Spontaneous and induced magnetic phase transitions in Tb0.9Er0.1Ni5

Abstract Magnetic and neutron powder diffraction measurements have been carried out on Tb0.9Er0.1Ni5 intermetallic compound. The intermetallide crystallizes in the hexagonal CaCu5-type structure and possesses a long-range magnetic order at temperatures below 22 K. A fan-like magnetic structure is described by two propagation vectors: k1 = 0 and k2 = 2π/c(0, 0, 0.036), at 20 K. The total Tb-ion magnetic moment has the ferromagnetic and modulated components. The latter is a transverse spin wave. When the sample is cooled at a temperature below 8 K, the module of the k2 vector does not change and is equal to k2 = 2π/c(0, 0, 0.027). An “incommensurate – lock-in” magnetic transition takes place at 8 K. The k2 vector exhibits a temperature hysteresis of about (5–6) K, whereas the intensities of Bragg reflections and satellites do not show up appreciable changes. When an external magnetic field is applied to the sample, the satellites and the module of the k2 vector decrease, while the Bragg intensities increase. The sample becomes a ferromagnetic at a field of ∼2 kOe, and the Tb-ion magnetic moment is equal to 8.3 μB. A general notion of the Tb0.9Er0.1Ni5 magnetic state evolution with an external field is given using the field dependence of the background intensity in diffraction patterns. First principle calculations for TbNi5 and Tb0.9Er0.1Ni5 are performed including the 4f states into the orbital basis and accounting for strong electronic correlations and spin-orbital coupling. This allowed obtaining both spin and orbital moments of the effective Tb-ion moment and estimating also the value of Tb-Tb exchange interaction.