抄録
The crystal of Ni (NO3)2·4H2O is found to contain two kinds of sites for Ni2+ ions in a unit cell. By the measurements of the isentrope, susceptibility and specific heat, two spin ordered states are observed applying a field along either of the two ion axes, zA and zB, corresponding to the two inequivalent Ni2+ sites. One of the spin orderings occurs between 12 kOe and 44 kOe (H⁄⁄zA) and the other at a higher field region than 35 kOe (H⁄⁄zB). The highest critical temperature is 0.57 K (H⁄⁄zA), and is lower than this when H⁄⁄zB.
