The Magnetic Properties of Cupric Formate Tetrahydrate at Low Temperatures

The magnetic susceptibility of single crystals of Cu(HCO 2 ) 2 ·4H 2 O was measured at temperatures between 1.4°K and 80°K by a. c. bridge and magnetic balance method. This salt is an example of the magnetic two dimensional lattice. The interaction between Cu 2+ ions is mainly the superexchange interaction through a formate ion in the same layer. From the Weiss constant of about -150°K, it is concluded that strength of superexchange interaction through a formate molecule, –(O–CH–O)–, has the same order as that through one diamagnetic atomic ion such as –(Cl)–. The existence of a broad maximum of the susceptibility at about 60°K implies the appearence of short range order in the two dimensional lattice. The antiferromagnetic transition accompanied by parasitic ferromagnetism was found at 17.0°K±0.2°K. The weak ferromagnetic moment in L 1 L 2 plane was about 150 c.g.s.e.m.u. at 0°K. Along L 3 axis, no ferromagnetic moment was found. The susceptibility of isomorphous Cu(HCO 2 ) 2 ·2H 2 O·2(NH 2 ) 2 CO was similar to that of Cu(HCO 2 ) 2 ·4H 2 O.