Spin-density-wave effects on the vibrational anharmonicity of acoustic phonons in Cr-Ir alloy single crystals

• Published in: Journal of physics. Condensed matter 1998-12, Vol.10 (50), p.11731-11742
• Main Authors: Martynova, J, Alberts, H L, Smit, P
• Format: Article
• Language: English
• Subjects: Anharmonic lattice modes; Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Lattice dynamics; Magnetic properties and materials; Magnetically ordered materials: other intrinsic properties; Metals. Metallurgy; Phonons and vibrations in crystal lattices; Physics; Spin-density waves
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/10/50/012

Measurements are reported of the dependences on hydrostatic pressure (p) of the elastic constants (c sub ij ) of Cr-Ir alloy single crystals containing 0.07 at.% and 0.20 at.% Ir. For the former concentration the alloy exhibits a transition from an incommensurate (I) spin-density-wave (SDW) to a paramagnetic state at the Neel temperature (T sub N ). dc sub ij /dp was studied as a function of temperature through T sub N . The concentration of the Cr sub 0.998 Ir sub 0.002 crystal is larger than the triple-point concentration on the Cr-Ir magnetic phase diagram and for this crystal there appears a phase transition from an ISDW to a commensurate (C) SDW at T sub IC . dc sub ij /dp was measured for this crystal as a function of temperature through T sub IC . The acoustic mode Gruneisen parameters were calculated for the two crystals as a function of temperature through T sub N (for Cr sub 0.9993 Ir sub 0.0007 ) and through T sub IC (for Cr sub 0.998 Ir sub 0.002 ). Large negative Gruneisen parameters are observed in the ISDW and CSDW phases of Cr sub 0.998 Ir sub 0.002 . The results indicate stronger magnetoelastic interactions in the CSDW than in the ISDW phase of this crystal. It is shown that the strong magnetoelastic coupling in the ISDW and CSDW antiferromagnetic phases of the Cr-Ir system takes mainly place through volume effects.