Polycrystalline Nd 2 CoIrO 6 double perovskite crystallizes in monoclinic crystal structure with P2 1 /n space group. The average grain size of powder sample is 400-500 nm. The dielectric, impedance and ac conductivity of the sample were studied in the temperature range 5-300 K and in the frequency range 20 Hz-2 MHz. Dielectric constant reveals a step like increase from low temperature value of ∼5 to colossal value of ∼10 4 at high temperature. High value of dielectric constant is associated with Maxwell-Wagner polarization due to large grain boundary capacitance. Cations (Co 2+ and Ir 4+ ) disorder leads to variable range hopping conduction of electrons in grain and grain boundary regions. Distribution of grain size induces distribution of relaxation time as confirmed from depressed semicircles in Nyquist plots. Frequency dependent conductivity follows universal power law behavior.

We report herein two multifunctional metal–organic frameworks (MOFs) that exhibit excellent mutually inclusive electrical and magnetic properties. Accordingly, two cobalt and nickel based MOFs (Co-MOF, Ni-MOF) were generated using a flexible bispyrazole based ligand and 2-sulphono terephthalic acid. The idea is to generate paramagnetic metal ion based magnetic MOFs, which can also be used to fabricate electrical devices by utilizing the immobilized free sulfonic groups and encapsulated H-bonded water clusters for active charge species generation and transportation. Further support comes from the intriguing structural features of the MOFs that include extensive H-bonded water clusters, free sulfonic acid moiety, or syn-anti bridged carboxylates, which make them highly suitable candidates for generating electrical and magnetic materials. Further complementary support for their candidature comes from the high thermal, chemical, and physical stability of the MOFs. The impedance spectroscopy data and I–V results unequivocally support the suitability of the MOFs for electronic device fabrication showing a befitting conductivity value of 1.80 × 10–4 S/m with an ideality factor of 1.06 for Ni-MOF. Interestingly, the Co-MOF shows a light-dependent behavior with conductivity values of 9.09 × 10–5 S/m (dark) and 6.31 × 10–4 S/m (light) and ideality factors of 0.78 (dark) and 0.92 (light). The MOFs, fitted with a free sulfonic acid moiety and extensive H-bonded water clusters, show high potential for proton exchange membrane fuel cells (PEMFCs) development with corroborating proton conductivity values of 1.95× 10–3 S/cm and 5.80 × 10–4 S/cm for Ni-MOF and Co-MOF, respectively, at 95% relative humidity and 85 °C. Moreover, the interesting structural aspects like syn-anti bridged carboxylates prompt us to explore the magnetic behavior of the MOFs. The Ni-MOF shows some interesting antiferromagnetic behavior. The Co-MOF reveals intriguing single molecule magnet behavior with a U eff value of 34 K and moderate relaxation time of 3.5× 10–8 s.

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Iridium-based double perovskites having mixed 3d-5d-4 f magnetic sub-lattices are expected to exhibit exotic magnetic phenomenon. In this paper, we report a study of structural, magnetic and transport properties of the mixed 3d-5d-4 f double perovskite Sm 2 CoIrO 6 (SMCO), which crystallizes in monoclinic structure with space group P2 1 /n and the crystal symmetry remains same throughout the measured temperature down to 15 K. High resolution synchrotron x-ray diffraction reveals an isostructural phase transition around 104 K. Magnetization measurements on polycrystalline samples indicate that SMCO orders ferrimagnetically at T FiM = 104 K; while, a second transition is observed below 10 K due to the rare-earth (Sm 3+ ) ordering. The ferrimagnetic transition is well-understood by Néel's two-sublattice model, which is primarily ascribed to antiferromagnetic coupling between Co 2+ and Ir 4+ sub-lattices. Electronic transport measurement shows the insulting behaviour of SMCO, which follows Mott variable-range hopping conduction mechanism. However, dielectric measurements as a function of temperature rules out the presence of magneto dielectric coupling in this compound.

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