Heat capacity as you know is a measure of the amount of energy (heat) required by a certain mass of a material to raise its temperaure by unit degree. The variable heat is required because heat gets absorbed into non-temperature raising modes also (other than kinetic or translational or vibrational). Can we control and hinder say rotational modes so that energy gets redistributed into kinetic ones only? This is very important because it can lead to self raising of the temerature of a given material having same energy, but diffrently divided.
@Joachim, it may be sligthly off topic, but the first reference You provided is interesting. Biological cell membrane potentials are of the same order as the field strengths mentioned. In case field induced phase changes occur in biological systems as well on a microscopic scale, it should be an interesting area of research. Anybody seen this mentioned before?
Regarding the possibility of increasing temperature by any method providing an external stimuli - shouldn´t that be impossible since You will decrese the enthrophy of the system by raising the temperature at a given energy? The only way this could work is if some stored energy could be converted to heat. Otherwise only a lower temperature seems possible since entrophy has to increase in any physical process.
Heat capacity or thermal capacity is the amount of heat energy required to raise the temperature of a substance (any mass) through one degree celsius.The formula to find Heat capacity of a substance is Heat capacity = H/t , where ‘H’ is the supplied heat energy in joules and ‘t’ is the rise or fall in temperature .The SI unit of Heat capacity is J/oK. Unlike specific heat capacity the heat capacity is independent of mass. A negative heat capacity results in negative temperature. Hence heat capacity of a substance cannot be altered by any external agency because it is a constant value.
Let me correct some of the statements above. Heat capacity C is an extensive thermodynamic quantity, and thus it is proportional to volume or mass or the number of degrees of freedom. Specific heat capacity c is heat capacity normalized by the number of degrees of freedom, and it's an intensive thermodynamic quantity (independent of mass/size).
In conducting solids the heat capacity has two contributions: energy can be stored in lattice vibrations or conducting electrons, which can be approximated by a Fermi gas. In the low temperature limit the electron gas contribution dominates c, leading to a linear dependence on T. However, there are materials where the electronic ground state is more complicated (e.g. spin waves), and in those cases c is dominated by excitations of such ground states.
Finally, the interesting question: can external fields (electric or magnetic) influence c? It depends on the temperature regime in question. At high enough T, where the lattice vibrational degrees of freedom dominate, external fields have no effect on perfect conductors (the situation is much more complicated for complex materials such as ferroelectrics; you can easily google for references on ongoing research). In the low-T regime an external magnetic field causes changes in the density of states close to the Fermi level and thus there's a (small) change in c. For materials with exotic ground states, however, significant influence from external fields is possible. This is a highly advanced topic.
Thanks for some replies. Joachim Pimiskern gave some interesting example but I am afraid is not relevant to my query. One of the replies stating electronic contribution is one possibility. However, firstly apologizing to coming on the site after some days, may I draw the attention of the curious readers of this question that as a adiabatic demagnetization is able to lower the temperature as the heat capacity control shifts to equivalent (entropy) at a lower a temperature, I would stretch carefully to a sudden magnetization to cause heating (as lower entropy would have to be compensated by increase in lattice entropy). Please think some other means also. I have a very important final analysis if we can achieve this.
Thermal properties of a material in an external field or undergoing nonequilibrium driving can still be summarized via the notion of heat capacity. These nonequilibrium heat capacities measure the excess heat in thermal relaxation when changing the environment temperature. Excess, because nonequilibrium systems dissipate heat even under stationary conditions, The resulting heat capacities can be quite different from their equilibrium values; they can also be negative. See the paper
Eliran Boksenbojm, Christian Maes, Karel Netočný and Jirka Pešek:
Heat capacity in nonequilibrium steady states, EuroPhysicsLetters 96, 40001 (2011).
for more details.
The answer to the original question is yes. Magnetic refrigerators are currently under development, they really work.
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