Spin-glass behavior of Sn0.9Fe3.1N: An experimental and quantum-theoretical study

Based on comprehensive experimental and quantum-theoretical investigations, we identify Sn0.9Fe3.1N as a canonical spin glass and the first ternary iron nitride with a frustrated spin ground state. Sn0.9Fe3.1N is the end member of the solid solution SnxFe4−xN (0 < x ≤ 0.9) derived from ferromagnetic γ′-Fe4N. Within the solid solution, the gradual incorporation of tin is accompanied by a drastic weakening of the ferromagnetic interactions. To explore the dilution of the ferromagnetic coupling, the highly tin-substituted Sn0.9Fe3.1N has been magnetically reinvestigated. DC magnetometry reveals diverging susceptibilities for FC and ZFC measurements at low temperatures and an unsaturated hysteretic loop even at high magnetic fields. The temperature dependence of the real component of the AC susceptibility at different frequencies proves the spin-glass transition with the characteristic parameters Tg = 12.83(6) K, τ* = 10−11.8(2) s, zv = 5.6(1) and ΔTm/(Tm ⋅ Δlgω) = 0.015. The time-dependent response of the magnetic spins to the external field has been studied by extracting the distribution function of relaxation times g(τ, T) up to Tg from the complex plane of AC susceptibilities. The weakening of the ferromagnetic coupling by substituting tin into γ′-Fe4N is explained by the Stoner criterion on the basis of electronic structure calculations and a quantum-theoretical bonding analysis.