Static and dynamic properties of Single-Chain Magnets with sharp and broad domain walls

We discuss time-quantified Monte-Carlo simulations on classical spin chains with uniaxial anisotropy in relation to static calculations. Depending on the thickness of domain walls, controlled by the relative strength of the exchange and magnetic anisotropy energy, we found two distinct regimes in which both the static and dynamic behavior are different. For broad domain walls, the interplay between localized excitations and spin waves turns out to be crucial at finite temperature. As a consequence, a different protocol should be followed in the experimental characterization of slow-relaxing spin chains with broad domain walls with respect to the usual Ising limit.Comment: 18 pages, 13 figures, to be published in Phys. Rev.

Lectures on quantum mechanics for material scientists

When speaking of quantum mechanics, one has typically a physics or chemistry student in mind. However, research on materials is now so advanced that students of material science must be trained to understand and above all use those deepest concepts of quantum mechanics that were reserved to physics students in the past. It is along these lines that these lectures discuss the fundamental concepts of modern Quantum Physics such as the failure of classical mechanics, the postulates and mathematical structure of Quantum Physics, the electronic structure of atoms, molecules and solids, the electron spin and time dependent perturbations. The lectures are constructed in such a way that the various concepts are introduced by starting from the explicit and detailed treatment of a simple example. These particular cases are then generalized and put into a ''moderately '' rigorous framework -- the word ''moderately'' meaning that the mathematics is not worked out in details but the essential steps are rigorous enough to withstand practical applications. The present manuscript summarizes the content of the various lectures. The lectures were distributed over a semester at ETH Zurich (about 13 weeks, four hours per week). The course included a set of problems that were intended to complement the lectures themselves with concrete examples and that were solved weekly by the students (one hour per week). Some of the experiments presented contain a link to the site ''Vorlesungsexperimente Departement Physik'' of ETH Zurich. The team that prepared these experimental demonstrations over the years has supported the present lectures with a large amount of experiments that could be performed in-situ and in real time. They also made their work available online. I am grateful to the team for their work in supporting these lectures, in particular, and the entire physics lecture businnes at ETH Zurich. The knowledge used to prepare these lectures was acquired by reading a large amount of literature on the subject. In particular, I would like to quote the lectures on quantum mechanics held by the late Prof. R. Jost at ETH Zurich during the academic year 1977-1978 and the manuscript by the late Prof. Hunziker. The present lectures show my personal understanding of the subject. This understanding also emerged during the interaction with the many students that frequented my courses. A thank goes also to them

Vectorial, non-destructive magnetic imaging with scanning tunneling microscopy in the field emission regime

When a scanning tunneling microscope is operated at tip-target distances ranging from few nanometers to few tens of nanometers (Fowler-Nordheim or field emission regime), a new electronic system appears, consisting of electrons that escape the tip-target junction. If the targetis ferromagnetic, this electronic system is spin polarized. Here, we use these spin polarized electrons to image magnetic domains in thin films.As two components of the spin polarization vector are detected simultaneously, the imaging of the local magnetization has vectorial charac-ter. The tip is nonmagnetic, i.e., the magnetic state of the target is not perturbed by the act of probing. We expect this spin polarized technol-ogy, which scales down scanning electron microscopy with polarization analysis by bringing the source of primary electrons in closeproximity to the target, to find its main applications in the imaging of noncollinear, weakly stable spin excitations.ISSN:0003-6951ISSN:1077-311

Critical exponents and scaling invariance in the absence of a critical point

The paramagnetic-to-ferromagnetic phase transition is classified as a critical phenomenon due to the power-law behaviour shown by thermodynamic observables when the Curie point is approached. Here we report the observation of such a behaviour over extraordinarily many decades of suitable scaling variables in ultrathin Fe films, for certain ranges of temperature T and applied field B. This despite the fact that the underlying critical point is practically unreachable because protected by a phase with a modulated domain structure, induced by the dipole–dipole interaction. The modulated structure has a well-defined spatial period and is realized in a portion of the (T, B) plane that extends above the putative critical temperature, where thermodynamic quantities do not display any singularity. Our results imply that scaling behaviour of macroscopic observables is compatible with an avoided critical point.ISSN:2041-172

Investigation of Fe/W(110) system with Field Emission Scanning Probe Microscopy

ISSN:0420-019