Alfred Hucht

Surface energies of stoichiometric FePt and CoPt alloys and their implications for nanoparticle morphologies

We have calculated surface energies and surface magnetic order of various low-indexed surfaces of monoatomic Fe, Co, and Pt, and binary, ordered FePt, CoPt, and MnPt using density-functional theory. Our results for the binary systems indicate that elemental, Pt-covered surfaces are preferred over Fe and Co covered and mixed surfaces of the same orientation. The lowest energy orientation for mixed surfaces is the highly coordinated (111) surface. We find Pt-covered (111) surfaces, which can be realized in the

Monte-Carlo study of the reorientation transition in Heisenberg models with dipole interactions

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Shape Memory Alloys: A Summary of Recent Achievements

structure only, to be lower in energy by about 400 meV/atom compared to the mixed

REORIENTATION TRANSITION OF ULTRATHIN FERROMAGNETIC FILMS

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Anisotropy of ultrathin ferromagnetic films and the spin reorientation transition

(111) surface. We conclude that in small nanoparticles this low surface energy can stabilize the

Reorientation of Spin Density Waves in Cr(001) Films Induced by Fe(001) Cap Layers

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Lattice dynamics and structural stability of ordered Fe3Ni, Fe3Pd and Fe3Pt alloys using density functional theory

structure, which is suppressed in bulk alloys. From the interplay of surface and bulk energies, equilibrium shapes of single-crystalline ordered nanoparticles and crossover sizes between the different orderings can be estimated.

Depinning transition and thermal fluctuations in the random-field Ising model

Abstract We simulated the classical two-dimensional anisotropic Heisenberg model with full long range dipole interaction with an algorithm especially designed for long range models. The results show strong evidence for a first order reorientation transition at a temperature T R T C for appropriate parameters of the model Hamiltonian.

Thermodynamic Casimir Effect in He 4 Films near T λ : Monte Carlo Results

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.

Characterization of the reorientation transition in classical Heisenberg models with dipole interaction

We demonstrate that the reorientation transition from out-of-plane to in-plane magnetization with decreasing temperature as observed experimentally in Ni films on Cu(001) can be explained on a microscopic basis. Using a combination of mean-field theory and perturbation theory, we derive an analytic expression for the temperature-dependent anisotropy. The reduced magnetization in the film surface at finite temperatures plays a crucial role for this transition as with increasing temperature the influence of the uniaxial anisotropies is reduced at the surface and is enhanced inside the film.