Effect of Cu substitution on the magnetic and dielectric properties of La2NiMnO6

In the continuation of our previous work [Biswal et al., J. Appl. Phys. 115, 194106 (2014)] of biphasic La2NiMnO6 (LNM) prepared via sol-gel technique, here we are reporting the effect of Cu substitution at Ni site of LNM. The powder x-ray diffraction results of La2Ni1-xCuxMnO6 (x = 0, 0.05, 0.1) confirm the biphasic nature (Pbnm vertical bar R-3c) for all samples along with increasing R-3c phase with Cu content in the sample. The temperature variation of magnetization (M) plot shows sharp ferromagnetic transitions of R-3c phase at 285 K, 278 K, and 270K (obtained from dM/dT plot) and that of Pbnm phase at 165 K, 145 K, and 145K for x = 0, 0.05, and 0.1, respectively. Weak antiferromagnetic type feature at 25K (x = 0), is getting pronounced with Cu content in the sample and is now seen at 32K & 266K (for x = 0.05) and 32K & 257K (for x = 0.1). Fitting of Curie-Weiss law in the paramagnetic region of chi(-1) vs T plot results slightly lower values of corresponding Tc's of R-3 c phase (277 K, 270 K, and 260 K), thus manifesting possibility of Griffiths like singularity. The onset temperature of Griffiths singularity occurs at 295K (x = 0) and 281K (x = 0.05 and 0.1), such that 295-277K in x = 0, 281-270K in x = 0.05, and 281-260K in x = 0.1 sample is in Griffith's phase. Temperature dependent dielectric constant (epsilon(r)) shows usual step-like transitions with corresponding relaxation peaks in the dielectric loss (D) part. Cu substitution in LNM makes the entire dielectric plot shifts towards lower temperature such that high temperature plateau of step transition becomes evident. The peaks in dielectric loss for all compositions are found to obey Arrhenius law with activation energies 237 meV, 207 meV, and 180 meV for x = 0, 0.05, and 0.1, respectively. (C) 2015 AIP Publishing LLC.