Magnetic Ordering in Polycrystalline NixZn1?xO Solid Solutions

Abstract

In order to examine the influence of the dilution of magnetic ions on the crystal and magnetic structure of NixZn1—xO (x = 1, 0.90, 0.80, 0.70) solid solutions we have performed neutron diffraction experiments on each sample at seven temperatures between 10 and 295 K. To determine the Néel temperatures, the magnetic susceptibility measurements were done in the temperature region between room temperature and 600 K. Starting from the known rhombohedral distortion the crystal structure has been refined in the trigonal space group R3¯m. In this space group the cations occupy octahedral 3a position (with the local symmetry 3¯m), while the oxygen anion is placed in the 3b position (with the local symmetry 3¯m). The magnetic structure for all concentrations x is found to be antiferromagnetic and the magnetic cell is the doubled nuclear cell along the c‐axis. The magnetic atoms are arranged in the planes (003) in respect to the nuclear cell. The magnetic moments of two Ni2+ ions in adjacent sheets are oriented antiparallely and the magnetic vector makes an angle of 66° with the c‐axis. The magnetic structure is preserved upon random site dilution of the magnetic ions. This is additionally confirmed from the Brillouin‐type dependence of the magnetization on temperature as well as from the t = TN(x)/TN(1) versus x variation obtained from the magnetic susceptibility measurements. Concentration dependence of the Néel temperature also shows that NixZn1—xO behaves like a Heisenberg antiferromagnet with the dominant nearest‐neighbor interaction, in agreement with the similar (Ni, Co)xMg1—xO solid solution.

Optical constants and band structure of trigonal NiO

“…For our purposes, it is suitable to assume that the sample is cubic. We ignore the small rhombohedral (trigonal) distortion of the rocksalt crystal lattice, 29 because the resulting birefringence is too small to be measurable with ellipsometry. 30 Spectroscopic ellipsometry 31,32 and transmission measurements were performed 33 using a modified J.A.…”

Long-Range Antiferromagnetic Order in a Rocksalt High Entropy Oxide

“…Secondly, no structural transition or deformation has been observed across the magnetic transition in MgO-HEO, in sharp contrast to the diluted FCC systems with nonmagnetic ions, which are tetragonal, rhombohedral or monoclinic in the antiferromagnetic state. [34][35][36][37] Thirdly, the absence of a λ-shape peak around the magnetic transition in heat capacity in MgO-HEO contrasts with that in CoO. 38 Such characteristics are related to the large degree of chemical disorder stabilized by high configuration entropy.…”

Two-phonon absorption in LiF and NiO from infrared ellipsometry

“…The a-axis of the hexagonal cell is one half of the face diagonal in the cubic rocksalt structure. 17 As one might expect, the magnetic conventional unit cell of NiO is the doubled chemical (hexagonal) unit cell with a ¼ 2.9609 Å and c ¼ 14.486 Å . The doubling occurs along the hexagonal axis, which is the same as the cubic (111) body diagonal.…”

“…While the primitive unit cell of the trigonal NiO lattice still contains only one NiO formula unit (just like the primitive unit cell in the rocksalt structure, from which it is derived), it is more convenient to describe the NiO crystal with a hexagonal lattice and a rhombohedral structure with three NiO formula units for each (rhombohedral, hexagonal) conventional unit cell. The lattice parameters of the hexagonal unit cell 17 are a ¼ 2.9549 Å and c ¼ 7.2320 Å . The space group for the trigonal NiO crystal structure is R 3m ð166; D 5…”

“…3d Þ, which is a subgroup of the Fm 3m ð225; O 5 h Þ FCC rocksalt space group. 17 The Ni and O atoms are located at the 3a and 3b Wyckoff positions of the R 3m lattice. The hexagonal c-axis is the cubic body diagonal in the rocksalt structure and also the magnetic axis.…”