Interplay of itinerant magnetism and reentrant spin-glass behavior in Fe${}_x$Cr${}_{1-x}$

When suppressing the itinerant antiferromagnetism in chromium by doping with the isostructual itinerant ferromagnet iron, a dome of spin-glass behavior emerges around a putative quantum critical point at an iron concentration $x \approx 0.15$. Here, we report a comprehensive investigation of polycrystalline samples of Fe${}_x$Cr${}_{1-x}$ in the range $0.05\le x\le 0.30$ using x-ray powder diffraction, magnetization, ac susceptibility, and neutron depolarization measurements, complemented by specific heat and electrical resistivity data for $x=0.15$. Besides antiferromagnetic ($x<0.15$) and ferromagnetic regimes ($0.15\le x$), we identify a dome of reentrant spin-glass behavior at low temperatures for $0.10\le x\le 0.25$ that is preceded by a precursor phenomenon. Neutron depolarization indicates an increase of the size of ferromagnetic clusters with increasing $x$ and the Mydosh parameter $\varphi$, inferred from the ac susceptibility, implies a crossover from cluster-glass to superparamagnetic behavior. Taken together, these findings consistently identify Fe${}_x$Cr${}_{1-x}$ as an itinerant-electron system that permits to study the evolution of spin-glass behavior of gradually varying character in unchanged crystalline environment.