THermodynamics of a magnetic system

1. Jan 5, 2005

Feynmanfan

I've been given the fundamental equation of a magnetic system .U(S,N,I)=...
I have to calculate some thermodynamic potentials such as U[T] etc.

One of them is the so called magnetic enthalpy and the expression for it is
U[p,B]. Another one is U[p]. How do I calculate it? I don't even know what it means.

Since I'm only used to pression, volume etc. I don't know what p is.

If S is entropy, I the equivalent of volume and B (magnetic field or whatever) the equivalent of pressure. WHat is p?

2. Jan 5, 2005

Andrew Mason

You haven't exactly explained the question very well.

Generally magnetic enthalpy is a state variable that will indicate whether the magnetic energy of the system (internal magnetic energy + magnetic work) has increased or decreased. It is just that there are different definitions of work and internal energy for a magnetic system (depending on what kind of magnetic system it is) than for an ideal gas system. You can have paramagnetic low temperature gases, paramagnetic solids, magnetic solids, nuclear magnetic or magnetic ion systems, or composite paramagnetic systems consisting of magnetic solids and gases. They have different parameters for work and internal energy.

AM