Sanjeev K. Nayak

Shape Memory Alloys: A Summary of Recent Achievements

The Ni-Mn-Ga shape memory alloy displays the largest shape change of all known magnetic Heusler alloys with a strain of the order of 10% in an external magnetic field of less than one Tesla. In addition, the alloys exhibit a sequence of intermediate martensites with the modulated structures usually appearing at c/a < 1 while the low-temperature non- modulated tetragonal structures have c/a > 1. Typically, in the Ni-based alloys, the martensitic transformation is accompanied by a systematic change of the electronic structure in the vicinity of the Fermi energy, where a peak in the electronic density of states from the non-bonding Ni states is shifted from the occupied region to the unoccupied energy range, which is associated with a reconstruction of the Fermi surface, and, in most cases, by pronounced phonon anomalies. The latter appear in high-temperature cubic austenite, premartensite but also in the modulated phases. In addition, the modulated phases have highly mobile twin boundaries which can be rearranged by an external magnetic field due to the high magnetic anisotropy, which builds up in the martensitic phases and which is the origin of the magnetic shape memory effect. This overall scenario is confirmed by first-principles calculations.

Fundamental Aspects of Magnetic Shape Memory Alloys: Insights from Ab Initio and Monte Carlo Studies

Ferromagnetic Heusler alloys like Ni-Mn-Z (Z = Al, Ga, In, Sn, Sb), which undergo a martensitic phase transformation, are on the edge of being used in technological applications involving actuator and magnetocaloric devices. The other class of ferromagnetic full Heusler alloys like Co-Mn-Z (Z = Al, Si, Ga, Ge, Sn) not undergoing a structural phase transition, are half-metals (in contrast to the Ni-based systems) with high spin polarization at the Fermi level and are of potential importance for future spintronics devices. On the basis of recent ab initio calculations, we highlight the main differences between the two classes of Heusler based materials.

Anisotropic ferromagnetism in carbon-doped zinc oxide from first-principles studies

A density functional theory study of substitutional carbon impurities in ZnO has been performed, using both the generalized gradient approximation (GGA) and a hybrid functional (HSE06) as exchange-correlation functional. It is found that the non-spinpolarized C

Monte Carlo simulations of diluted magnetic semiconductors using ab initio exchange parameters.

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Theory of k→⋅π→+U formalism for diluted magnetic semiconductors: Application to p-type Sn1−xGdxTe

impurity is under almost all conditions thermodynamically more stable than the C

Effect of hydrostatic pressure and uniaxial strain on the electronic structure of Pb1-xSnxTe

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Soft phonon mode dynamics in Aurivillius-type structures

impurity which has a magnetic moment of

Simulating Structure, Magnetism and Electronic Properties of Monoatomic, Binary and Ternary Transition Metal Nanoclusters

2\mu_{\mathrm{B}}

Possible one-dimensional structures obtained from transition metal atom doped silicon nanoclusters

, with the exception of very O-poor and C-rich conditions. This explains the experimental difficulties in sample preparation in order to realize

Absence of ferromagnetic interaction in Co-Co nearest neighbor impurity pairs in ZnO: An analysis from GGA+U studies

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