Magneto Caloric Effect: Exploring Internal Energy Change

In summary, the magnetocaloric effect is when a substance's temperature increases when exposed to an external magnetic field. This effect is due to the decrease in entropy that occurs when the magnetic dipoles are aligned in a specific direction.
  • #1
gursimran
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In magneto caloric effect, we see that when a substance in an adiabetic closure is exposed to external magnetic field, its temperature increases. But the internal energy of the substance has to be constant so this implies decrease in internal potential energy. However the application of magnetic field can only directly change the external potential energy of the substance as a whole. How it can affect the internal energy of the substance??

For example like gravitational field can't effect the internal energy of the substance..
 
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  • #2


Even the gravitational field can affect the internal energy of a sample although the gravitational field of Earth is quite weak to make this effect observable: Think about an container of fixed volume containing water vapour just above its condensation temperature. If you bring this container at in a strong gravitational field while keeping its temperature constant, it will be energetically more favorable for water to condense and collect as a liquid at the bottom of the container where its potential energy is lower. In that process, heat will be released, just like in the magnetocaloric effect.
 
  • #3


DrDu said:
Even the gravitational field can affect the internal energy of a sample although the gravitational field of Earth is quite weak to make this effect observable: Think about an container of fixed volume containing water vapour just above its condensation temperature. If you bring this container at in a strong gravitational field while keeping its temperature constant, it will be energetically more favorable for water to condense and collect as a liquid at the bottom of the container where its potential energy is
lower. In that process, heat will be released, just like in the magnetocaloric effect.

Thanks for answer but I'm having a hard time understanding this all..

So can I generalize that all force fields can effect the internal energy of the substance (it can affect the amount in which it is distributed in potential and kinetic energy) but it in itself does not contribute to internal energy. eg - if I turn on the magnetic field/ electric does the internal energy(KE+PE) of the substance changes in amount??

Secondly, how does it effect. If applying the magnetic field alligns all the dipoles in the dierction of magnetic field. How that effect the internal energy distribution of the gas. Please justify.

Thanks in advance. ...
 
  • #4
What is the physical significance of the entropy linked to magnetic field.

I was reading a research paper on magetocalorific effect. It says magnetic component of entropy but entropy being a state function should not get affected by the external fields. Just like it does not get affected by gravitational and electric field. Also can't magneto calorific effect be explained in terms of internal energy changes. For example if we adiabetically magnetise a material the temperature should rise. It means thermal agitation has increased and because dq=0 so KE should have converted to internal potentail energy. But how is internal potentail energy affected by the application of magnetic field?

Is there a good book which explains the basic theory of magnetocaloric effect with rigor?
 
  • #5


Why do you open a new thread? You asked essentially the same question before. I also showed you that a gravitational field can produce the same effects as a magnetic field.
So why do you say it doesn't?
Entropy is a state function, but the state depends on the magnetic field just like it depends on e.g. volume. When you magnetize e.g. a paramagnetic material, you create a preferred orientation for the magnetic dipoles. When the dipoles relax into these orientation, their entropy decreases, the heat capacity of the dipoles decreases, and they release energy which is taken up by the lattice vibration and the lattice temperature increases. This effect may be strongly enhanced near a ferromagnetic phase transition were you observe the giant magnetocaloric effect.
 
  • #6


DrDu said:
Why do you open a new thread? You asked essentially the same question before. I also showed you that a gravitational field can produce the same effects as a magnetic field.
So why do you say it doesn't?
Entropy is a state function, but the state depends on the magnetic field just like it depends on e.g. volume. When you magnetize e.g. a paramagnetic material, you create a preferred orientation for the magnetic dipoles. When the dipoles relax into these orientation, their entropy decreases, the heat capacity of the dipoles decreases, and they release energy which is taken up by the lattice vibration and the lattice temperature increases. This effect may be strongly enhanced near a ferromagnetic phase transition were you observe the giant magnetocaloric effect.

oh I apologize for that. Ya you won't believe but its true that I almost forget that I had already asked this question before. Still I don't remember what were the replies. Thanks anyway for replying. Could you suggest me some books on this to get out of this dilemma or confusion..
 
  • #7


gursimran said:
Thanks for answer but I'm having a hard time understanding this all..

So can I generalize that all force fields can effect the internal energy of the substance (it can affect the amount in which it is distributed in potential and kinetic energy) but it in itself does not contribute to internal energy. eg - if I turn on the magnetic field/ electric does the internal energy(KE+PE) of the substance changes in amount??

Secondly, how does it effect. If applying the magnetic field alligns all the dipoles in the dierction of magnetic field. How that effect the internal energy distribution of the gas. Please justify.

Thanks in advance. ...

oh here it is. I was not convinced. If you say that external gravitational field can affect the internal energy. Then so can psuedo gravitational field due to gas in a accerlating frame. But I have read it essentially many times that systematic motion of a gas as a whole can't change the internal energy of a gas. You can see that in wikipedia as well.

You can read this " It is the energy needed to create the system, but excludes the energy to displace the system's surroundings, any energy associated with a move as a whole, or due to external force fields." Taken from http://en.wikipedia.org/wiki/Internal_energy
 
  • #8


Two different threads have been merged.

Zz.
 

1. What is the Magneto Caloric Effect (MCE)?

The Magneto Caloric Effect is a phenomenon in which the temperature of a material changes when it is subjected to a magnetic field. This change in temperature is caused by the internal energy of the material being affected by the magnetic field.

2. How does the MCE work?

The MCE is based on the principle that when a magnetic field is applied to a material, the magnetic moments of the atoms within the material align with the direction of the field. This alignment causes a change in the internal energy of the material, leading to a change in temperature.

3. What applications does the MCE have?

The MCE has potential applications in refrigeration and cooling systems. By using materials with a strong MCE, it is possible to create more efficient and environmentally friendly refrigeration systems without the need for harmful refrigerants. It can also be used in magnetic cooling devices for healthcare, such as MRI machines.

4. How is the MCE measured?

The MCE is measured by monitoring the change in temperature of a material when a magnetic field is applied. This change in temperature can be quantified by calculating the specific heat capacity of the material, which is the amount of heat required to raise the temperature of the material by a certain amount.

5. Are there any challenges in utilizing the MCE?

One of the main challenges in utilizing the MCE is finding materials with a strong enough effect to be practical for real-world applications. Another challenge is the cost of producing these materials and developing the technology to incorporate them into refrigeration systems. Additionally, there are still some uncertainties and limitations in our understanding of the MCE, which require further research to overcome.

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