Aparna Chakrabarti

Designing shape-memory Heusler alloys from first-principles

The phase diagrams of magnetic shape-memory Heusler alloys, in particular, ternary Ni-Mn-Z and quarternary (Pt, Ni)-Mn-Z alloys with Z = Ga, Sn, have been addressed by density functional theory and Monte Carlo simulations. Finite temperature free energy calculations show that the phonon contribution stabilizes the high-temperature austenite structure while at low temperatures magnetism and the band Jahn-Teller effect favor the modulated monoclinic 14M or the nonmodulated tetragonal structure. The substitution of Ni by Pt leads to a series of magnetic shape-memory alloys with very similar properties to Ni-Mn-Ga but with a maximal eigenstrain of 14%.

PROPERTIES AND IDENTIFICATION OF OXYGEN SITES AT THE V2O5(010) SURFACE : THEORETICAL CLUSTER STUDIES AND PHOTOEMISSION EXPERIMENTS

Density functional theory cluster studies and angular resolved photoemission (ARUPS) measurements were performed to examine properties of differently coordinated surface oxygens at the V 2O5(010) surface. Calculations on embedded clusters as large as V16O49H18 confirm the ionic character of the oxide. The computed width of the O 2sp dominated valence band region of V2O5 and the work function value of V2O5 (010) are in good agreement with the present photoemission data for freshly cleaved V2O5(010) samples. Cluster derived total and partial densities of states (DOS, PDOS) can be used to identify differently coordinated surface oxygens. The PDOS referring to terminal (vanadyl) oxygens is localized near the center of the valence band whereas the PDOS’s of the different bridging oxygens yield a broad distribution covering the full energy range of the valence bands. The shape of the experimental ARUPS curves for V2O5(010) is well reproduced by the cluster DOS. Thus, the most prominent central peak in the experimental spectrum can be assigned to emission from terminal oxygen while the peripheral peaks at the top and bottom of the valence energy region are characterized as mixtures of vanadium with bridging oxygen induced contributions. This interpretation forms a basis to get insight into microscopic features at the real V 2O5(010) surface such as imperfections and adsorbate binding. The present study suggests that the different O 2sp derived peaks observed in the photoemission experiment may be taken as monitors of the differently coordinated oxygens at the oxide surface and can be used to study details of catalytic surface reactions in which these oxygens participate. q 1999 Elsevier Science B.V. All rights reserved.

Theoretical prediction of shape memory behavior and ferrimagnetism in Mn2NiIn

Using density functional theory, we show that in Mn2NiIn a phase transition from cubic to tetragonal structure results in a lowering of the total energy, indicating occurrence of martensitic phase transition. The structural phase transition is nearly volume conserving, which is a characteristic of a shape memory alloy. The magnetic ground state is ferrimagnetic with antiparallel Mn spin moments and the total spin magnetization is 0.51μB in the martensitic phase. Thus, we predict that Mn2NiIn would behave like a magnetic shape memory alloy. The electronic structure and magnetic properties are explained by the spin polarized density of states.

Martensitic transition, ferrimagnetism and Fermi surface nesting in Mn2NiGa

The electronic structure of Mn2NiGa has been studied using density functional theory and photoemission spectroscopy. The lower-temperature tetragonal martensitic phase with c/a= 1.25 is more stable compared to the higher-temperature austenitic phase. Mn2NiGa is ferrimagnetic in both phases. The calculated valence band spectrum, the optimized lattice constants and the magnetic moments are in good agreement with experiment. The majority-spin Fermi surface (FS) expands in the martensitic phase, while the minority-spin FS shrinks. FS nesting indicates occurrence of phonon softening and modulation in the martensitic phase.

Theoretical prediction and experimental study of a ferromagnetic shape memory alloy: Ga2MnNi

We predict the existence of a ferromagnetic shape memory alloy

Influence of Ni doping on the electronic structure of Ni2MnGa

{\text{Ga}}_{2}\text{MnNi}

Magnetoresistance behavior of ferromagnetic shape memory alloy Ni 1.75 Mn 1.25 Ga

using density-functional theory. The martensitic start temperature

Direct band gaps in group IV-VI monolayer materials: Binary counterparts of phosphorene

({T}_{M})

Ab Initio Density Functional Theory Studies of Hydrogen Adsorption at the V2O5(010) Surface

is found to be approximately proportional to the stabilization energy of the martensitic phase

Antiferromagnetic exchange interactions in the Ni2Mn1.4In0.6ferromagnetic Heusler alloy

(\ensuremath{\delta}{E}_{\text{tot}})