Tailoring the Griffiths-like cluster formation in the insulator ferromagnet spin-glass ${\mathrm{Gd}}_2{\mathrm{Ni}}_x{\mathrm{Co}}_{1-x}\mathrm{Mn}{\mathrm{O}}_6$ double perovskite

In this paper we present the effects of the composition on structural, vibrational, magnetic, and electronic properties of double perovskite 3d based manganese oxides ${\mathrm{Gd}}_2{\mathrm{Ni}}_x{\mathrm{Co}}_{1-x}\mathrm{Mn}{\mathrm{O}}_6$ (GNCMO) powder (for $0<x<1$) prepared by high temperature solid state chemistry. These compounds have a great research interest due to their specific physical properties. We have shown that the synthesized compounds exhibit ferromagnetic interaction between the spins of (${\mathrm{Mn}}^{4+}, {\mathrm{Co}}^{2+}$), and (${\mathrm{Mn}}^{4+}, {\mathrm{Ni}}^{2+}$) cations via oxygen ions and antiferromagnetic interactions between (${\mathrm{Gd}}^{3+}, {\mathrm{Co}}^{2+}$), (${\mathrm{Gd}}^{3+}, {\mathrm{Ni}}^{2+}$) and (${\mathrm{Gd}}^{3+}, {\mathrm{Gd}}^{3+}$) and present a paramagnetic to ferromagnetic phase transition. The paramagnetic Curie-Weiss temperature of GNCMO ($T_{\mathrm{c}}$) increases from 121to 128K as the nickel content increases from 0.2 to 0.8. Further, temperature dependent inverse magnetic susceptibility $\chi {\left(T\right)}^{–1}$ shows deviation from Curie Weiss behavior around $T_G$ which depicts that Griffiths phase already observed in several perovskite compounds. The value of the GP percentage and the exponent of ($\lambda <1$) are found to increase as the nickel content increases. The hysteresis curve at $T=20\mathrm{K}$ for $x=0.2$ displays a metamagnetic transition explained by the reorientation of the Gd spin moments towards the Mn, Co, and Ni spin moments. The imaginary part of susceptibility ${\chi }^{\prime \prime }$ shows a small shift of the peak $\sim 1\mathrm{K}$ indicating the presence of spin or cluster glass behavior.

Figure 1

X-ray diffraction profiles of experimental (...) and calculated patterns (- - - - -) for $x=0.25$. Inset (a) the lattice parameters as a function of nickel content ($x$). Inset (b) show the monoclinic structure with $P{2}_1/n$ space group.

Figure 2

Raman spectra for the five oxides. Inset the energy of the phonons versus the nickel content x.

Figure 3

The partial density of states (PDOS) and the calculated band structure of ${\mathrm{Gd}}_2{\mathrm{Ni}}_{0.5}{\mathrm{Co}}_{0.5}\mathrm{Mn}{\mathrm{O}}_6$ for spin up and spin down using (GGA+U) and (GGA) approximations.

Figure 4

${\left(\alpha \mathrm{h}\nu \right)}^2$ versus photon energy (hν) for ${\mathrm{Gd}}_2{\mathrm{Ni}}_x{\mathrm{Co}}_{1-x}\mathrm{Mn}{\mathrm{O}}_6$ ($x=0.25$, 0.5) compounds.

Figure 5

Results from the $M$($T$) measurements for the five oxides in the magnetic field of 50 Oe: thermal variation of ZFC-FC molar susceptibility (${\chi }_{\mathrm{M}}$). Inset the Curie temperature $T_{\mathrm{C}}$ and Néel-temperature $T_{\mathrm{N}}$ as a function of the nickel content $x$.

Figure 6

Curve-fit to ${\chi }^{–1}\left(T\right)$ using a modified Curie-Weiss equation. Inset $\log 10{\chi }^{–1}\left(T\right)$ versus $\log 10(T-T_C^R)$ plots, the red solid lines represent the fit to the experimental data.

Figure 7

Evolution of Griffiths phase percentage (GP%) and value of λ as a function of the nickel content $x$. ${\chi }^{-1}\left(T\right)=A{(T-T_C^R)}^{1-\lambda }$.

Figure 8

Field dependent magnetization for the five oxides at 43 K in the field range from −4 T to 4 T. Inset field dependent magnetization for the five oxides at 300 K in the field range from 0 to 7 T.

Figure 9

Field dependent magnetization for ${\mathrm{Gd}}_2{\mathrm{Ni}}_x{\mathrm{Co}}_{1-x}\mathrm{Mn}{\mathrm{O}}_6$ ($x=2$) at 5, 20. 43, and 80 K in the field range from −4 T to 4 T. Inset (a) the temperature dependence of $M_{\mathrm{s}}$ moments. Inset (b) the derivative of $M$($H$) versus H at 20 K.

Figure 10

Thermal variation of the real and imaginary molar susceptibilities (${\chi }^{\prime }$ and ${\chi }^{\prime \prime }$) for $x=0.5$ and 0.75 oxides in an AC magnetic field of 3 Oe with three frequencies (50, 141.6, and 400.6 Hz).