Low temperature magnetization study on high spin iron (III) porphyrins

Abstract

Accurate and detailed measurements of average magnetic susceptibility (4–100 K) and magnetization (2–20 K and 10–50 kOe) are reported on a number of high spin iron (III) prophyrins, namely protoporphyrin-, octaethylporphyrin-, and deuteroporphyrin iron (III) chlorides. Adequate precautions were taken to ensure that the crystallites did not orient during the magnetization measurements, in high magnetic fields at low temperatures. The experimental magnetization data show complete saturation below 4 K at magnetic fields above 40 kOe and the saturation moment 〈μ〉 lies between 3.0–3.4 in these compounds, indicating large deviation from the expected value of 5.0, due to sizeable zero-field splitting. The magnetization results at low temperatures show varying degrees of exchange interaction, which was considered within molecular field framework to quantitatively account for the data. A fit to the data gave reasonable values for the zero-field splitting and exchange-interaction parameters.