Anisotropic magnetocaloric effect in nanostructured magnetic clusters

We report the first experimental observation of anisotropic magnetocaloric effect (MCE) in the Fe8 clusters. It is found that the magnetic anisotropy plays a very important role in the determination of the magnetocaloric effect. The maximum and minimum MCE's are observed when the applied magnetic fields are parallel and perpendicular to the easy axis, respectively. The quantum spin Hamiltonian of a Fe8 cluster is used to calculate the partition function and the magnetization in a range of temperature and magnetic field. Excellent quantitative agreement between the experimental data and calculation is observed.     

Anisotropic low temperature thermal resistance in polycrystalline magnetic thin films

The scattering of spin waves and the thermal resistance due to this scattering are calculated for polycrystalline magnetic thin films with a small overall uniaxial anisotropy. The scattering is caused by the random orientation of crystallites, and also by the magnetization ripple, which is likewise produced by this random orientation. The wavelength spectra of the ripple and of the spin waves at low energy are essentially influenced by the magnetostatic interaction, which is taken into account within Harte's linearized thin film approximation, and for comparison also within Hoffmann's approximation. Due to the anisotropy of the spectra, the contribution of the spin waves to the thermal resistance of permalloy films should be highly anisotropic at temperatures of 2 K and below.     

Anisotropic magnetoresistance in thin inhomogeneous gold films

We investigate the magnetoresistance (MR) of thininhomogeneous gold films applying the magnetic field perpendicular as well as parallel to the film plane. The MR-data show a strong anisotropy which can be well explained within the theory of weak electron localization (WEL) in 2d for both field orientations. The important results is that fitting the MR-data for both orientations by the corresponding theoretical expressions we obtain nearly identical values for the phase coherence lengthsL and its temperature dependence. This confirms (i) the correctness of the fitting process and (ii) the validity of the theory. From this we conclude that WEL in 2d can also be used to describe the MR ofinhomogeneous films.     

Anisotropic metal-insulator transition in epitaxial thin films

By comparing the properties of In and Pb quantum wells in a scanning tunneling microscopy subsurface imaging experiment, we found the existence of lateral bound states, a 2D Mott-Hubbard correlation gap, induced by transverse confinement. Its formation is attributed to spin or charge overscreening of quasi-2D excitations. The signature of the 2D confinement-deconfinement transition is also experimentally observed, with the correlation gap being pinned in the middle of the conduction band. A self-organized 2D Anderson lattice is suggested as a new ground state.     

Barkhausen effect in magnetic thin films: Experimental noise spectra

In this paper Barkhausen noise spectra are shown that were measured on thin uniaxial 83-17 Ni?Fe films and these spectra were compared with the known magnetic behaviour of these films. On these types of sample the Barkhausen effect had been investigated by Lambeck [1], but their Barkhausen noise spectra have not been investigated so far. The film thicknessd _m in our experiments ranged between 400 and 2400 Å. In this range a change occurs in the dynamics of the magnetization behaviour caused by transitions of the type of domain wall. The results presented here show the very strong dependence of the Barkhausen noise spectra on the type of domain wall. Films with Bloch walls always show a frequency dependence off ^?1.7 in the higher frequency range. Samples in the thickness range where the transition occurs from the Néel wall via the cross-tie wall to the Bloch wall, have exponents between ?1 and ?2. The frequencyf _c above which the measured noise intensity begins to decrease varies very much for the different films. The curve off _c versus film thicknessd _m has the same form as the curve of the domain wall mobilitym versusd _m.     

Mössbauer effect studies on magnetic thin films

The electric and magnetic hyperfine interactions measured in Mössbauer experiments and their general relations to magnetic properties of solids are summarized briefly. The particular possibilities and experimental difficulties, which arise in applications of the Mössbauer method to thin film problems, are discussed. The main results of the so far rather scarce Mössbauer studies of magnetic thin films are reviewed.     

Anisotropic diffusion of single molecules in thin liquid films

The European Physical Journal E - Single molecule wide field imaging is applied to study the diffusion in ultrathin liquid films on solid surfaces. The results show a broad distribution of...     

Anisotropic diffusion of single molecules in thin liquid films

Single molecule wide field imaging is applied to study the diffusion in ultrathin liquid films on solid surfaces. The results show a broad distribution of diffusion coefficients. This is tentatively ascribed to an anisotropy of the diffusion coefficient perpendicular to the surface and a slow exchange of molecules between regions of different diffusion coefficients. We have evidence, that these changes as well as the slow motion perpendicular to the surface are related to the molecular layering of the liquid close to the surface.     

Influence of strain on the galvanomagnetic effect in magnetic thin films

A study of the influence of uniaxial stresses on the planar galvanomagnetic effect in thin Ni-Fe-Mo films evaporated in vacuum has been performed. Galvanomagnetic voltage was measured at different value of stress and applied field, rotated in the plane of the sample. Magnetoelastic hysteresis depending on the applied field was found.     

Anisotropic pinning in Nb thin films with triangular pinning arrays

A superconducting thin film with regular triangular arrays has been fabricated to explore the anisotropic vortex pinning behavior. We found that the critical currents for these films depend strongly on the current directions. Some interesting temperature-dependent phenomena are observed and discussed. We also made molecular dynamic simulations to study the dynamics of the vortex motion. The simulation results confirm the anisotropic features we found in the experiments.     

Quantum size effects for the extraordinary Hall effect in thin magnetic films

A theory for the extraordinary Hall effect in thin films is derived using the Kubo formalism. We calculate the skew-scattering contribution to the Hall resistivity. Oscillations of the resistivity with the thickness of the magnetic layers are obtained similar to the diagonal resistivity, but as the Hall current is due to d-electrons, the period of these oscillations is connected with the Fermi wave vector of the d-electrons.     

Self-focusing magnetostatic beams in thin magnetic films

The possibility of generation of stable self-focusing beams in in-plane magnetized thin magnetic films is considered, and theoretical conditions for the existence of such localized solutions are discussed. It is shown that for the definite direction between static magnetizing field and preferential direction of radiation from a microwave antenna, the problem reduces to the one-dimensional nonlinear Schrödinger equation. For such angles it is possible to generate stable self-focusing beams. Particular values of beam width and propagation angles versus magnitude of magnetizing field are calculated in order to suggest a realistic experimental setup for the observing the discovered effect.Received: 3 July 2004, Published online: 12 October 2004PACS: 85.70.Ge Ferrite and garnet devices - 75.30.Ds Spin waves - 76.50. + g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance     

First-order magnetic phase transitions in thin films

Using the simple Landau model, we discuss near-surface magnetic effects for thin films corresponding to first-order phase transitions. The size effects observed in ultrathin ferroelectric films are in agreement with this theoretical interpretation. The presence of a weak external field is also formulated. The text was submitted by the authors in English.     

Vanishing magnetic interactions in ferromagnetic thin films

We have used element-specific hysteresis measurements, based on the x-ray magnetic circular dichroism technique, to investigate magnetic trilayer structures composed of Fe and Ni layers. Within a critical regime we have discovered a class of structures in which the exchange interaction, the mechanism responsible for the macroscopic magnetism, can become vanishingly small. The experimental observations are supported by first principles theory and are explained as arising from a cancellation of several competing magnetic interactions. Hence, we have discovered a system with a novel exchange interaction between magnetic layers in direct contact that replaces the conventional exchange interaction in ferromagnets.     

Microwave magnetic properties of soft magnetic thin films

We review our works that focus on the microwave magnetic properties of metallic,ferrite and granular thin films.Soft magnetic material with large permeability and low energy loss in the GHz range is a challenge for the inforcom technologies.GHz magnetic properties of the soft magnetic thin films with in-plane anisotropy were investigated.It is found that several hundreds of permeability at the GHz frequency was achieved for Co100-xZrx and Co90Nb10 metallic thin films because of their high saturation magneti...     

Critical behavior of magnetic thin films

We study the critical behavior of magnetic thin films as a function of the film thickness. We use the ferromagnetic Ising model with the high-resolution multiple histogram Monte Carlo (MC) simulation. We show that though the 2D behavior remains dominant at small thicknesses, there is a systematic continuous deviation of the critical exponents from their 2D values. We explain these deviations using the concept of “effective” exponents suggested by Capehart and Fisher in a finite size analysis. The shift of the critical temperature with the film thickness obtained here by MC simulation is in an excellent agreement with their prediction.     

Finite-size effect on magnetic ordering temperatures in long-period antiferromagnets: holmium thin films

The thickness dependence of the helical antiferromagnetic ordering temperature T(N) was studied for thin Ho metal films by resonant magnetic soft x-ray and neutron diffraction. In contrast with the Curie temperature of ferromagnets, T(N) was found to decrease with film thickness d according to [T(N)(infinity)-T(N)(d)]/T(N)(d) proportional variant (d-d(0))(-lambda(')), where lambda(') is a phenomenological exponent and d(0) is of the order of the bulk magnetic period L(b). These observations are reproduced by mean-field calculations that suggest a linear relationship between d(0) and L(b) in long-period antiferromagnets.