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H. Michor, H. Rosner, M. Doerr, J. Perenboom, M. Rotter, W. Schnelle, U. Schwartz, E. Bauer, G. Hilscher:
"Itinerant magnetism and magneto-volume coupling in YCo₉Si₄ and LaCo₉Si₄";
Vortrag: International Workshop on Exotic States in Materials with Strongly Correlated Electrons, Sinaia, Romania; 07.09.2007 - 10.09.2007.

Abstract:
YCo₉Si₄ exhibits a weak itinerant ferromagnetism below T_C = 25 K and an ordered moment of 1.4 μB/f.u. Isostructural LaCo₉Si₄ on the other hand is a strongly exchange Pauli paramagnet which exhibits itinerant electron metamagnetism above 3T. The paramagnetic ground state of the latter is counter-intuitive because of the larger unit cell volume as compared to YCo₉Si₄ and appears inconsistent with ab initio studies indicating that both compounds shall have a ferromagnetic ground state. A possible explanation for these disagreements may be strong spin-fluctuations which are clearly revealed by transport properties but not taken into account in the electronic structure studies. We thus performed pressure dependent resistivity measurements on YCo₉Si₄ and pressure dependent magnetisation measurements on LaCo₉Si₄. The studies reveal a negative dT_C/dp for YCo₉Si₄ and an initial increase of the metamagnetic critical field for LaCo₉Si₄; i.e., a positive magneto-volume coupling in both cases. The latter is corroborated by forced magneto-striction studies on YCo₉Si₄ as well as LaCo₉Si₄ and is in line with LDA calculations yielding a gradual reduction of the ordered moment as the volume is reduced.