Multi-step magnetic transitions in EuNIIN₄

Magnetism in EuNiIn₄ is studied using specific heat, magnetic susceptibility, magnetization, ¹⁵¹Eu Mössbauer spectroscopy, and neutron diffraction experiments. The specific heat exhibited two magnetic transitions at T_N1 = 15.2 K and T_N2 = 14.3 K at zero magnetic field. An antiferromagnetic ground state of EuNiIn₄ was observed to have a uniaxial magnetic anisotropy along the b axis using magnetic susceptibility and ¹⁵¹Eu Mössbauer spectroscopy. Further, single crystal neutron diffraction experiments illustrated that this antiferromagnetic structure in the ground state is characterized by the commensurate propagation vector q ¼ ð1=2; 1=2; 1=2Þ, which reveals no distinct anomaly at T_N2. The magnetization curve along the b axis at 2 K was observed to exhibit four successive magnetic field-induced transitions up to 50 kOe, following which it increased linearly, resulting in saturated magnetization of 7 μ_B=f.u. above 195.2 kOe, as expected of Eu²⁺ free ions. The magnetic phase diagram for H ∥ b in EuNiIn₄ was found to have unique characteristics with five magnetic states in low magnetic fields.