Speaker
Mr
Resta Susilo
(UNSW Canberra)
Description
R2Fe2Si2C (R = rare-earths) compounds crystallise in the monoclinic Dy2Fe2Si2C-type structure with the C2/m space group. Previous magnetic studies revealed no magnetic phase transition in Y2Fe2Si2C down to 2 K [1], thus indicating that Y2Fe2Si2C acts as an ideal non-magnetic reference material for investigating the magnetism of the R2Fe2Si2C system. Accordingly, we have used Y2Fe2Si2C as a reference material to estimate the magnetic contribution to the total specific heat of magnetic R2Fe2Si2C compounds [2-4]. Despite the significance of R2Fe2Si2C for enhanced understanding of the magnetism of R2Fe2Si2C compounds, no detailed studies have so far been reported for Y$_2$Fe$_2$Si$_2$C.
In this work, we report our detailed investigations of the structural and thermal properties, specific heat ($C_P$) together with $^{57}$Fe Mössbauer studies and first-principles calculations on Y$_2$Fe$_2$Si$_2$C. The thermal expansion of Y$_2$Fe$_2$Si$_2$C follows the Debye-Grüneisen relation with no pronounced anomalies observed between 20 K and 300 K. By comparison, the $C_P$ data over the temperature range of 2 K - 300 K cannot be described adequately by the Debye model; rather, the $C_P$ data have been described fully by the Debye-Einstein model including anharmonic corrections, suggesting the importance of optical contributions (Einstein terms) to the phonon spectrum in Y$_2$Fe$_2$Si$_2$C. The low-temperature $C_P$ measurements (2 - 17 K) yield a rather large Sommerfeld coefficient γ = 16.3(5) mJ/mol. K$^2$, reflecting a large density of states (DOS) at the Fermi energy ($E_F$) which suggests that Y$_2$Fe$_2$Si$_2$C might be an itinerant ferromagnet. On the other hand, $^{57}$Fe Mössbauer spectra measured from 10 K to 300 K show no magnetic splitting, confirming that the Fe atom is in a non-magnetic state. While electronic structure calculations reveal a large DOS at the Fermi energy, the DOS of the Fe-3d states at $E_F$ is only 1.1 states/eV per Fe atom. This value corresponds to $N(E_F)I$ = 0.51 which is far below the Stoner criterion for ferromagnetism, thereby establishing that Y$_2$Fe$_2$Si$_2$C is far from being magnetic.
[1] D. Schmitt, D. Paccard, and L. Paccard. Solid State Commun., 84, 357-361 (1992)
[2] R.A. Susilo, J.M. Cadogan, W.D. Hutchison and S.J. Campbell, Physica Status Solidi (A), 211, 1087 - 1091, (2014)
[3] R.A. Susilo, J.M. Cadogan, R. Cobas, W.D. Hutchison, M. Avdeev and S.J. Campbell, J. Appl. Phys., 117, 17C113 (2015)
[4] R.A. Susilo, J.M. Cadogan, W.D. Hutchison, M. Avdeev, R. Cobas, S. Muñoz Pérez and S.J. Campbell, J. Alloys Compd., 654, 392 - 398 (2016)
Primary author
Mr
Resta Susilo
(UNSW Canberra)
Co-authors
Mr
Chuang-Han Hsu
(Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546)
Dr
Hsin Lin
(Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546)
Prof.
Sean Cadogan
(UNSW Canberra)
Prof.
Stewart Campbell
(UNSW Canberra)
Dr
Wayne Hutchison
(The University of New South Wales)
