Magnetic and structural properties of Ni-substituted magnetoelectric Co$_4$Nb$_2$O$_9$

TL;DR

This study investigates the magnetic and structural properties of Ni-substituted Co$_4$Nb$_2$O$_9$ using neutron diffraction, magnetization, heat capacity measurements, and DFT calculations, revealing different magnetic behaviors and structures depending on Ni content.

Contribution

It provides new insights into how Ni substitution alters the magnetic structures and properties of Co$_4$Nb$_2$O$_9$, including detailed magnetic configurations and anisotropy energies.

Findings

x=1 compound is antiferromagnetic below 31 K

x=2 compound exhibits ferrimagnetism below 47 K

Magnetic structures and anisotropy energies were determined

Abstract

The magnetic and structural properties of polycrystalline Co$_{4-x}$ Ni$_x$ Nb$_2$ O$_9$ (x=1,2) have been investigated by neutron powder diffraction, magnetization and heat capacity measurements, and density functional theory (DFT) calculations. For x=1, the compound crystallizes in the trigonal P$\bar{3}$c1 space group. Below T$_N$ = 31 K it develops a weakly non-collinear antiferromagnetig structure with magnetic moments in the ab-plane. The compound with x=2 has crystal structure of the orthorhombic Pbcn space group and shows a hard ferrimagnetic behavior below T$_C$ =47 K. For this compound a weakly non-collinear ferrimagnetic structure with two possible configurations in ab plane was derived from ND study. By calculating magnetic anisotropy energy via DFT, the ground-state magnetic configuration was determined for this compound. The heat capacity study in magnetic fields up to 140 kOe provide further information on the magnetic structure of the compounds.