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Here, we report the temperature dependent Raman spectroscopic studies on orthorhombically distorted perovskite YCrO3 over a temperature range of 20–300 K. Temperature dependence of DC-magnetization measurements under field cooled and zero field cooled protocols confirmed a Néel transition at TN ∼ 142 K. Magnetization isotherms recorded at 125 K show a clear loop opening without any magnetization saturation up to 20 kOe, indicating a coexistence of antiferromagnetic (AFM) and weak ferromagnetic (WFM) phases. Estimation of exchange constants using mean-field approximation further confirm the presence of a complex magnetic phase below TN. Temperature evolution of Raman line-shape parameters of the selected modes (associated with the octahedral rotation and A(Y)-shift in the unit-cell) reveal an anomalous phonon shift near TN. An additional phonon anomaly was identified at T* ∼ 60 K, which could possibly be attributed to the change in the spin dynamics. Moreover, the positive and negative shifts in Raman frequencies between TN and T* suggest competing WFM and AFM interactions. A close match between the phonon frequency of B3g (3)-octahedral rotation mode with the square of sublattice magnetization between TN and T* is indicative of the presence of spin-phonon coupling in multiferroic YCrO3.

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We investigate the temperature dependent (83 K≤T≤523 K) frequency shift of 2Ag1 and 1Eg2 phonon modes in the three dimensional topological insulator Bi2Se3, using Raman spectroscopy. The high quality single crystals of Bi2Se3 were grown using a modified Bridgman technique and characterized by Laue diffraction and high resolution transmission electron microscopy. A significant broadening in the line shape and red-shift in the frequencies were observed with increase in temperature. Polarized Raman scattering measurement shows a strong polarization effect of Ag1 and Ag2 phonon modes which confirms the good quality single crystals of Bi2Se3. Temperature co-efficient for A1g1, Eg2, and A1g2 modes was estimated to be −1.44 × 10−2, −1.94 × 10−2, and −1.95 × 10−2 cm−1∕K, respectively. Our results shed light on anharmonic properties of Bi2Se3.

The time decay of the thermoremanent magnetization(TRM) of the Fe 80−x Ni x Cr 20 (14 ≤ x ≤ 30) alloys has been measured for four different magnetic phases within the fcc γ-phase using a SQUID magnetometer. In the spin-glass phase(SG)(X=19) very distinct ageing effects are observed where M(t) can be described as M (t) = M 0 (t/t w ) −γ exp[−(t/τ ) 1−n ] for the entire time domain. In the reentrant spin-glass(RSG)(X= 23 and 26), M(t) can be better represented by the stretched exponential with an addition of a constant term which can be well explained by the Gabay-Toulouse(GT) model.We have also measured the linear and non-linear ac susceptibilities for the sample X=23 and confirmed the presence of the ferromagnetic(FM) ordering down to the lowest temperature. In the RSG(X=23), the TRM shows a minimum near T c and a local maximum just above T c . In the FM phase (X=30) the popular prediction of the power law decay of the TRM is observed. The latter is indistinguishable from the stretched exponential in the antiferromagnetic(AF) phase (X=14).

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Bulk micromachining in Si (110) wafer is an essential process for fabricating vertical microstructures by wet chemical etching. We compared the anisotropic etching properties of potassium hydroxide (KOH), tetra-methyl ammonium hydroxide (TMAH) and ethylene di-amine pyro-catechol (EDP) solutions. A series of etching experiments have been carried out using different etchant concentration and temperatures. Etching at elevated temperatures was found to improve the surface quality as well as shorten the etching time in all the etchants. At 120°C, we get a smooth surface (Ra = 21.2 nm) with an etching rate 12.2 lm/min in 40wt% KOH solution. At 125°C, EDP solution (88wt%) was found to produce smoothest surface (Ra = 9.4 nm) with an etch rate of 1.8 lm/min. In TMAH solution (25wt%), the best surface roughness was found to be 35.6 nm (Ra) at 90°C with an etch rate of 1.18 lm/min. The activation energy and preexponential factor in Arrhenius relation are also estimated from the corresponding etch rate data.