Ferromagnetic and antiferromagnetic interactions in two-dimensional layered β-Co1-xNix(OH)2 (x = 0.25; 0.50; 0.75) double hydroxides

Abstract

In this work, we present a complete crystallographic, morphological and structural characterization joined with a focused feature and discussion of the magnetic properties in two-dimensional layered β-Co1-xNix(OH)2 (x = 0.25; 0.50; 0.75) sheets. These polycrystalline samples were prepared via colloidal method at 80 °C. Powder X-ray diffraction (PXRD) patterns at room temperature, showed layered structures belonging to P3m1 space group. Xray photoelectron spectroscopy (XPS) determined the M2 + oxidation state in both cobalt and nickel elements in the surface hydroxides. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) micrographsrevealed clear hexagonal structures for Co0.75Ni0.25(OH)2 and Co0.50Ni0.50(OH)2. However, agglomerated particles were observed in the sample with the highest Ni content. The magnetization of all studied compositions was investigated over a temperature range of 5–300 K and at different applied magnetic fields. At low temperatures (10–30 K) the magnetic ordering temperature (Tc) was identified. This latter follows a linear behavior, increasing with the Ni content (x) in the hydroxides. From the magnetic susceptibility at high temperatures (T > TC), the data can be well described with a Curie-Weiss law, obtaining the Curie constant and Curie-Weiss temperature. The effective magnetic moment obtained is in a good agreement with the spin only for the Ni2+ (3d8) and for a Co2+ (3d7) with some orbital coupling. This comprehensive characterization is crucial forunderstanding these 2D materials and highlights their potential for advanced spintronics and magnetic data storage applications.