Jagrati Sahariya

Investigation of orbital magnetization in inverse spinel cobalt ferrite using magnetic Compton scattering

We present the spin momentum densities of CoFe2O4 measured at 8 and 300 K using magnetic Compton scattering. The magnetic Compton profiles were decomposed into component profiles of constituents namely Fe and Co, to determine their role in the formation of total spin moment. It is seen that the major contribution (about 80%) in the spin moment is from Co, whereas the itinerant electrons show a small reverse polarization. Moreover, it is clearly visualized that the spin moment at Co reduces from 2.55 → 2.35 μB/f.u. while going from 8 → 300 K. The magnetic Compton profiles, when compared with the magnetization data, show about 17% contribution of orbital moment to the total magnetic moment at both temperatures. The origin of the orbital moment is explained on the basis of rotation of hole on t2g orbital of Co+2 ion.

Electronic properties of RDX and HMX: Compton scattering experiment and first-principles calculation.

The first-ever electron momentum density (EMD) measurements of explosive materials, namely, RDX (1,3,5-trinitro-1,3,5-triazacyclohexane, (CH2-N-NO2)3) and HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane, (CH2-N-NO2)4), have been reported using a 740 GBq (137)Cs Compton spectrometer. Experimental Compton profiles (CPs) are compared with the EMDs derived from linear combination of atomic orbitals with density functional theory. It is found that the CPs deduced from generalized gradient approximation (GGA) with Wu-Cohen exchange energies give a better agreement with the corresponding experimental profiles than those from local density approximation and other schemes of GGA. Further, Mulliken population, energy bands, partial and total density of states, and band gap have also been reported using GGA calculations. Present ground state calculations unambiguously show large band gap semiconductor nature of both RDX and HMX. A similar type of bonding in these materials is uniquely established using Compton data and density of states. It is also outstandingly consistent with the Mulliken population, which predicts almost equal amount of charge transfer (0.84 and 0.83 e(-)) from H1 + H2 + N2 to C1 + N1 + O1 + O2 in both the explosives.

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.

Electronic properties of WC nano-compound: Compton spectroscopy and band structure calculations

We present the electronic properties of tungsten carbide (WC) nano-compound using the Compton scattering technique. We have measured the Compton profile (CP) of nano-powder using our 137Cs Compton spectrometer. To determine the theoretical CPs of WC nano-compound, we have employed linear combination of atomic orbitals (LCAO) with Hartree-Fock and density functional theory. Although all the LCAO-based calculations show similar agreement with the experiment, the second-order generalised gradient approximation gives a marginally better agreement with the measured CP data. Layered structures and slight over-lapping in energy bands show a small role of exchange and correlation potentials in case of WC nano-compound, which is in contrast to bulk WC.

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.

A magnetic Compton scattering study of Ga rich Co–Ni–Ga ferromagnetic shape memory alloys

The temperature dependent spin momentum densities of Co(1.8)NiGa(1.2) and Co(2)Ni(0.76)Ga(1.24) alloys have been measured using the magnetic Compton scattering technique. The individual contributions of constituents in the formation of the total spin moment are also calculated using Compton line shape analysis. The magnetic Compton data when compared with the magnetization data obtained using a vibrating sample magnetometer show a negligible orbital contribution. The spin moments deduced from the experimental Compton data are compared with the theoretical results obtained from the full potential linearized augmented plane wave method and are found to be in good agreement. The origin of the magnetism in both alloys is also described in terms of the e(g) and t(2g) contributions of Ni and Co.

Compton scattering studies and electronic properties of cerium

Experimental electron momentum density of γ-Ce was measured at an intermediate resolution (0.38 a.u.) using 20 Ci 137Cs Compton spectrometer. The experiment was compared with the first ever theoretical Compton profiles computed using spin polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) method within atomic sphere approximation; and linear combination of atomic orbitals (LCAO) within generalised gradient approximation (GGA) and recently developed second order generalised gradient approximation (SOGGA). It was seen that the Compton profile derived from LCAO with GGA and SOGGA schemes gave a reasonable agreement with the experimental Compton line shape. Theoretical anisotropies in Compton profiles derived along [100], [110] and [111] directions were explained in terms of degenerate states in the energy bands.

Electronic Structure and Magnetic Properties of Ni2MnSn Heusler Alloy

The spin dependent momentum densities in Ni 2 MnSn Heusler alloy have been measured at 10 and 300 K using magnetic Compton scattering. For these measurements, we have used 182.79 keV circularly polarized synchrotron radiation at SPring8, Japan. Spin dependent electron momentum densities are analyzed in terms of Mn 3d, Ni 3d and itinerant electrons to calculate their role in formation of net spin moment. Magnetic moments at different sites of constituent atoms have also been compared with the present full potential linearised augmented plane wave calculations and other available data.