Magnetization steps in [Fe(salen)Cl]2

The differential susceptibility dM/dH of [Fe(salen)Cl](2) where salen is N,N'-ethylenebis(salicylideneiminato), was measured in pulsed magnetic fields up to 550 kOe. The samples were in a capsule that was immersed in a liquid-helium bath maintained at a temperature 1.5 less than or equal to T(bath)less than or equal to 4.2 K. Three magnetization steps (MST's) arising from energy-level crossings for the Fe3+ dimer were observed as peaks in dM/dH. The intradimer exchange constant obtained from the MST's is J = -8.4 +/- 0.2 cm(-1), assuming a g factor of 2.00. The line shapes of the peaks in dM/dH strongly suggest the existence of weak interactions that are not included in the conventional model of independent dimers with isotropic intradimer exchange only. The missing weak interactions are yet to be identified. The narrow widths of the peaks in dM/dH indicate strong departures from thermal equilibrium with the helium bath during the field pulse (milliseconds duration). Such narrow widths are the result of cooling by the magnetocaloric effect. The cooling, and therefore the line shapes of the dM/dH peaks, depended on the arrangement for the sample-to-bath heat flow during the field pulse. With one heat-flow arrangement hysteresis was observed. Computer simulations of the line shape resulting from the magnetocaloric effect during the field pulse reproduce the narrow widths and the hysteresis. Data for the low-field magnetic susceptibility between 2 and 300 K, measured in steady fields, gave J congruent to -8 cm(-1). [S0163-1829(99)08101-1].