We report a comprehensive investigation of the triple perovskite iridate Ba 3 CoIr 2 O 9 . Stabilizing in the hexagonal P6 3 /mmc symmetry at room temperature, this system transforms to a monoclinic C2/c symmetry at the magnetic phase transition. On further reduction in temperature, the system partially distorts to an even lower symmetry (P2/c), with both these structurally disparate phases coexisting down to the lowest measured temperatures. The magnetic structure as determined from neutron diffraction data indicates a weakly canted antiferromagnetic structure, which is also supported by first-principles calculations. Theory indicates that the Ir 5+ carries a finite magnetic moment, which is also consistent with the neutron data. This suggests that the putative J = 0 state is avoided. Measurements of heat capacity, electrical resistance noise, and dielectric susceptibility all point toward the stabilization of a highly correlated ground state in the Ba 3 CoIr 2 O 9 system.

We critically investigate the purported existence of a multiglass state in the quantum paraelectrics SrTiO3 and KTaO3 doped with magnetic 3d transition metals. We observe that the transition metals have limited solubility in these hosts, and that traces of impurity magnetic oxides persist even in the most well processed specimens. Our dielectric measurements indicate that the polar nano-regions formed as a consequence of doping appear to lack co-operativity, and the associated relaxation process exhibits a thermally activated Arrhenius form. At lower temperatures, the dielectric susceptibility could be fit using the Barrett's formalism, indicating that the quantum-paraelectric nature of the host lattices are unaltered by the doping of magnetic transition metal oxides. All these doped quantum paraelectrics exhibit a crossover from the high temperature Curie-Weiss regime to one dominated by quantum fluctuations, as evidenced by a T 2 dependence of the temperature dependent dielectric susceptibility. The temperature dependence of the magnetic susceptibility indicate that magnetic signatures observed in some of the specimens could be solely ascribed to the presence of impurity oxides corresponding to the magnetic dopants used. Hence, the doped quantum paraelectrics appear to remain intrinsically paramagnetic down to the lowest measured temperatures, ruling out the presence of a multiglass state.

The interface of two dissimilar materials is well known for surprises in condensed matter, and provides avenues for rich physics as well as seeds for future technological advancements.We present some exciting magnetization (M) and remnant magnetization (µ) results, which conclusively arise at the interface of two highly functional materials, namely the graphitic shells of a carbon nanotube (CNT) and α-Fe2O3, a Dzyaloshinskii-Moriya Interaction (DMI) driven weak ferromagnet (WFM) and piezomagnet (PzM). We show that the encapsulation inside CNT leads to a very significant enhancement in M and correspondingly in µ, a time-stable part of the remanence, exclusive to the WFM phase. Up to 70% of in-field magnetization is retained in the form of µ at the room temperature. Lattice parameter of CNT around the Morin transition of the encapsulate exhibits a clear anomaly, confirming the novel interface effects. Control experiments on bare α-Fe2O3 nanowires bring into fore that the weak ferromagnets such as α-Fe2O3 as are not as weak, as far as their remanence and its stability with time is concerned, and encapsulation inside CNT leads to a substantial enhancement in these functionalities.Hematite (or α-Fe2O3) is an earth abundant and environment-friendly oxide, generally considered as a menace, for its appearance as common rust over elemental Fe, but technologically, it is well known for a very diverse range of applications. [1] However, the observation of WFM [2,3] nearly six decades ago in hematite and its connection to spin orbit coupling (SOC) has had profound implications in the field of spintronics. A variety of nontrivial topological spin structures in chiral magnets stabilizing through DMI/SOC have triggered new research areas such as antiferromagnetic spintronics and spin orbitronics [4,9] .Generation of WFM in α-Fe2O3 is due to a slight canting of its inherent AFM sublattice [2,3] which persists from 950 K (TN) down to 265 K, well-known Morin Transition temperature (TM). Below TM, the spins turn from "a" axis to "c" axis (rhombohedral unit cell in hex setting) and the canting vanishes for hematite. Many of such canted AFM, either DMI driven or systems in which canting takes place due to other mechanism, are also known to exhibit the phenomenon of piezomagnetism. [10,14] Here, PzM implies that magnetization can be tuned by stress alone.Another important point is the occurrence of WFM which is concurrent with PzM as theoretically predicted [10] and experimentally observed [11,14] . Dzyaloshinskii also showed that the spin canting effect is larger for compounds with smaller TN [2] . Thus, WFM / PzM is seen to be the weakest in α-Fe2O3 with TN ~950 K as compared to MnCO3 or NiCO3 (TN below 50 K).This work centers around remanence µ, which, in general, is an important parameter for any magnetic material for a variety of practical applications related to permanent magnets, soft or hard, relate to this quantity [15,17] . In addition, it is an important tool for probing fundamental magnetic interactions in conventional lon...

Using detailed synchrotron diffraction, magnetization, thermodynamic and transport measurements, we investigate the relationship between the mixed valence of Ir, lattice strain and the resultant structural and magnetic ground states in the geometrically frustrated triple perovskite iridate Ba3NaIr2O9. We observe a complex interplay between lattice strain and structural phase co-existence, which is typically not observed in this family of compounds. The low temperature magnetic ground state is characterized by the absence of long range magnetic order, and points towards the condensation of a cluster glass state from an extended regime of short range magnetic correlations.

The anomalous thermal expansion in a layered 3d-5d based triple perovskite iridate Ba 3 CoIr 2 O 9 is investigated using high resolution synchrotron diffraction. Below the magnetostructural transition at 107 K, the onset of antiferromagnetic order is associated with a monoclinic distortion of the hexagonal structure. Deeper within the magnetically ordered state, a part of the monoclinic phase distorts even further, and both these structural phases co-exist down to the lowest measured temperatures. We observe negative thermal expansion in this phase co-existence regime, which appears to be intimately connected to the temperature driven relative fractions of these monoclinic phases. The significant NTE observed in this system could be driven by magnetic exchange striction and is of relevance to a number of systems with pronounced spin orbit interactions.