Investigation of magnetic exchange interactions in Cr-dopedCa0.5Sr0.5RuO3

The value of Curie temperature (TC) and resistivity forCa0.5Sr0.5Ru1-xCrxO3are found to increase with increase inxfrom 0 to 0.1. TheTCincreases from 38 K to 107 K. In this work, we investigate the increment using spin polarised density functional theory. The compounds exhibit Griffiths phase. Our results show that to understand the behaviour of the increase inTC, it is important to consider not only the competing super exchange and super-super exchange interactions between Ru/Cr-Ru/Cr ion pairs but also the increment in the value of the magnetic moment due to the localized character of the dopant (Cr) ion. Our results suggest that the increased resistivity with Cr doping could be due to increased scattering rate and strong on-site coulomb repulsion due to Cr doping. It is also important to note that the behaviour ofTCwith the Ru-O-Ru bond angle is not in line with the functional form reported for ferrites, chromites and some ferromagnetic oxides. We believe that our results will be helpful in further exploring the origin of magnetism and transport on Cr doping in perovskite ruthenates.

Prevalence of Oral Manifestations in COVID-19-Diagnosed Patients at a Tertiary Care Hospital in Kerala

Background

COVID-19, a pandemic since 2019, is still causing significant healthcare burden across the world. Although the disease primarily presents with respiratory symptoms, a multitude of signs and symptoms may be manifested elsewhere in the body.

Aim

This study was to estimate the prevalence of oral manifestations in COVID-19 diagnosed patients and thereby understand the effects of corona virus disease on oral health.

Materials & methods

A total of 472 patients were evaluated using a questionnaire and further examined visually using a mouth mirror and a light source.The patients were evaluated for erythema, ulcers, macule, papule, vescicles, bullae or any other abnormal changes within the oral cavity.

Results

103 patients (21%) were found to have oral lesions and 41 (39.8%) of them presented with palatal enanthem which was macular in nature. Candidiasis was noted in 19 (18.4%) patients, ulcer in 4 (3.8%), mucositis in 5 (4.8%), angular cheilitis in 3 (2.9%), white coating on tongue in 25 (24.2%) & depapillated tongue with glossitis in 6 (5.8%). Multivariate analysis was done using logistic regression.Tobacco chewing, malignancies and altered taste sensation were found to be independently associated with oral lesions.

Conclusion

The study thus confirms the presence of oral lesions in diagnosed COVID-19 patients prompting healthcare professionals on a multidisciplinary approach towards this novel disease.

Structural and physical properties of Ni1-xVxalloys around and away from quantum critical point

We investigate the room temperature structure (global and local), temperature dependent magnetic and transport behaviour of Ni1-xVx(0⩽x⩽0.13) alloys. Our Energy Dispersive Analysis of x-rays results show that the prepared compositions are stoichiometric. With increase in V doping, the compounds exhibit a quantum phase transition aroundxc= 0.12, where the ferromagnetic phase is suppressed. Our results show that all the compounds stabilize in face centred cubic structure at RT and the lattice parameter shows unusual behaviour close toxc. The magnetic and heat capacity studies show signature of Griffiths phase on either side ofxc. From 25 K to the lowest collected temperature, we observe a linear T dependence of resistivity atx = 0.1 and aroundxc, which is separated by a Fermi-liquid region aroundx = 0.106. This suggests that the origin of the transport behaviour is different around the quantum critical point and away from it. Our Ni K-edge x-ray Absorption Spectroscopy results show that there is a significant reduction in the first coordination number around Ni central atom on doping. Further, with doping, there is distortion in the first coordination shell around Ni. This suggests, with V doping, the local structure around Ni is different from the global structure as obtained from the x-ray Diffraction results. Interestingly, with doping, we observe a direct connection between the extent of distortion at RT and the magnetic disorder obtained at 2 K. We believe our results will motivate the scientific community to further study the interplay between the structural disorder and quantum fluctuations with temperature at the local level.

Pseudogap in BaPbxBi1‒xO3(x = 0.7, 0.75 and 1.0)

In this work, we have investigated the crystal and electronic structure of the orthorhombic phase of BaPbxBi1-xO3(BPBO) forx = 0.7 (BPBO70), 0.75 (BPBO75) and 1.0 (BPO), using temperature dependent x-ray diffraction measurements, photoemission spectroscopy, and electronic structure calculations. Our results show the importance of particle size and strain in governing superconductivity. Interestingly, the temperature evolution of the structural parameters in the case of BPBO70 is similar to that of BPBO75 but the magnitude of the change is diminished. The BPBO75 and BPO compounds exhibit metallic nature, which is corroborated by the core level studies. The electronic structure calculations in conjunction with the core level studies suggest that oxygen vacancies play an important role for metallicity observed in the end compound. The exponent to the spectral line shape close to the Fermi level suggests the origin of pseudogap to be due to other contributions in addition to disorder in the case of BPBO70 and BPO. The core level studies also show that as one goes fromx = 0.70 to 1.0, there occurs chemical potential shift towards the valence band suggesting hole doping. Our results open the venue to further study these compounds as a function of particle size, nature of carriers for its transport behaviour, electronic structure belowTC, composition at the grain boundaries and microscopic origin of pseudogap in the non-superconducting phase. We believe that our results call for a revision of the temperature-doping phase diagram of BPBO to include the pseudogap phase.

Orbital hybridisation effects in B2 phase Cr doped Co2MnAl

We investigate here the magnetic, transport, local structural and electronic properties of Co$_2$Mn$_1$$_-$$_x$Cr$_x$Al (x=0, 0.05, 0.1 and 0.2). Our results show that all the compounds stabilise in B2 phase and are ferromagnets. The results reveal disorder at the structural and magnetic levels. X-ray absorption near edge structure (XANES) analysis reveal signature of antisite disorder between Mn and Al atoms with equal ratio. The electronic structure calculations suggest enhancement in the half metallicity, localisation of electrons at the Fermi level and an increment in density of states (DOS) with doping. The combined results of electronic structure calculations and XANES studies suggest transfer of electrons to the Co site. The results of high temperature resistivity measurements suggest the conduction electrons are undergoing transition from delocalisation to weak localisation to activated behaviour with Cr doping. The extended x-ray absorption spectroscopic (EXAFS) analysis shows that the local structure around Mn atom is different from the global structure as obtained from the x-ray diffraction results.The behaviour of the edge region is in line with the trend as obtained from the compositional analysis. We observe link between the hybridisation of 3$\emph{d}$ like states at the Mn, Cr sites with that at the Co site and the transport properties. This could help in understanding the unusual decrement in the lattice parameter with doping. These results reveal the role of local structure in understanding the physical properties of such systems.

Lattice effects on the physical properties of half-doped perovskite ruthenates

We investigate the unusual phase transitions in SrRuO₃and Sr_0.5Ca_0.5Ru1-xCr_xO₃(x = 0, 0.05 and 0.1) employing x-ray diffraction, resistivity, magnetic studies and x-ray photoemission spectroscopy. Our results show the compounds undergo a crossover from itinerant ferromagnetism to localized ferromagnetism. The combined studies suggest Ru and Cr be in the 4+ valence state. A Griffith phase and an enhancement in Curie temperature (T_c) from 38 K to 107 K are observed with Cr doping. A shift in the chemical potential towards the valence band is observed with Cr doping. In the metallic samples, interestingly, a direct link between the resistivity and orthorhombic strain is observed. We also observe a connection between orthorhombic strain andT_cin all the samples. Detailed studies in this direction will be helpful to choose suitable substrate materials for thin-film/device fabrication and hence manoeuvre its properties. In the non-metallic samples, the resistivity is mainly governed due to disorder, electron-electron correlation effects and a reduction in the number of electrons at the Fermi level. The value of the resistivity for the 5% Cr doped sample suggests semi-metallic behaviour. Understanding its nature in detail using electron spectroscopic techniques could unravel the possibility of its utility in high-mobility transistors at room temperature and its combined property with ferromagnetism will be helpful in making spintronic devices.

Evidence of lattice strain as a precursor to superconductivity in BaPb0.75Bi0.25O3

In this work, we have investigated the precursor effects to superconductivity in BaPb_0.75Bi_0.25O₃using temperature dependent resistivity, x-ray diffraction technique and photoemission spectroscopy. The present compound exhibits superconductivity around 11 K (TC). The synthesis procedure adopted is much simpler as compared to the procedure available in the literature. In the temperature range (10 K-25 K) i.e. aboveTC, our results show an increase in both the orthorhombic and tetragonal strain. The well screened features observed in Bi and Pb 4f7/2core levels are indicative of the metallic nature of the sample. The compound exhibits finite intensity at the Fermi level at 300 K and this intensity decreases with decrease in temperature and develops into a pseudogap; the energy dependence of the spectral density of states suggests disordered metallic state. Furthermore, our band structure calculations reveal that the structural transition upon Pb doping results in the closing of the band gap at the Fermi level.

Synthesis and structural link to the electronic and magneto-transport properties of spin-orbit Mott insulator Sr2IrO4

We investigate the effect of sample preparation conditions on the link between the structural and physical properties of polycrystalline spin-orbit Mott insulator, Sr₂IrO₄. The samples were prepared in two batches. With the first batch prepared as per the commonly adopted procedure in literature and the second batch prepared adopting the same procedure as the first batch but with an additional annealing in vacuum. Interestingly, our results show that without change in the value of the Curie temperature (T_C), there occurs increase in the value of magnetization, resistivity, magneto-resistance (MR) and an increase in temperature range of stabilization of the canted antiferromagnetic structure. The temperature behaviour of the difference in the irreversible magnetization between the samples is in line with the difference in the Ir-O-Ir in-plane bond angle. At low temperatures, the conduction mechanism in the first batch of the sample is mainly governed by disorder while in the case of the other sample it is of Arrhenius type. The magneto-transport results have shown its strong link with the disorder and structural results. Although the nature and mechanism of the disorder needs to be investigated further, the present results throw light on the role of disorder and its connectivity between the structure and physical properties to understand its complex behaviours.

Structural and electronic effects in GdCu alloy

We have studied structural and electronic phenomena in GdCu using x-ray diffraction (xrd), photoemission spectroscopic (PES) techniques and band structure calculations. Our structural studies show that the as prepared GdCu sample does not stabilise completely in cubic CsCl phase even at room temperature (RT). The thermal hysteresis is observed in the lattice parameter that appears to be due to strain and dislocations at the surface. The behaviour of the intensity of the most intense xrd peak suggests phase coexistence and structural link with magnetic properties. After undergoing thermal cycling to RT, with an increase in polishing depth, the GdCu sample shows different surface and bulk crystal structures at RT. This behaviour is in contrast to the behaviour of the asprepared one. The surface is predominantly cubic while the bulk exposes more its hidden orthorhombic FeB phase with an increase in the depth of polishing. To understand the manifestation of phase separation on the electronic structure, we have used DFT and DFT + U calculations and PES studies. Our results show the importance of on-site Coulombic interaction in Gd 4f and Cu 3d orbitals. At the Fermi edge, in addition to the significant contribution of Gd 5d and Cu 3d, there is also a contribution of Cu 4p states. The PES studies exhibit chemical potential shift as one compares the asprepared GdCu and the GdCu that has undergone thermal cycling. We have discussed the effect of the chemical potential shift on the valence band and core- level spectra. We believe our results will be helpful in providing insight into the generic property displayed by systems that exhibit strain dominated phase separation.

Interplay of lattice distortion and electronic structure in BaBiO3

We investigate room temperature core level and valence band spectra of BaBiO₃ using x-ray photoemission spectroscopy and band structure calculations. The features in the valence band spectrum were studied using density functional theory (DFT) under local density approximation (LDA) and Tran Blaha modified Becke Johnson (TB mBJ) exchange potential. The calculations were performed for three different structural parameters; monoclinic, cubic and monoclinic (M[Formula: see text]). Our results of the core level spectrum and DFT calculations rule out charge disproportionation of the Bi ions. The valence band spectrum displays gap at the Fermi edge and fine structures in the region close to the Fermi edge. The DFT calculation under TB mBJ for the monoclinic structure is able to generate gap and match the energy positions of the fine structure in a better way. Our calculation results show that there are holes in the O 2[Formula: see text] states and unequal transfer of electrons to the states of the Bi ions. Such mechanism could lead to bond disproportionation and its association with the fine structures in the valence band. The current results reveal the significance of strong link between the lattice distortion and electronic structure and hence to its physical properties.

Electronic structure of EuFe2As2

Employing high resolution photoemission spectroscopy, we studied the temperature evolution of the electronic structure of EuFe2As2, a unique pnictide, where antiferromagnetism of the Eu layer survives within the superconducting phase due to 'FeAs' layers, achieved via substitution and/or pressure. High energy and angle resolution helped to reveal the signature of peak-dip features, having significant p orbital character and spin density wave transition induced band folding in the electronic structure. A significant spectral weight redistribution is observed below 20 K manifesting the influence of antiferromagnetic order on the conduction electrons.

Stress and coping behaviors among smokers

Positive association has been seen between stress and smoking behavior. This relationship has not been explored in relation to one's coping behavior and desire to quit smoking. The present study examined stress, coping and readiness to change among smokers. 50 smokers were selected using a cross sectional design. Assessment Proforma, Fagerstrom test for Nicotine Dependency, General Health Questionnaire, Perceived Stress Scale, Coping Checklist and Readiness to Change Questionnaire were administered on them. Stress was related to smoking behavior as well as initiation and maintenance of smoking. Individuals in the early adulthood stage were using maladaptive coping strategies. Perceived stress was higher among the middle age group. Stress and maladaptive coping behaviors were found to be associated with initiation and maintenance of smoking. It has implications for psychosocial interventions in tobacco cessation.

Importance of conduction electron correlation in a Kondo lattice, Ce₂CoSi₃

Kondo systems are usually described by the interaction of the correlation induced local moments with the highly itinerant conduction electrons. Here, we study the role of electron correlations among conduction electrons in the electronic structure of a Kondo lattice compound, Ce₂CoSi₃, using high resolution photoemission spectroscopy and ab initio band structure calculations, where Co 3d electrons contribute in the conduction band. High energy resolution employed in the measurements helped to reveal the signatures of Ce 4f states derived Kondo resonance features at the Fermi level and the dominance of Co 3d contributions at higher binding energies in the conduction band. The lineshape of the experimental Co 3d band is found to be significantly different from that obtained from the band structure calculations within the local density approximations, LDA. Consideration of electron-electron Coulomb repulsion, U, among Co 3d electrons within the LDA + U method leads to a better representation of experimental results. The signature of an electron correlation induced satellite feature is also observed in the Co 2p core level spectrum. These results clearly demonstrate the importance of the electron correlation among conduction electrons in deriving the microscopic description of such Kondo systems.

Relaxation of arterial smooth muscle by water-soluble derivatives of coenzyme Q (ubiquinone)

Treatment of coenzyme Q with ozone, permanganate, and ferrous sulfate in presence of ascorbate or hydrogen peroxide yielded water-soluble degradation products, possibly having truncated side-chain and modified ring.These derivatives, but not the intact lipid-quinone, showed relaxation of phenylephrine-contracted rat arterial rings. Representative samples of these also decreased blood pressure when injected into the femoral vein in the rat.These effects offer an explanation for the hypotensive action of exogenous coenzyme Q regardless of its side-chain length.

Relaxation of arterial smooth muscle: a new function of a water-soluble degradation product of coenzyme Q (ubiquinone)

Treatment of coenzyme Q with ozone yielded a degradation product having unmodified ring that retained its spectral characteristics and a truncated side-chain that made it water-soluble. This derivative, but not the intact lipid-quinone, showed relaxation of phenylephrine-contracted rat arterial rings. This effect offers an explanation for the known hypotensive action of exogenous coenzyme Q regardless of its side-chain length.