19 research outputs found
Local Atomic Structure of Martensitic NiMnGa: An EXAFS Study
The local atomic structure of NiMnGa with 0
0.16 alloys was explored using Mn and Ga K-edge Extended X-ray Absorption Fine
Structure (EXAFS) measurement. Inorder to study the atomic re-arrangements that
occur upon martensitic transformation, room temperature and low temperature
EXAFS were recorded. The changes occurring in the L2 unit cell and the bond
lengths obtained from the analysis enables us to determine the modulation
amplitudes over which the constituent atoms move giving rise to shuffling of
the atomic planes in the modulated structure. The EXAFS analysis also suggests
the changes in hybridization of Ga- and Ni- orbitals associated with the
local symmetry breaking upon undergoing martensitic transition.Comment: Accepted for publication in Physical Review
Magnetic properties and magnetostructural phase transitions in Ni2+xMn1-xGa shape memory alloys
A systematic study of magnetic properties of Ni2+xMn1-xGa (0 \le x \le 0.19)
Heusler alloys undergoing structural martensite-austenite transformations while
in ferromagnetic state has been performed. From measurements of spontaneous
magnetization, Ms(T), jumps \Delta M at structural phase transitions were
determined. Virtual Curie temperatures of the martensite were estimated from
the comparison of magnetization in martensitic and austenitic phases. Both
saturation magnetic moments in ferromagnetic state and effective magnetic
moments in paramagnetic state of Mn and Ni atoms were estimated and the
influence of delocalization effects on magnetism in these alloys was discussed.
The experimental results obtained show that the shift of martensitic transition
temperature depends weakly on composition. The values of this shift are in good
correspondence with Clapeyron-Clausius formalism taking into account the
experimental data on latent heat at martensite-austenite transformations.Comment: 7 pages, 8 figure
Modified Spin Wave Thoery of the Bilayer Square Lattice Frustrated Quantum Heisenberg Antiferromagnet
The ground state of the square lattice bilayer quantum antiferromagnet with
nearest and next-nearest neighbour intralayer interaction is studied by means
of the modified spin wave method. For weak interlayer coupling, the ground
state is found to be always magnetically ordered while the quantum disordered
phase appear for large enough interlayer coupling. The properties of the
disordered phase vary according to the strength of the frustration. In the
regime of weak frustration, the disordered ground state is an almost
uncorrelated assembly of interlayer dimers, while in the strongly frustrated
regime the quantum spin liquid phase which has considerable N\'eel type short
range order appears. The behavior of the sublattice magnetization and spin-spin
correlation length in each phase is discussed.Comment: 15 pages, revtex, figures upon reques
Comparison of pressure standards in the range 10 kPa to 140 kPa
NRC publication: Ye