Magnetic Properties of CuF2

Abstract

We have measured the moment of a pressed powder sample of monoclinic CuF2 from 4.2° to 300°K in fields to 25 kOe. χ(T) indicates an AFM transition at TN=69°K, and analysis gives ḡ≈2.3 and Θ≈−200°K. TN and Θ are consistent with magnetic ordering of the first kind with AFM exchange interactions J1(corner-bc)≈34°K and J2≈22°K. Weak ferromagnetism of anisotropic exchange origin is expected on the grounds of symmetry; the measured ferromagnetic moment is σ0≈1 G cm3/mole, corresponding to a canting angle φ≈0.01°. Assuming magnetic dipolar anisotropy and estimating principal axes and values for the anisotropic g tensor, we find the spin axis to be about 2° from c and 99° from a in the ac plane with anisotropy field HA∼2000 Oe, and the weak moment to be parallel to the monoclinic axis b with canting field HDM∼1000 Oe. Pseudodipolar anisotropy may be expected to change the orientation, but not the order of magnitude of these fields. The uniform mode AFM resonances are not degenerate in general, but both would be expected to occur at v/c∼9 cm−1 using these values.