Weak itinerant magnetic phases of La2Ni7

Abstract

La2Ni7 is an intermetallic compound that is thought to have itinerant magnetism with small moment ( 0.15 µB/Ni) ordering below 65 K. A recent study of single crystal samples by Ribeiro et. al. [Phys. Rev. B 105, 014412 (2022)] determined detailed anisotropic H-T phase diagrams and revealed three zero-field magnetic phase transitions at T1 61.0 K, T2 56.5 K, and T3 42 K. In that study only the highest temperature phase is shown to have a clear ferromagnetic component. Here we present a single crystal neutron diffraction study determining the propagation vector and magnetic moment direction of the three magnetically ordered phases, two incommensurate and one commensurate, as a function of temperature. The higher temperature phases have similar, incommensurate propagation vectors, but with different ordered moment directions. At lower temperatures the magnetic order becomes commensurate with magnetic moments along the c direction as part of a first-order magnetic phase transition. We find that the low-temperature commensurate magnetic order is consistent with a proposal from earlier DFT calculations.

Electronic signatures of successive itinerant, magnetic transitions in hexagonal La2Ni7

“…The crystal structure of La 2 Ni 7 is shown in Fig. 1 Motivated by the clear delineation of multiple magnetic phases in the H-T phase diagram (based on features in magnetization, specific heat and electrical resistivity data) [35] and results of recent neutron scattering [43], we performed ARPES studies to understand the effects of the magnetic transitions on the electronic structure.…”

“…In this paper, we report direct measurements of the band structure using the ARPES and compare them to DFT calculations for both paramagnetic (PM) and the lowest temperature AFM state that has had it magnetic structure predicted by DFT and confirmed by neutron scattering measurements [43]. We find that magnetic transitions in La 2 Ni 7 are accompanied by observable changes in the band structure, both at E F and well below.…”

“…Among them, Ni5 (2a) acts as the boundary separating the cell into two blocks along the c-axis with each occupying one of the two prisms in the half-cell blocks. Using the A state with block-wise AFM configuration identified by neutron study [43], we have calculated the moment on Ni sites as 0.11 µ B on Ni1 (12k), 0.27 µ B on Ni2 (6h), 0.17 µ B on Ni3 (4f), 0.19 µ B on Ni4 (4e) and 0.00 µ B on Ni5 (2a), which are in a good agreement with the earlier DFT calculation [42].…”

“…La 2 Ni 7 is a rare example of a small moment (∼ 0.1 µ B /Ni), itinerant magnetic system that shows a cascade of three magnetic ordering temperatures: T 1 ∼ 61 K, T 2 ∼ 57 K and T 3 ∼ 42 K [35] corresponding to C, B and A phases, respectively. The low temperature state has long been thought to be associated with wAFM ordering [35][36][37][38][39][40][41] and recent band structure predictions [42] have proposed a wAFM associated with a long wavelength periodicity along the c-axis, which even more recently have been borne out by single crystal neutron diffraction measurements [43]. Recent single crystal growth and characterization of this system [35] has made it very attractive as a possible wAFM that could be amenable to ARPES measurements.…”

“…Recent single crystal growth and characterization of this system [35] has made it very attractive as a possible wAFM that could be amenable to ARPES measurements. Indeed the neutron scattering study [43] has identified the propagating wave vectors of these three wAFM phases as all along the c-axis. While the C and B phases have the same incommensurate wave vectors, the direction of the magnetic moments are different and can be tilt away from the c-axis.…”