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Expansión térmica negativa uniaxial en una fase ferromagnética débil-ininerante de CoZr₂H_3.49

Yuto Watanabe¹, Kota Suzuki², Takayoshi Katase^2,3

¹Department of Physics, Tokyo Metropolitan University, 1-1 minami-Osawa, Hachioji, Tokyo 192-0397, Japan.

Journal of the American Chemical Society

|February 10, 2026

Resumen

CoZr2H3.49 hidrogenado exhibe expansión térmica negativa uniaxial (NTE) en su fase ferromagnética. Esto contrasta con los superconductores no hidrogenados, que indican hidrógeno.

Área de la Ciencia:

Física de la materia condensada Física de la materia condensada
Ciencia de los materiales Ciencia de los materiales.
El magnetismo es el magnetismo.

Sus antecedentes:

Los fenómenos de expansión térmica anómala, incluida la expansión térmica negativa (NTE), son de gran interés en la ciencia de los materiales.
La interacción entre el magnetismo, la estructura electrónica y la expansión térmica es crucial para comprender las propiedades de los materiales exóticos.
Estudios previos sobre los superconductores CoZr2 destacaron la expansión térmica anómala impulsada por fonones.

Objetivo del estudio:

Para investigar el comportamiento de expansión térmica de los compuestos hidrogenados de cobalto-circonio (CoZr2).
Explorar el surgimiento de la expansión térmica negativa (NTE) en la fase ferromagnética de CoZr2H3.49.
Para aclarar la relación entre el ferromagnetismo itinerante, la estructura electrónica y el NTE en este sistema.

Principales métodos:

Se empleó difracción de rayos X sincrotrón en polvo para analizar los cambios estructurales con la temperatura.
Se realizaron mediciones de magnetización y análisis de gráficos de Arrott para caracterizar las propiedades magnéticas.
Se calculó la relación Rhodes-Wohlfarth para determinar la naturaleza itinerante del ferromagnetismo.

Principales resultados:

La expansión térmica negativa uniaxial (NTE) se observó exclusivamente en la fase ferromagnética débil-itinerante de CoZr2H3.49 por debajo de la temperatura de Curie (139 K).
El eje c se contrajo al calentarse, mientras que el eje a mostró una expansión térmica positiva.
Una relación Rhodes-Wohlfarth de 3,49 confirmó la naturaleza itinerante del ferromagnetismo.

Conclusiones:

La inserción de hidrógeno en CoZr2 altera significativamente la estructura electrónica y los mecanismos de expansión térmica, induciendo NTE uniaxial.
La NTE observada se atribuye a la agudización de los estados antienlace Co3dz2, favoreciendo la expansión del eje c al enfriarse en el estado ferromagnético.
El sistema CoZr2Hx sirve como una valiosa plataforma para estudiar la superconductividad acoplada, el ferromagnetismo itinerante y el NTE.

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