Physics and applications of

magnetocaloric materials

K. G. SURESHDept. of Physics

I. I. T. Bombay

http://www.iitb.ac.in/

Plan of talk

Introduction

History

Major breakthroughs

Novel materials

Future

Challenges

What is magnetocaloric effect?

Basically has roots in Adiabatic Demagnetization

Can be used for magnetic cooling

Concept of a magnetic refrigerator/ magnetic heat

pump

E. Warburg (1880)

P. Debye(1926)

W. F. Giaque

(1927)

http://en.wikipedia.org/wiki/File:Emil_Gabriel_Warburg_(1846-1931).jpghttp://en.wikipedia.org/wiki/File:Debye100.jpg

T (T+T)

H1 H2

MAGNETIZATION

DEMAGNETIZATION

H2>H1

Analogy between gas-based refrigerator and magnetic

refrigerator

Squeezing out the entropy produces cooling!

Thermodynamics of MCE

)()(),(),( TSTSHTSHTS ElLatM

SM

T

H2

H1

SM

Tad

H2>H1

(∆SM)max=R ln(2J+1)

SM

T

H2

H1

SM

Tad

H2>H1

M

TTC

Magnetization and MCE

SM

or

Tad

T

∆SM = ∆SM (T, ∆H)

∆Tad = ∆Tad (T, ∆H)

HT T

HTM

H

HTS

,,

dH

T

HTMHTS

H

H

H

M

2

1

,),(

dHT

HTM

HTC

TT

H

H

H H

ad

2

1

,

,

Calculation of MCE

/

0

/

// )0,(),(),( dT

T

TCHTCHTS

T

M

SHHHad IFSTSTTT ])()([)(

H

ii

ii

iavM dHHTMHTMTT

HTS0

1

1

, ),(),(1

,

C-H-T

M-H-T

An efficient magnetic refrigerator =

A giant MCE material +

A high energy-density permanent magnet +

An ingenious design

Hot Cold

Magnetize Demagnetize

refrigerant

Q Q’

2001 Astronautics demonstrates permanent

magnet rotary AMR

2000 Giant Magnetocaloric effect alloys

made by AMES Lab

1997 Demonstrate high power NRT AMR

1991 Astronautics demonstrates to 40K high efficiency AMR

1989 Navy demonstrates AMR Magnetic refrigerator

1978 Los Alamos DOE Lab produces AMR magnetic refrigerator

1949 Nobel Prize awarded to Giauque for Magnetic refrigeration

1926 Magnetic refrigerator proposed by Debye and Giauque

Time Line

Chronological development of magnetic refrigeration technology

Higher efficiency

Eco-friendly nature

Better adaptability

Solid-state based

Long life

Advantages of Magnetic Refrigerators

K. A. Gschneidner, Jr. V. K. Pecharsky

Ames Lab, Iowa

Discovery of GMCE

Intermetallics for GMCE

Present scenario of GMCE materials

Gd-Si-Ge: THE material!

GMCE without rare earths!!!

GMCE in certain magnetic shape memory alloys

A. Nayak, et al., J. Phys. D: Appl. Phys. 42 (2009) 035009

MCE in magnetic molecules

Impact of MCE studies

New cryogenic technology

Novel passive and active regenerators

Renewed interest in permanent magnet

materials

Better understanding of the magnetic and

magneto-thermal properties

Discovery of similar/associated effects

Something about the

technology of magnetic

refrigeration

Four step AMR Cycle

Magnetic Refrigerator

Using Permanent Magnets

Projected applications of magneto caloric materials

refrigerators/air conditioners

Food preservation

Low temperature electronics

Liquefaction of gases, especially natural gases and

hydrogen

Cryogenic detectors spanning the entire electromagnetic

spectrum

Storage of cryogenic propulsion fuels for long-term

space missions

Heat pumps

Magnetic hyperthemia?

Main obstacles in the way of commercialization

Better and more GMCE materials

Hysteresis and eddy current losses

Bulk production of such materials

High quality permanent magnets

Improved design

New and more efficient thermodynamic cycles

International conference on

Magnetic Refrigeration

…….. By E. C. Stoner

Ferromagnets: Truly multi-functional…..

-----Thank You-----