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Amorphous and nanocrystalline Fe 80.5 Nb 7 B 12.5 ribbons were investigated using nuclear magnetic resonance (NMR). A direct observation of the Nb environments was performed. The local anisotropy of the Nb-containing grains or phases is almost the same for the as-cast and the sample heat treated at 510°C for 1 h. After a 610°C/1 h annealing, the presence of pure α-Fe is observed and the anisotropy of the Nb phase decreases.

A magnetic depth profile study was performed on the system Au/CoO/Co. In situ sputtering at 300 K was followed by X-ray magnetic circular dichroism measurements from the CoO layer to the pure Co layer. Sum rules were applied to determine magnetic moments of Co. The orbital moment and the ml/ms ratio tends to decrease close to the interface.

A combined nuclear magnetic resonance (NMR) and Mossbauer effect (ME) study of Nd2Fe14B has been carried out, which uses the Fe hyperfine field (HF) values obtained by NMR experiments in the ME fitting process. Taking the advantages of both NMR in determining the HF values at different Fe sites and ME in determining the intensity ratios of subspectra, the determination of the Fe HF values and their assignment can be made more precisely and more reliably. It can be deduced from the present result that the existence of a nearest Fe neighbor leads to an increase in the Fe HF of about 15 kOe/Fe, while a nearest B neighbor atom reduces it at a larger rate. The nearest Nd neighbor atom seems to have no significant effect on the Fe HF. The analysis concerning the various contributions to the HF and their correlation with the atomic magnetic moment demonstrates that the hyperfine interaction study for the case of Fe provides a simple means to measure Fe sublattice magnetization and relevant properties of the R2Fe14B system.

The nanostructure and local strain of [111] fcc Co/Cu multilayers are studied by means of nuclear magnetic resonance. The atomic topology of the interface can be deduced from the NMR spectrum and the local strains from the shift in the hyperfine fields. The results show that the Co/Cu interface is a mixed monolayer and that the Co layers, including the interface, have uniform strain inversely proportional to the Co thickness (within experimental error) with the proportionality constant depending on the Cu thickness.

Spin-dependent transport in ferromagnet–semiconductor structures is a field of growing interest, driven by the possibility to realize solid-state MRAMs compatible with existing memory technology. Ferromagnet–semiconductor contacts play a crucial role in all structures where spin injection into semiconductors is involved. We have investigated the properties of Co contacts on InAs, the latter being known for its tendency to form Schottky barrier-free ohmic contacts to metals. Co layers of different thicknesses have been deposited by thermal evaporation. The macroscopic magnetization has been studied using SQUID magnetometry. Structural properties and intermixing have been investigated by nuclear magnetic resonance spectroscopy. Patterned Co contacts have been characterized by I / V measurements at different temperatures. Our data indicate a partial intermixing over several monolayers at the interface resulting in a thin layer with ferromagnetic properties. The I / V characteristics show low contact resistance and a linear behaviour down to 60 K.

The field of molecule-based magnets involves the design and complex study of molecular compounds that exhibit a spontaneous magnetic ordering below a critical temperature. During the last two decades there is an increasing interest in the synthesis and investigation of this type of complexes as shown by a growing number of publications and review articles (see for example [1, 2]). As a class, molecule-based magnets possess many properties of organic polymeric compounds combined with the magnetic properties of classical bulk magnets that includes low specific density, flexibility, optical transparency, compatibility with polymers for composites, solubility, biocompatibility, high magnetic susceptibility etc. Many of these nonmagnetic characteristics are not available with conventional metal oxide-based magnets but are very important technological attributes. Therefore molecular magnetism is one of the most challenging research areas in the development of new technologies. For example, among the possible applications there are high-density information storage, magneto-optical devices, magnetic switches etc. Research interest in this field is motivated by the need for a better understanding of the fundamental principles that govern magnetic behavior. To synthesize new improved molecular magnetic materials with specific magnetic and electronic properties a deeper insight into the relation between the molecular structures and the macroscopic physical properties is required.

A systematic study of $\mathrm{Co}({\mathrm{SiO}}_{2})$ granular films by means of transmission electron microscopy (TEM), dc and ac initial magnetic susceptibility, and thermoremanent magnetization (TRM) is presented. The experimental results are compared with simulations of zero-field-cooled (ZFC) and field-cooled (FC) magnetization and TRM curves obtained using a simple model of noninteracting nanoparticles. The simulated ZFC/FC curves, using the actual parameters obtained from the TEM images, show a different behavior than the experimental magnetic data. The effect of the dipolar interaction among particles introduces a self-averaging effect over a correlation length \ensuremath{\Lambda}, which results in a larger average ``magnetic'' size of the apparent particles together with a narrower size distribution. The analysis of the ZFC/FC curves in the framework of independent ``particle clusters'' of volume ${\ensuremath{\Lambda}}^{3},$ involving about 25 real particles, explains very well the observed difference between the experimental data for the median blocking temperature $〈{T}_{B}〉$ and their distribution width with respect to the ones expected from the structural observations by TEM. The experimental TRM curves also differ from those obtained from the theoretical model, starting to decrease at a lower temperature than expected from the model, also indicating the strong influence of dipole-dipole interactions.

59Co NMR was studied in a series of Nd2(Co1−xFex)14B compounds with x=0.001, 0.01, 0.02, 0.05, 0.10 between 4.2 and 77 K. A fast increase of the canting angle between the magnetization and c axis upon Fe substitution has been found. Nonregular local environment effects in the form of rapidly developing satellite structure with significant intensity have been observed and tentatively attributed to the Fe influence on the crystal field experienced by the Nd sublattice.

The analysis of 59Co NMR for a series of R2Co14B with different magnetic configurations gives experimental evidence for the existence of conical domain walls in the canted Nd2Co14B. Such walls extrapolate to regular 90° walls in planar configuration: the NMR features in Nd2Co14B (canted) interpolate between those of Y2Co14B (easy plane) and Pr2Co14B (uniaxial).

Spectroscopies based on hyperfine interactions such as Nuclear Magnetic Resonance (or Mossbauer effect, Perturbed Angular Correlation,…) use nuclei as local probes of the magnetic (or electric) properties of the electrons on their site and in the close vicinity. Their basic yield is the strength of the magnetic hyperfine field HF or the electric field gradient EFG acting on nuclei in the material. As such HF and EFG data are of fundamental interest although a comparison with theory involves heavy calculations. Their origin will not be discussed in details here. The emphasis will be put rather on the information one can get about the local structure and magnetic properties of metallic systems, magnetic multilayers and thin films, without going into detailed electronic structure calculations. Indeed the hyperfine field HF, the electric field gradient EFG are brought about by the spatial distribution of charges and magnetic moment around the observed nucleus and, thus, they are signatures of the various topological, chemical and magnetic environments in the material. In this chapter, the stress is put only on the magnetic hyperfine interaction1 and its distribution in the sample, in short, the NMR spectrum. This spectrum contains the relevant information for sample characterization: chemical and topological short range order, local moments and magnetic anisotropy.

The nanostructure and local strain of \111] FCC Co/Cu and Co/Ni multilayers is studied by means of nuclear magnetic resonance. The atomic topology of the interface can be deduced from the NMR spectrum, the local strains from the shift in the hyperfine fields. The results show that the Co/Cu interface is a mixed monolayer and that the Co layers, including the interface, have uniform (tensile) strain inversely proportional to the Co thickness (within experimental error) with the proportionality constant depending on the Cu thickness. In Co/Ni the interface consists of two mixed layers and the Co layers have uniform compressive strain inversely proportional to the Co thickness.

145 Nd NMR has been studied in Nd 2 (Co 1− x Fe x ) 14 B compounds in the full substitution range. From the first stages of iron substitution, the onset of a new NMR spectrum, shifted down in frequency by aboyt 70 MHz and rapidly increasing in intensity, is observed. This discontinuous change of hyperfine field is explained by changes in its intra-ionic part resulting from a passage through a non-fully polarized state of Nd 3+ ion.

Knight-shift and spin-lattice relaxation time have been measured on 31P in an amorphous (Mo0.5Ru0.5)80P20 alloy obtained by splat-cooling. Measurements were carried out in applied fields of 5.2 and 8.7 kG in the normal state and in the mixed superconducting state for temperatures down to 1.4°K (Tco = 5.4°K). Just below Tc (Tc/T = 1.1), the reduced relaxation rate peaks at a value Rs/Rn of 1.5; then, it decreases, for 1.2 ⩽ Tc/T ⩽ 2.5, according to an exponential law yielding an energy gap value in excellent agreement with BCS prediction for weak-coupled superconductors.

The 63Cu NMR on CuNi alloys in the critical concentration range for the transition to the paramagnetic state (45 at.%

To investigate the possibility of building Co/Pt modulated multilayers, attention has been paid to the early stages of interface formation between cobalt and platinum. The growth of cobalt layers less than 10 monolayers thick on Pt(100) surfaces has been studied by Auger electron spectroscopy. Growth kinetics obtained by AES show that two different models of interface formation can be possible: the Volmer-Weber case (cobalt islands) or an interdiffusion process between the two metals (similar to suicide formation). Looking at the fine structure of the low-energy platinum Auger transitions suggests that there is a strong interaction between cobalt and platinum as soon as the equivalent of a cobalt 2 monolayer coverage is deposited. This would favor the interdiffusion process model.

It is found from magnetic and 11B NMR studies of amorphous and crystalline Ni-B alloys that neither the bulk (conduction electron susceptibility), nor the local (Knight shift and spin-lattice relaxation time) electronic parameters are influenced appreciably by the lack of long-range order. Together with previous quadrupole NMR study on the same samples this supports the conclusion that the basic building units in amorphous Ni-B alloys are similar to trigonal prisms occuring in the crystalline Ni3B and Ni4B3 compounds.

Presents the results of an experimental study of electrodeposited amorphous Ni1-cPc alloys in the concentration range 0.5

From a thorough NMR study of the 55Mn hyperfine field distribution in Mn5(Ge1-xSix)3 alloys the authors shown that the transition from the ferromagnetic Mn5Ge3 to the antiferromagnetic Mn5Si3 occurs inhomogeneously in three steps. At the early stage of the substitution of Si for Ge (x or approximately=0.8. Then for 0.5 or=0.8 bulk antiferromagnetism occurs but a metamagnetic transition is still observed for Hext>30 kOe.

We have performed 29 Si NMR measurement in Ce(La–Y)Ru 2 Si 2 compounds with Ce being partialy substituted by La or Y in order to probe the Ce spin fluctuations in this Kondo system. From NMR relaxation time and Knight shift measurements the thermal dependence of the electronic relaxation rate \(\varGamma\) is deduced for compound with T K varying between 9 K–80 K as deduced from specific heat measurement. We show that the spin fluctuation rate \(\varGamma\) scales with T K and obeys a universal thermal behavior \(\varGamma/T_{\text{K}}{=}f(T/T_{\text{K}})\). This universal curve is qualitatively compared with theoretical result. A possible agreement is found between experiment and theory for a two fold degeneracy at T =0 and a four fold degeneracy at moderated high temperature ( T

The author presents new relaxation time measurements in dilute VT alloys (T:Co, Mo, Rh, Ta, W, Re, Os, Ir) and concentrated sigma VCo, VCo3, VRh3 and VIr3 alloys. From these experimental results and previous bulk susceptibility and Knight shift measurements made by Devos (1972) the author calculates the various contributions to the bulk susceptibility of these alloys and particularly the Pauli and Van Vleck vanadium susceptibilities. This allows a systematic study of the magnetic behaviour of vanadium alloys with transition metals as a function of the nature and the concentration of the impurity. New NMR results (Knight shifts, line widths and relaxation rates) in concentrated V1-cNic alloys (85%

NMR measurements can yield some insight into the electronic structure of metallic glasses through the Korringa ratio in non-magnetic alloys and through the mean value of the hyperfine field in amorphous ferromagnets. Some information on the local symmetry around a given nuclear site is provided by analysis of the quadrupolar NMR spectra. Spin echo NMR spectra in amorphous ferromagnets exhibit structures whose origin is discussed for each family of alloy. These structures originate either from quadrupolar interactions, or from different magnetic states of the resonant species, or from well-defined regions of different local environments with different domain wall regimes.

Knight-shift and nuclear spin-lattice relaxation time measurements have been performed between 4.2°K and room temperature on 11 B and 31 P in amorphous NiPB alloys near the para-ferromagnetic transition. The EFG parameters on 11 B were found to be ν Q =200(±20)kHz and η = 0.35 (±0.10). Knight-shift and Korringa spin-lattice relaxation are mainly due to mechanisms involving p electrons. The effect of Ni magnetic clouds results in a broadening of the linewidth. We observed also the occurence of a Giovannini-Heeger-like contribution to the spin-lattice relaxation rate.

Revue de quelques etudes par RMN dans des metaux amorphes qui montrent l'apport de cette technique a l'elucidation de la structure de ces systemes

The NMR line shift contributions originating from demagnetizing fields due to classical macroscopic magnetic effects are discussed for ellipsoidal samples. It is shown that by measuring the line shifts along two main axes of the ellipsoid, the measured difference is sufficient to correct for demagnetizing effects in materials with homogeneous magnetization. It is also found that for special sample geometries even the demagnetizing factors are unnecessary for calculating the demagnetization correction term. Based on line shift and magnetization measurements, the measured and calculated differences of the NMR line positions are compared for sandwich-type samples. Alloys with inhomogeneous magnetization are also briefly discussed. Die durch makroskopische Entmagnetisierungseffekte auftretende Beitrage zur Verschiebung der Linien bei kernmagnetischer Resonanz werden fur Proben betrachtet, deren Gestalt ein Ellipsoid ist. Es wird gezeigt, das man, durch Messung der Linienverschiebungen entlang zweier Hauptachsen des Ellipsoids den Unterschied fur die Entmagnetisierungseffekte in Substanzen mit einer homogenen Magnetisierungsverteilung korrigieren kann. Fur spezielle Probenformen sind zu dieser Korrektur nicht einmal die Entmagnetisierungsfaktoren notig. Messungen der Linienverschiebungen und Magnetisierungen ermoglichten einen Vergleich der gemessenen und der berechneten Differenzen der Linienpositionen fur Sandwich-Proben. Der Fall von Legierungen mit inhomogener Magnetisierung wird kurz betrachtet.