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We report here a comprehensive study on structural, magnetic, caloric and electronic properties of the monoclinic phase of double perovskite compound Tm2CoMnO6 (TCMO) in its polycrysttaline format. Magnetic measurements confirm the presence of thermal hysteresis in magnetization indicates towards a first order magnetic transition at its critical point (Tc). Our study finds the metamagnetic jump in isothermal M(H) at 2 K that signifies the rare earth spin allignement in loop cycling above a certain critical field. This jump is only present at very low T that dies out as the T raises. M(H) measurements at different temperature stipulate that Co2+ and Mn4+ do not order completely inspite of strong ferromagnetic correlation that is against the previous study on TCMO. The concurrence of structral, magnetic and dielectric anomaly at Tc suggest its possible magnetostructural copuling. We found a high dielectric constant (2700) in TCMO and the Maxwell-Wagner electrial loss spectrum analysis hints towards a long range hopping mechanism. Sizeable magnetocaloric effect in terms of entropy change across the transition temperatures has been obtained from heat capacity data that clearly corroborates its intrinsic behaviour.

The chiral magneto-electric compound Ni3TeO6 is investigated through temperature-dependent synchrotron-based powder x-ray diffraction and x-ray absorption spectroscopy between 15 to 300 K. Our work provides direct evidence for the exchange-striction in the material around the concomitant onset point of collinear antiferromagnetic and magneto-electric phases. The x-ray absorption near edge spectra and x-ray photoelectron spectra show that the sample consists of both Ni2+ and Ni3+ ions in the lattice. The ionic state of Ni is found to be quite robust, and it is largely independent of the preparation route. Additionally, the minority Te4+ state is found to coexist with the majority Te6+ state, which may arise from the charge disproportionation between Ni and Te ions (Ni2+ + Te6+ --> Ni3+ + Te4+). The observed mixed valency of Ni is also confirmed by the total paramagnetic moment per Ni atom in the system. This mixed valency in the metal ions and the exchange-striction may be attributed to the observed magneto-electric effect in the system., Comment: 10 pages, 8 figures