Srivathsava Surabhi

Controlled morphology of MWCNTs driven by polymer-grafted nanoparticles for enhanced microwave absorption

The development of a lightweight electromagnetic (EM) wave absorber with a wider bandwidth and reflection loss at a low loading is of great interest for applications ranging from conventional electronic devices to specific devices or instruments of the military and aerospace. Although nano-filler (i.e. carbon nanotubes, magnetic nanoparticles, etc.) based polymer nanocomposites (PNCs) have shown great promise in this area of research, typically poor control of their surface modification and dispersion has prevented further development of these materials for application in EM wave absorbers. Here, we introduce and demonstrate a simple and robust platform based on polymer-grafted nanoparticles to facilitate a controlled morphology of nano-fillers, providing a route for strategically designing nanostructured EM wave absorbers with a percolated MWCNT network as well as a controlled NP arrangement. At equal loadings of nano-fillers (1 wt% of MWCNTs), much deeper reflection loss (RL = −26.9 dB at 5.4 GHz) and a wider bandwidth (4.9 GHz for RL < −10 dB) are observed compared to the conventional PNCs. We show that polymer-grafted nanoparticles serve as a matrix for unfunctionalized CNTs and show a much enhanced dispersion of CNTs, providing a novel opportunity for the multi-functional PNCs by combining functions arising from the controlled dispersion of heterogeneous materials (i.e. inorganic nanoparticles and CNTs) in a new type of CNT/NP/polymer nanostructure.

Observation of transverse spin Nernst magnetoresistance induced by thermal spin current in ferromagnet/non-magnet bilayers

Electric generation of spin current via spin Hall effect is of great interest as it allows an efficient manipulation of magnetization in spintronic devices. Theoretically, pure spin current can be also created by a temperature gradient, which is known as spin Nernst effect. Here, we report spin Nernst effect-induced transverse magnetoresistance in ferromagnet/non-magnetic heavy metal bilayers. We observe that the magnitude of transverse magnetoresistance in the bilayers is significantly modified by heavy metal and its thickness. This strong dependence of transverse magnetoresistance on heavy metal evidences the generation of thermally induced pure spin current in heavy metal. Our analysis shows that spin Nernst angles of W and Pt have the opposite sign to their spin Hall angles. Moreover, our estimate implies that the magnitude of spin Nernst angle would be comparable to that of spin Hall angle, suggesting an efficient generation of spin current by the spin Nernst effect.Pure spin current generated thermally in nonmagnetic materials known as spin Nernst effect has not been demonstrated experimentally. Here, the authors report the observation of spin Nernst effect by studying the thermally-induced transverse magnetoresistance in ferromagnet/non-magnet heavy metal bilayers

Configurable plasmonic substrates from heat-driven imprint-transferred Ag nanopatterns for enhanced photoluminescence

Despite substantial progress in metal nanopatterning, fabricating ultra-large-area plasmonic substrates with well-defined and well-controlled nanopatterned arrays remains a major technological challenge. Here, we describe a novel facile technology (i.e., configurable metal nanoimprint transfer based on geometric reconfiguration during thermal annealing) to fabricate ultra-large-area tunable plasmonic substrates. The simultaneous transfer and imprint of the metal layers from the patterned mold surface results in metal nanopatterns embedded in a partially cured photoresist, the shape of which can be modified systematically by optimized heat treatments. The plasmonic properties of the metal nanopattern array could be precisely tuned through the heat-driven shape reconfiguration of metal patterns. The shape transformation leads to sharp and blue-shifted extinction spectra and unusual strong excitation of the transverse mode of metal nanopatterns. Coarse tuning of the plasmon resonance wavelength is achieved by varying the diameter of the nanopatterned features, and fine tuning is accomplished by reconfiguring the geometry of the nanopatterned features via thermal annealing. Only three master patterns are required to cover the wavelength range 535–837 nm. By applying the plasmon substrates to photoluminescence (PL) measurements, an enhancement in the green photoluminescence (PL) intensity of a factor more than 9.4 is achieved due to the improved matching between the wavelengths for PL emission and plasmon resonance. The fabrication strategy described here enables us to achieve various plasmonic properties using a single master pattern, which provides both tailorable plasmonic properties and remarkable process flexibility.

Publisher Correction: Observation of transverse spin Nernst magnetoresistance induced by thermal spin current in ferromagnet/non-magnet bilayers

The original version of this Article contained an error in ref. 27, which was incorrectly given with the wrong journal name as:Meyer, S. et al. Observation of the spin Nernst effect. Nat. Phys. 16, 977–981 (2017).The correct form of ref. 27 is:Meyer, S. et al. Observation of the spin Nernst effect. Nat. Mater. 16, 977–981 (2017).This has now been corrected in the PDF and HTML versions of the Article.

Study on Proton Radiation Resistance of 410 Martensitic Stainless Steels under 3 MeV Proton Irradiation

In this study, we report on an investigation of proton radiation resistance of 410 martensitic stainless steels under 3 MeV proton with the doses ranging from 1.0 × 10 15 to 1.0 × 10 17 p/cm² at the temperature 623 K. Vibrating sample magnetometer (VSM) and X-ray diffractometer (XRD) were used to study the variation of magnetic properties and structural damages by virtue of proton irradiation, respectively. VSM and XRD analysis revealed that the 410 martensitic stainless steels showed proton radiation resistance up to 10 17 p/cm². Proton energy degradation and flux attenuations in 410 stainless steels as a function of penetration depth were calculated by using Stopping and Range of Ions in Matter (SRIM) code. It suggested that the 410 stainless steels have the radiation resistance up to 5.2 × 10 −3 dpa which corresponds to neutron irradiation of 3.5 × 10 18 n/cm². These results could be used to predict the maintenance period of SUS410 stainless steels in fission power plants.

Precise Determination of the Temperature Gradients in Laser-irradiated Ultrathin Magnetic Layers for the Analysis of Thermal Spin Current

We investigated the temperature distribution induced by laser irradiation of ultrathin magnetic films by applying a finite element method (FEM) to the finite difference time domain (FDTD) representation for the analysis of thermal induced spin currents. The dependency of the thermal gradient (∇T) of ultrathin magnetic films on material parameters, including the reflectivity and absorption coefficient were evaluated by examining optical effects, which indicates that reflectance (R) and the apparent absorption coefficient (α*) play important roles in the calculation of ∇T for ultrathin layers. The experimental and calculated values of R and α* for the ultrathin magnetic layers irradiated by laser-driven heat sources estimated using the combined FDTD and FEM method are in good agreement for the amorphous CoFeB and crystalline Co layers of thicknesses ranging from 3~20 nm. Our results demonstrate that the optical parameters are crucial for the estimation of the temperature gradient induced by laser illumination for the study of thermally generated spin currents and related phenomena.