Effect of B-site Co substitution on the structure and magnetic properties of nanocrystalline neodymium orthoferrite synthesized by auto-combustion.

Edwin Akongnwi Nforna,Julius Numbonui Ghogomu,John Ngolui Lambi,Hypolite Mathias Kamta Tedjieukeng,Roussin Lontio Fomekong,Patrice Kenfack Tsobnang

doi:10.1098/rsos.201883

Abstract

Samples of cobalt-doped neodymium orthoferrite compounds, NdCoxFe1−xO3 (0.0 ≤ x ≤ 0.5) were synthesized via glycine auto-combustion between 250 and 300°C and calcined at 500°C for 2 h. X-ray diffraction showed that all compounds had an orthorhombic perovskite structure with space group Pbnm. Increasing cobalt doping gradually reduced the lattice parameters and contracted the unit cell volume. Both X-ray diffraction and scanning electron microscopy showed that the particles were spherical and in the nano-sized range (19–52 nm) with pores between grains. Vibrating sample magnetometry at room temperature indicated that NdFeO3 has a high coercive field (1950 Oe) and cobalt substitution for iron led to a decrease in the coercive field, saturation and remanent magnetization, which was as a result of decreased magnetic moments in the crystal and reduced canting of the FeO6 octahedra. The increase in magnetization and coercive fields with increase of Co was connected to the microstructure (bond lengths and angles, defects, pores, grain boundaries) and crystallite size. The compounds NdCoxFe1−xO3 show antiferromagnetism with weak ferromagnetism due to uncompensated non-collinear moments. These compounds could serve as prototypes for tuning the properties of magnetic materials (ferromagnetic and antiferromagnetic) with potential applications in data storage, logic gates, switches and sensors.

Highlights

Mixed metal oxides with the perovskite structure (ABO3) have attracted much attention due to such fascinating properties as catalytic, sensor, magnetic, ferroelectric, magnetoresistive and other physical properties [1,2,3,4,5,6]
Neodymium orthoferrite crystallizes in a distorted orthorhombic perovskite structure with four formula units per unit cell and Pbnm space group
The average crystallite size, phase purity, polycrystalline structure and lattice parameters were obtained from the analysis of powder X-ray diffraction (XRD) data

Summary

Introduction

Mixed metal oxides with the perovskite structure (ABO3) have attracted much attention due to such fascinating properties as catalytic, sensor, magnetic, ferroelectric, magnetoresistive and other physical properties [1,2,3,4,5,6]. The perovskite rare-earth orthoferrites, RFeO3 (R = rare-earth metal), in particular, are compounds with interesting electronic and magnetic phenomena which arise from structural features such as inter-ionic distances, types of ions present, symmetry and bond angles [2,7]. These compounds can be substituted in the A- and/or B-sites maintaining the structure while modifying the properties. The anisotropic HNd−Fe induces magnetic spin reorientations in the Fe sublattice at temperatures far below room temperature These magnetic orderings of NdFeO3 at low temperatures have been widely studied [13,14,15,16,17]

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