Strained tetragonal states and Bain paths in metals

Paths of tetragonal states between two phases of a material, such as bcc and fcc, are called Bain paths. Two simple Bain paths can be defined in terms of special imposed stresses, one of which applies directly to strained epitaxial films. Each path goes far into the range of nonlinear elasticity and reaches a range of structural parameters in which the structure is inherently unstable. In this paper we identify and analyze the general properties of these paths by density functional theory. Special examples include vanadium, cobalt and copper, and the epitaxial path is used to identify an epitaxial film as related uniquely to a bulk phase.Comment: RevTeX, 4 pages, 4 figures, submitted to Phys. Rev. Let

Large exchange bias induced by polycrystalline Mn3Ga antiferromagnetic films with controlled layer thickness

Polycrystalline Mn3Ga layers with thickness in the range from 6-20 nm were deposited at room temperature by a high target utilisation sputtering. To investigate the onset of exchange-bias, a ferromagnetic Co0.6Fe0.4 layer (3.3-9 nm thick) capped with 5 nm Ta, were subsequently deposited. X-ray diffraction measurements confirm the presence of Mn3Ga (0002) and (0004) peaks characteristic of the D019 antiferromagnetic structure. The 6 nm thick Mn3Ga film shows the largest exchange bias of 430 Oe at 120 K with a blocking temperature of 225 K. The blocking temperature is found to decrease with increasing Mn3Ga thickness. These results in combination with X-ray reflectivity measurements confirm that the quality of the Mn3Ga/Co0.6Fe0.4 interface controls the exchange bias, with the sharp interface with the 6-nm-thick Mn3Ga inducing the largest exchange bias. The magneto-crystalline anisotropy for 6 nm thick Mn3Ga thin film sample is calculated to be 9×10^4 J/m^3. Such a binary antiferromagnetic Heusler alloy is compatible with the current memory fabrication process and hence has a great potential for antiferromagnetic spintronics

Tests of a density-based local pseudopotential for sixteen simple metals

A comprehensive study of the lattice dynamics, elastic moduli, and liquid metal resistivities for 16 simple metals in the bcc and fcc crystal structures is made using a density-based local pseudopotential. The phonon frequencies exhibit excellent agreement with both experiment and nonlocal pseudopotential theory. The bulk modulus is evaluated by the long wave and homogeneous deformation methods, which agree after a correction is applied to the former. Calculated bulk and Voigt shear moduli are insensitive to crystal structure, and long-wavelength soft modes are found in certain cases. Resistivity calculations confirm that electrons scatter off the whole Kohn-Sham potential, including its exchange-correlation part as well as its Hartree part. All of these results are found in second-order pseudopotential perturbation theory. However, the effect of a nonperturbative treatment on the calculated lattice constant is not negligible, showing that higher-order contributions have been subsumed into the pseudopotential by construction. For bcc sodium, the band structures of local and nonlocal pseudopotentials are found to be almost identica