arXiv subjects

Bipin Lamichhane

Publications and source records attributed to Bipin Lamichhane.

3 recordsLinked to original sources

arXiv2023

First-principles prediction of structural, magnetic properties of Cr-substituted strontium hexaferrite, and its site preference

To investigate the structural and magnetic properties of Cr-doped M-type strontium hexaferrite (SrFe$_{12}$O$_{19}$) with x = (0.0, 0.5, 1.0), we perform first-principles total-energy calculations relied on density functional theory. Based on the calculation of the substitution energy of Cr in strontium hexaferrite and formation probability analysis, we conclude that the doped Cr atoms prefer to occupy the 2a, 12k, and 4f$_{2}$ sites which is in good agreement with the experimental findings. Due to Cr$^{3+}$ ion moment, 3 {$μ_B$}, smaller than that of Fe$^{3+}$ ion, 5 {$μ_B$}, saturation magnetization (M$_{s}$) reduce rapidly as the concentration of Cr increases in strontium hexaferrite. The magnetic anisotropic field $\left(H_{a}\right)$ rises with an increasing fraction of Cr despite a significant reduction of magnetization and a slight increase of magnetocrystalline anisotropy $\left(K_{1}\right)$.The cause for the rise in magnetic anisotropy field $\left(H_{a}\right)$ with an increasing fraction of Cr is further emphasized by our formation probability study. Cr$^{3+}$ ions prefer to occupy the 2a sites at lower temperatures, but as the temperature rises, it is more likely that they will occupy the 12k site. Cr$^{3+}$ ions are more likely to occupy the 12k site than the 2a site at a specific annealing temperature (>700°C).

cond-mat.mtrl-sci↗

arXiv2022

First principle investigations of the structural, electronic, and phase stability in 2D layered ZnSb

Recently, the two dimensional (2D) materials have become a potential candidates for various technological applications in spintronics and optoelectronics. In the present study, the structural, electronic, and phase stability of 2D layered ZnSb compounds of four different phases viz. wurzite(w), tetragonal (t), hexagonal (h), and orthorhombic (o) have been tuned using the first principle calculations based on density functional theory (DFT). We invoked the Perdew-Burke-Ernzerhof (PBE) functional and the projected augmented wave (PAW) method during all the calculations. Based on our numerical results, we predicted the novel tetragonal phase as stable phase of ZnSb next to existing orthorhombic structure. We reported the pressure induced phase transition between orthorhombic to tetragonal phase at 12.48 GPa/atom. The projected density of states indicates the strong p-d hybridization between Sb-5p and Zn-3d states confirming the nature of strong covalent bonding between them. The electronic band structures suggest that t-ZnSb, w-ZnSb, and h-ZnSb are metallic in nature whereas o-ZnSb is semiconducting with narrow band gap of 0.03 eV using PBE. We predicted the possibility of extracting the two dimensional (2D) monolayer sheet in t-ZnSb and o-ZnSb according to the exfoliation energy criterion. In addition, the 2D monolayer (ML) of o-ZnSb has been predicted to be dynamically stable but that of t-ZnSb is not stable as manifested in phonon dispersion bands. Surprisingly, the semiconducting band gap nature of o-ZnSb changes from indirect and narrow to direct and sizable while going from 3D bulk to 2D ML structure. Further, we estimated the value of work functions for the surfaces of t-ZnSb and o-ZnSb as 4.61 eV and 4.04 eV respectively. Such materials can find the niche applications in next generation electronic devices utilizing 2D hetero-structures.

physics.comp-ph↗

arXiv2018

Correlation between site preference and magnetic properties of Zn-Sn-substituted strontium hexaferrite

The site preference and magnetic properties of Zn, Sn and Zn-Sn substituted M-type strontium hexaferrite (SrFe$_{12}$O$_{19}$) have been investigated using first-principles total energy calculations based on density functional theory. The site occupancy of substituted atoms were estimated by calculating the substitution energies of different configurations. The distribution of different configurations during the annealing process at high temperature was determined using the formation probabilities of configurations to calculate magnetic properties of substituted strontium hexaferrite. We found that the magnetization and magnetocrystalline anisotropy are closely related to the distributions of Zn-Sn ions on the five Fe sites. Our calculation show that in SrFe$_{11.5}$Zn$_{0.5}$O$_{19}$, Zn atoms prefer to occupy $4f_1$, $12k$, and $2a$ sites with occupation probability of 78%, 19% and 3%, respectively, while in SrFe$_{11.5}$SnO$_{19}$, Sn atoms occupy the $12k$ and $4f_2$ sites with occupation probability of 54% and 46%, respectively. We also found that in SrFe$_{11}$Zn$_{0.5}$Sn$_{0.5}$O$_{19}$, (Zn,Sn) atom pairs prefer to occupy the ($4f_1$, $4f_2$), ($4f_1$, $12k$) and ($12k$, $12k$) sites with occupation probability of 82%, 8% and 6%, respectively. Our calculation shows that the increase of magnetization and the reduction of magnetic anisotropy in Zn-Sn substituted M-type strontium hexaferrite as observed experimentally is due to the occupation of (Zn,Sn) pairs at the ($4f_1$, $4f_2$) sites.

cond-mat.mtrl-sci↗