Adiabatic demagnetization of paramagnetic salts (cryogenic trading entropy for temperature) is a half-century old. Einstein patented a magnetic refrigerator. At modest scale, the optimum solution (cheap, fast, effective) is an SOP Sears freon refrigerator. Civilization knows what it is doing. Enviro-whiners are against everything of value.
Look at the spin orientation energy gap of unpaired electrons (paramagnet) in a 1 tesla field. You get maybe a score in a thousand net population inversion near room temp. Do the Boltzmann distribution thermodynamics, N2/N1 = exp[-(E2-E1)/kT].http://en.wikipedia.org/wiki/Population_inversion
It's horribly crappy in terms of watts/mass or watts/volume. Even with a higher efficiency magnetic amorphous metal alloy you still drive heat flow with electron orientational entropy. Electrons are ~0.03 mass-% of a solid. 99.7 mass-% of the working fluid is inert.
...today's equivalent gas fridges that require environmentally toxic gases to operate.
That should have been your first clue. /_\G = /_\H - T/_\S. /_\H is typically three orders of magnitude larger than T/_\S. What does that tell you about heat engines vs. entropy engines? Also note the magnetic alloy is "being developed." It's Official Truth (bullsh*t).