Magnetic Structure of Divalent Europium Compound EuGa₄Studied by Single-Crystal Time-of-Flight Neutron Diffraction

Abstract

The magnetic structure of the intermetallic compound EuGa 4 was investigated using single-crystal neutron diffraction with the time-of-flight (TOF) Laue technique on the new diffractometer SENJU at MLF of J-PARC. In spite of high neutron absorption of Eu, a vast number of diffraction spots were observed without isotope enrichment. The magnetic reflections were appeared at the positions with the diffraction indices of h + k + l 2n below 16 K, indicating that the ordering vector is q=(0 0 0). Continuous evolution of magnetic reflection intensity below T N follows a squared Brillouin function for S =7/2. By adopting a wavelength-dependent absorption collection, the magnetic structure of EuGa 4 was revealed that a nearly full magnetic moment of 6.4 µ B of Eu lies within the basal plane of the lattice. The present study reveals a well-localized divalent Eu magnetism in EuGa 4 and demonstrates a high ability of SENJU to investigate materials with high neutron absorption.

Spin order and fluctuations in the EuAl4 and EuGa4 topological antiferromagnets: A μSR study

“…By contrast, in EuGa 4 , λ T (T ) follows the typical behavior of materials with a long-range (anti)ferromagnetic order [36], i.e., diverging at T N and continuously decreasing at T < T N . Such λ T (T ) suggests a very homogeneous distribution of local fields, consistent with the commensurate magnetic propagation vector in EuGa 4 [32]. At T = 1.5 K, in EuGa 4 , λ T is found to be ∼0.72 μs −1 , a value which is almost three orders of magnitude smaller than that of EuAl 4 .…”

“…4(a) and 5(a), the above model describes the data reasonably well, yielding the parameters listed in Table I. In EuAl 4 , the first AFM phase (AFM1) is characterized by B int (0) = 0.57(5) T. The change in magnetic [31,32]. The temperature dependence of the transverse and longitudinal μSR relaxation rates λ T (T ) and λ L (T ) are summarized in Figs.…”

“…At the same time, the modification of magnetic structure from q 2 to q 3 is too tiny to have a measurable effect on B int . By contrast, the AFM structure of EuGa 4 is rather simple [its magnetic vector being q = (0, 0, 0)] and it persists down to 2 K [32]. As a consequence, in EuGa 4 , B int decreases monotonically as the temperature increases.…”

“…According to neutron diffraction studies, in the AFM state, the magnetic q vector of EuAl 4 changes from q 1 = (0.085, 0.085, 0) at T N = 13.5 K to q 2 = (0.170, 0, 0) at 11.5 K and slightly to q 3 = (0.194, 0, 0) at 4.3 K [31]. Unlike the complex incommensurate transitions observed in EuAl 4 , the AFM structure of EuGa 4 is described by a simple q = (0, 0, 0) magnetic vector, with the Eu moments lying in the basal ab plane [32]. Noncollinear spins with incommensurate propagation vectors have been reported also in the isostructural EuGa 2 Al 2 [13].…”

Determination of Crystallographic Planes for a Polyhedral Single Crystal

“…The integrated intensities measured for crystal structure and magnetic structure analyses using SENJU are usually corrected for the Lorentz factor, incident spectrum and detector sensitivity difference. Moreover, materials with large neutron absorption cross sections require absorption correction [2].…”