Magnetic Microstructural Analysis Research Articles

Magnetic microstructure analysis of sputter deposited permalloy thin films on a spin-on polyimide substrate

We have performed magneto-optical measurements of sputter deposited permalloy (NiFe 81/19) thin films on a polyimide based spin-on substrate and a silicon oxide substrate. Experiments were performed by means of the magneto-optic Kerr effect in order to complement the findings concerning soft magnetic behaviour on the macroscopic scale presented previously (Rittinger et al., Impact of different polyimide-based substrates on the soft magnetic properties of NiFe thin films, SPIE Microtechnologies. International Society for Optics and Photonics, Bellingham, pp 95171R, 2015) with new insights into the magnetic domain structures of such samples. First, magnetization curves (R---H-, B---H-curves) are compared with corresponding magneto-optical hystereses. Second, by taking into consideration the results of the magnetic microstructure analysis, further aspects of the interactions between the substrate and the functional thin film are revealed in form of analogies between observations on the microscopic scale and variations of macroscopic magnetization curves of analysed samples. Furthermore, the shape and detailed spatial arrangement of domains and their boundaries are determined for the investigated samples, supplying further information on the properties and state of stress of the thin films. Doing so, we aim to provide precise and reliable anisotropic magnetoresistive (AMR) sensors on flexible polymer substrates in the future.

Magnetic Microstructure Analysis of Ferromagnetic Shape Memory Alloys and Related Compounds

We performed magnetic imaging of Ni-based ferromagnetic shape memory alloys. The magnetic microstructure was revealed by Lorentz microscopy and electron holography, which are powerful tools based on transmission electron microscopy. Observations of Ni51Fe22Ga27 and Ni50Mn25Al12.5Ga12.5 alloys, both of which have an L21-ordered structure in the parent phase, demonstrated that the antiphase boundaries (i.e., a type of planer defects) caused significant changes in the magnetization distribution due to depression of the atomic order—actually, the magnetization in these alloys depends upon the degree of chemical order. We propose a method which estimates the important magnetic parameters (the magnetocrystalline anisotropy constant and exchange stiffness constant) based on transmission electron microscopy observations. This method should be useful in magnetic measurements of nanometer-scale areas, for which conventional techniques cannot be applied.

Two-dimensional analysis of magnetic microstructures in the DC-demagnetized state and magnetization fluctuations in the transition region using MFM images

This study analyzed the directional dependence of magnetic microstructures of media by focusing on the distribution of magnetic poles. Media, whose magnetic poles tend to be distributed along a specific direction in the DC-demagnetized state, have larger magnetization fluctuations in the transition region, larger medium noise and higher partial erasure (PE) probability than media with uniform magnetic pole distribution.

Magnetic Domains. The Analysis of Magnetic Microstructures

A. Hubert and R. Schafer, Magnetic Domains. The Analysis of Magnetic Microstructures, Springer-Verlag, Berlin, Heidelberg, New York ~1998!, 720 pp., 400 figs., ISBN 3-540-64108-4 An overwhelming majority of magnetic materials used in science and engineering exist in the polydomain state. Hence the physical properties of magnetic domains and their evolution in external magnetic fields determine most of the functional characteristics of devices containing magnetic components. Decades of intensive studies have yielded numerous methods for observing and analyzing magnetic domains and a large body of experimental results, as well as different theoretical methods which were developed for describing the polydomain states. Recent advances in the field of nanotechnology have led to the production of basically new magnetic materials, which has further stimulated fundamental and applied research of magnetic domains. This is mainly due to the fact that at the current level of miniaturization of magnetoelectronic instruments, the behavior of individual domains affects significantly the functioning of such devices. In spite of the large number of monographs and reviews devoted to individual aspects of the physics of magnetic domains, the present book is the first attempt in the world literature to present this comprehensive branch of magnetism in a single volume. The book is authored by Prof. Alex Hubert, a leading authority in the field of magnetic materials science, and his pupil Dr. R. Schafer, a specialist in magneto-optical research. It should be recalled that Hubert’s monograph entitled ‘‘Theorie der Domanenwande in Geordneten Medien’’ ~Theory of Domain Walls in Ordered Media! ~Springer-Verlag, Berlin, 1974!, which was also translated into Russian in 1977 by Mir Publishers, Moscow, continues to be one of the most veritable publications on the basic principles of the physics of domain walls in condensed media. The authors of the project realized it at the expense of enormous efforts and time. The book was written over a very long time ~beginning in 1984!. During this period, the authors gathered, analyzed and systematized a very large number of publications devoted to the experimental, theoretical and applied aspects of the investigations of domain structure. The monograph has an elegant and carefully planned structure. The historical review presented in Chapter 1 is followed by a detailed description of the methods of

Microstructural Analysis of CoCr Thin Films by Small-Angle Neutron Scattering

Small-angle neutron scattering is applied to the analysis of latent microstructures in compositionally separated CoCr thin films. A fine in-grain structure less than 10 nm in size is observed in a film deposited at 200°C using small-angle scattering. This structure coincides with that observed by means of transmission electron microscopy (TEM) in chemically etched thin films. The fine in-grain structure disappears when the deposition temperature is increased to 400°C. This experiment confirms the existence of latent microstructures in CoCr films and reveals that further analysis of magnetic microstructures is possible using neutron scattering.

Surface Magnetic Microstructural Analysis using Scanning Electron Microscopy with Polarization Analysis (SEMPA)

High resolution imaging of magnetic microstructure has important ramifications for both fundamental studies of magnetism and the technology surrounding the magnetic recording industry. In SEMPA, a focused beam of electrons excites secondary electrons on a ferromagnet's surface. The secondaries leave the solid with an electron spin polarization which is characteristic of the net spin density in the ferromagnet. This is related directly to the sample magnetization. By scanning the beam and analyzing the secondary electron spin polarization at each point, a magnetization map of the ferromagnet's surface is generated.As SEMPA is a surface sensitive, magnetic microstructural analysis technique, the environment local to the specimen must be ultra-high vacuum. A schematic of our SEMPA instrument is shown in figure 1. The probe forming electron optical column of a SEMPA system must produce small probes with high currents (> 1 nA) at long working distances ( > 10 mm). The SEMPA system may be equipped with a single, or multiple spin detectors as in figure 1. Two detectors are used for the acquisition of all three orthogonal components of the polarization vector signal. The inefficiency of all polarimeters makes SEMPA time consuming when compared to conventional SEM. The polarized secondary electrons must be extracted efficiently without introducing any deleterious effects into the focused incident electron beam. This imposes limits on incident beam energies and extraction voltages for the transport optics. Additionally, the transport optics must map the scanned spot of the secondary electrons produced under the incident rastered beam, to a (stationary) position on the spin detector such that undesirable instrumental asymmetries are not introduced.