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Simultaneous tuning of magnetic, transport and electrochemical properties through strategic doping of cobalt (Co) ions in hydrothermally treated multi-layered MoS2 nanoflakes (NFs).

Supercapacitor and hydrogen-based fuel cells are cheap and environmental-friendly next-generation energy storage devices that are intended to replace Lithium-ion batteries. Metal oxide nanostructures having perovskite crystal structure have been found to exhibit unique electrochemical properties owing to its unique electronic band structure and multiple redox-active ions. Herein, MgTiO3 nanoparticles (MTO-1) were synthesized by wet-chemical sol–gel technique with an average particle size of 50–55 nm, which exhibited superior supercapacitor performance of capacitance (C) = 25 F/g (at 0.25 A/g), energy density (ED) = 17 Wh/kg, power density (PD) = 275 W/kg and 82.41% capacitance retention (after 1000 cycles). Aqueous 1 M Mg(ClO4)2 solution was used as the electrolyte. MTO-1 revealed an overpotential (η) = 1.329 V and Tafel slope (b) = 374 mV/dec towards Oxygen Evolution Reaction (OER) electrocatalyst and exhibited η = 0.914 V and b = 301.4 mV/dec towards Hydrogen Evolution Reaction (HER) electrocatalyst, both in presence of alkaline 1 M KOH solution, making these MgTiO3 nanoparticles very promising for potential use in various technologically important electrochemical applications.

Herein this work, we have used the sol-gel chemical synthesis method to prepare spherical shaped MgFe2O4 nanoparticles having size 45–50 nm. Using 1 mol L−1 Sodium Perchlorate (NaClO4) electrolyte, a capacitance of 61 F/g, a capacitance retention of 82.91% (after undergoing 1000 cycles), and an energy density of 41 Wh/kg have been achieved. Using 1 mol L−1 Magnesium Perchlorate (Mg(ClO4)2) as electrolyte, a capacitance of 43 F/g, a capacitance retention of 82.15%, and an energy density of 29 Wh/kg have been realized. Furthermore, MgFe2O4 nanospheres exhibited an overpotential (η) = 1.09 V, a Tafel slope (b) = 317 mV/dec in regard to alkaline Oxygen Evolution Reaction (OER) electrocatalyst. It also achieved η = 402 mV and b = 241 mV/dec in regard towards alkaline Hydrogen Evolution Reaction (HER) electrocatalyst. These results signify the suitability of MgFe2O4 nanoparticles for high energy density aqueous supercapacitor and water splitting electrocatalyst applications.

Molybdenum disulfide (MoS2) nanosheets, due to having a highly active nature, being low cost and having unique physical and chemical properties, have shown their efficacy in the catalytic reduction of nitroarenes. Doping of transition metal ions in molybdenum disulfide (MoS2) nanosheets is a well-known strategy to enhance their catalytic efficiency for the reduction of nitroarenes, however, finding the optimum dopant amount is still a subject of ongoing research. Herein, we have synthesized few-layered cobalt (Co) doped MoS2 nanosheets with different cobalt content (2%, 4%, 6% and 8%) through the solvothermal approach, taking sodium molybdate dihydrate (Na2MoO4·2H2O), thiourea (CH4N2S) and cobalt acetate tetrahydrate [Co(CH3COO)2·4H2O] as precursors and their catalytic performance has been affirmed by monitoring the reduction of p-nitrophenol by NaBH4 in real time using UV-visible absorption spectroscopy. The 6% Co doped MoS2 nanosheets have exhibited superior catalytic activity with a pseudo-first order rate constant of 3.03 × 10−3 s−1 attributed to the abundant defects in the active edge sites having a dominant metallic 1T phase with Co ion activated defective basal planes, sulphur (S) edges, synergistic structural and electronic modulation between MoS2 and Co ions and enhanced electron transfer assisted through redox cycling in the active sites. An attempt has also been made to study the manipulation of structural and optical properties with cobalt doping in MoS2 nanosheets to establish a correlation between the catalytic efficiency and dopant content. This study demonstrates that proper tuning of Co doping in MoS2 nanosheets paves the way in searching for a potential alternative of a noble metal catalyst for the catalytic reduction of nitroarenes.

Combining experimental investigations and first-principles density functional theory (DFT) calculations, we report physical and magnetic properties of Gd-substituted Y

We report here the cost-effective synthesis of Magnesium Cobalt Oxide (MgCoO2) sample by the sol-gel synthesis route labeled as MCO - 3. In presence of aqueous 1 M Lithium Sulphate (Li2SO4) electrolyte, we obtained a capacitance of 56 F/g, an energy density of 38 Wh/kg and a capacitance retention of 92.53 % (at 5 A/g) after undergoing 1000 charge-discharge cycles. For the aqueous 1 M Sodium Perchlorate (NaClO4) electrolyte system, we found the capacitance, energy density and capacitance retention of 47 F/g, 31 Wh/kg and 91.41% (at 3.5 A/g for 1000 charge-discharge cycles), respectively. These results establish MgCoO2 as suitable electrode material in aqueous lithium-ion and sodium-ion supercapacitor devices. Further, MCO - 3 in the presence of aqueous 1 M Potassium Hydroxide (KOH) electrolyte showed an overpotential of 400 mV and a Tafel slope of 174 mV/dec, making it a suitable candidate for alkaline Hydrogen Evolution Reaction (HER) electrocatalyst.

In recent times, an engrossing and newly discovered class of materials with unique electronic band properties, namely, zero-spin-gap half-metal, has gained acute attraction worldwide because of its...

In this work, we have successfully synthesized MgNiO2 using a sol-gel wet chemical synthesis technique named MNO - 3. Electrochemical measurements in the presence of aqueous 1 M Li2SO4 electrolyte indicate that MNO - 3 samples exhibit a capacitance value of about 30 F/g and an energy density of about 20 Wh/kg. Subsequently, in the experiment involving aqueous 0.5 M Na2SO4 electrolyte system, it has been found that the capacitance for MNO - 3 sample is about 34 F/g and the energy density is about 23 Wh/kg for MNO - 3 sample. Finally, in the presence of aqueous-based 1 M Mg(ClO4)2 electrolyte, MNO - 3 sample is found to exhibit a capacitance of about 26 F/g and an energy density of about 17 Wh/kg, respectively. In all three electrolyte systems, the MNO -3 sample exhibit a long cycle capacitance retention of greater than 85% for 1000 charge-discharge cycles.

Combining experimental investigations and first-principles DFT calculations, we report physical and magnetic properties of Gd-substituted Y$_2$CoMnO$_6$ double perovskite, which are strongly influenced by antisite-disorder-driven spin configurations. On Gd doping, Co and Mn ions are present in mixed-valence (Co$^{3+}$, Co$^{2+}$, Mn$^{3+}$ and Mn$^{4+}$) states. Multiple magnetic transitions have been observed: i) paramagnetic to ferromagnetic transition is found to occur at \textit{T}$_C$=95.5 K, ii) antiferromagnetic transition at \textit{T}$_N$=47 K is driven by $3d-4f$ polarisation and antisite disorder present in the sample, iii) change in magnetization below \textit{T}$\leq$20 K, primarily originating from Gd ordering, as revealed from our DFT calculations. AC susceptibility measurement confirms the absence of any spin-glass or cluster-glass phases in this material. A significantly large exchange bias effect (\textit{H}$_{EB}$=1.07 kOe) is found to occur below 47 K due to interfaces of FM and AFM clusters created by antisite-disorder., Comment: 19 pages, 12 figures

The present study reports a one-step clean synthesis of carbon dots (CDs) using clove buds and polyvinylpyrrolidone (PVP) as the starting precursor via hydrothermal routes. The adopted technique is facile, reproducible, and cost-effective for the production of externally passivated carbon dots owing to an environmentally friendly process utilizing natural precursors. The study evidenced the synergetic effect of passivation on light absorption and fluorescence properties in comparison to non-passivated carbon dots (CCDs). The structural and morphological study revealed that the PVP-passivated clove-derived carbon dots (PPCCDs) were spherical with an average diameter of ~ 2 nm and crystalline with an interlayer spacing of 0.33 nm. The PPCCDs showed excellent antioxidant activity against DPPH free radicals and also showed good catalytic activity for the degradation of Rhodamine-B (Rh-B) dye under studied conditions. Synthesized PPCCDs showed dose-dependent toxicity in L929 (mouse fibroblast) cell lines, while the appropriate concentration used in biological studies was found to be biocompatible as evidenced by MTT assays and also revealed in bioimaging potential. To conclude, synthesised PPCCDs is an economically potent candidate with multifunctional aspects, which can serve as an excellent antioxidant, catalyst, and efficient multicolor bioimaging tool.

Electron- and hole-doped ${\mathrm{La}}_{2}{\mathrm{CoMnO}}_{6}$(LCMO) are investigated using first-principles DFT calculations. Hole and electron doping are achieved, respectively, by introducing ${\mathrm{Sr}}^{2+}$ at ${\mathrm{La}}^{3+}$ sites and by inducing O-site vacancies in LCMO. Electronic structure calculations suggest that hole doping alters the charge and valence state of Co ions, whereas electron doping influences the Mn ions. Introduction of defects is found to enhance antisite disorder (ASD) at Co/Mn site, which is expected to influence the magneto-dielectric properties of the system. Our calculations suggest that while ASD and/or hole doping induces half-metallicity in LCMO, electron doping restores its insulating state. Mean-field calculations performed using exchange constants obtained by mapping DFT total energies of different collinear spin configurations onto the Ising Hamiltonian find that defects tend to reduce the Curie temperature $({T}_{C})$. Interestingly, the calculated linear optical properties of the system suggest that the material becomes optically active with high values of birefringence in the presence of defects, a property that is highly sought-after in the optical communications and laser industry.

Supercapacitor and hydrogen-based fuel cells are cheap and environmental-friendly next-generation energy storage devices that are intended to replace Lithium-ion batteries. Metal oxide nanostructures having perovskite crystal structure have been found to exhibit unique electrochemical properties owing to its unique electronic band structure and multiple redox-active ions. Herein, MgTiO₃ nanoparticles (MTO-1) were synthesized by wet-chemical sol-gel technique with an average particle size of 50-55 nm, which exhibited superior supercapacitor performance of capacitance (

Gadolinium doping effects on structural-, electronic transport and magnetic properties of Pr0.6Gd0.1Sr0.3MnO₃ (PGSMO) nanomanganite (40-65 nm) have been investigated. We have considered the core-shell structure of our PGSMO nanoparticles, which can explain its intriguing magnetic and transport properties. It is reported 65 nm sample exhibits higher metal to insulator transition temperature, TP (∼215 K) and less resistive behavior compare to its nano counterparts. Enhanced low-field magnetoresistance (LFMR) is observed with a reduction of particle size; however maximum change in magnetoresistance (MR), ∼72% is recorded for 65 nm sample around TP at 60 kOe field. Low-temperature magnetization data reveals the existence of glassy phase in the compound. It is revealed that substitution of optimal Gd doping at A site on nanometric scale promotes exotic magnetic and transport properties on nanoscale without adding any external physical perturbation or introducing any significant lattice distortion.

Noticeably large ferromagnetism and enhanced dielectric constant have been observed in 10% Cobalt doped BiFeO3 multiferroics. Significant anomalies have also been observed in temperature dependent dielectric study from 1 kHz to 1 MHz frequency range. Enhancement of saturation magnetization (MS ∼8.1 emu/gm) and coercivity (HC ∼1.74 T) at the ground state (5 K) have also been observed in our 10% Co doped BiFeO3 (BiFe0.9Co0.1O3) nanoceramics.

We have investigated here the structural and magnetic properties of polycrystalline La1.5Ca0.5CoMnO6 double perovskite. The room temperature structural analysis reveals good crystallinity of the sample without presence of any impurity phase. Reitveld refinement of obtained x-ray diffraction and neutron powder diffraction data using Fullprof Suite programme shows that our double perovskite system has monoclinic (P21/n) crystal structure. The presence of antisite disorders (either, Co-O-Co or Mn-O-Mn) in this system suggest antiferromagnetic ordering at ∼200 K due to the presence of Co2+/Co3+-O2--Co2+/Co3+ or/and Mn3+/Mn4+-O2--Mn3+/Mn4+ magnetic interactions along with ferromagnetic ordering below 157 K due to the presence of Co2+–O2-–Mn4+ superexchange interactions.

Griffiths phase like behavior has been investigated in details in size modulated Sm1.5Ca0.5CoMnO6 double perovskite, having ferromagnetic entities in the paramagnetic matrix. Temperature dependent real and imaginary part of ac susceptibility confirms that Sm1.5Ca0.5CoMnO6-1150 °C bulk-sample has spin-glass like ordering below Tg ∼ 34.88(3) K. This glassy behavior is attributed to the antisite disorders (∼7.12%) along with and magnetic frustration in the system. However, the ground state of Sm1.5Ca0.5CoMnO6-600 °C nanometric-sample is observed to be antiferromagnetic in nature due to the presence of large antisite disorder (∼53.58%). The observed unusual co-existence of antiferromagnetism with Griffiths-like phase in Sm1.5Ca0.5CoMnO6-600 °C sample is rare in nature. Interesting magnetic spin dynamics and aging effect are also observed in both the compounds suggesting different spin relaxation processes in low temperature regime. The observed magnetism in these compounds can be tuned by nearest neighbor Co-O-Mn and/or Co-O-Co/Mn-O-Mn exchange interactions as well as the next nearest neighbor Co-O-O-Co/Mn-O-O-Mn interactions.

In recent years, solid solutions have shown promising results as functional materials for different applications. These materials have tunable physiochemical properties and electronic properties, and are being intensively studied for next generation electrochemical charge storage as well as noble metal free low cost electrocatalyts. In the present work, Magnesium Nickel Oxide (MgNiO₂) solid solution is prepared by molten salt synthesis. MgNiO₂ particles having octahedron shaped morphology with size of 550 nm with an agglomerative behavior was observed through morphological studies. Raman studies revealed presence of three two-phonon modes as well as two one-phonon modes, which confirm the phase purity of MgNiO₂ sample. MgNiO₂ particles behaved as a promising supercapacitor candidate by exhibiting a large specific capacitance of 76 F/g. It also revealed electrochemical stability over an expansive potential range under the presence of 0.5 mol L

The exchange bias effect at the magnetic interfaces and multi-magnetic phases strongly depends on the antisite disorder (ASD) driven spin configuration in the double perovskite systems. The percentage of ASD in double perovskites is extensively accepted as a key for designing diverse new nanospintronics with tailored functionalities. In this regards, we have investigated such ASD driven phenomena in Ca

The injection of spin-polarized electrons from a magnetic material into semiconductor is currently one of the foremost challenges in semiconductor spin electronics. Here, we have studied the efficient electrical spin injection and detection from nickel doped Fe3O4 (NFO) into the p-Si having (100) crystal orientation via MgO thin insulating tunnel barrier with the help of three-terminal Hanle measurement. The NFO/MgO/p-Si heterojunction has been prepared using pulsed laser deposition (PLD) technique. Clear Hanle and Inverted Hanle signals have been noticed in spin injection and detection condition of the heterojunction. A large value of Hanle signal (ΔV = 2.4 mV) has been detected at room temperature (300 K). Pure spin accumulation in p-Si resulted from spin injection from strong ferromagnetic NFO via MgO tunnel barrier has been corroborated by a meticulous experiment incorporating a non-magnetic Ag/MgO/p-Si heterostructure. The bias dependent ΔV and spin lifetime (τ) suggest that the transport of the heterojunction is governed by the spin tunnelling via pin-hole free MgO tunnel barrier. Hence the oxide magnetic materials establish a decent platform in spin injection and detection for the development and improvement of room temperature spin-based electronic devices.

In this work magnetic properties, magnetoimpedance (MI) and field sensitivity (η) of rapidly solidified (Fe0.7Co0.3)80B19M1 (M = B, Al, Si & Cu) ribbons have been investigated in the frequency range 0.5 – 13 MHz. Present study shows replacement of boron (B) by a nonmagnetic element (Al, Si or Cu) can alter the thermal stability, soft magnetic and magnetoimpedance properties of the (Fe0.7Co0.3)80B20 ribbons. It is found that saturation magnetization reaches the largest value for Cu-containing sample and the smallest value for Al-containing sample. The MI studies show maximum MI ratios 30% at 5 MHz, 23% at 7 MHz, 26% at 3 MHz and 39% at 4 MHz for M = B, Al, Si & Cu respectively. Variation of MI with external magnetic field shows single peak behavior of Al-content ribbon over the entire frequency range, whereas for all other samples single peak converted to double peak at higher frequency, which indicates existence of stronger longitudinal magnetic anisotropy in Al-containing ribbon. The MI variation with magnetization, M and damping constant, α is also validated through numerical simulations using standard electrodynamics models. Present study reveals that the variations of MI response are associated with formation of soft magnetic phase and development of anisotropy with replacement of B by an additional element.

Spin-dependent electronic transport has been investigated on granular 99.95% La0.7Sr0.3MnO3-0.05% Paraffin wax nanocomposite. Although, the composite exhibits usual signature of spin-polarized tunnelling magnetoresistance (MR) of polycrystalline La0.7Sr0.3MnO3 (LSMO) within the temperature range of 50–300 K; it differs significantly at low temperature region (T

We have investigated the current (I) - voltage (V) characteristics and vortex dynamics of Ba0.54K0.46Fe2As2 single crystal (BaK122) in H ‖ a b -plane and H ‖ c -axis orientations. The single crystal has been prepared by conventional growth method using self flux and characterized by onset Tc = 38.5 K, ΔTc = 1.0 K (offset-onset criterion) and residual resistivity ratio (RRR) ≈ 8. Usually for high-Tc superconductors, I - V curve shows exponential behavior due to flux creep at low magnetic field and it changes to near-linear nature with increase of magnetic field due to flux flow. We have shown that I –V characteristics differ significantly in H ‖ a b orientations compared to H ‖ c orientation which might be due to the presence of second magnetization peak (SMP). We have also estimated the activation energy using the Arrhenius plot in the thermally activated flux flow (TAFF) regime from the temperature dependent resistivity curves in both field orientation and have shown the variation of activation energy with magnetic field.

The first order martensite transition has been observed clearly through magnetic, electronic- and magneto-transport studies in Ni45Mn44Sn11 disordered ferromagnetic shape memory Heusler alloy. The alloy also shows second order ferromagnetic → paramagnetic phase transition, near the Curie temperature of austenite phase. From calorimetric measurement, the lattice entropy due to martensite transformation is found to be 38 Jkg−1K−1, both for heating and cooling cycle. Technologically important noticeably large positive magnetic entropy change has also been clearly noticed in this alloy near martensite phase transition. Maximum isothermal magnetic entropy changes at 275 K for the application of 5 T magnetic field are found to be 15 Jkg−1K−1 and 24 Jkg−1K−1, for field increasing and field decreasing protocol, respectively. A maximum temperature change −5.1 K is observed at 276 K under 5 T magnetic field in adiabatic condition. The noticeable maximum magnetoresistance of −38% for the field change of 5 T is observed at 266 K. The austenite and martensite phase fractions in the sample depend on the magnetic and thermal path history, which are the most possible reasons to observe different values of magnetic entropy change and magnetoresistance in Ni45Mn44Sn11 Heusler alloy at 275 K.

Ni 45 Mn 44 Sn 11 melt spun ribbons have been prepared by melt spinning technique. A single austenite L2 1 phase with lattice constant 5.945 A is confirmed at room temperature. The first order martensite transition is observed from calorimetric, electronic transport and magnetic measurements in our Ni 45 Mn 44 Sn 11 melt spun ribbon sample. The change in lattice entropy due to martensite transformation is found to be nearly 15 J kg −1 K −1 from calorimetric data, both for heating and cooling cycle. A noticeable shift (−7.5 K) of reverse martensite transition for the application of 8 T magnetic field has been clearly observed from temperature dependent resistivity measurement. Field induced transformation of martensite phase to austenite phase has also been noticed directly from the field dependent isothermal resistivity data inside martensite transition regime. As a result large negative magnetoresistance of 38% has been observed at 265 K. Sharp increase of magnetization, on heating, near reverse martensite transition is also observed due to transformation of weak magnetic martensite phase to ferromagnetic austenite phase. Isothermal magnetization data show magnetic hysteresis near the martensite transition regime due to difference in austenite and martensite phase fraction between increasing and decreasing field. A maximum positive magnetic entropy change of 7.2 J kg −1 K −1 is observed for the field change of 5 T. Magnetic hysteresis and refrigerant capacity are the important parameters for magnetic refrigerant material. The maximum value of magnetic hysteresis loss is 16.6 J kg −1 . However, the net refrigerant capacity is found to be 30.4 J kg −1 for Ni 45 Mn 44 Sn 11 melt spun ribbon sample. The adiabatic temperature change is found to be of −2.68 K for application of 5 T magnetic field at 276 K.

The influence of rare earth site substitution on structural, transport and magnetic characteristics of polycrystalline Ln2CoMnO6 (Ln = La, Sm and Gd) has been systematically investigated in details. The room temperature X-ray diffraction data confirm the monoclinic crystal structure of the samples, having P21/n space group. The magnetic study reveals that the ferromagnetic transition temperature (TC1 ∼ 233.2 K) of La2CoMnO6 decreases very fast due to a decrease of ionic radii in Ln site and TC2 (∼150 K) disappears in the Gd2CoMnO6 system due to the presence of only Co2+ and Mn4+ ion pair. The field dependent magnetization data at 5 K exhibit antiferromagnetic ordering induced in the Sm2CoMnO6 and Gd2CoMnO6 systems due to structural distortion and 4f-3d negative magnetic interactions. The temperature dependent resistivity data of La2CoMnO6 display semiconductor like behavior in a temperature range of 150–300 K and this behavior has been best described by the variable range hopping conduction mechanism. On the other hand, the resistivity of Sm and Gd based samples follows variable range hopping model in the temperature range of 200–300 K. Large magnetoresistance of ∼−26.35% has been observed at 160 K at a magnetic field of 60 kOe in La2CoMnO6 and it decreases to −8.28% for Sm2CoMnO6, and −1.01% for Gd2CoMnO6 as ionic radii decrease at the Ln site.

The low temperature spin accumulation in p-Si using Co2CrAl/SiO2 tunnel junction has been investigated in detail. The heterojunction has been fabricated using electron beam evaporation (EBE) technique. The 3-terminal contacts in Hanle geometry has been made for spin transport measurements. The electrical transport properties have been investigated at different isothermal conditions in the temperature range of 10-300 K. The current-voltage characteristics of the junction shows excellent rectifying magnetic diode like behaviour in lower temperature range (below 200 K). At higher temperature, the junction shows nonlinear behaviour without rectifying characteristics. We have observed spin accumulation signal in p-Si semiconductor using SiO2/Co2CrAl tunnel junction in the low temperature regime (30-100 K). Hence the highly spin polarized Full Heusler alloys compounds, like Co2CrAl etc., are very attractive and can act as efficient tunnel device for spin injection in the area of spintronics devices in near future. The estimated spin life time is τ = 54 pS and spin diffusion length inside p-Si is LSD = 289 nm at 30 K for this heterostructure.

We have investigated the room temperature magnetoelectric coupling, temperature dependent impedance and dielectric properties of xZn0.3Ni0.7Fe2O4 – (1-x) Pb (Zr0.58Ti0.42)O3 (x = 0.2, 0.3, 0.4 and 0.5) nanocomposites. The nanocomposites have been prepared through low temperature chemical pyrophoric reaction process followed by solid state reaction route. The magnetoelectric coupling has been measured as a function of applied magnetic field at different frequencies and different angles between applied magnetic field and measured electric field. The observed magnetoelectric coupling may be due to the field dependent magnetostriction of the piezomagnetic phase of the composite. Noticeably, the magnetoelectric coupling is strongly depended on the frequencies, angles and volume fraction of the piezomagnetic phase of the nanocomposites. Polarization – Electric field loop shows the room temperature ferroelectric nature of nanocomposites. The ac electrical properties of the nanocomposites have been studied employing impedance spectroscopy technique. The temperature dependent impedance studies reveal the grain boundaries plays the dominating role. Thermally tunable dielectric properties of nanocomposites exhibit the Maxwell – Wagner interfacial polarization in the system. Electromechanical resonance response is observed at the higher frequency region. The ac conductivity of the nanocomposites has been investigated at different temperatures and fitted by Jonscher's power law. The conduction mechanism is mainly due to the small and large polaronic hopping in the system.

Doping at the post-transition metal site by trivalent rare-earth ions and 3d transition metal site by transition metal ions in perovskite lattice has observed a variety of magnetic and electronic orders with spatially correlated charge, spin and orbital degrees of freedom. Here, we report large ferromagnetism and enhanced dielectric constant (at ∼100 Hz) in chemically synthesized single phase multiferroic Bi1−xNdxFe1−yCoyO3 (x = 0, 0.10; y = 0, 0.10) nanoparticles (average particles size ∼45 nm). We have also examined the ferroelectric nature of our chemically synthesized samples. The Rietveld refinement of the XRD data reveals the structural symmetry breaking from distorted rhombohedral R3c structure of BiFeO3 to the triclinic P1 structure in Bi0.9Nd0.1Fe0.9Co0.1O3 (BNFCO) without having any iron rich impurity phase. The magnetization in these nanoceramics most likely originates from the coexistence of mixed valence states of Fe ion (Fe2+ and Fe3+). A high room temperature dielectric constant (∼1050) has been observed at 100 Hz of BNFCO sample. The frequency dependent anomalies near Neel temperature of antiferromagnet in temperature variation of dielectric study have been observed for all the doped and co-doped samples exhibiting typical characteristic of relaxor ferroelectrics. A spectacular enhancement of remanent magnetization MR (∼7.2 emu/gm) and noticeably large coercivity HC (∼17.4 kOe) at 5 K have been observed in this BNFCO sample. Such emergence of ferromagnetic ordering indicates the canting of the surface spins at the surface boundaries because of the reduction of particle size in nanodimension. We have also observed P-E hysteresis loops with a remanent polarization of 26 μC/cm2 and coercive field of 5.6 kV/cm of this sample at room temperature. From impedance spectroscopy study the estimated activation energy of 0.41 eV suggests the semiconducting nature of our nanoceramic BNCFO sample.

We have investigated magnetoelectric effect and ac electrical properties of xLa0.7Sr0.3MnO3 (LSMO) - (1-x) HoMnO3 (HMO) (x = 0.1, 0.3 and 0.5) multiferroic nanocomposites prepared through low temperature pyrophoric reaction method. The series of nanocomposites have been found to exhibit room temperature ferroelectric and ferromagnetic behaviour. The magnetoelectric response has been detected in this series of lead free nanocomposites at room temperature. The ac electrical properties of this series of composite have been studied employing impedance spectroscopy technique. The value of impedance has been found to be decreased with increase in magnetic field. This observation has been attributed to the depinning of LSMO domain walls at the grain boundaries pinning centres and thereby enhancing the spin dependent transport mechanism in the composites. Moreover, impedance has been observed to decrease with increase in both frequency and temperature due to the charge carrier or polarons of the system acquiring sufficient amount of thermal energy to overcome the high resistive barrier. Nyquist plots at different temperatures have been fitted using parallel combinations of grain boundaries resistance and grain boundaries capacitance for LSMO and HMO grains, where grain boundaries resistances are found to decrease with increase in temperatures. Furthermore, we have estimated activation energy of those composites at a same temperature range using Arrhenius relation.

The magnetoelectric coupling of x NiFe 2 O 4 –(1- x )HoMnO 3 ( x = 0.1 and 0.3) multiferroics nanocomposites prepared through low temperature chemical pyrophoric reaction process has been investigated at room temperature. The signature of magnetoelectric coefficient of these nanocomposites is mainly due to the magnetostriction and magnetodielectric properties of the materials. These nanocomposites show the ferroelectric behaviour at room temperature. AC electrical properties of nanocomposites have been studied with applied magnetic fields and temperatures. Nyquist plots at different magnetic fields and temperatures have been fitted using parallel combinations of resistance-capacitor circuits. Moreover, we have estimated activation energy of those composites using Arrhenius relation, which indicates that same kinds of charge carrier are responsible for relaxation process in grain boundaries and grain of the sample. Furthermore, from the analysis of ac conductivity data as a function of frequency is attributed to the large polaronic hopping in the conduction process in the system.

Room temperature spin injection and detection in non-magnetic p-Si semiconductor have been studied in details in our Co2CrAl (CCA)/MgO/p-Si heterojunction. The electrical transport properties have ...

The effect of Mo doping on the structural and dielectric properties has been investigated in detail for Co-Zn spinel ferrite. Solid state reaction technique has been used to prepare the CZMO. The structural analysis is performed using HRXRD technique which confirms the inverse spinel structure of the material. The frequency and temperature dependence of dielectric constant are studied which reveals that the dielectric dispersion is due to Maxwell-Wagner type polarization in agreement with Koop's phenomenological theory. The contribution of grain and grain boundary at high and low frequency respectively are evident in the dielectric constant. The variation of dielectric loss tangent with both the temperature and frequency has been studied. The room temperature and high frequency dielectric loss is observed to be very small. Also it is revealed that the dielectric loss tangent decreases with Mo substitution.

Single-phase polycrystalline La 1.5 Ca 0.5 CoMnO 6 double perovskite nanoparticles (∼25 nm) have been synthesized by chemical sol-gel method. We report here the structural, magnetic and transport properties using X-ray diffraction, dc magnetization, ac susceptibility, exchange bias and dc resistivity measurements. The Rietveld refinement of X-ray diffraction pattern reveals that the La 1.5 Ca 0.5 CoMnO 6 (LCCMO) system crystallizes in orthorhombic structure with pbnm space group. Mn and Co ions are not completely ordered on the B sites due to the presence of about 30% antisite-disorder in the system. The ordering of Co 2+ and Mn 4+ gives rise to the ferromagnetism below 145 K. A spin glass like ground state has also been observed near 37.6(4) K, arising mainly due to the presence of competing magnetic interactions and antisite-disorder in the LCCMO nanoparticles. The frequency dependence peak shift of the Ac-susceptibility peak in the glassy state follows the critical slowing down model. The observed memory effect in ac susceptibility data reveals the existence of interacting clusters in a competing magnetic interactions state. The presence of noticeable exchange bias effect can be best explained on the basis of uncompensated interface (ferromagnetic/spin-glass) spins of antisite-disordered LCCMO system. This anti-site disordered nanocompound exhibits semiconducting behavior with variable range hopping kind of electronic conduction mechanism in the temperature range of 200–300 K. We have also observed large negative magnetoresistance (−30% at 100 K and 60 kOe) mainly due to the spin-polarized transport across the grain boundaries.

Nanoparticles of spinel cubic Mn0.5Zn0.5Fe2O4 are first prepared by the coprecipitation method and then subjected to conventional solid-state sintering and microwave processing techniques. Particle sizes are estimated by field emission scanning electron microscopy (FESEM) to be in the nanometer (5–13 nm) range. Transmission electron microscopy (TEM) also supports the FESEM data. The magnetization measurement by vibration sample magnetometry of the conventionally sintered sample shows a paramagnetic nature at room temperature, a superparamagnetic behaviour at low temperature, and a ferromagnetic nature at even lower temperature. The blocking temperature is estimated to be nearly 110 K. Microwave-processed samples show a superparamagnetic nature even at room temperature. The Fe3+ cations are found at both the sites confirmed by X-ray photoelectron spectroscopy (XPS), are prepared by microwave processing, and have better magnetic properties as compared to the conventionally sintered particles.

The chemically synthesized high purity spinel NiCr2−xDyxO4 (x = 0, 0.1) samples have been characterized using magnetic and dielectric measurements in presence of high magnetic field. Crystal and magnetic structure of the samples have been determined by analyzing neutron diffraction data recorded between temperature of 6 K and 300 K. NiCr2O4 crystallizes in tetragonal phase with the space group of I41/amd whereas NiCr1.9Dy0.1O4 crystallizes in the mixed phase of cubic (space group of Fd 3 ¯ m ) and tetragonal phases at room temperature. An additional phase of DyCrO3 with orthorhombic structure has been found in the Dy doped compound. The lattice parameter a increases and the c decreases in tetragonal structure with the substitution of Dy in Cr site. Both the samples show superlattice reflection peak indicating the presence of long range AFM ordering (transverse component) below 40 K. But the saturation magnetization slightly increases after Dy doping. An anomaly observed near Curie temperature in e′ (T) of NiCr2O4 and NiCr1.9Dy0.1O4 demonstrates the contribution of coupling between ferroelectricity and ferrimagnetism in the compounds. A linear correlation between the difference in dielectric constant and the field dependent squared magnetization for both the samples has been observed. The spin–spin interactions are most likely responsible for the observed magnetodielectric (MD) effect due to the magnetodielectric hysteresis in both parent and doped samples. Interestingly the MD% is found to increase with Dy doping.

Isofield magnetization curves have been recorded and analyzed in optimally doped Ba1−xKxFe2As2 single crystal in two main crystallographic directions (H||c-axis and H||ab-planes). Near transition temperature ( T ) c , magnetization exhibits temperature dependence − M ∝ [ T a ( H ) − T ] m , where T a is the apparent transition temperature and represents onset of phase coherence of the superconducting order parameter. We have shown that T a behaves differently in two main crystallographic directions: d T a ( H ) / d H > 0 for H||ab-planes and d T ( H ) a / d H 0 for H||c-axis. In H||ab-planes we have observed T a ( H ) > T c which implies that magnetic field can probe a region above T c where phase correlation persists. We suggest that multiband character may be the possible reasons for anomalous behavior of T a . The obtained values of fitting exponents ( m ) are larger than 0.5 and increase with magnetic field.

We have investigated the structure and the electrical properties of CoFe2O4, Ni0.5Co0.5Fe2O4 and Zn0.5Co0.5Fe2O4 nanoparticles, prepared through a chemical pyrophoric reaction technique. The study of the dielectric constant reveals evidence of Rabinkin and Novikova polarisation in the system. The increased value of the dielectric constant at low frequency is attributed to the presence of interfacial and dipolar polarisation in the system. The impedance for Zn0.5Co0.5Fe2O4 nanoparticles is found to decrease with increase in temperature, indicating the presence of a temperature-dependent electrical relaxation process in the system. Nyquist plots have been fitted using parallel combinations of grain boundaries resistance and grain boundaries capacitance. The activation energy is estimated from Nyquist plots, dc and ac conductivity data using the Arrhenius relation. This is indicating that the same type of charge carrier is responsible for the relaxation and the conduction processes in the system. Ac ...

Investigations of structural and magnetic properties of polycrystalline hole doped double perovskite La 1.5 Ca 0.5 CoMnO 6 has clearly revealed the existence of structural antisite-disorder (either, Co–O–Co or Mn–O–Mn) in the system. The ordering of Co 2+ and Mn 4+ gives rise to a ferromagnetic transition around 157 K. A spin-canted antiferromagnetic transition is found in this material at T CAFM ~9 K. The effect of antisite-disorder in the double perovskite structure is most likely the prime reason for antiferromagnetic interaction. The temperature dependent inverse susceptibility exhibits Curie-Weiss like behaviour and it yields an effective paramagnetic moment of 6.49 μ B . At very low temperature (T CAFM ), it shows a strong hysteresis loop shift with large exchange bias (EB) field of H EB ~5.5 kOe and can be tuned by the cooling field. The presence of zero-field cooled spontaneous EB effect (P-type and N-type) is confirmed to be not an experimental artefact - an inherent property of this double perovskite material. A phenomenological model has been proposed to explain the exchange coupling between the ferromagnetic and canted-antiferromagnetic interfaces of antisite-disordered La 1.5 Ca 0.5 CoMnO 6 mainly on the basis of uncompensated interface spins.

Gadolinium doping effects on structural-, electronic transport and magnetic properties of Pr

The exchange bias effect at the magnetic interfaces and multi-magnetic phases strongly depends on the antisite disorder (ASD) driven spin configuration in the double perovskite systems. The percentage of ASD in double perovskites is extensively accepted as a key for designing diverse new nanospintronics with tailored functionalities. In this regards, we have investigated such ASD driven phenomena in Ca2+ doped bulk and polycrystalline La2−x Ca x CoMnO6 (0 ⩽ x ⩽ 1) series of samples. The structural and Raman studies provide evidence of an increase in the disorder due to the increment of Ca concentration in the parent compound (x = 0). The enhancement of disorder in the doped system induces various magnetic orderings, magnetic frustration and cluster glass-like behavior, which have been confirmed from AC and DC magnetic studies and neutron diffraction studies. As a result, significantly large exchange bias effects, namely zero-field cooled (spontaneous) and field-cooled (conventional) exchange bias, are found. These results reveal the tuning of ASD by doping, which plays an active role in the spin configuration at the magnetic interfaces.

Ni-Mn-Co-Sn based Heusler alloys have drawn immense attention lately due to their significant magnetocaloric (MC) and magnetoresistance (MR) properties near their first-order magneto-structural martensite transformation (MT). Here, we have studied the influence of thermal and magnetic hysteretic behaviours in the temperature and field dependent magnetization and resistivity in Ni45Mn39Co5Sn11 bulk Heusler alloy across the MT regime. This is critical since hysteresis losses could significantly compromise the MC and MR properties in these compounds in practical applications. Isothermal X-ray diffraction measurements at different temperatures reveal that the MT temperature is near room temperature in Ni45Mn39Co5Sn11 alloy. Thermodynamic analyses of isothermal field dependent magnetization data result in large isothermal magnetic entropy changes (ΔS = 17–18 J kg−1 K−1) under a field change (ΔH = 8 T) at 364 K across the MT regime. The calculated refrigeration capacity values (RC = 173–179 J kg−1) for decreasing and increasing fields are significant and independent of magnetic hysteresis across the MT regime. A large adiabatic temperature change (│ΔT│ = 10.4 K for ΔH = 8 T at 364 K) is being reported in Ni45Mn39Co5Sn11 Heusler alloy, which makes it promising for MC applications. Further, the influence of martensite-austenite phase fractions on the MC and MR properties in Ni45Mn39Co5Sn11 alloy has been studied across the MT regime using isofield and isothermal magnetic and magneto-transport measurements. A strong correlation has been established between the observed MR (−36.8%) and the transformed austenite phase fraction using both experimental data and theoretical model. The large RC, │ΔT│, MR values close to the room temperature and the role played by the thermal and magnetic hystereses on the MC and MR properties make the Ni45Mn39Co5Sn11 Heusler alloy an interesting material for technological applications in magnetic refrigeration and switching devices.

Metal oxides with spinel structure exhibit interesting electrochemical properties, arising from their unique crystal structure and presence of multiple redox centers. In this investigation, MgCr2O4 nanoparticles were synthesized by a chemical sol-gel reaction process to explore its improved aqueous supercapacitor and alkaline electrocatalyst applications. We obtain a polycrystalline sample with spherical morphology, with an average particle size of 12–20 nm. These nanoparticles of MgCr2O4 are suitable for electrochemical operations. The hollow and porous microstructure of these MgCr2O4 nanoparticles enabled efficient ionic diffusion and electrons’ movement during electrochemical measurements. In the presence of aqueous 1 M Li2SO4 electrolyte system, we observed the value of capacitance of about 17 F/g (at 0.25 A/g), an energy density of about 11 Wh/kg, and a power density of about 275 W/kg. On the other hand, in presence of aqueous 1 M NaClO4 electrolyte systems, approximately C = 21 F/g (at 0.5 A/g), E = 14 Wh/kg and P = 550 W/kg, were found. Capacitance retention of more than 84% after undergoing 1000 charge-discharge cycles was observed in both cases, indicating long term cyclic stability performance of the system. These qualities make MgCr2O4 nanoparticles a suitable electrode material for future aqueous energy storage devices. MgCr2O4 also showed promising performance as alkaline water splitting electrocatalyst. As an Oxygen Evolution Reaction (OER) catalyst, it showed an overpotential of 1.174 V, and a Tafel slope of about 349 mV/dec was recorded. As a Hydrogen Evolution Reaction (HER) electrocatalyst, an overpotential of 631 mV was observed, and a Tafel slope of about 169 mV/dec was recorded. Our analysis clearly showed that the chemically synthesized MgCr2O4 nanoparticles are very promising for aqueous supercapacitor and alkaline OER and HER bi-functional electrocatalyst applications.