Giant Magneto-Caloric Effect Research in Vietnam -

The Personal Impact of NP Thuy

Tribute to Prof. Nguyen Phu Thuy

Motivations

Development of magnetic refrigeration• Demonstration of an Active Magnetic Refrigerator [C.

Zimm et al. (1996), Zimm et al., Adv. Cryogen. Eng. 43(1998)1759]: – 3 kg pure Gd metal – 5 T superconducting magnet – Cooling power: 600W, Efficiency: 60%.– New design (possibly a Stirling Cycle prototype with

Nd2Fe14B magnet)

• Discovery of the Giant MCE [Gschneidner, Pecharsky et al. (1997), IOWA State Univ. News Release (2001)]: GMCE material Gd5(Si1-xGex)4

• Magneto-Caloric Effect - (MCE) is the change in temperature of a magnetic material due to the adiabatic change of the external applied magnetic field. Application of the MCE: Magnetic refrigeration.

VNU Key Research Project(QGTD-00-01)(NP Thuy formulated, proposed and got approved)

Title: Fabrication and investigation of materials with giant magneto-caloric effect for use in a new generation of magnetic refrigerators.Proposer and Coordinator: Nguyen Phu Thuy

Duration: 2 (two) years Budget: 300 Millions VND (about 20,000 US$ at that time)

Contents of the Research

• Investigation on the off-stoichiometric Gd5(SiGe)4 systems

• Investigation of the R5(SiGe)4 systems

• Other intermetallic alloy systems• Perovskite and other like compounds• Experimental methodology and techniques• Magnetic Cooling Effect demonstration (Cryo-Lab, CMS, Solid State Dep, Faculty of Chemistry, ITIMS,

HUT Chemistry Faculty, IMS and many others participated)

Results in R5(Si,Ge)4 systems

Gd5(SixGe1-x)4 system with excess Gd, off-stoichiometric compounds, data measured on SQUID and Pulsed Field Magnetometer (PFM) for comparison

-S

ma

g[J/k

g·K

]

B = 5T

MCE Determination: Isothermal magnetisation curves measured on PFM do not show enough details from the magnetisation of the materials in the temperature range around the Curie Transition Temperature.

Magnetic field(T)

0 1 2 3 4 5 6

Ma

gn

etiz

ati

on

(em

u/g

)

0

20

40

60

80

100

120

140

160

180

148 K

77 K

170 K

§ êng liÒn nÐt: PFM§ êng cã ®iÓm: SQUID

Gd5(SixGe1-

x)4

x=0.2525

The R5Si2Ge2 Compounds (proceedings of APPC 2000 conference) Replacing Gd by Rare Earths in R5Si2Ge2

All compounds formed in similar crystal

structure as that of Gd5Si2Ge2.

Magnetic Properties varied with R: either

ferro- or antiferromagnetic structure, complex

magnetic structure at low temperatures.

Spin reorientation transition observed in

Er5Si2Ge2.

Giant MCE in Tb5(SixGe1-x)4, associated with

structural and other field-induced phase

transitions.

Spin reorientation in Er5Si2Ge2

(Collaboration with Ho of Cincinatti University)

T (K)

0 10 20 30 40

S (

J /

mo

l K

)

a

1

2

3

4

20

40

60

80

100

120

Er5Si2Ge2

(a)

(b)

C /

T (

J /

mo

l K

2)

Er5Si2Ge2

Lu5Si2Ge2

Lu5Si2Ge2

(a)

T(K)

0 50 100 150 200 250 300

1/

Tkg

/ A

m2

0.0

0.2

0.4

0.6

0H = 0.01T

T(K)

0 10 20 30 40

1/ (

Tkg/

Am

2 )

0.00

0.02

0.04

0.06

Er5Si2Ge2

1.5T

0.5T

0H = 0.01T

Stoichiometric Tb5(SixGe1-x)4 compounds, measured on SQUID and PFM

50 100 150 200 250 300 3500

4

8

12

16

20

24

28

32

36

40

Sm

ag [J/

kg

.K]

T [K]

x = 0.6 x = 0.6 - PFM x = 1

0

1

2

3

4

5

6

7

8

9

10

Tb5(SixGe1-x)4

B = 5 T x = 0.4

SM

ag[J

/kg

.K]

Giant MCE in the Tb5(SixGe1-x)4 system

10

100 150 200 250 300

0

4

8

12

16

20

24

28

32

ΔS

mag

[J/k

g·K

]

Temperature [K]

0

1

2

3

4

5

6

7

8

9Tb5(SixGe1-x)4

ΔB = 5 T

x = 0.6 x = 1

x = 0.5

x = 0.75

x = 0.4

ΔS

mag

[J/

kg

·K]

Results on the Tb5(SixGe1-x)4 system

Magnetic Order

0 50 100 150 200 2500

20

40

60

80

100

120

140

0 100 200 3000.0

0.1

0.2

0.3

B = 1 T

T [K]

B = 1 T

B = 0.01 T

x13

x13Mag

net

isat

ion

[A

·m2 ·

kg-1]

Temperature [K]

FC

ZFC

ZFC FC

1/[

Tk

g/A

m2 ]

Temperature [K]0 50 100 150 200 250 300 350

0

25

50

75

100

125

150

175

200

B = 0.01TB = 5T

x 50

Tb5Si2.4Ge1.6

Mag

net

isat

ion

[A

·m2 ·

kg-1

]

Tb5Si2Ge2

Field-induced transition in Tb5(SixGe1-x)4

0 10 20 30 40

100

150

200

250

0 10 20 30 40100

150

200

Mag

neti

zati

on

[A

m2/k

g]

Magnetic field [T]

Tb5Si3Ge Tb5Si2Ge2

Magnetic field [T]

Mag

neti

zati

on

[A

m2/k

g]

Tb5Si2Ge2

Structural Phase Transition in the vicinity of the Curie Temperature (TC) in the Tb5(SixGe1-x)4 system

Inte

nsit

y [

arb

. u

nit

s]

2 [degree]20 22 24 26 28 30 32 34 36 38 40 42

100K

110K

115K

120K

130K

150K

Tb5Si2.4Ge1.

6

Collaboration with TU Dresden

Temperature Dependence of the Lattice Parameters of Tb5Si2.4Ge1.6:

Orthorhombic below TC=150KMonoclinic above TC= 150K

50 100 150 200 250 300

7.44

7.46

7.48

7.50

Latt

ice p

ara

mete

rs [

Å]

Temperature [K]

7.70

7.72

7.7414.64

14.66

14.68bo (T)

am (T)

bm (T)

ao (T)

co (T)

cm (T)

TC = 150 K

TC = 150 K

Orthorhombic Lattice parameters of Tb5Si3Ge in the temperature range from 50 to 300 K. An anomaly (a kink in the curves) occurs at 210 K, its Curie Temperature.

100 150 200 250 300

7.42

7.43 a (T)Latt

ice p

ara

mete

rs [

Å]

Temperature [K]

7.69

7.70

7.71

7.72

c (T)

b (T)

14.62

14.63

14.64

50

TC = 210 K

Effect of Cooling Cycle

Temperature dependence of the electrical resistivity and the magnetization in magnetic field up to 1 T between 10 and 300 K of the compounds Tb5(SixGe1−x)4 with x=0.6, 0.75, and 1.0 were studied.

All samples exhibit irreversible changes in the electrical resistance on thermal cycling between room temperature and 10 K. The irreversible effect is reduced with increasing x from 0.6 to 1.0, and it is not observed in the magnetisation studies.

The resistance irreversible effect may be due to micro-cracks formed during the thermal cycling associated with the induced structural phase transition).

Important to application: working substance can be destroyed!

Collaboration with D. Yao (Taiwan)

MCE in the La1-xNdx(Fe,Si)13 sytems

- Giant MCE.

-TC above 200K.

- Metamagnetic phase transition.

-Main part of material is Fe, therefore cost advantage.

FWHM = 40 K

FWHM = 26 K

T2T1

MCE in RCo2 system

0

T [K]

-ΔS

Mag

[J/

kg

·K]

Er(Co1-xSix)2

RCo2 (R=Dy, Tb, Gd)

0.10

100 200 3000

10

20

30

40

0.15

x = 0

0.05

0.075

0.02

MCE in Perovskite Compounds La1-xAxBO3

(A= Ca,Sr,Pb,Ag,Na; B=Mn,Co,Cu,Cr)

- Ceramic materials, simple preparation technology. Low cost of materials.

- Reasonably high MCE, comparable to pure Gd.

- High TC from 260K to above room temperature.

-S

mag

[J/

kgּK

]

TC [

K]

100

150

200

250

300

350

0.05 0.15 0.25 0.35

Smag sol-gel samples

Smag ceramic samples

TC sol-gel samplesTC ceramic samples

1

1.5

2

2.5

3

3.5

4

La1-xAgxMnO3 system

x

Other perovskite compounds

0

2

4

6

200 240 280 320

- S

Mag[J

/kg

·K

]

T [K]

La1-xCaxMnO3-δ system,

B=1, 3 vµ 5 T

MCE demonstration device

Schematic working principle:

Gd metal plates

Pneumatic sample handling system

Keithley Microvoltmeter to record the

temperature changes using a thermo -couple

(glued in between the Gd plates)

Computer to display the

sample temperature

changes

N SMagnet Pole

Magnet Pole

Results The magnet arrangement

B(d): Induction as dependent on the clearance between the NdFeB magnet poles

d [cm]

B [

mT

]

0

200

400

600

800

1000

1200

0 1 2 3 4 5 6

Measured on the magnet pole surface

Measured in the gap in between the magnet poles

Prepared in LT Tai responsibility

with NdFe14B material

Demonstration Experimental Setup

Temperature of the sample + holder + thermocouple in the absence of the magnetic field

290

290.5

291

291.5

292

0 20 40 60 80 100Thêi gian [täa ®é tï y ý tÝnh b»ng gi©y]

Nhi

Öt ®

é cñ

a m

Éu v

µ cÆ

p nh

iÖt ®

iÖn

(K)

Temperature of the sample holder and the thermo couple during magnetisation and demagnetisation process

290

290.5

291

291.5

292

0 20 40 60 80 100

Thêi gian [täa ®é tï y ý tÝnh b»ng gi©y]

Nhi

Öt ®

é cñ

a g¸

mÉu

vµ

cÆp

nhiÖ

t ®iÖ

n [K

]

291.0

291.2

291.4

291.6

291.8

292.0

292.2

292.4

0 20 40 60 80 100

Time [arbitary reference in seconds]

Sam

ple

Tem

pera

ture

[K

]

Actual sample temperature changes during magnetisation and demagnetisation cycles

Absolute sample temperature change at room temperature (291 K) during magnetisation and demagnetisation cycles

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 20 40 60 80 100

Time [arbitary reference in seconds]

Sam

ple

Tem

pera

ture

[K

]

Concluding remarks:•Well designed, organised and sucessfully implemented•Publications:

Total number of papers published: 42Number of papers published internationally: 16

•Education:Number of Bachelor Theses: 15Number of Master Theses: 02PhD Project proposed and started: 01

•Research continued after this project: Cryo-Lab, Solid State Department, CMS, ITIMS, IMS etc. (about 20 % of international scientific publications of the Vietnamese Physics Community in the last 8 years deal with MCE)• International Cooperation promotion: extension, lot of new relationships and programmes established

NP Thuy: •A decent and modest person, a bright and intelligent physicist with a sucessful career, featured by deep insight in every topic he approached, long term vision and sharp sense, great scientific imagination, intuitivity and creativity, always with an open mind and endless enthousiasm to catch up and to start with new topics, ideas and technologies.•A kind colleague with strong attraction and capability to link together and to encourage both students and co-workers