Magnetization of the Two-Dimensional Heisenberg Ferromagnet K₂CuF₄ with Small XY-Like Anisotropy

Abstract

The temperature variation of magnetization in the quadratic layer ferromagnet K 2 CuF 4 has been investigated by measuring the NMR frequency of Cu 63 or out-of-layer F 19 nuclei at zero and applied fields in the temperature region of 0.27≦ T / T c ≦0.67. The results are analyzed by a two-dimensional spin wave theory. Under the external field the dipole interaction is approximated in a form of the effective field. The X Y -like anisotropy of exchange interaction is taken into consideration. Good agreement between the theory and the experimental results is obtained. The X Y -like anisotropy itself is not effective to the magnetization, but its contribution to the magnetization cannot be neglected when it cooperates with the external field. The parameter of the exchange interaction J within the layer is obtained to be 12.37 K. The NMR result at zero applied field is also discussed.