xCo

x

Ni2+x

MnGaFex

Ni2Mn

1-xGaFe

x

Ni2MnGa

1-xFe

x

C'

(GPa

)

e/ a

2 4 6 8 10

50

100

150

200

250

300

350

400

450

7.44 7.52 7.60 7.68 7.76

50

100

150

200

250

300

350

400

450

Ni2+x

MnGaCox

Ni2Mn

1-xGaCo

x

Ni2MnGa

1-xCo

x Ni

2+xMnGaFe

x

Ni2Mn

1-xGaFe

x

Ni2MnGa

1-xFe

x

TM (K

)

C' (GPa)

Ni2+x

MnGaCux

Ni2Mn

1-xGaCu

x

TM (K

)

e/ a

Phys. Rev. B 84, 024206 (2011)

Results and DiscussionElastic modulus and TM

0.0 0.2 0.4 0.6 0.8 1.0

6

8

10

12

14

16

C' (

GPa

)

Atomic fraction of Al, c

C'

100

120

140

160

180

200

TM

TM (K

)

Ni2Mn(Ga1-xAlx)

Acta Mater. 59, 5938(2011)

Outline


Summary

Results and DiscussionPhase stability of Ni2Mn(Ga1-xAlx)

)sinsin(sin 56

254

152 jAjAjj

Acta Mater. 59, 5938(2011)

Martynov et al.. J. Phys. III 2, 739(1992)

a

a

Two degrees of freedom optimization:

Shear: c/a; Shuffle:

5L modulated martensite:

Results and DiscussionPhase stability of Ni2Mn(Ga1-xAlx)

0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5

-1

0

1

2

3 (a) Ni2MnGa

non-modulated modulated

E (m

Ry)

c/a

0.90 0.92 0.94 0.96

-0.12

-0.10

-0.08

-0.06

-0.04

E

(mR

y)

c/a

0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5

-1

0

1

2

3 (b) Ni2Mn(Ga

0.9Al

0.1)


E (m

Ry)c/a

0.90 0.92 0.94 0.96

-0.08

-0.06

-0.04

-0.02

0.00

E (m

Ry)

c/a

0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5

-1

0

1

2

3 (c) Ni2Mn(Ga

0.8Al

0.2)


E (m

Ry)

c/a

0.90 0.92 0.94 0.96

-0.03

0.00

0.03

0.06

0.09

E (m

Ry)

c/a

0.00 0.05 0.10 0.15 0.20 0.25 0.30

0.00

0.03

0.06

0.09

0.12

EA

M (

mR

y)

c

Critical point

0.0 0.1 0.2 0.3 0.9 1.0

0

50

100

150

200

TM

(K

)

c

No MT

Exp.

EAM=EA-EM

Martensite more stable

Results and DiscussionPhase stability of Ni2(Mn1-xFex)Ga

2 4 6 8 10

50

100

150

200

250

300

350

400

450

7.44 7.52 7.60 7.68 7.76

50

100

150

200

250

300

350

400

450

Ni2+x

MnGaCox

Ni2Mn

1-xGaCo

x

Ni2MnGa

1-xCo

x Ni

2+xMnGaFe

x

Ni2Mn

1-xGaFe

x

Ni2MnGa

1-xFe

x

TM (K

)

C' (GPa)

Ni2+x

MnGaCux

Ni2Mn

1-xGaCu

x

TM (K

)

e/ a

Results and DiscussionPhase stability of Ni2(Mn1-xFex)Ga

L21 austinite becomes elastically softer with increasing Fe: Lattice vibration contribute more to the free nergy accordingly, stabilizing L21

EAM=EA-EM

Outline


Summary

Summary

• We predict that indrect site-occupation occurs in some of the off-stoichiometric and Fe/Co/Cu doped Ni2MnGa alloys.

• The general TM~C′ correlation works for some of the alloys for

which the TM~e/a correlation fails. However, there are several cases

where both the general TM~C′ and TM~e/a correlations break down.

• We present a feasible approach to study the 5-layer modulated (5M) martensitic structure of Ni2MnGa-based alloy using first-principles

methods. By using this approach, the 5M martensitic structure of Ni2MnGa is reasonably reproduced and the Al/Fe-doping effects are

predicted.

Thank you for your attention!

Composition dependent properties of Ni 2 MnGa based ferromagnetic shape memory alloys Qing-Miao Hu...

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