Structurally Induced Magnetic Transition in Manganese Phthalocyanine Thin Films*

Manganese phthalocyanine (MnPc) thin films were fabricated on both insulating and metallic substrates at different deposition temperatures ranging from 32^oC to 260^oC using thermal evaporation. Two crystal structures are found: one set of thin films shows the MnPc (200) 2θ peak between 6.732^o and 7.004^o corresponding to a lattice constant ranging from 2.280 nm to 2.395 nm. The second set deposited at 230^oC and 260^oC has a MnPc (001) 2θ peak at 7.12^o consistent with MnPc in the β-phase and a lattice constant corresponding to c = 1.306 nm. The structural change is accompanied by changes in the magnetism. The magnetic properties of all MnPc thin films are characterized with the vibrating sample magnetometer. The temperature-dependent static susceptibility shows a large increase at low temperatures for samples deposited in the β-phase, simultaneously the low-temperature magnetic hysteresis loops have a large saturation magnetization for the same set of samples. The net magnetization disappears for the low-temperature sample set. This is characteristic for a magnetic transition with the parameter being the crystalline order of the material.