Determination of exchange constants from relaxation specific heat measurements on GdCl₃

Measurements of the magnetic contribution to the specific heat have been made on polycrystalline samples of GdCl3 at temperatures between 20° and 77°K, using a relaxation method with frequencies up to 40 Mc/sec. The results, when combined with the Weiss constant determined by Marquard and Wyatt, give two sets of values for the nearest- and next-nearest-neighbor exchange interaction between Gd3+ ions. The first set gives ferromagnetic values for both Jnn(+0.071±0. 005°K) and Jnnn(+0.011±0.005°K), while the other gives a small antiferromagnetic Jnn(-0.020±0.011°K) and a larger ferromagnetic Jnnn(+0.041±0.002°K). These results are discussed in terms of other experimental data. © 1965 The American Institute of Physics.