We have studied a model compound for purely organic ferrimagnets by single crystal cw-ESR spectroscopy. The system under study is composed of two kinds of nitronylnitroxide molecules with the ground states of S=1/2 and S=1. These molecules arc stacked in an alternating chain in the crystal. The cw-ESR signal of the compound split below 10 K into two lines, which were reproduced by the superposition of two Lorentzian lines. The X-ray measurements at 9.6 K disclosed that the crystal structure remained unchanged at low temperatures, indicating that the origin of the ESR line splitting is not attributable to structural phase transitions but to some change inherent in the spin state: Two distinguishable spin species appear in the crystal to give the line splitting. The magnetic interaction fields from the two species are elucidated on the basis of the angular dependence of the ESR linewidths: One is a three-dimensional interaction field, while the other is a one-dimensional interaction field which is axially symmetric along the alternating chain. The appearance of the two kinds of spin species demonstrates that the classical picture of ferrimagnetic states (antiparallel alignment of adjacent spins with different spin quantum numbers) can not apply to purely organic ferrimagnets and it leads to miss an essential part of their nature. This results from the internal magnetic degree of freedom within the S=1 molecule, i.e., finite intramolecular ferromagnetic interaction.
|Number of pages||7|
|Journal||Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals|
|Publication status||Published - 1997|
ASJC Scopus subject areas
- Condensed Matter Physics