Amorphous ribbons of composition Fe/sub 74.5-x/Cu/sub x/Nb/sub 3/Si/sub 13.5/B/sub 9/ (x=0, 1 at.%) have been annealed between about 500 degrees C and 900 degrees C. This produced a series of crystallized samples with grain sizes between about 10 nm and 300 nm and with coercivities H/sub c/ and initial permeabilities mu /sub i/ varying over several orders of magnitude. The best soft magnetic properties (H/sub c/ approximately=0.01 A/cm and mu /sub i/ approximately=80*10/sup 3/) were observed for the smallest grain sized of about 10 nm. With increasing grain size D, coercivity steeply increases following a D/sup 6/-power law (up to D approximately=50 nm). H/sub c/ then runs through a maximum of H/sub c/ approximately=30 A/cm and decreases again for grain sizes above 150 nm according to the well-known 1/D law for polycrystalline magnets. The initial permeability was found to vary in a similar manner, essentially being inversely proportional to coercivity. The variation of the soft magnetic properties with the average grain size is discussed and compared with the predictions of the random anisotropy model and other theories for the magnetization reversal. >

Grain size dependence of coercivity and permeability in nanocrystalline ferromagnets

The various origins of a frequency-dependent conductivity in amorphous semiconductors are reviewed, stressing particularly recent advances and the influences that factors such as correlation and non-random spatial distributions of electrically active centres can have on the a.c. conductivity. A comprehensive survey is given of the experimental a.c. data for two types of amorphous semiconductor, namely chalcogenide and pnictide materials. It is concluded that the a.c. behaviour at intermediate to high temperatures is well accounted for by the correlated-barrier-hopping model, whereas the low-temperature behaviour is probably due to atomic tunnelling.

A.c. conduction in amorphous chalcogenide and pnictide semiconductors

Recent developments in the theoretical analysis and experimental study of frequency-dependent loss by relaxation in amorphous semiconductors are reviewed. A unified theoretical treatment of the complex a.c. conductivity is given, within the pair approximation, for single electron tunnelling and hopping in both uncorrelated and strongly correlated cases, and the discussion is then extended to pair processes and to atomic relaxation. The problems associated with measuring the frequency dependent conductivity of amorphous samples are considered, and relevant measurements reported for the different classes of amorphous semiconductors, tetrahedral and group V materials and chalcogenides are reviewed in the light of the available theoretical models. The similarity in the magnitudes and frequency, temperature and electric field dependences of the losses observed in many different systems at liquid helium temperatures is noted, and the possible physical reasons for this are examined.

Frequency-dependent loss in amorphous semiconductors

In this paper an attempt is made to establish the nature of free charge carriers and of charge carriers bound to centres in p-type NiO, CoO and MnO and in n-type MnO and α-Fe2O3. For free charge carriers, d.c. conductivity, Seebeck coefficient and Hall effect are considered. Effects arising from inhomogeneous conduction and impurity conduction are discussed. Impurity conduction appears to have a strong influence on transport properties in the case of α-Fe2O3, less so in NiO, whereas no influence of this effect has been found in CoO and MnO. It is shown that NiO and CoO do not exhibit the features characteristic of small-polaron conductors but rather can be consistently conceived of as large-polaron band semiconductors. It is suggested that magnetic resistance due to exchange coupling between charge-carrier spin and cation spins plays an important role. The anomalous behaviour of the Hall effect in NiO and α-Fe2O3 is extensively discussed. In contradistinction to NiO, CoO and n-type MnO, free char...

Small-polaron versus band conduction in some transition-metal oxides

The formation kinetics and electric properties of anodic barrier oxides on Al, Hf, Nb, Ta, Ti, and Zr depend on the migration of ions, controlled by an electric field strength of up to 107 V cm−1. The high field model, based on ideas of Guntherschulze, Betz, Verwey, Mott, and Cabrera, explains only parts of the experiments. Contradictory models and investigations of the last 60 years are compared with new results, which enable a more detailed understanding of many aspects of the high field model, e.g. the shape of experimental transients, the time and field dependent concentration of mobile ions, the nature of the mobile species and the interaction of anion and cation transport, and the location of the rate determining step.

Thin anodic oxide layers on aluminium and other valve metals: high field regime

The impedance of a growing anodic oxide layer is inductive in a certain frequency range. This effect is related to the occurrence of transients after changes in current density or applied electric field. Measurements on aluminum samples in the frequency range 5 mHz‐10 kHz and the current density range and in various electrolytes are presented and compared with a theory in which the relaxation effect is ascribed to a buildup of surface charge at the metal‐oxide interface.

https://iopscience.iop.org/article/10.1149/1.2129138/pdf

Impedance Measurements during Anodization of Aluminum

The magnetic and structural properties of ion beam sputtered Fe/CoNbZr multilayers were studied as a function of the CoNbZr and Fe layer thickness. Good soft‐magnetic properties (coercivity 1000) are obtained only when the Fe grains are small, which is the case for multilayers with Fe layer thicknesses below 10 nm and CoNbZr layer thicknesses above 4 nm. Thick CoNbZr layers (>4 nm) are amorphous and repeated nucleation of Fe grains is observed. When the CoNbZr layers are too thin (<3 nm) they are crystalline and do not interrupt the Fe grain growth. The resulting columnar growth of Fe throughout the total film thickness leads then to a drastic decrease of permeability and increase of coercivity.

Soft‐magnetic properties and structure of Fe/CoNbZr multilayers

An anodischen Al2O3-Filmen mit Dicken zwischen 200-2500 A werden dielektrische Durchschlage gemessen (nonshorting-Methode) und gezeigt, das die Durchschlagsfeldstarke, die dicht bei der Anodisierungsfeldstarke liegt, unabhangig von der Dicke ist.

The Dielectric Breakdown of Anodic Aluminum Oxide

Electrical conductivity of Li doped MnO

Uniaxial anisotropy induced by magnetic annealing was studied on amorphous CoFeSiB and CoNbZr layers. The kinetics of inducing the anisotropy is slowed down by a preanneal at 400°C. This effect is much stronger for CoNbZr than for CoFeSiB. An addition of 2% transition metal (TM) atoms does not influence the kinetics after preannealing appreciably. Simultaneously with inducing anisotropy magnetic annealing changes the magnetostriction. Two effects determine the anisotropy, orientation of pairs of different magnetic atoms and a contribution which also occurs in alloys with a single magnetic atom. The latter contribution is independent of type and size of the non-magnetic atom(s) and is attributed to Co - clusters.

H.J. de Wit

Papers

Impedance Measurements during Anodization of Aluminum

Soft‐magnetic properties and structure of Fe/CoNbZr multilayers

The Dielectric Breakdown of Anodic Aluminum Oxide

Electrical conductivity of Li doped MnO

Induced anisotropy of amorphous CoFeSiB and CoNbZr magnetic materials