By electric transport measurements on high-purity bulk molybdenum single crystals at helium-temperature, it is shown that when approaching the ideal metallic crystal structure, there are deviations from Ohm’s law that can exceed 30% even at low current densities ≅3A/mm2. This is due to the intrinsic circular magnetic field of the measuring current in the range of B≅1mT, which generates a magnetoresistance according to the two-band conduction model. With increasing lattice vibrations and/or crystal defects, this inherent uncertainty finally reduces to immeasurably small values. Finally, Ohm’s law for a nearly ideal lattice structure can be strictly exact only in the theoretical limiting case of an infinite lattice plane, because then the magnetic fields of all electrons of the current compensate to zero.

The interaction of electron–electron scattering with the size‐effect, with electron–phonon scattering, and with electron‐impurity scattering is measured and interpreted on high‐purity and W‐doped single crystalline molybdenum in the temperature range T = 1.6…30 K. On a set of more than 30 single crystals with different axis orientations the range down to 1 at · ppm impurities was realized, resulting in residual resistance ratios up to RRRimp = 1 × 106 and in electron mean free paths up to λimp = 12 mm. The interference of normal electron–electron scattering (NEES) with the size‐effect (Gurzhi effect, Knudsen effect) is proved in crystals with RRRimp ≥ 100 000. Relaxation times for NEES and electron‐umklapp scattering are estimated. Different types of magnetoresistance (MR) are measured in longitudinal and transverse magnetic fields . An orientation‐independent ωCτ value for Mo is deduced. The size‐effect reduction in longitudinal field is shown to be consistent with the Chambers calculations under consideration of NEES. The high‐field transverse magnetoresistance (TMR) of the high‐purity crystals is dominated by the static skin effect: the surface TMR short circuits the compensation‐induced bulk TMR which is shown to follow over 10 orders of magnitude without any sign of saturation.

High spatial resolution magnetic x-ray spectromicroscopy at x-ray photon energies near the cobalt L3 resonance was applied to probe an amorphous 50 nm thin SmCo5 film prepared by off-axis pulsed laser deposition onto an x-ray transparent 200 nm thin Si3N4 membrane. Alternating gradient magnetometry shows a strong in-plane anisotropy and an only weak perpendicular magnetic anisotropy, which is confirmed by magnetic transmission soft x-ray microscopy images showing over a field of view of 10 μm a primarily stripe-like domain pattern but with local labyrinth-like domains. Soft x-ray ptychography in amplitude and phase contrast was used to identify and characterize local magnetic and structural features over a field of view of 1 μm with a spatial resolution of about 10 nm. There, the magnetic labyrinth domain patterns are accompanied by nanoscale structural inclusions that are primarily located in close proximity to the magnetic domain walls. Our analysis suggests that these inclusions are nanocrystalline Sm2Co17 phases with nominally in-plane magnetic anisotropy.

On a set of 12 bulk and highly pure [residual resistance ratio (RRR) up to 6000] iron single crystals with different crystallographic orientation and on polycrystalline material the "hidden" basic resistivity rho(T, B --> 0) and magnetoresistive effects (anisotropic magnetoresistance, longitudinal and transverse Lorentz resistance) are quantitatively disentangled. The temperature-dependent basic resistivity for T <= 30 K follows a Delta rho(T, B --> 0) = aT(2) + bT(5) law, proving that electron-electron and electron-phonon scattering (with a resistive Debye temperature Theta(R) congruent to 450 K) are dominant also in iron, similar to nonferromagnetic transition metals. Here the crystal-orientation dependence of the intrinsic longitudinal magnetoresistance in the single-domain state could be quantitatively evaluated in accordance with the symmetry of the Fermi surface. The transverse magnetoresistance (TMR) turns out to be the sum of the so-called "two-band conduction term" and the unboundedly growing TMR term in compensated metals. It is proven that the second term is not restricted to the high-field limit (as usually discussed up to now) but acts down to lowest TMR or omega(C)tau values. This conclusion is verified by TMR measurements on highly pure molybdenum single crystals (RRR congruent to 100 000). Supported by Kerr microscopy, a small positive domain wall resistance (DWR) could be isolated from the dominating negative DWR in the multidomain state of iron, resulting in a relation of larger than 5:1 for the electrons to pass a domain wall with spin tracking compared to scattering with spin conservation.

By manipulating the magnetic domains of high-purity bulk iron single crystals (characterized by residual resistance ratios up to 5700) in small magnetic fields, resistivity changes up to a factor of 100 are measured at low temperature. Domain observation by Kerr microscopy shows that domain wall creation and annihilation is the origin of the resistivity changes. A qualitative model is suggested in which the walls act as channels for the electric current due to specific Lorentz trajectories around the walls. It is expected that this fundamental negative wall resistance effect contributes to magnetoresistance phenomena in any material and device containing domain walls.

For the improvement of the properties of Nb films in view of a possible application in TESLAtype resonators, knowledge about the connection of film structure/topography and electrical properties is necessary. Therefore, Nb films from different sites of a 1.5 GHz resonator were investigated and compared with results of usual planar deposition. The present results give information on topography and electrical properties of this Nb films. The films were deposited on quartz substrates in the resonator and on various substrates by planar dc magnetron deposition. The topography of the films was examined by scanning electron microscopy (SEM) and by atomic force microscopy (AFM). The residual resistance ratio (RRR) and critical temperature (Tc) were measured.

The paper presents resistivity and magnetization measurements on nearly stoichiometric Fe3Si films epitaxially grown on GaAs substrates by electron-beam evaporation in an ultrahigh vacuum chamber. In the low-temperature resistivity a T3 term was found in all samples. A term like that is known to describe the anomalous single-magnon scattering processes in half-metallic materials and confirms so for our samples the hypothesis of half-metallic ferromagnetism in Fe3Si. The films show an anisotropic magnetoresistance in low magnetic fields. In high magnetic fields a negative longitudinal and transverse magnetoresistance (MR) has been observed linearly depending on the field strength. In the vicinity of 200 K the MR shows maximum absolute values up to 1.5% at magnetic fields of about 8 T. From the magnetization measurements a magnetic moment of 0.86μB/atom was obtained, which is close to that of bulk Fe3Si.

We show an efficient way to investigate the magnetic behavior of nanotube stubs based on the embedding of aligned iron-filled carbon nanotubes in silicon oxide using thermal chemical vapor deposition and gradual mechanical polishing afterwards. On the one hand, during the covering process the saturation magnetization moment rises due to the transformation of Fe3C into body-centered-cubic-Fe and graphite. On the other hand, the coercivity drops, mainly induced by changes in the shape of the nanowires. Further magnetization measurements of the embedded sample point to most of the ferromagnetic nanowires being located near the surface of the substrate. The coercivity increases when reducing the thickness of the nanotube array. The anomalous high coercivity of the Fe nanowires encapsulated by non magnetic carbon nanotubes make them suitable for high density data storage applications.

Changes in the magnetization structure of an antiferromagnetically afm -coupled metallic multilayer as a function of the applied field H along the easy axis may involve both spin-flip and spin-flop events. The latter are widely discussed as the origin of the characteristic shapes of the magnetization M H and giant magnetoresistance GMR curves. In this work, we demonstrate the influence of spin-flip processes, which result in very different magnetization reversal and resistivity characteristics as compared to the spin-flop case: sharp, steplike GMR and magnetization changes for both the surface and internal layers—including magnetic viscosity effects—are observed. By means of Kerr microscopy, Kerr magnetometry, GMR, and magnetization measurements we show that spin-flip transitions via domain wall displacement constitute the relevant mechanism of magnetization reversal, provided that the anisotropy field HK in the multilayer surpasses the antiferromagnetic coupling field Hafm. In this case, a linear dependence of the GMR on the magnetization is observed, whereas for fields applied along the hard axis magnetization rotation results in a quadratic dependence. The strong change of the ratio HK /Hafm could be realized for measuring temperatures between 4.2 and 470 K in a series of wedge-type NiFe /Cu multilayers prepared by dc magnetron sputtering and showing GMR amplitudes of up to 12% 300 K and 28% 4.2 K in the second afm coupling maximum with extremely low values of the afm coupling strength.

This paper concerns with giant magnetoresistance (MR) effects in organic spin valves, which are realized as layered (La,Sr)MnO3 (LSMO)-based junctions with tris-(8, hydroxyquinoline) aluminum (Alq3)-spacer and ferromagnetic top layers. The experimental work was focused on the understanding of the transport behavior in this type of magnetic switching elements. The device preparation was carried out in an ultrahigh vacuum chamber equipped with a mask changer by evaporation and sputtering on SrTiO3 substrates with LSMO stripes deposited by pulsed laser technique. The field and temperature dependences of the MR of the prepared elements are studied. Spin-valve effects at 4.2K have been observed in a broad resistance interval from 50Ω to MΩ range, however, without systematic dependence on spacer layer thickness and device area. In some samples, the MR changes sign as a function of the bias voltage. The observed similarity in the bias voltages dependences of the MR in comparison with conventional magnetic tunnel junctions with oxide barriers suggests a description of the found effects within the classical tunneling concept. This assumption is also confirmed by a similar switching behavior observed on ferromagnetically contacted carbon nanotube devices. The proposed model implies the realization of the transport via local Co chains embedded in the Alq3 layer and spin dependent tunneling over barriers at the interface Co grains∕Alq3∕LSMO. The existence of conducting Co chains within the organics is supported by transmission electron microscopic∕electron energy loss spectroscopic studies on cross-sectional samples from analogous layer stacks.

Thin films of the Heusler alloy Co(2)Cr(0.6)Fe(0.4)A1 have been prepared by means of magnetron sputtering under varying conditions (sputter power, sputter pressure and substrate temperature). All the films are polycrystalline with the cubic 132 structure. The extent of Co-Al antisite defects, lattice constants, internal stress states are influenced by the sputter conditions which is related to differences in the saturation magnetization. The magnetic moment can be increased by additional annealing up to an optimum temperature of 400 degrees C, but does not reach the theoretically predicted value. Above 600 degrees C the metastable 132 phase transforms into either (epsilon)-Co/Cr or (alpha)-Co/Cr. (C) 2007 Elsevier B.V. All rights reserved.

Arrays of vertically aligned Fe-filled multi-wall carbon nanotubes (MWNTs) on oxidized silicon substrates were prepared by pyrolysis of ferrocene in a dual furnace system and characterized by electron microscopy and magnetometry measurement. The effect of the growth temperature on both the filled nanotube morphology and their magnetic behavior was studied. Increasing the growth temperature in the range of 845-1035 degrees C the nanotube alignment becomes worse and the diameter of the encapsulated Fe nanowires increases from 10 to 40 nm. Both the coercivity and the remanence ratio of the arrays of Fe-filled MNVNTs decrease with the increase of the growth temperature. Factors causing the observed magnetic behavior are discussed.

Vertically aligned Fe-filled multi-wall carbon nanotubes (MWNTs) have been grown selectively on the SiO2 surfaces of patterned amorphous carbon (a-C)/SiO2/Si substrates. Their morphology, structure and magnetic properties have been studied. The a-C patterns were prepared using conventional lithography processes combined with a sputter-deposition of a-C (thickness of 100 nm). The aligned Fe-filled MWNTs were produced by pyrolysis of ferrocene in a CVD reactor with a two zone furnace system and have high filling yield. The encapsulated Fe nanowires grown on the SiO2 structures of the patterned a-C/SiO2/Si substrates have diameters of 10-20 nm and can reach a few micrometers in length. The described method enables the preparation of complex architectures of Fe-filled MWNTs and may be used for future applications based on filled nanotubes.

Multifunctional nanocontainers can be produced based on partially filled Fe-multi walled carbon nanotubes (MWCNTs). Using thermal decomposition ferrocene filled nanotubes can be grown aligned on substrates. The encapsulated metal nanowires have diameters of 5-30 nm and a length up to few microns. They consist of single-crystalline of α and γ-Fe- phases. Using heat treatment, it is possible to transform γ-Fe into α-Fe. With the aid of wet chemical methods the nanotubes can be opened and additionally filled with an agent, e.g., therapeutic agents (carboplatin) or other metals (copper). Initial studies do not show a high toxicity over a period of 440 days. These materials can be used for drug delivery and hyperthermia. The specific absorption rate (SAR) is greater than 100W/(g-α-Fe) in a magnetic field of 18kA/m (f = 250kHz).

We have investigated the magnetic properties of the Heusler phase CoCrl-,Fe,Al in the composition regime (x = 0.3 - 0.5) in the disordered B2 phase. Both bulk and surface static and dynamic magnetic aspects were addressed by employing alternating gradient magnetometry (AGM), magneto-optical Kerr effect (MOKE) and Brillouin light scattering (BLS). All samples show ferromagnetic hysteresis loops and a tendency of increasing saturation magnetization M-5, with the iron content. With BLS the behavior of bulk spin waves and the Damon Eshbach (DE) surface spin wave mode have been studied. The spectra are typical for opaque bulk ferromagnetic samples with strong exchange. The measured spin wave frequencies as a function of magnetic field are in good agreement with the calculated values. Saturation magnetization and gyromagnetic ratio g have been determined from the field-dependent peak positions of the bulk and the DE modes. The g-factor extracted from the DE mode shows a clear tendency of increase with increasing Fe-content. However, we could not find any peculiarities of the alloy with x = 0.4, which had been proposed as a Hensler phase on the basis of electronic structure calculations [T. Block, C. Felser, G. Jakob, J. Ensling, B. Muhling, P. Gutlich, R.J. Cava, J. Solid State Chem. 176 (2003) 646]. (C) 2007 Elsevier B.V. All rights reserved.