Calorimetric investigation of the magnetic transition in quasi-one-dimensional molecule-based ferrimagnets: [Mn(OC14H29)4TPP][TCNE]·MeOH and [MnF4TPP][TCNE]·0.5MeOH

Heat capacity study was performed, for the first time, for [MnF4TPP][TCNE]·0.5MeOH and [Mn(OC14H29)4TPP][TCNE]·MeOH complexes in the 1.8–100K temperature range under the 0–9T magnetic field and disclosed new aspects inherent in such strongly coupled charge-transfer Mn–porphyrin–TCNE linear chain sys...

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Bibliographic Details
Published in:The Journal of physics and chemistry of solids 2005-01, Vol.66 (1), p.147-154
Main Authors: Bhattacharjee, Ashis, Falk, Karsten, Haase, Wolfgang, Sorai, Michio
Format: Article
Language:English
Subjects:
A. Magnetic materials
Condensed matter: electronic structure, electrical, magnetic, and optical properties
Critical-point effects, specific heats, short-range order
D. Magnetic properties
D. Phase transitions
D. Specific heat
D. Thermodynamic properties
Exact sciences and technology
Magnetic properties and materials
Molecular magnets
Physics
Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
Studies of specific magnetic materials
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Summary:Heat capacity study was performed, for the first time, for [MnF4TPP][TCNE]·0.5MeOH and [Mn(OC14H29)4TPP][TCNE]·MeOH complexes in the 1.8–100K temperature range under the 0–9T magnetic field and disclosed new aspects inherent in such strongly coupled charge-transfer Mn–porphyrin–TCNE linear chain systems, where TPP=5,10,15,20-tetraphenylporphyrinato, TCNE=tetracyanoethylene and MeOH=methanol. Any heat capacity anomaly due to the onset of the magnetic long-range-order was not detected, whereas the magnetic phase transition has clearly been observed around 20K by previous magnetic studies. As these materials are well approximated by quasi-one-dimensional ferrimagnetic Heisenberg chains with very large intrachain spin-spin interactions, the most part of the magnetic entropy is retained above the phase transition temperature as the dominant short-range order. This is the reason why no magnetic phase transition was detected by calorimetry. On the other hand, the big effect observed in the magnetic susceptibility is well accounted for if the formation of magnetic domains is assumed in the crystal.
ISSN:0022-3697
1879-2553
DOI:10.1016/j.jpcs.2004.09.001