This presentation discusses magnetic and nuclear cooling techniques. Magnetic cooling uses the magnetocaloric effect where applying or removing a magnetic field from certain materials causes a temperature change. The process involves magnetizing a material, transferring heat away, demagnetizing to cool the material, and transferring the cold to the target. Very low temperatures below 1K can be achieved using nuclear demagnetization which exploits the magnetic dipoles of atomic nuclei. This technique allows cooling to temperatures as low as 0.001K and is useful for experimental applications. Magnetic and nuclear refrigeration provide advantages over conventional cooling like reduced energy costs and avoiding ozone-depleting refrigerants.

1. PRESENTATION ONPRESENTATION ON
MAGNETIC & NUCLEAR COOLINGMAGNETIC & NUCLEAR COOLING
PRESENTED BYPRESENTED BY
PADMADHAR GARGPADMADHAR GARG
DEPARTMENT OF MECHANICAL ENGINEERING,DEPARTMENT OF MECHANICAL ENGINEERING,
MALVIYA NATIONAL INSTITUTEMALVIYA NATIONAL INSTITUTE OF TECHNOLOGY JAIPUROF TECHNOLOGY JAIPUR

2.  It is possible to attain a temperature of aboutIt is possible to attain a temperature of about
0.8K (-272.2C) through the lowering of pressure0.8K (-272.2C) through the lowering of pressure
over liquid helium.over liquid helium.
 Giauque and Debye proposed the adiabaticGiauque and Debye proposed the adiabatic
demagnetization of magnetic salt for attainingdemagnetization of magnetic salt for attaining
the lower temperature.the lower temperature.
 The lowest recorded temperature as low asThe lowest recorded temperature as low as
0.001K may be obtained by adiabatic0.001K may be obtained by adiabatic
demagnetization of certain paramagnetic saltdemagnetization of certain paramagnetic salt
previously cooled by liquid helium and subjectedpreviously cooled by liquid helium and subjected
to a strong magnetic field.to a strong magnetic field.

3. Content:Content:
>>Basic principles of magnetic refrigerationBasic principles of magnetic refrigeration
>Thermodynamic cycle>Thermodynamic cycle
>>Materials : Working materialsMaterials : Working materials
>Nuclear demagnetization>Nuclear demagnetization
>Advantages>Advantages

4. Introduction : PrincipleIntroduction : Principle
 Mageto calorific effect is the basic principle on whichMageto calorific effect is the basic principle on which
the cooling is achieved.the cooling is achieved.
 All magnets bears a property called Currie effect i.e. IfAll magnets bears a property called Currie effect i.e. If
a temperature of magnet is increased from lower toa temperature of magnet is increased from lower to
higher range at certain temperature magnet looses thehigher range at certain temperature magnet looses the
magnetic field.magnetic field.
 Currie temperature. Depends on individual property ofCurrie temperature. Depends on individual property of
each material.each material.
 As Energy input to the magnet is increased theAs Energy input to the magnet is increased the
orientation of the magnetic dipoles in a maget startsorientation of the magnetic dipoles in a maget starts
loosing orientation. And vice a versa at currieloosing orientation. And vice a versa at currie
temperature as magnet looses energy to the media ittemperature as magnet looses energy to the media it
regains the property.

5. Thermo dynamic cycleThermo dynamic cycle

6. Adiabetic Demagnetization apparatusAdiabetic Demagnetization apparatus

7. Details Of the Thermodyanamics CycleDetails Of the Thermodyanamics Cycle
 PROCESS IS SIMILAR TO GAS COMPRESSION ANDPROCESS IS SIMILAR TO GAS COMPRESSION AND
EXPANSION CYCLE AS USED IN REGULAREXPANSION CYCLE AS USED IN REGULAR
REFRIGERATION CYCLE.REFRIGERATION CYCLE.
Steps of thermodynamic cycle -Steps of thermodynamic cycle -
 Adiabatic magnetizationAdiabatic magnetization
 Isomagnetic enthalpic transferIsomagnetic enthalpic transfer
 Adiabatic demagnetizationAdiabatic demagnetization
 Isomagnetics entropic transferIsomagnetics entropic transfer

8. Adiabatic magnetizationAdiabatic magnetization
 Procedure to be followed :Procedure to be followed :
 Substance placed in insulated environment.Substance placed in insulated environment.
 Magnetic field +H increased.Magnetic field +H increased.
 Magnetic dipoles of atoms to align, therebyMagnetic dipoles of atoms to align, thereby
material decreases.material decreases.
 Total Entropy of the item is not reduced, andTotal Entropy of the item is not reduced, and
item heats upitem heats up

9. Isomagnetic enthalpic transferIsomagnetic enthalpic transfer
 Added heat removed by fluid, gas –Added heat removed by fluid, gas –
gaseous or liquid heliumgaseous or liquid helium
 Magnetic field held constant to prevent theMagnetic field held constant to prevent the
dipoles from reabsorbing the heat.dipoles from reabsorbing the heat.
 After a sufficient cooling magnetocaloricAfter a sufficient cooling magnetocaloric
material and coolant are seperatedmaterial and coolant are seperated

10. Adiabatic DemagnetizationAdiabatic Demagnetization
 Substance returned to another adiabatic ( insulated ) conditionSubstance returned to another adiabatic ( insulated ) condition
 Entropy remains constantEntropy remains constant
 Magnetic field is decreased,Magnetic field is decreased,
 Thermal energy causes the magnetic moments to overcomeThermal energy causes the magnetic moments to overcome
the field and sample cools ( adiabatic temperature change )the field and sample cools ( adiabatic temperature change )
 Energy transfers from thermal entropy to magnetic entropyEnergy transfers from thermal entropy to magnetic entropy
( disorder of the magnetic dipoles )( disorder of the magnetic dipoles )

11. Isomagnetic entropic transferIsomagnetic entropic transfer
 Material is placed in thermal contact with theMaterial is placed in thermal contact with the
environment being refrigerated.environment being refrigerated.
 Magnetic field held constant to prevent from heatingMagnetic field held constant to prevent from heating
back upback up
 Because the working material is cooler than theBecause the working material is cooler than the
refrigerated environment, heat energy migrates into therefrigerated environment, heat energy migrates into the
working material ( +Q )working material ( +Q )
 Once the refrigerant and refrigerated environment are inOnce the refrigerant and refrigerated environment are in
thermal equillibrium, the cycle begins a newthermal equillibrium, the cycle begins a new

12. Working MaterialsWorking Materials
 Magneto caloric effect is an intrinsic porperty of magnetic solid.Magneto caloric effect is an intrinsic porperty of magnetic solid.
 Ease of application and removal of magnetic effect is mostEase of application and removal of magnetic effect is most
desired property of material. It is individual characteristics anddesired property of material. It is individual characteristics and
strongly depends on :strongly depends on :
 Curie temperatureCurie temperature
 Degree of freedom for magnetic dipoles during ordering andDegree of freedom for magnetic dipoles during ordering and
randomization of particles.randomization of particles.
 Ferrimagnets, antiferromagnets and spin glass sytems are notFerrimagnets, antiferromagnets and spin glass sytems are not
suitable for this applicationsuitable for this application
 Alloys of gadolinium producing 3 to 4 K per tesla of change inAlloys of gadolinium producing 3 to 4 K per tesla of change in
magnetic field are used for magnetic refrigeration or powermagnetic field are used for magnetic refrigeration or power
generation purposes.generation purposes.

13. Refrigeration Below 1KRefrigeration Below 1K

14. NUCLEAR DEMAGNETIZATIONNUCLEAR DEMAGNETIZATION
 This type is one of the variant that continues to find substantialThis type is one of the variant that continues to find substantial
research application.research application.
 It follows the same principle, but in this case the cooling powerIt follows the same principle, but in this case the cooling power
arises from the magnetic dipoles of the nuclei of refrigent atomsarises from the magnetic dipoles of the nuclei of refrigent atoms
rather than their electronic configuration.rather than their electronic configuration.
 Since these dipoles are of much smaller magnitude, they are lessSince these dipoles are of much smaller magnitude, they are less
prone to self alignment and have lower intrinsic minimum field.prone to self alignment and have lower intrinsic minimum field.
 This allows NDR to cool the nuclear spin system to very lowThis allows NDR to cool the nuclear spin system to very low
temperatures, often 1 micro Kelvin.temperatures, often 1 micro Kelvin.
 Magnetic fields of 3 telsa or greater are often needed for the initialMagnetic fields of 3 telsa or greater are often needed for the initial
mgneization step of NDRmgneization step of NDR

15. Nuclear Demagnetization ProcessNuclear Demagnetization Process

16. Steps of Nuclear DemagnetizationSteps of Nuclear Demagnetization
 Nuclear demagnetization is a single-shotNuclear demagnetization is a single-shot
technique which consists of three steps:technique which consists of three steps:
 Magnetization:Magnetization:
 Decoupling and demagnetization:Decoupling and demagnetization:
 Experiments:Experiments:

17. MagnetizationMagnetization
 The nuclear spins in the material serving as a refrigerator andThe nuclear spins in the material serving as a refrigerator and
by applying a large magnetic field Bi, a thermodynamic spinby applying a large magnetic field Bi, a thermodynamic spin
polarization is generated. The heat arising during this processpolarization is generated. The heat arising during this process
is drained by the cooling power of the Mixing Chamber untilis drained by the cooling power of the Mixing Chamber until
the system is equilibrated at base temperature Ti.the system is equilibrated at base temperature Ti.

18. Decoupling and demagnetization:Decoupling and demagnetization:
 Without disconnecting the electrical contact, the thermalWithout disconnecting the electrical contact, the thermal
contact between the NR and the MC is cut by acontact between the NR and the MC is cut by a
superconducting heat switch.superconducting heat switch.
 In a next step, the magnetic field is reduced adiabatically to BfIn a next step, the magnetic field is reduced adiabatically to Bf
. The final temperature in an ideally adiabatic process. The final temperature in an ideally adiabatic process
 isis

19. Experiments:Experiments:
 For a finite time, experiments can be performed atFor a finite time, experiments can be performed at
these low temperatures. The time, typically on thethese low temperatures. The time, typically on the
order of days or even weeks, depends on the size oforder of days or even weeks, depends on the size of
the polarized spin reservoir and on the heat leakingthe polarized spin reservoir and on the heat leaking
into the system.into the system.

20. Molar nuclear spin entropy versus nuclear spin temperature for differentMolar nuclear spin entropy versus nuclear spin temperature for different
magnetic fields.magnetic fields.

21. Advantages of Nuclear and MagneticAdvantages of Nuclear and Magnetic
RefrigerationRefrigeration
 Purchase cost may be high, but running costs arePurchase cost may be high, but running costs are
20% less than the conventional chillers Thus life20% less than the conventional chillers Thus life
cycle cost is much less.cycle cost is much less.
 Ozone depleting refrigerants are avoided in thisOzone depleting refrigerants are avoided in this
system, hence it more eco-friendly.system, hence it more eco-friendly.
 Energy saving would lessen the strain on ourEnergy saving would lessen the strain on our
household applianceshousehold appliances
 Energy conservation and reducing the energyEnergy conservation and reducing the energy
costs are added advantages.costs are added advantages.

22. ReferencesReferences
 http://en.wikipedia.org/wiki/Magnetic_refrigerationhttp://en.wikipedia.org/wiki/Magnetic_refrigeration
 Maradan_MScThesis_FINALMaradan_MScThesis_FINAL
 T. Bandi, Semester thesis, University of Basel (2008).T. Bandi, Semester thesis, University of Basel (2008).