Antiferromagnetism in a Cr86Ru14 alloy

The magnetic behaviour of an antiferromagnetic polycrystalline Cr86Ru14 alloy has been investigated experimentally through electrical resistivity (ρ), thermal expansion, elastic constants and neutron diffraction measurements. This Cr-Ru alloy represents an important and interesting position on the magnetic phase diagram, just below the concentration where Ru addition totally suppresses antiferromagnetism in the Cr-Ru system. The neutron diffraction investigation shows the alloy to have commensurate (C) spin-density-wave (SDW) ordering below the Néel temperature TN = 294 K. Magnetic anomalies are observed in the temperature and pressure dependences of ρ, giving dTN/dP = −41 K/GPa, which is more than an order of magnitude smaller in its absolute value than that observed for the CSDW to paramagnetic Néel temperature of very diluted Cr-Ru alloys, such as Cr99.7Ru0.3. The thermal expansion measurements give a magnetovolume of |Δω(77 K)| = 2 × 10−4 for CSDW Cr86Ru14 at 77 K compared to a much larger value, |Δω(77 K)| = 32 × 10−4, for CSDW diluted Cr99.7Ru0.3. The long-wavelength acoustic-mode Grüneisen parameters for Cr86Ru14 calculated from the temperature and hydrostatic pressure dependences of the elastic constants show that the effects of the CSDW on the vibrational anharmonicity near TN is substantially weaker than that observed in the diluted Cr99.7Ru0.3 alloy. Anomalous elasticity behaviour is observed for Cr86Ru14 in the temperature region of the Néel transition that is ascribed to antiferromagnetic Q-domain effects.