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Ajuste magnético de aleaciones binarias totalmente orgánicas entre dos radicales estables
Gonca Seber1, Rafael S Freitas, Joel T Mague
1Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003, USA.
Journal of the American Chemical Society
|February 11, 2012
Resumen
Las soluciones sólidas de nitróxidos de benzimidazol fluorados y no fluorados forman aleaciones con propiedades magnéticas sintonizables. Estos materiales exhiben un comportamiento ferromagnético cuasi unidimensional impulsado por cadenas enlazadas con hidrógeno.
Área de la Ciencia:
- Ciencia de los materiales Ciencia de los materiales.
- Química del estado sólido.
- El magnetismo es el magnetismo.
Sus antecedentes:
- Las mezclas de 2-(4,5,6,7-tetrafluorobenzimidazol-2-il)-4,4,5,5-tetrametil-4,5-dihidro-1H-imidazol-3-óxido-1-óxilo (F4BImNN) y 2-(benzimidazol-2-il)-4,4,5,5-tetrametil-4,5-dihidro-1H-imidazol-3-óxido-1-óxilo (BImNN) son soluciones en forma sólida.
- Estas soluciones sólidas exhiben fases cristalográficas distintas (ortorhómbicas y monoclínicas) dependiendo de la composición (x).
Objetivo del estudio:
- Investigar las propiedades estructurales y magnéticas de soluciones sólidas binarias de F4BImNN y BImNN.
- Comprender la relación entre la composición, la estructura cristalina y el comportamiento magnético.
Principales métodos:
- Síntesis y cristalización de soluciones sólidas binarias (F4BImNN)
- Cristalografía de rayos X para determinar las estructuras celulares unitarias.
- Las mediciones de susceptibilidad magnética van desde 0,4 K hasta 300 K.
Principales resultados:
- Las soluciones sólidas se forman a través de una amplia gama de composiciones, exhibiendo estructuras cristalinas ortorrómbicas (x < 0.8) y monoclínicas (x ≥ 0.9).
- Las cadenas unidimensionales (1D) de enlaces de hidrógeno dominan el empaque intermolecular, lo que lleva al intercambio ferromagnético cuasi-1D (J/k = 12-22 K).
- El ordenamiento antiferromagnético se produce a bajas temperaturas (0,4-1,2 K) debido a un intercambio intercatenario más débil, que es de 33 a 150 veces más débil que el intercambio intracatenario.
Conclusiones:
- La temperatura de ordenamiento magnético en muestras ortorrómbicas aumenta linealmente con el aumento del contenido de BImNN, en correlación con la disminución de las distancias entre cadenas y las interacciones de intercambio.
- La fase monoclinica exhibe diferentes arreglos entre cadenas, que se desvían de la tendencia observada en la fase ortorrómbica.
- El control de la composición permite ajustar las propiedades magnéticas de estos materiales magnéticos cuasi 1D.
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