Research Highlight

Quantum critical behavior in a concentrated solid solution: a new twist on structural alloys

Concentrated transition metal alloys with the formula NiCoCrx, with x≈1, and a simple cubic crystal structure, display transport, magnetic and thermodynamic signatures exhibited by more structurally complex compounds near a quantum critical point (QCP). These alloys provide ideal systems to study the effects of chemical disorder on emergent properties near a QCP.

Linear low-temperature resistivity of NiCoCr alloy (a) and –TlnT behavior of heat capacity (b) are signatures of quantum critical point physics. Lower panels illustrate result of theory calculations of magnetic spin-up and spin-down band structures for NiCoCr, including lifetime effects. Linear low-temperature resistivity of NiCoCr alloy (a) and –TlnT behavior of heat capacity (b) are signatures of quantum critical point physics. Lower panels illustrate result of theory calculations of magnetic spin-up and spin-down band structures for NiCoCr, including lifetime effects.  (hi-res image)

QCPs have been associated with some of the most exotic states of matter, including  high-temperature superconductivity. In the current study researchers found the model alloy NiCoCr is close to the Cr concentration where the ferromagnetic transition temperature goes to T=0 K. Near this composition, these alloys exhibit a linear resistivity in temperature to 2 K, a linear magnetoresistance, and an excess –TlnT contribution to the low temperature heat capacity. In addition, the depression of the magnetic ordering temperatures and saturation moments with increasing x is exponential, in contrast to the linear dependence expected by theory. All of the low-temperature electrical, magnetic and thermodynamic properties of the alloys with compositions near x≈1 are not typical of a Fermi liquid and suggest strong magnetic fluctuations and frustration associated with a quantum critical region. The extreme chemical disorder in this material thus provides a unique platform to study quantum critical behavior in a highly tunable system.

B. C. Sales, K. Jin, H. Bei, G. M. Stocks, G. D. Samolyuk, A. F. May, and M. A. McGuire, “Quantum Critical Behavior in a Concentrated Solid Solution,” Scientific Reports 6, 26179 (2016).  DOI: 10.1038/srep26179

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