Electron Spin Resonance (ESR) studies on GdCuBi₂ intermetallic antiferromagnet

We report temperature dependent X-Band (ν≈ 9.5 GHz) Electron Spin Resonance (ESR) on the GdCuBi₂ intermetallic compound. This compound presents a metallic Curie–Weiss paramagnetic behavior at high temperatures and orders antiferromagnetically at T_N = 14.3 K. Well above T_N (T > 250 K), the ESR experiments revealed temperature independent g-values spectra composed of a single Dysonian Gd³⁺ ESR line for the studied compound. Within the same temperature range, the Gd³⁺ ESR linewidth ΔH presents a linear broadening temperature dependence known as Korringa behavior. The obtained Korringa rate (ΔH/ΔT) and g-shift (Δg) from the ESR measurements, along with the study of the macroscopic properties of GdCuBi₂ (e.g. specific heat data and magnetic susceptibility) made it possible to explore Gd³⁺ spin dynamics in this system based on evaluation of the exchange parameters between the Gd³⁺ ESR probes and the conduction-electrons (ce) in this compound. Our results indicate that the exchange bottleneck effects and a q-dependent exchange interaction (J_fs(q)) between the Gd³⁺4f and the ce are likely to be present in GdCuBi₂. Disregarding the bottleneck effects in the simplest approximation, we extract the exchange parameters J_fs(q=0) ≈ 380 meV and <J_fs²(q)>^1/2≈ 3.0 meV for the Gd³⁺ spin dynamics in GdCuBi₂. These values of J_fs(q) and <J_fs²(q)>^1/2 are typical of Gd³⁺ local moments in intermetallic materials and the small ratio [<J_fs²(q)>/J_fs²(0)] ≈ 0.008 suggests a strongly anisotropic (or quasi-2D) Fermi surface for GdCuBi₂.