Effect of Cu doping on the magnetism of MnCo$_{2}$$_{-}$$_{x}$Cu$_{x}$O$_{4}$ cubic spinels

MnCo$_{2}$$_{-}$$_{x}$Cu$_{x}$O$_{4}$ is a cubic spinel whose magnetic properties are not yet properly understood [1]. Here we report changes in the magnetic properties of MnCo$_{2}$$_{-}$$_{x}$Cu$_{x}$O$_{4}$ samples with change in {\it x} = 0, 0.05 and 0.20. X-ray diffraction measurements of the samples, synthesized by the sol-gel method followed by calcination at 700 $^\circ$C for 2 hours, showed lines only due to the cubic spinel phase without any CuO impurity. Measurements of the magnetization ``M'' vs. temperature ``T'' in H=100 Oe for the ZFC and FC modes showed ferrimagnetic ordering at T$_{c}$ = 175 K, 175 K and 166 K for {\it x} =0, 0.05 and 0.20 samples, respectively. However, for T ${\ll }$T$_{c}$, M for { \it x} = 0.05 (0.20) is smaller (larger) by a factor of three (five) as compared to that for the {\it x} = 0 sample. Hysteresis loops for the {\it x} = 0.20 sample show strong domain wall pinning. These unusual changes in the magnetic properties observed with Cu doping will be discussed in terms of changes in the site occupancies of Cu$^{2+}$ ions on the A and B sites [2]. \\[4pt] [1] P.A. Joy et al, J. Magn. Magn. Mater. 218, 229 (2000).\\[0pt] [2] J. D. Rall et al, Appl. Phys. Lett. 100, 252407 (2012).