S. R. Herd

Bio: S. R. Herd is an academic researcher. The author has contributed to research in topics: Coercivity & Magnetic domain. The author has an hindex of 1, co-authored 1 publications receiving 29 citations.

Magnetic domain structures in multilayered NiFe films

Abstract: The coercivity of NiFe (80/20) films can be lowered by laminating several layers with nonmagnetic spacers. A reduction by a factor of 10 can be achieved with a simple bi‐layer, regardless of spacer material, provided the spacer thickness is below a critical value. No further reduction is found for multilayers. Two peaks of Hc near thicknesses of 250A and 1000A for single layer films, associated with changes in domain structure, are suppressed by lamination. After a minimum spacer thickness (S) of 10–15A, the domain walls in the separate layers no longer coincide but track closely, their separation depending on S. With S?100A the layers switch independently, giving rise to multiple values of Hc.

Magnetic properties of multilayered Fe‐Si films

Abstract: The coercivity and permeability of Fe‐Si films can be improved by laminating several layers with either nonmagnetic (SiO2, Al2O3, Al or Mo) or ferromagnetic (Ni, Fe, Co or 20‐wt. % Fe–Ni) spacers. It is also found that films made with soft magnetic laminations have an advantage over nonmagnetic or hard magnetic ones. Such behavior is concluded to be attributed to the smaller grain size, and pinhole or exchange coupling of multilayered Fe‐Si films by observing domain and grain structures.

Magnetic and structural characterization of sputtered FeN multilayer films

Abstract: The magnetic and structural properties of ferromagnetic FeN thin films, FeN/FeN (ferromagnetic/paramagnetic), and FeN/SiO2 multilayers deposited in a rotational dc magnetron sputter system were investigated. Monolithic films containing ≂2 at. % N2 had 4πMs values ≂25 kG. The Fe16N2 phase has been identified by electron microdiffraction in these films. Saturation magnetostriction (λs) has been related to N2 content and can be varied from −3×10−6 to 5×10−6 in a range of compositions where 4πMs is ≳22 kG. Lamination reduced easy and hard axis coercivity to <1 Oe and produced single domain configurations in yoke‐shaped structures. Lorentz microscopy indicated that the ferromagnetic FeN layers in the FeN/FeN films were exchanged coupled while those in the FeN/SiO2 films were magnetostatically coupled.

Nanostructure and chemical inhomogeneity in TbFe magneto-optical films

Abstract: High spatial resolution chemical imaging results provided the first direct experimental evidence illustrating nanosegregation in thin films of sputtered Tb-Fe alloys. The observed chemical segregation appeared to result from the initial nucleation and growth of stable Fe-rich amorphous phase. The measured properties such as local fluctuation and magnetization reversal processes are explained on the basis of this chemical segregation effect. >

A magnetostatic-coupling based remote query sensor for environmental monitoring

Abstract: A new type of in situ, remotely monitored magnetism-based sensor is presented that is comprised of an array of magnetically soft, magnetostatically-coupled ferromagnetic thin-film elements or particles combined with a chemically responsive material that swells or shrinks in response to the analyte of interest. As the chemically responsive material changes size the distance between the ferromagnetic elements changes, altering the inter-element magnetostatic coupling. This in turn changes the coercive force of the sensor, the amplitude of the voltage spikes detected in nearby pick-up coils upon magnetization reversal and the number of higher-order harmonics generated by the flux reversal. Since the sensor is monitored through changes in magnetic flux, no physical connections such as wires or cables are needed to obtain sensor information, nor is line of sight alignment required as with laser telemetry; the sensors can be detected from within sealed, opaque or thin metallic enclosures.

Wall clusters and domain structure conversions

Abstract: The significance of wall clusters, which is a new concept in the theory of soft magnetic materials, is experimentally demonstrated in thin Permalloy configurations. The wall cluster is a collection of domain walls that have one intersection line in common. The transformation of the domain structures takes place through a coherent movement of the domain walls. The correlation between the walls is especially dominant at the intersection line of the walls, called the cluster knot. Relations for the mutual positions of the walls in the wall clusters of great practical relevance are derived explicitly and verified experimentally. The domain structure is formed by the concatenation of wall clusters. The clock sense of the rotation over the walls in the clusters determine which walls of two clusters are linked during the formation of the domain structure. The creation of new clusters takes place through the unfolding of the walls of the clusters which originally coincide with the so-called creation line. As is demonstrated fully, the application of these ideas improves the insight into the complex process of domain structure transformations.