${\mathrm{Cr}}_2\mathrm{B}$ displays temperature-independent paramagnetism. We induce ferromagnetism by replacing less than $3\%$ of the Cr atoms by Fe. By the lowest Fe doping level made, Curie-Weiss behavior is observed; ${\Theta }_{\mathrm{CW}}$ changes from $-20$K for $0.5\%$ Fe-doped ${\mathrm{Cr}}_2\mathrm{B}$ to positive values of about 50 K by $5\%$ Fe doping. The ferromagnetic $\mathit{T}{}_C$ is 8 K for $2.5\%$ Fe doping and increases linearly to 46 K by $5\%$ doping; we infer that a quantum phase transition occurs near the $2.0\%$ Fe level. Magnetic fluctuations at the intermediate doping levels are reflected in the linear resistance and an anomalous heat capacity at low temperatures. Imaging and chemical analysis down to the atomic scale show that the Fe dopant is randomly distributed.

• Received 21 May 2014
• Revised 16 June 2014

DOI:https://doi.org/10.1103/PhysRevB.89.224417