Structural and Magnetic Properties of Cubic Zirconia/Co Composites Synthesized by Microwave Route

Zirconium dioxide (zirconia) has three allotropes: mono‐clinic, tetragonal and cubic. The disruptive phase transformation between the first two can be suppressed by total stabilization in the cubic form. Using microwave route, high‐temperature cubic phase of ZrO₂ is synthesized without any stabilizing dopant. Here, we report on the structural and magnetic studies of Co‐doped ZrO₂ composites doped up to 30%. The XRD profile of the as‐prepared bulk powder and 400°C sintered Zr_1‐xCo_xO₂ compositions do not show any impurity peaks up to 30% doping. The presence of Co²⁺O²⁻ impurity beyond 30% doping serves as an evidence for substitution of Co at Zr‐site. A volume contraction of the crystal lattice for Co‐doped ZrO₂ cell further signifies the incorporation of Co dopant in the host lattice. The magnetic hysteresis shows an increase in magnetic moment with increase in Co concentration. The magnetic moment calculated per cobalt atom is 0.06 µ_B for 10%; 0.11 µ_B for Co=20, 30 and 0.22 µ_B for 40% Co. The M vs. H plots for the as‐prepared as well as 400°C annealed samples essentially show typical hysteresis loops, indicating that they are room temperature ferromagnetic. M vs. T curves at 500 Oe also follow the same trend as that of M vs. H measurements, showing magnetization to be retained up to room temperature. Our magnetic data indicates that Co could induce true room temperature ferromagnetism in ZrO₂.

Keywords:

• ferromagnetism
• microwave synthesis
• zirconia

TRS thanks Indian Institute of Technology Kanpur for a doctoral research fellowship and providing facilities. Authors thank CSIR for financial grant (Project No. CHM/CSIR/20040262).