Study of spin configuration in Mn formate di-urea by proton NMR

Antiferromagnetic spin arrangement of Mn formate di-urea is studied by prot on NMR measurements below T-N (3.78 K). Observed spectra are compared with possible spin arrangements. The antiferromagnetic moments within the layer point to the direction rotating 15 degrees around the c-axis from the middl e direction between the [001]- and [(1) over bar 00]-directions. The layer including antiferromagnetic moments rotates following to the stacking of fo ur-fold screw axis along the c-axis, The origin of this spin arrangement is discussed.