Magnetic-field induced melting of long-range magnetic order akin to Kitaev insulators in the metallic compound Tb5Si3.

There have been constant efforts to find 'exotic' quantum spin-liquid (QSL) materials. Some of the transition metal insulators dominated by the direction-dependent anisotropic exchange interaction ('Kitaev model' for honeycomb network of magnetic ions) are considered to be promising cases for the same. In such Kitaev insulators, QSL is achieved from the zero-field antiferromagnetic state by the application of magnetic-field, suppressing other exchange interactions responsible for magnetic order. Here, we show that the features attributable to long-range magnetic ordering of the intermetallic compound, Tb5Si3, (TN= 69 K), containing honey-comb network of Tb ions, are completely suppressed by a critical applied field,Hcr, in heat-capacity and magnetization data, mimicking the behavior of Kitaev physics candidates. The neutron diffraction patterns as a function ofHreveal that it is an incommensurate magnetic structure that gets suppressed, showing peaks arising from multiple wave vectors beyondHcr. Increasing magnetic entropy as a function ofHwith a peak in the magnetically ordered state is in support of some kind of magnetic disorder in a narrow field range afterHcr. Such a high-field behavior for a metallic heavy rare-earth system to our knowledge has not been reported in the past and therefore is intriguing.

A reentrant phenomenon in magnetic and dielectric properties of Dy2BaNiO5 and an intriguing influence of external magnetic field.

We report that the spin-chain compound Dy2BaNiO5, recently proven by us to exhibit magnetoelectric coupling below its Néel temperature (TN) of 58 K, exhibits strong frequency-dependent behavior in ac magnetic susceptibility and complex dielectric properties at low temperatures (<10 K), mimicking the 'reentrant' multiglass phenomenon. Such a behavior is not known among undoped compounds. A new finding in the field of multiferroics is that the characteristic magnetic feature at low temperatures moves towards higher temperatures in the presence of a magnetic field (H), whereas the corresponding dielectric feature shifts towards lower temperatures with H, unlike the situation near TN. This observation indicates that the alignment of spins by external magnetic fields tends to inhibit glassy-like slow electric-dipole dynamics, at least in this system, possibly arising from peculiarities in the magnetic structure.

Selective nanoprobes for 'signalling gases'.

The use of arrays of chemical detectors has been realized in electronic nose applications. Recently attention has been focused on the application of e-Noses in the medical arena. These are electronic devices that typically employ non-selective gas sensitive elements for the monitoring of odours and other gaseous analytes. Currently, the lack of relative specificity to a mixture of gaseous analytes for these sensing elements makes the use of pattern recognition algorithms to process the signal and match the acquired data profile to a known pattern necessary, thus identifying the signature of the odour or gas detected. An alternative approach to chemical detection through the use of small arrays (two or three elements) of selective gas sensors made of nanostructured semiconducting films and membranes is described in this work. Sensor selectivity is defined here as higher sensitivity to a given gas or class of gases in the presence of interfering gaseous species. Transition metal oxides are key sensing elements of resistive type chemical detectors. A given oxide may be found in several polymorph phases, each having a distinct structural configuration. Gas-oxide interactions are strongly dependent on the 'structure sensitivity' of the polymorph used in sensing. This paper reviews the effect of polymorphism on the gas specificity and the importance of nanoscale processing for stabilizing the desirable oxide phases, and it introduces a gas-polymorph selection library for building the next generation of gas sensing systems with inherent selectivity to be used as non-invasive disease diagnosis tools.