Interactions in rare earth trihalides

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Abstract
High frequency measurements have been made of the field dependence of the adiabatic differential susceptibility of CeCl3, CeBr3, and GdCl3. This has permitted the determination of the leading coefficients in the high temperature expansion CM/R=JCn/Tn for the magnetic specific heat and λ/χT= (T+JBn/Tn−1) for the inverse isothermal susceptibility. For CeCl3 and CeBr3, these coefficients have been combined with earlier EPR measurements allowing an unambiguous determination of the nondipolar interaction constants. The analysis shows that the interactions are quite similar for these two compounds and that the antiferromagnetic ordering is dominated by the antiferromagnetic nearest‐neighbor coupling. However, there are a number of other terms both ferromagnetic and antiferromagnetic in sign and precise ordering is therefore determined by a subtle balance between these interactions. The results for GdCl3 have produced more accurate values for the nearest‐ and next‐nearest‐neighbor exchange interactions than earlier measurements. In addition, upper limits were also obtained for the third‐nearest‐neighbor exchange interactions.