Abstract
The magnetic structure in Er3Cu4Sn4 has been determined using high-resolution powder neutron diffraction, supported by symmetry analysis. At low temperatures, Er3Cu4Sn4 assumes a crystal structure of the Tm3Cu4Sn4 type (in the monoclinic space group C2/m). The Er atoms occupy two distinct Wyckoff sites: 2c and 4i. It has been found that the Er magnetic moments on the 2c site form a commensurate antiferromagnetic structure (k1 = [0, 0, ½]) below 6 K. The magnetic moments reach 8.91 (8) μB at 1.4 K and are parallel to the b axis. The Er magnetic moments on the 4i site order below 2 K and form an incommensurate antiferromagnetic sine-modulated structure (k2 = [1, 0.4667 (1), ½]), with magnetic moments lying in the ac plane and perpendicular to the a axis. The amplitude of modulation equals 8.7 (1) μB at 1.4 K.
Highlights
The R3T4X4 family of compounds, where R is a rare earth element, T is a transition metal] and X is Si, Ge or Sn, has been investigated extensively for decades
In the first description, which is used in this work, the rare earth atoms occupy the 2c and 4i sites, while each of the two remaining elements (T and X) resides on two 4i sites
According to the commensurate antiferromagnetic structure with magnetic Rietveld refinement, the incommensurate component of the moments parallel to the b axis and the magnetic unit cell magnetic structure disappears at about 2 K, while the doubled along the [001] direction with respect to the crystal commensurate one persists to about 6 K
Summary
The R3T4X4 family of compounds, where R is a rare earth element, T is a transition metal (i.e. an element with a partially filled d-electron sub-shell)] and X is Si, Ge or Sn, has been investigated extensively for decades. Interpretation of the previous neutron diffraction data, based on the orthorhombic crystal structure, led to magnetic order described by the propagation vector k1 = [12, 12, 0] on the 2d site and k2 = [0, 0, 0.08] on the 4e one, below 6.0 K (Wawrzynska et al, 2003). Such a model of the magnetic structure was characterized by relatively large values of the reliability factors Rmagn of 21.61 and 22.99% for the 2d and 4e sites, respectively. This work reports new studies of the Er3Cu4Sn4 magnetic structure which have been performed using the E6 and E9 diffractometers installed at the BERII reactor in HelmholtzZentrum Berlin Both instruments are equipped with highefficiency position-sensitive area detectors. NN indicates the distance between the nearest neighbours and NNN refers to the nearest neighbours
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