I have prepared a series of manganite samples with Curie temperature 140-36K. I want to know these materials will be suitable for refrigeration purpose?
With Regards
Dinesh Kumar
It depends on the temperatures involved and what exactly you intend to use the samples for. If you want to use the samples as permanent magnets, then you will need to be operating below their Curie temperature. At liquid helium temperatures (~4K), all of the samples will function as permanent magnets, but at liquid nitrogen temperatures (~77K), those with lower Curie temperatures will not.
For refrigeration purpose you need to study the magnetocaloric performance of these samples. Based on that the sample can be choose because only Curie temperature is not a sufficient parameter. The important property is rate of change of magnetization per degree change in temperature, i.e, pyromagnetic co-efficient (in working range of temperature) will be more suitable parameter.
Dear Dinesh,
I have to agree with Kinnari and Keith. A lot depends on what you want to use the materials for, their adiabatic temperature change and capacity for heat extraction. You will find good literature online for deciding which material you have to choose. For example you might want a temperature invariant response if you are looking at a fluctuating thermal load while for a fixed load, you could benefit from a higher delta T.
I myself have done quite a lot of research on electrocaloric effect which operates along the same line.
I hope this was helpful
http://pubs.rsc.org/is/content/articlehtml/2013/ta/c3ta01289a
http://iopscience.iop.org/article/10.1088/0022-3727/38/23/R01/meta
http://www.sciencedirect.com/science/article/pii/S0304885399003972
If you are using magnetic materials, you want them to stay magnetic at really low temperatures, so low Tc is the answer i guess.
All answers are on the ball . One perfectly general point . Magnetic cooling is no different from the humble food fridge . Both extra heat (entropy) by exploiting phase changes eg ferromagnetic and ordering - liguid vapour . Thus in your case Tc needs to be in the range of temperatures required in the application. For a magnetic version of the food fridge Gd is probably the best known material with a Tc close to room temp..
I would be interested to hear how magnetic cooling is going. Ten years ago I came to the conclusion that all magnetic latent heats were simply way too small ( by 2 or 3 orders if I recall correctly)t o be practical . Then I didn't buy the increased efficiency argument ,even for industrial scale coolers. Even ammonia is a much better bet as a working substance for a heat engine,not least because it is a liquid and so a natural for efficient heat exchangers.
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