Magnetization steps in the model magnetic dimer mu-oxalatotetrakis(acetylacetonato)Fe-2(III) - art. no. 094422

The Fe3+ dimer in mu -oxalatotetrakis(acetylacetonato)Fe-2(III) is ideally suited for a magnetization-step study. Using pulsed magnetic fields up to 5 00 kOe (50 T), all five predicted magnetization steps (MST's) from this dim er were observed. The MST's appeared as peaks in the differential susceptib ility dM/dH. Using the convention in which the exchange interaction between the two Fe(III) ions is -2JS(1) . S-2, the magnetic fields at the MST's gi ve an intradimer exchange constant J = -3.610.1 cm(-1). The powder sample w as in a Delrin capsule that was immersed in a 1.5 K liquid-helium bath. The shapes and widths of the MST's were strongly affected by the thermal conta ct between the sample and the liquid-helium bath. Preventing the liquid hel ium from entering the capsule containing the sample apparently resulted in nearly adiabatic conditions during the milliseconds duration of the held pu lse. In this case, as each of the MST's was approached, the strong cooling by the magnetocaloric effect caused the dM/dH peaks to be very narrow. Much broader dM/dH peaks were observed when liquid helium entered the capsule c ontaining the sample. In addition to magnetization-step experiments in puls ed fields, the magnetic susceptibility chi was measured between 2 and 170 K using a steady magnetic field of 3 kOe. The susceptibility led to an intra dimer exchange constant which was in good agree ment with the value obtaine d from the MST's.