Thermal transport properties, magnetic susceptibility and neutron diffraction studies of the (Cr100-x Al x )95Mo5 alloy system
Abstract Previous electrical resistivity ( ρ ) and specific heat ( C P ) studies on the ternary (Cr 100 -x Al x ) 95 Mo 5 alloy system suggested that it harbours two quantum critical points (QCPs). This study reports comprehensive investigations of this alloy system through Seebeck coefficient ( S ) , thermal conductivity ( κ ) , magnetic susceptibility ( χ ) and neutron diffraction ( N D ) measurements in the concentration range 0 ≤ x ≤ 8.6. The results of S and χ show that spin-density-wave (SDW) antiferromagnetism is suppressed to temperatures below 2 K for concentrations in the range 1.4 ≤ x ≤ 4.4. Plots of d S / d T in the limit as T → 2 K depict two minima, i.e. just above x = 1.4 and 4.4. This parameter has been used as a key indicator of quantum critical behaviour (QCB) in Cr alloys. Analyses against the Nordheim-Gorter relationship demonstrates a positive slope for the incommensurate (I) SDW alloys and a negative slope for the commensurate (C) SDW alloys. Extrapolations of these two slopes intercept at a concentration of 3.2 at.% Al indicating the occurrence of band structure modifications when Al is added into the Cr 95 Mo 5 base alloy. The Lorenz number ( L ) for the alloys with x = 0 and 0.5 shows interesting anomalous behaviour associated with band structure effects and SDW magnetic ordering. N D measurements as a function of temperature confirm that alloys with x x > 4.4 show commensurate (C) SDW order. Power law fits of the form T N ∝ 1.40 − x 0.35 ± 0.05 for the ISDW to P phase transition and T N ∝ x − 4.40 0.63 ± 0.03 for the P to CSDW phase transition rendered the critical exponents 0.35 ± 0.05 and 0.63 ± 0.03 respectively. Overall the results of S , κ , χ and N D corroborate the existence of two QCPs at x ≈ 1.4 and 4.4. Highlights Thermal transport and magnetic susceptibility measurements to study the quantum critical behaviour in the (Cr 100- x Al x ) 95 Mo 5 alloy system. Two quantum critical points are observed on the magnetic phase diagram. ISDW-P and P-CSDW quantum critical points observed in one phase diagram. Nordheim-Gorter rule applied gives two lines intercepting at 3.2 at.% Al, probably linked to band structure modification. Neutron diffraction used to confirm the quantum critical points on the magnetic phase diagrams.
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