arXiv subjects

Diptikanta Swain

Publications and source records attributed to Diptikanta Swain.

6 recordsLinked to original sources

arXiv2026

Different critical exponents on two sides of the magnetic transition in two dimensions

The possibility of different critical exponents on two sides of a magnetic transition has been theoretically predicted [PRB 13, 2222 (1976), PRL 115, 200601 (2015)] and experimentally realized [PRL 128, 015703 (2022)] in three-dimensional systems. However, the emergence of such a scenario in two dimensions is not yet established. Here, we report distinct two-dimensional (2D) critical exponents below and above the magnetic transition temperature (TC) through critical scaling analysis in a quasi-2D non-centrosymmetric, Dzyaloshinskii-Moriya interaction (DMI) active hybrid perovskite (C7H9NBr)2CuBr4. The system exhibits critical exponents of 2D Ising-type below TC and 2D XY-type above TC . In contrast, isostructural Cl and centrosymmetric Br analogs, in which the DMI effect is expected to be weaker, exhibit symmetric 2D critical behavior. These results highlight the crucial role of DMI in (C7H9NBr)2CuBr4 as a symmetry-breaking perturbation that alters the magnetic critical behavior differently above and below TC . Our study is the experimental realization of hitherto unreported asymmetric 2D critical behavior in structurally flexible and dimensionally tunable hybrid perovskites.

cond-mat.mtrl-sci↗

arXiv2026

Griffiths-like phase, spin-phonon coupling, and exchange-bias in the disordered double perovskite GdSrCoMnO$_{6}$

We report structural, magnetic, and Raman studies of the disordered double perovskite GdSrCoMnO$_{6}$~(GSCM). DC magnetization shows a ferromagnetic transition at $T_{C} \approx 153$~K. The inverse susceptibility exhibits a downturn above $T_{C}$ and is consistent with a Griffiths-like regime extending up to $T_{G} \approx 172$~K. Raman measurements show a deviation of the phonon frequency from the anharmonic background near the magnetic-ordering region, consistent with spin-phonon coupling. AC susceptibility indicates slow magnetic dynamics below the freezing temperature $T_{f} \approx 30$~K. These results point to magnetic inhomogeneity generated by the random distribution of mixed-valence Co and Mn ions and by the resulting competition between ferromagnetic and antiferromagnetic interactions. In the low-temperature regime, an exchange-bias effect is observed up to 50~K, with an exchange-bias magnitude $|H_{EB}| = 379$~Oe at 5~K. Structural disorder therefore plays an important role in the magnetic correlations, spin dynamics, and spin-lattice response of GSCM.

cond-mat.mtrl-sci↗

arXiv2022

Magnetic structure and properties of a vanthoffite mineral Na6Mn(SO4)4

A detailed analysis of the magnetic properties of a vanthoffite type mineral Na6Mn(SO4)4 basedon dc magnetization, low temperature neutron powder diffraction and theoretical calculations is reported. The mineral crystallizes in a monoclinic system with space group P21/c, where MnO6 octahedra are linked via SO4 tetrahedra. This gives rise to super-exchange interaction between two Mn2+ ions mediated by two nonmagnetic bridging anions and leads to an antiferromagnetic ordering below 3 K. The magnetic structure derived from neutron powder diffraction at 1.7 K depicts an antiferromagnetic spin arrangement in the bc plane of the crystal. The magnetic properties are modelled by numerical calculations using exact diagonalization technique, which fits the experimental results and provides antiferromagnetic ground state of Na6Mn(SO4)4.

cond-mat.mtrl-sci↗

arXiv2019

Potassium L-ascorbate monohydrate: a new metal-organic nonlinear optical crystal

Large size single crystals of potassium L-ascorbate monohydrate (KLAM), (KC6H7O6.H2O) are grown using solution growth technique by lowering the temperature at the rate of 0.24 °C/h, where water was used as solvent. The structure of KLAM was solved by single crystal XRD. KLAM crystallizes in non-centrosymmetric, monoclinic, P21 space group with lattice parameters a = 7.030(5) Å, b = 8.811(5) Å, c = 7.638(5) Å and \b{eta} = 114.891(5)°. The crystal grows with bulky morphology in all three directions having (100), (-100), (-110), (0-1-1), (0-11), (001) and (00-1) prominent faces. TGA and DSC measurements show that KLAM is stable up to 80 °C. The crystal shows good optical transparency with a lower cut off as low as 297 nm. Second harmonic conversion efficiency measured on powder sample is 3.5 times that of potassium dihydrogen phosphate (KDP). Phase matching (PM) is observed on a plate of the KLAM. Noncollinear phase matching rings are also observed near the PM directions which help to identify the locus of PM directions. Presence of noncollinear SHG rings up to third order suggests large birefringence and nonlinear optical coefficients. Laser damage threshold value of the crystal is found to be 3.07 GW/cm2, at 1064 nm in 100 direction.

cond-mat.mtrl-sci↗

arXiv2014

Effect of pressure on octahedral distortions in RCrO3 (R = Lu, Tb, Gd, Eu, Sm): The role of R-ion size and its implications

The effect of rare-earth ion size on the octahedral distortions in rare-earth chromites (RCrO3, R = Lu, Tb, Gd, Eu, Sm) crystallizing in the orthorhombic structure has been studied using Raman scattering and synchrotron powder x-ray diffraction up to 20 GPa. From our studies on RCrO3 we found that the octahedral tilts (distortions) increase with pressure. This is contrary to the earlier report which suggests that in LaCrO3, the distortions decrease with pressure leading to a more ordered phase at high pressure. Here we observe that the rate of increase in distortion decreases with the increase in R-ion radii. This occurs due to the reduction in the compression of RO12 polyhedra with a corresponding increase in the compression of the CrO6 octahedra with increasing R-ion radii. From the Raman studies, we predict a critical R-ion radii, above which we expect the distortions in RCrO3 to reduce with increasing pressure leading to what is observed in the case of LaCrO3. These Raman results are consistent with our pressure dependent structural studies on RCrO3 (R = Gd, Eu, Sm). Also, our results suggest that the pressure dependence of Néel temperature, TNCr, (where the Cr3+ spin orders) in RCrO3 is mostly affected by the compressions of Cr-O bonds rather than the alteration of octahedral tilts.

cond-mat.mtrl-sci↗

arXiv2011

Griffiths phase-like behaviour and spin-phonon coupling in double perovskite Tb$_{2}$NiMnO$_{6}$

The Griffiths phase-like features and the spin-phonon coupling effects observed in Tb$_2$NiMnO$_6$ are reported. The double perovskite compound crystallizes in monoclinic $P2_1/n$ space group and exhibits a magnetic phase transition at $T_c \sim$ 111 K as an abrupt change in magnetization. A negative deviation from ideal Curie-Weiss law exhibited by 1/$χ(T)$ curves and less-than-unity susceptibility exponents from the power-law analysis of inverse susceptibility are reminiscent of Griffiths phase-like features. Arrott plots derived from magnetization isotherms support the inhomogeneous nature of magnetism in this material. The observed effects originate from antiferromagnetic interactions which arise from inherent disorder in the system. Raman scattering experiments display no magnetic-order-induced phonon renormalization below $T_c$ in Tb$_2$NiMnO$_6$ which is different from the results observed in other double perovskites and is correlated to the smaller size of the rare earth. The temperature evolution of full-width-at-half-maximum for the {\it stretching} mode at 645 cm$^{-1}$ presents an anomaly which coincides with the magnetic transition temperature and signals a close connection between magnetism and lattice in this material.

cond-mat.str-el↗