Origin of soft spin structure in Mn formate di-urea

Proton NMR measurements at low temperature show that Mn moment direction in Mn formate di-urea easily changes by temperature as well as the replacemen t of hydrogen with deuterium atom in urea. The chang in the moment directio n is due to the competition of the magnetic anisotropy caused by the dipole interaction with the anisotropy caused by the surrounding ligand ions. The observed spin structure of four-fold screw rotations of antiferromagnetic layers is well understood by very small interlayer exchange interactions an d magnetic anisotropies. The possibility is pointed out that the dipole int eraction between the first nearest neighboring layers is the important orig in of the transition to the three-dimensional long range order of this comp ound.