Influence Of Annealing Effects Research Articles

Terahertz emission from Y<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub>(YIG)/Pt heterostructures via ultrafast spin Seebeck effect

Recently, ferromagnetic/non-magnetic heterostructures have been widely studied for the generation of terahertz (THz) emitter based on spin-to-charge conversion. Actually, thermal spintronics effectively combines thermal transport with magnetism for creating and detecting non-equilibrium spin transport. A spin current or voltage can be induced by a temperature bias applied to a ferromagnetic material, which is called spin Seebeck effect (SSE). In this paper, we present a SSE based THz emission by using the heterostructures made of insulating ferrimagnet yttrium iron garnet (Y<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub>, YIG) and platinum (Pt) with large spin orbit coupling. Upon exciting the Pt layer with a femtosecond laser pulse, a spin Seebeck current arises, applying a temperature gradient to the interface. Based on the inverse spin Hall effect, the spin Seebeck current is converted into a transient charge current and then yields the THz transients, which are detected by electrooptic sampling through using a ZnTe crystal at room temperature. The polarity of the THz pulses is flipped by 180° when the direction of the external magnetic field is reversed. By changing the direction of the pump beam excitation geometry to vary the sign of the temperature gradient at the YIG/Pt interface, the polarity of the THz signal is reversed. Fast Fourier transformation of the THz signals yields the amplitude spectra centered near 0.6 THz with a bandwidth in a range of 0.1–2.5 THz. We systematically investigate the influence of annealing effect on the THz emission from different YIG/Pt heterostructures. It can be found that the THz radiation is achieved to increase ten times in the YIG/Pt grown on a Gd<sub>3</sub>Ga<sub>5</sub>O<sub>12 </sub>(GGG) substrate through high-temperature annealing. The mechanism of annealing effect can be the increase of the spin mixing conductance of the interface between YIG and Pt. Finally, we investigate the pump fluence dependent THz peak-to-peak values for the annealed YIG/Pt grown on the Si substrate. Due to the spin accumulation effect at the interface of the YIG/Pt heterostructure, the THz radiation intensity gradually becomes saturated with the increase of pump fluence. Our results conclude that annealing optimization is of importance for increasing the THz amplitude, and open a new avenue to the future applications of spintronic THz emitters based on ultrafast SSE.

Annealing effect on terahertz emission enhancement from ferromagnetic heterostructures

We systematically investigate the influence of annealing effect on terahertz (THz) generation from CoFeB/heavy metal heterostructures driven by femtosecond laser pulses. The THz yield is achieved to increase triply in W/CoFeB through annealing effect, and doubly in Pt/CoFeB. The annealing effect originates from both the decrease of synthetic effect of THz absorption and the increase of hot electron mean free path induced by crystallization, with the latter being dominant, which is experimentally corroborated by THz transmission measurement of time-domain spectrum and four-probe resistivity <i>t</i>. Our observations not only deepen understand the spintronic THz radiation mechanism but also provide a novel platform for high speed spintronic opto-electronic devices.

Influence of annealing effects on polyaniline for good microstructural modification

H2SO4 doped polyaniline (PANI) has synthesized by chemical oxidation method. The prepared Polyaniline were annealed at 150°C, 200°C and 250°C for 30min in vacuum. Crystal size, percentage of crystallinity, total percentage of crystallinity properties of untreated and heat treated PANI samples were studied by using X-ray diffraction pattern. The molecular structure of untreated and heat treated samples were examined by using Fourier transform infrared spectrophotometer. UV study shows π–π* transition of untreated and heat treated of polyaniline were found at 328 and 636nm. The peak at 636nm reveals the extension of conjugated polymer. Thermal properties of untreated and heat treated PANI sample measured by using thermo gravimetric analysis and differential scanning calorimetric spectroscopy.

Effects of post-heat treatment on the characteristics of chalcopyrite CuInSe 2 film deposited by successive ionic layer absorption and reaction method

The influence of annealing effects in CuInSe 2 ternary films prepared by successive ionic layer absorption and reaction method has been investigated. The films have firstly been deposited on glass substrates at room temperature and then heat-treated under Ar atmosphere at various annealing temperatures. CuInSe 2 films were characterized using X-ray diffraction (XRD), scanning electron microscopy, X-ray photoelectron spectra, optical absorption spectrum and Hall system. XRD results showed that the proper post-annealing process can lead to a complete formation of chalcopyrite structure CuInSe 2 with high degree of preferred orientation towards (112) reflection. After annealing process, the composition of annealed films was close to the standard stoichiometry and O, Cl impurities decreased. The direct band gap increased from 0.94 to 0.98 eV and resistivity showed a big decrease with the increase of annealing temperature.

Influence of annealing on the magnetic entropy changes in Fe 81.6Mo 4Zr 3.3Nb 3.3B 6.8Cu 1 amorphous ribbons

We have prepared amorphous Fe 81.6Mo 4Zr 3.3Nb 3.3B 6.8Cu 1 ribbon by melt-spinning. Differential thermal analysis (DTA) is used to determine the crystallization temperature of the as-quenched ribbon. As-quenched ribbons were annealed at 300 and 400 °C. After thermal treatment, an elevated magnetic entropy change (∣Δ S M∣) is observed. The influence of annealing effects on the ∣Δ S M∣ and the potential application of annealed amorphous ribbons as a working material for magnetic refrigerants have been discussed.

Growth, spectra and influence of annealing effect on laser properties of Nd:YVO 4 crystal

Nd:YVO 4 single crystal has been grown by the Czochralski method. The effective segregation coefficients k eff of Nd, Y and V elements have been measured for crystals with different neodymium-doped concentrations. The absorption and fluorescence spectra of Nd:YVO 4 crystal have been measured. The lasers at 1.06 μm have been demonstrated when the crystal samples of annealed and non-annealed Nd:YVO 4 are pumped by laser diode (LD). The influence of annealing effect on laser properties is discussed.

Study on the influence of annealing effects in GaN VPE

The effects of annealing that occur during VPE growth of GaN were investigated. GaN powder (and epilayers) samples were annealed under Ar, N 2, H 2, NH 3, HCl + N 2 and HCl + H 2 (N 2, H 2 and HCl + N 2) for a range of experimental conditions of interest for preparing electroluminescent devices. Good surface appearance Zn doped epilayers were also used N 2 in order to investigate surface morphology changes due to thermal decomposition. It was found that GaN reacts with H 2, remains stable under NH 3, and the effects of thermal decomposition are somewhat enhanced with HCl. The epilayer's behaviour under thermal decomposition and HCl are interpreted by the greater stability of the (0001) crystal plane, which accounts for the improvement of the surface quality under special growth conditions. Significant observations are reported concerning GaN decomposition in different ambients.