Ferromagnetism in the nanostructures of undoped oxide semiconductors has become an exciting problem nowadays for its potential future applications in spintronics. In order to elucidate the room temperature d0 ferromagnetism of oxide semiconductors, we have investigated the changes in magnetic property of ZnO nanoparticles with the reduction of size by mechanical milling. We have observed that ferromagnetic ordering appears in the sample when the particle size decreases from 39 ± 1 nm to 30 ± 1 nm. This observation strongly supports the idea of the effect of specific grain boundaries in nanoparticles. The results of Raman scattering also support this observation. From photoluminescence spectra shifted green emissions have been found for ferromagnetic samples. This indicates clearly two different origins for green emissions that are strongly related to the changes in magnetic property. Observations from electron spin resonance spectra suggest that zinc related interstitial defects are significant to give rise to this ferromagnetic coupling. An impurity level formed by the interstitial defects at the surfaces could satisfy the Stoner criteria for the occurrence of band ferromagnetism for these samples. © The Royal Society of Chemistry.

DEBNARAYAN JANA

Physics

S GHOSE

T RAKSHIT

R RANGANATHAN

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

RSC Advances

Magnetic and optical properties of Ru-doped ZnS have been investigated using first principles calculations. Due to Ru dopants, nonmagnetic ZnS becomes magnetic. Ru induces half metallic ferromagnetism with a total magnetic moment of 2.0μB/supercell. Furthermore, the origin of ferromagnetism in Ru-doped ZnS can be explained by Ruderman-Kittel-Kasuya-Yosida (RKKY) like exchange interaction. Curie temperature analysis indicates the possibility of room temperature ferromagnetism from the structures. Moreover, reflectivity spectra in optical calculations successfully describe the metallic properties introduced in the doped system. Static dielectric constant for 6.25% Ru doping gives approximately six times higher value in long wavelength limit compared to the pristine. With a significant amount of Ru, the doped system becomes efficient for visible light absorption. The study reveals that Ru-doped ZnS can be a promising candidate for potential applications in spintronic and optoelectronic devices. © 2019 Elsevier Ltd

Fulltext

Journal of Physics and Chemistry of Solids

Half metallic ferromagnetic and optical properties of ruthenium-doped zincblende ZnS: A first principles study

Optical band gap (Eg) and photoluminescence (PL) of ZnO; both are highly sensitive to the modification of lattice structure due to the presence of defects in the material. Due to the complexity of this dependence, material engineering by controlling the defects of ZnO is still not being achieved. We have studied here the changes in optical band structure during the size reduction by mechanical milling process. Interestingly, UV-visible absorption spectroscopy reveals that the optical band of ZnO undergoes a red shift initially with enhanced band tailing; but for higher defects density, Eg is shifted to a higher value with a reduction in band tailing parameter (E0). Raman scattering indicates that the suppression of vibration related to oxygen atoms plays crucial role for the blue shift of ZnO band structure. PL of these ZnO nanoparticles shows interesting correlation with the shift of Eg and the changes in E0. The defect-related broad emission (DBE) decreases for ZnO samples with red shift in Eg whereas a sharp increase in this DBE is associated with the increment in Eg value or blue shift. Illuminating engineering society colorimetric parameters are consistent with inverted variation for blue shift of Eg. Results altogether indicates that the position Zn atom in the lattice structure is playing crucial role for this inverted variation of band structure

Materials Research Express

Defect dependent inverted shift of band structure for ZnO nanoparticles

Borophene nanosheet has been doped with lithium, beryllium, carbon, and hydrogen atom(s). Modification of electronic properties through the splitting and shifting of the Dirac point has been explored within the framework of ab initio density functional theory (DFT). Doping the Pmmn borophene structure with lithium, beryllium, carbon, and hydrogen atoms leads to semiconductor–metallic transitions as well as absorption of light within the different parts of the electromagnetic spectrum. Indirect band-gap opening is noticed when the system is doped with one hydrogen atom. But when the doping is made double, the system becomes metallic. For lithium and beryllium doping, the split Dirac point has been observed to be situated at the conduction band (CB). However, for single-site carbon atom doping, it is seen to be situated at the valence band (VB), while, for double doping, the system becomes semiconducting with an indirect bandgap of 528 meV. Optical properties calculations show that, for parallel and perpendicular polarization, the excitations have mainly occurred within the low- and high-energy regions, respectively. The effective number of valence electrons does not show any saturation effect for all the doped systems in parallel as well as for perpendicular polarizations. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.

Applied Physics A: Materials Science and Processing

Electronic and optical properties of the supercell of 8-Pmmn borophene modified on doping by H, Li, Be, and C: a DFT approach

The chemical nature of point defects, their segregation, cluster or complex formation in ZnO is an important area of investigation. The evolution of a defective state with MeV Ar ion irradiation fluence 1 10 14 and 1 10 16 ions cm -2 has been monitored here using x-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and Raman spectroscopy. The XPS study shows the presence of oxygen vacancies (V O ) in Ar irradiated ZnO. Zn(LMM) Auger spectra clearly identifies a transition involving metallic zinc in the irradiated samples. An intense PL emission from interstitial Zn (I Zn )-related shallow donor bound excitons (DBX) is visible in the 10 K spectra for all samples. Although overall PL is largely reduced with irradiation disorder, DBX intensity is increased for the highest fluence irradiated sample. The Raman study indicates damage in both the zinc and oxygen sub-lattice by an energetic ion beam. Representative Raman modes from defect complexes involving V O , I Zn and I O are visible after irradiation with intermediate fluence. A further increase of fluence shows, to some extent, a homogenization of disorder. A huge reduction of resistance is also noted for this sample. Certainly, high irradiation fluence induces a qualitative modification of the conventional (and highly resistive) grain boundary (GB) structure of granular ZnO. A low resistive path, involving I Zn related shallow donors, across the GB can be presumed to explain resistance reduction. Open volumes (V Zn and V O ) agglomerate more and more with increasing irradiation fluence and are finally transformed to voids. The results as a whole have been elucidated with a model which emphasizes the possible evolution of a new defect microstructure that is distinctively different from the GB-related disorder. Based on the model, qualitative explanations of commonly observed radiation hardness, colouration and ferromagnetism in disordered ZnO have been put forward. A coherent scenario on disorder accumulation in ZnO has been presented, which we believe will guide further discussion on this topic. © 2018 IOP Publishing Ltd.

Journal of Physics D: Applied Physics

Clustered vacancies in ZnO: Chemical aspects and consequences on physical properties

Among other two-dimensional (2D) novel materials, graphene and silicene both have drawn intense research interest among the researchers because they possess some unique intriguing properties which can change the scenario of the current electronic industry. In this work we have studied the electronic and the magnetic properties of a new kind of materials which is the hybrid of these two materials. Density functional theory (DFT) has been employed to calculate the relevant electronic and magnetic properties of this hybrid material. The pristine structure is modified by substitutional doping or by creating vacancy (Y-X, where one Y atom (Si or C) has been replaced by one X atom (B, N, Al, P or void)). The calculations have revealed that void systems are unstable while Si-B and Si-N are most stable ones. It has been noticed that some of these doped structures are magnetic in nature having induced mid-gap states in the system. In particular, Si-void structure is unstable yet it possess the highest magnetic moment of the order of 4 μB (μB being the Bohr magneton). The estimated band gaps of modified silicene/graphene hybrid from spin polarized partial density of states (PDOS) vary between 1.43–2.38 eV and 1.58–2.50 eV for spin-up and spin-down channel respectively. The implication of midgap states has been critically analysed in the light of magnetic nature. This study may be useful to build hybrid spintronic devices with controllable gap for spin up and spin down states. © 2016 Elsevier B.V.

Materials Chemistry and Physics

Electronic and magnetic properties of modified silicene/graphene hybrid: Ab initio study

Role of Zn-interstitial defect states on d0 ferromagnetism of mechanically milled ZnO nanoparticles

Room temperature ferromagnetic ordering has been observed in a high purity polycrystalline SnO2 sample due to irradiation of 96 MeV oxygen ions. Ab initio density functional theory calculation indicates that tin vacancies are mainly responsible for inducing the magnetic moment in SnO2 whereas oxygen vacancies in SnO2 do not contribute any magnetic moment. Positron annihilation spectroscopy has been employed to characterize the chemical identity of irradiation generated defects in SnO2. Results indicate the dominant presence of Sn vacancies in O ion irradiated SnO2. The irradiated sample turns out to be ferromagnetic at room temperature. This journal is © The Royal Society of Chemistry 2015.

Defect driven ferromagnetism in SnO 2 : A combined study using density functional theory and positron annihilation spectroscopy

Here, we report the cation vacancy-induced room-temperature ferromagnetism (RTFM), photoluminescence (PL) and electrical properties of different group-IA alkali-metal (Li, Na, K)-doped ZnO thin films fabricated by pulse laser deposition. The experimental evidence indicates that the Zn vacancies are responsible for the visible green luminescence and RTFM in the alkali-doped ZnO films. The alkali-metal ions are found to have a crucial role in the formation and stabilization of the Zn vacancies and also to introduce the p-type conductivity to mediate the long-range ferromagnetic interaction in the films. The Li-doped ZnO films are found to exhibit the most intense green luminescence due to the presence of a large concentration of Zn vacancies and consequently, they exhibited the strongest RTFM with the highest saturation moment (M S) and Curie temperature (TC). The concentration of the Zn vacancy as well as the carrier (hole) density of the alkali-doped ZnO films decrease gradually when the alkali-dopants are varied from Li to Na, then to K, resulting in a decrease in both the MS and TC. This study demonstrates that the alkali elements are promising dopants to stabilize and tune high temperature FM in ZnO which can be an exciting way to prepare a new class of ZnO-based magnetic semiconductors. © 2013 The Royal Society of Chemistry.

CrystEngComm

Zinc vacancy-induced high-TC ferromagnetism and photoluminescence in group-1 alkali-metal substituted p-type ZnO thin films

Bulk ZnO is a diamagnetic material but ferromagnetism (FM) has been observed by several groups in its nanostructures. In order to elucidate the room temperature (RT) FM of ZnO nanostructures, magnetic property of mechanically milled and subsequently annealed nano-ZnO powder has been investigated. Sample that has been milled and then annealed at 200 °C in ambient condition shows highest value of saturation magnetization (Ms), whereas lowest value of Ms has been noticed for the sample pre-annealed at 500 °C before milling. The variation of Ms with annealing temperatures closely resembles with the variation of average positron lifetime (τav) and S-parameter reported earlier for these nano-systems. It has also been found that Ms decreases systematically for increasing average grain size of the ZnO nanoparticles. Room temperature photoluminescence of the as-milled sample shows broad defect related emission centered ∼2.23 eV. Enhancement of such emission has been observed due to 200 °C annealing. Results altogether indicate that ferromagnetism in ZnO depends critically on the nature of disorder (open volume defects as well as defect clusters) at the grain surface region. In this connection, the possible role of zinc vacancy defects has also been emphasized. © 2013 AIP Publishing LLC.

Journal of Applied Physics

Surface defects induced ferromagnetism in mechanically milled nanocrystalline ZnO

In this short topical review, a brief account of the evolution of defects due to controlled changes in polycrystalline zinc oxide has been presented. X-ray diffraction, Positron annihilation spectroscopy and optical absorption spectroscopy has been employed to understand various defective states of ZnO. Thermogravimetric analysis, room temperature resistivity and photoluminescence measurements (just mentioned) have been used to throw more light on this topic. A coherent scenario in the light of previous works in this field has been discussed. At the end discussion on the magnetic studies on ZnO-based systems has been added in short. © 2008 Elsevier Ltd. All rights reserved.

Journal	Data powered by TypesetRSC Advances
Publisher	Data powered by TypesetRoyal Society of Chemistry
ISSN	2046-2069
Open Access	No