The Magnetochemistry of Supramolecular Particles: The Transition from the Molecular to the Solid-State
Abstract
The magnetic properties of nanometer-sized molecular complexes or clusters that contain an increasing number ii of superexchange-coupled iron ions (10 < n < 20) participating in 3-D or lower-dimensional magnetic interactions were examined. The experimental criteria that establish the onset of incipient solid-state magnetic correlation effects in these molecules were emphasized. These chemical structures are beyond the molecular realm but convergence to the bulk has not yet been attained. Thus, they afforded appropriate experimental systems to test theoretical predictions that the onset of incipient solid-state phenomena - such as the emergence of a conduction band in metallic clusters and collective magnetic interactions responsible for magnetic ordering in solids - occurs at the vicinity of n > 10, where n is the number of atoms or interacting spins in the cluster. The study provided, by means of Mossbauer spectroscopy with a characteristic measuring time tau - 10-8 sec the first experimental observation of the onset of intramolecular magnetic ordering in 10 A diameter clusters whose magnetic exchange interaction network among iron ions was three-dimensional. Owing to the extremely small size of the magnetic domain transitional magnetic behavior and superparamagnetic relaxation phenomena dominated the Mossbauer spectra. In addition, preliminary magnetization studies on a mixed valent cluster containing iron ions primarily in the ferrous state indicate the presence of hysteric effects at low temperatures, which also attests to the existence of collective magnetic interactions and particle-like magnetic behavior of these macromolecules. This is the first time that hysteresis has been observed in nanometer-sized molecular systems. Due to spin fluctuation effects lower dimensional clusters failed to produce collective magnetic correlation phenomena within the Mossbauer time window down to pumped liquid helium temperatures.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1992
- Accession Number
- ADA253126
Entities
People
- Georgia C. Papaefthymiou
Organizations
- Massachusetts Institute of Technology