Alpa Dashora

Temperature dependent spin momentum densities in Ni-Mn-In alloys.

The spin-dependent electron momentum densities in Ni(2)MnIn and Ni(2)Mn(1.4)In(0.6) shape memory alloy using magnetic Compton scattering with 182.2 keV circularly polarized synchrotron radiation are reported. The magnetic Compton profiles were measured at different temperatures ranging between 10 and 300 K. The profiles have been analyzed mainly in terms of Mn 3d electrons to determine their role in the formation of the total spin moment. We have also computed the spin polarized energy bands, partial and total density of states, Fermi surfaces and spin moments using full potential linearized augmented plane wave and spin polarized relativistic Korringa-Kohn-Rostoker methods. The total spin moments obtained from our magnetic Compton profile data are explained using both the band structure models. The present Compton scattering investigations are also compared with magnetization measurements.

Reversal of orbital magnetic moment on substitution of Bi in multiferroic Co2MnO4: A magnetic Compton scattering study

Temperature and field dependent magnetic Compton profiles of BixCo2−xMnO4 (x=0 and 0.3) multiferroics are reported. The magnetic Compton profiles and total spin moments are interpreted in terms of Mn/Co-3d contribution. Mn spin moments are found to be dominating in total magnetization whereas a small contribution of Co spin moment couples antiferromagnetically with that from Mn sites. The magnetic Compton data when compared with magnetization data, interestingly, show a reverse trend of orbital magnetic moments which are explained in terms of exchange interaction between the ions at different sites via O2− ions.

Feasibility of magnetic Compton scattering in measurement of small spin moments: A study on LaFe1−xNixO3 (x = 0.4 and 0.5)

Remarkable applicability of magnetic Compton scattering (MCS) in deducing site specific small spin moments like those in LaFe1−xNixO3 (x = 0.4 and 0.5) is established. The MCS measurements revealed that Fe site gives a dominant contribution (although small) to total magnetic moment, while the contribution of Ni spin moment is found to be antiparallel to that of Fe moment. Present work, which instigates insignificant role of orbital moment and diffused components in the formation of total magnetic moment, triggers era of applications of MCS in ferrimagnetic compounds with small magnetic moments.

Enhancement of ferromagnetism in Ni excess Cu1−xNixMnSb half Heusler alloys

Spin momentum densities of Cu1−xNixMnSb (for x = 0.17 and 0.22), derived from experimental magnetic Compton profiles (MCPs), show an increase in magnetic moment while going from x = 0.17 → 0.22, which is attributed to Mn 3d states. MCPs along with magnetization data suggest a negligible contribution of orbital moment. The MCPs and spin moments at Mn 3d states computed using the spin polarized relativistic Korringa-Kohn-Rostoker technique are in good agreement with the experimental data. An unusual increase in magnetic moment (2.77 ± 0.03 μB/f.u. for x = 0.17 to 3.94 ± 0.03 μB/f.u. for x = 0.22) is due to significant rise in local magnetic moment on Mn site. For x = 0.22 (0.17), presence of antiferromagnetic phase is observed to be 2 (31)%.

On the role of Al doping in La0.7Ca0.3MnO3: A magnetic Compton scattering study

Spin and orbital magnetic moments in hole doped manganite La0.7Ca0.3Mn1−xAlxO3 (x = 0, 0.02, and 0.06) have been scrutinized using experimental spin momentum densities. An analysis of magnetic Compton profiles shows that the spin moment of Mn 3d has a major contribution towards the total spin moment and its contribution decreases as we increase the concentration of Al. The present experiment along with magnetization data predict orbital moment of −0.29 ± 0.03 μB/f.u. in the parent compound (x = 0), which almost disappears on substitution of Al. The results are explained on the basis of imbalance in Mn3+ and Mn4+ charge ratio in these compounds.

Study of spin and orbital magnetization in Dy- and Gd-doped Co ferrite using magnetic Compton scattering

Temperature dependent experimental magnetic Compton profiles (MCPs) of inverse spinel CoFe2−xRExO4 (x = 0.05; RE = Dy, Gd) have been decomposed into constituent profiles to determine site-specific spin moments. A comparison of MCPs of doped and undoped CoFe2O4 shows a decrease in spin moment on 5% doping of Dy and Gd. Reduction in spin moment is explained on the basis of migration of Co2+ ions from octahedral to tetrahedral sites, which is also supported by photoelectron spectroscopy measurements. The orbital moments deduced from combination of spin momentum density and magnetization data are found to be almost similar in doped ferrites.

Evaluation of orbital moment in Ni-Zn ferrites: A magnetic Compton scattering study

Temperature dependent magnetic Compton profiles of Ni1−xZnxFe2O4 (x = 0.0, 0.1, 0.2) ferrites have been decomposed into component profiles to determine the site-specific magnetic moments. For a quantitative evaluation of orbital moment, the spin momentum density data have been combined with magnetization data. Interestingly, the orbital magnetic moment decreases from 0.25 ± 0.03 μB/f.u. (for x = 0.0) to 0.09 ± 0.03 μB/f.u. (for x = 0.2) which is in contrast to spin moment. A decrease in ratio of orbital to spin moments in Ni rich ferrites is explained on the basis of spin-orbit coupling and crystal field interaction.

Compton profiles and electronic structure of HgBr2 and HgI2

In this paper, we present the first-ever experimental Compton line shapes of HgBr(2) and HgI(2) using (137)Cs Compton spectrometer. To compare our experimental momentum densities, we have computed the Compton profiles using Hartree-Fock and density functional theory within linear combination of atomic orbitals. We have also computed the energy bands and density of states using the linear combination of atomic orbitals and full potential linearized augmented plane wave method. On the basis of equal-valence-electron-density profiles, it is seen that HgI(2) is more covalent than HgBr(2) which is in agreement with the valence charge densities. The experimental isotropic profiles are found to be relatively in better agreement with the Hartree-Fock data. We have also discussed the photoluminescence and detection properties of both the halides.

Use of chalcopyrite semiconductors CuXSe2 (X=Al, Ga and In) in solar cells: a theoretical study

The energy of sunlight falling on surface of the earth can be directly converted into electricity by means of the solar cells. Among the various materials used for photovoltaics, the chalcopyrite compounds CuXSe2 (X=Al, Ga, In) are very promising as semiconductors and have received much attention in the recent years. To check the applicability of these materials in solar cells, we have computed the energy bands, density of states, optical dielectric tensors, reflectivity, refraction and absorption coefficients using the full potential linearized augmented plane wave method. It is seen that the energy bandgap reduces from X=Al→In. The dielectric property of these materials is discussed in terms of interband transitions. The absorption coefficients of these materials in the region of solar radiation (0–5 eV energy) are discussed to explore their use in the fabrication of solar cells.

Temperature and field dependent magnetic Compton scattering study of Heusler alloy Co2MnSi

Temperature and field dependent spin polarized electron momentum distributions in ternary Heusler compound Co2MnSi have been measured using the magnetic Compton spectrometer at SPring-8, Japan. The experimental magnetic Compton profile at 10 K reconciles well with the theoretical profile computed using the spin polarized relativistic (SPR) Korringa–Kohn–Rostoker (KKR) method. The temperature and field dependent experimental magnetic profiles have been mainly analyzed to check the role of Mn 3d electrons in the formation of magnetic moments in Co2MnSi. The diffuse contribution from conduction electrons is antiferromagnetically coupled to the spin moment arising from 3d electrons of Co and Mn. The spin moments calculated using SPR-KKR calculations are in good agreement with the present measurements.