Magnetic phase transition and thermal expansion in LaFe13-x-yCoySiz

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Australian Institute of Physics
The structural and magnetic properties of a series of LaFe13-x-yCoySix compounds have been investigated by X-ray diffraction, thermal expansion, magnetic and Mössbauer effect measurements. As is evident from the thermal expansion curves of Fig. 1(a), the Curie temperatures of LaFe13-xSix compounds increase with increasing Si content from TC~219 K for x=1.6 to TC~250 K for x=2.6. Further enhancement in the Curie temperature from TC~250 K to TC~281 K is obtained on substitution of Co for Fe in LaFe10.4Si2.6 to LaFe9.4CoSi2.6. A pronounced positive spontaneous volume magnetostriction has been observed below the Curie temperature TC (see Fig. 1(a)). The anomalous thermal expansion can be attributed to the volume dependence of the magnetic energy. Both the magnetization and Mössbauer spectroscopy studies (e.g. Fig. 1(b)) indicate that the type of the magnetic phase transition at TC changes from first order for LaFe11.4Si1.6 to second order for LaFe10.4Si2.6 and LaFe9.4CoSi2.6. The different natures of the magnetic transitions in LaFe13-x-yCoySix are discussed in terms of the classical model for itinerant ferromagnets and the volume dependence of the magnetic energy which is very sensitive to the distance between first-neighbor transition-metal atoms.
Phase transformations, Thermal expansion, Lanthanum, Iron, Cobalt, Silicon, Curie point, X-ray diffraction
Wang, J. L., Campbell, S. J., Kennedy, S. J., Shamba, P., Zeng, R., & Dou, S. X. (2012). Magnetic phase transition and thermal expansion in LaFe13-x-yCoySiz. Poster presented to the 36th Annual Condensed Matter and Materials Meeting, Wagga 2012, Charles Sturt University, Wagga Wagga, NSW 31st January – 3rd February, 2012. Retrieved from: