Critical behavior in tetragonal antiperovskite GeNFe3 with a frustrated ferromagnetic state.

ABSTRACT

Tetragonal GeNFe3 has a second-order ferromagnetic (FM) to paramagnetic transition at 76 K. Our integrated investigations indicate that the ground FM state is frustrated and the tetragonal symmetry is retained below 550 K based on the results of variable temperature X-ray diffraction. Critical behavior was analyzed by a systematic bulk magnetization study. The estimated critical exponents by three different methods (modified Arrott plot, the Kouvel-Fisher method, and critical isotherm analysis) conformably suggest that long-range magnetic coupling described by mean-field (MF) theoretical model is dominant in GeNFe3. The experimental M-T-H data collapse into two independent branches according to the scaling equations m = f±(h) with the renormalized magnetization m = ε-ßM(H, ε) and the magnetic field h = Hε-(ß+γ). The exchange distance is estimated as J(r) ∼ r-4.8 on the basis of the ß and γ values, which lies between the long-range MF model (r-4.5) and the short-range 3D Heisenberg (3DH) model (r-5). Our results indicate that the competition between local magnetic moments of iron 3d electronic state and itinerant covalent interactions of N-Fe bonds should be responsible for critical behavior in this system.