10,618 research outputs found
Microstructure of severely deformed metals from X-ray line profile analysis
Two essentially different materials, cubic Ti(49.8)Ni(50.2) shape memory alloy and hexagonal AZ91 Mg alloy, were deformed by equal channel angular pressing (ECAP). The microstructure developed as a result of severe plastic deformation was studied by X-ray line profile analysis. The correlation between the microstructure and the mechanical behavior was also investigated. Below 100 degrees C the tensile strength of the Mg alloy increased as a consequence of the increase of the dislocation density owing to ECAP. Above 200 degrees C the strength decreased and the ductility increased as a result of the breakage of the Al(12)Mg(17) precipitates due to ECAP. The analysis of the dislocation contrast factors of Ti(49.8)Ni(50.2) revealed that {110} dislocations with line vector formed during ECAP
Detection of bottom ferromagnetic electrode oxidation in magnetic tunnel junctions by magnetometry measurements
Surface oxidation of the bottom ferromagnetic (FM) electrode, one of the
major detrimental factors to the performance of a Magnetic Tunnel Junction
(MTJ), is difficult to avoid during the fabrication process of the MTJ's tunnel
barrier. Since Co rich alloys are commonly used for the FM electrodes in MTJs,
over-oxidation of the tunnel barrier results in the formation of a CoO
antiferromagnetic (AF) interface layer which couples with the bottom FM
electrode to form a typical AF/FM exchange bias (EB) system. In this work,
surface oxidation of the CoFe and CoFeB bottom electrodes was detected via
magnetometry measurements of exchange-bias characterizations including the EB
field, training effect, uncompensated spin density, and coercivity. Variations
of these parameters were found to be related to the surface oxidation of the
bottom electrode, among them the change of coercivity is most sensitive.
Annealed samples show evidence for an oxygen migration back to the MgO tunnel
barrier by annealing.Comment: 5 pages, 4 figues, submitted to J. Appl. Phy
Topology in thermodynamics of regular black strings with Kaluza-Klein reduction
We study the topological defects in the thermodynamics of regular black
strings (from a four-dimensional perspective) that is symmetric under the
double Wick rotation and constructed in the high-dimensional spacetime with an
extra dimension compactified on a circle. We observe that the thermodynamic
phases of regular black strings can be topologically classified by the positive
and negative winding numbers (at the defects) which correspond to the
thermodynamically stable and unstable branches. This topological classification
implies a phase transition due to the decay of a thermodynamically unstable
regular black string to another which is thermodynamically stable. We confirm
these topological properties of the thermodynamics of regular black strings by
investigating their free energy, heat capacity, and Ruppeiner scalar curvature
of the state space. The Ruppeiner scalar curvature of regular black strings is
found to be always negative, implying that the interactions among the
microstructures of regular black strings are only attractive.Comment: 21 pages, 10 figure
Effects of selective dilution on the magnetic properties of La_{0.7}Sr_{0.3}Mn_{1-x}M'_xO_3 (M' = Al, Ti)
The magnetic lattice of mixed-valence Mn ions in
LaSrMnO is selectively diluted by partial substitution of
Al or Ti for Mn. The ferromagnetic transition temperature and
the saturation magnetization both decrease with substitution. By
presenting the data in terms of selective dilution, in the
low-doping region is found to follow the relation
, where refers to
the undiluted system and is the dilution concentration defined
as or for Al or Ti,
respectively. The scaling behavior of can be
analyzed in the framework of the molecular-field theory and still valid when Mn
is substituted by both Al and Ti. The results are discussed with respect to the
contributions from ferromagnetic double exchange and other possible
antiferromagnetic superexchange interactions coexisting in the material.Comment: Revtex4, 4 pages, 4 figures, 2006 Halong Conference Repor
Memory and superposition in a spin glass
Non-equilibrium dynamics in a Ag(Mn) spin glass are investigated by
measurements of the temperature dependence of the remanent magnetisation. Using
specific cooling protocols before recording the thermo- or isothermal remanent
magnetisations on re-heating, it is found that the measured curves effectively
disclose non-equilibrium spin glass characteristics such as ageing and memory
phenomena as well as an extended validity of the superposition principle for
the relaxation. The usefulness of this "simple" dc-method is discussed, as well
as its applicability to other disordered magnetic systems.Comment: REVTeX style; 8 pages, 4 figure
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