Surface Domain Patterns Research Articles

Fabrication of chemical patterns from graphoepitaxially assembled block copolymer films by molecular transfer printing

Fabrication of chemical patterns by electron beam lithography or extreme ultraviolet interference lithography is either low-throughput or prohibitively expensive to practice at sub-50 nm feature dimension. Here we report a new high-throughput approach that combines the advantages of both graphoepitaxy and molecular transfer printing (MTP) to fabricating chemical patterns at low cost for directed assembly of block copolymers. In this new approach, a cylinder-forming block copolymer ternary blend film is directed to assemble on a topographic HSQ substrate with sub-Lo, where Lo is the natural period of the block copolymer, relief structures to increase the feature density by a factor of ∼20, the surface domain pattern is replicated using MTP to create 1:1 chemical pattern, and then a lamellae-forming block copolymer is directed to assemble on the chemical pattern to realize high-aspect ratio Manhattan type nanostructures. This combined strategy allows us to fabricate chemical patterns with feature dimension below the resolution limit of current lithographic tools.

Effect of field cooling process and ion-beam bombardment on the exchange bias of NiCo/(Ni, Co)O bilayers

The research on exchange coupled ferromagnetic/antiferromagnetic (FM/AF) bilayers has been the foundation of spintronic applications such as hard disk reading heads and spin torque oscillators. In order to further explore the exchange bias behavior of NiCo/(Ni, Co)O bilayers, effect of field cooling process, magnetic angular dependence, and ion-beam bombardment was investigated. The difference in film composition resulted in remarkable distinction in crystalline structures and domain patterns. The exchange bias field (Hex) in the bilayer systems exhibited a strong angular dependence. The negative Hex after a field cooling process indicated that the polarity of Hex can be defined by aligning the magnetization orientation of the FM NiCo layer with the applied field. Moreover, enhanced exchange bias effect was observed in the NiCo/(Ni, Co)O bilayers that resulted from the surface of the (Ni, Co)O layers bombarded with different Ar+ ion-beam energies using End-Hall voltages from 0V to 150V. The interface spin structures as well as the surface domain patterns were altered by the ion-beam bombardment process. These results indicated that the exchange bias field of NiCo/(Ni, Co)O bilayer systems could be tailored by field cooling process, angular dependence of magnetic properties, and post ion-beam bombardment.

Piezoresponse force microscopy studies on the domain structures and local switching behavior of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals

The static domain structures and local switching behavior of relaxor ferroelectric 0.29Pb(In1/2Nb1/2)O3-0.44Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 single crystals at three crystal orientations are studied using piezoresponse force microscopy (PFM). PFM domain imaging shows that both the [001] and [111] oriented crystals exhibit a labyrinth-like surface domain pattern while at the [110] crystal orientation the domains are preferentially aligned along 〈110〉 directions. Vertical and lateral PFM images are used in combination to discuss the polarization vector alignment underlying the observed domain behaviour. Piezoresponse hysteresis loops acquired from these crystals indicate that the [111] crystal orientation has distinct local switching characteristics from the other two orientations in terms of, e.g., coercive voltage. Moreover, we investigate the tip-induced domain growth kinetics on an externally poled [001] crystal, the results of which exemplify an important role of extrinsic factors, e.g., the charge injection effect, in the domain patterning process.

Multiscale magnetic study of Ni(111) and graphene on Ni(111)

We have investigated the magnetism of the bare and graphene-covered (111) surface of a Ni single crystal employing three different magnetic imaging techniques and ab initio calculations, covering length scales from the nanometer regime up to several millimeters. With low temperature spinpolarized scanning tunneling microscopy (SP-STM) we find domain walls with widths of 60 - 90 nm, which can be moved by small perpendicular magnetic fields. Spin contrast is also achieved on the graphene-covered surface, which means that the electron density in the vacuum above graphene is substantially spin-polarized. In accordance with our ab initio calculations we find an enhanced atomic corrugation with respect to the bare surface, due to the presence of the carbon pz orbitals and as a result of the quenching of Ni surface states. The latter also leads to an inversion of spinpolarization with respect to the pristine surface. Room temperature Kerr microscopy shows a stripe like domain pattern with stripe widths of 3 - 6 {\mu}m. Applying in-plane-fields, domain walls start to move at about 13 mT and a single domain state is achieved at 140 mT. Via scanning electron microscopy with polarization analysis (SEMPA) a second type of modulation within the stripes is found and identified as 330 nm wide V-lines. Qualitatively, the observed surface domain pattern originates from bulk domains and their quasi-domain branching is driven by stray field reduction.

MFM studies of magnetic domain patterns in bulk barium ferrite (BaFe 12O 19) single crystals

Magnetic domain patterns in bulk barium ferrite (BaFe 12O 19; BaM) single crystals on the basal plane and the prism plane were measured and studied by magnetic force microscopy (MFM). The surface domain pattern is in the form of flowers or star on the basal plane and long elongated spikes or stripe domains on the prism plane. The change in domain structure with applied field ( H app) and the thickness ( T) dependence on domain width ( δ) was observed. The domain width decreased from 32 to 9 μm for the crystals of 800–100 μm thicknesses, respectively.

Molecular Growth Determined by Surface Domain Patterns

The growth of iron phthalocyanine (FePc) on InSb(001) c(8 x 2) at submonolayer coverage has been investigated with scanning tunneling microscopy (STM). FePc adsorbs flat centered on the In rows both at 70 K and at room temperature (RT). However, the shapes of the two-dimensional molecular islands are fundamentally different; while the RT growth results in chainlike structures along the [I 10] direction, as already observed for other Pc's adsorbed on the same surface, the islands are prolonged along [110], i.e., perpendicular to the substrate rows, at 70 K. These observations are explained on the basis of a recently observed new surface phase at low temperature, resulting in structural domains on the surface. The molecular growth front follows the propagating domain boundary that freezes at low temperature.

Surface domains in inhomogeneous yttrium iron garnet films

We have studied magnetic domain structures in yttrium iron garnet films with inhomogeneous anisotropy field distribution across the film thickness. Two methods of domain visualization were used: (1) magnetic force microscopy and (2) magneto-optics. The experiments have revealed an existence of surface domains. The transformations of the surface domain pattern in the external magnetic field have been also observed.

Structured Surfaces and Morphological Wetting Transitions

Recent theoretical and experimental studies have shown that structured surfaces, which contain patterns of lyophilic surface domains, lead to morphological wetting transitions at which the wetting layer changes its shape in a characteristic and typically abrupt manner. These transitions have been determined for several specific surface domain patterns consisting of circular, striped, or ring-shaped domains, as well as for slit pores and slabs bounded by striped surfaces. Such transitions are predicted to be rather generic and to occur for any type of structured surface.

Wavelength dependent neutron depolarization in some metallic glasses

Ferromagnetic metallic glass ribbons Fe 34.6Ni 36.5Mo 6B 22.9, (Fe 50Ni 50) 94.9B 5.1, Fe 78Co 8.1B 13.9 and Fe 56.2Co 7Ni 15.6 Si 4B 17.2 were studied by magneto-optical methods (Kerr effect, magnetic colloid fluid technique) sensitive to the surface in combination with bulk domain structure determination by means of the neutron depolarization technique. The dependence of polarization of a polychromatic beam of polarized neutrons transmitted through the samples on the neutron wavelength was analysed by fitting to the data domain structure models consistent with the surface domain patterns; it enabled to estimate the mean domain size as well as the mean magnetic induction, its fluctuations, and orientation with respect to applied magnetic field.

Coercivity and microstructure of Sm(Co0.87Cu0.13)7.8

The magnetic hardness of Sm(Co0.87Cu0.13)7.3 in bulk form is caused by pinning of the domain walls at precipitates which are of the Sm(Co,Cu)5 type. The hard magnetic properties of both the 2 : 17 matrix and the 1 : 5 precipitate phase have been investigated in the temperature range between 77 and 800 K. The domain-wall energies have been determined from the surface domain patterns observed by means of the magneto-optical Kerr effect. It is shown that the coercivity mechanism in Sm(Co0.87Cu0.13)7.8 cannot be explained by the difference of the magnetic crystal anisotropy constants K1 of matrix and precipitate phase only. However, the coercivity may be described by the decrease in the domain-wall energy γ at the precipitates. γ of the 2 : 17 matrix was found to be five times that of the 1 : 5 precipitate phase (38 and 7.5 erg cm−2, respectively) resulting in an attractive interaction between the precipitates and the domain wall. The magnetic field necessary to overcome this attractive interaction has been estimated to be approximately 5 kOe, i.e., comparable to the experimentally obtained value of 4 kOe.

Influence of sample surface on thermomagnetic effects in Fe40-Ni60

It is shown that the effect of an induced anisotropy energy due to directional order in Fe40-Ni60 is strongly dependent on the sample-to-volume ratio. Torodial samples of various thickness (6,3,1,0.5 mm) were machined from the same ingot, chemically etched, and annealed at 1300°C in H 2 . All further annealings were performed at 450°C in N 2 in one of the following magnetic conditions: a) demagnetized state; b) under magnetic field; c) remanent state. After these annealings loops show a constricted shape (a), a closely square shape with small coercive field H c (b), or a square shape with large H c (c). However, the width of the constricted region after annealing a), and the magnitude of H c after b) or c), are found to increase for decreasing sample thickness; in general, changes of loop shape induced by a given annealing are markedly stronger on thinner specimens. These differences are attributed to some influence of sample surface on the thermomagnetic treatment. This conclusion was further checked by electrochemically etching off a sample layer (0.01-0.1 mm); as a consequence the shapes of the loops obtained by the previous annealing suffered changes which were strongly different depending on the original thickness of the sample. It is qualitatively observed that the induction of a directional anisotropy energy K u occurs according to the domain pattern present during annealing, and that surface patterns are certainly characterized by smaller spacings of 180° domains and larger densities of 90° closure domains than are bulk patterns. Therefore the effectiveness on the loop shape of a K u distribution in a surface layer is stronger than the one of a K u distribution induced in a bulk layer. By etching off a sample layer, the new surface domain pattern bears little correlation to the old K u distribution, and there is a memory loss of previous annealing results, which is more pronounced on samples with larger surface-to-volume ratios.

Magnetic domain observations on 0.014-inch 50-percent Ni-Fe strip

The Kerr effect was used to observe and photograph surface domain patterns in the 0.014-inch 50-percent Ni-Fe strip after high temperature vacuum annealing treatments on commercial cold rolled material. The type of domain pattern observed depended on the recrystallization texture and also on the duration of the annealing treatment. The domain structure in primary recrystallization textures,

Magnetic domain observations in 50-percent Ni-Fe tapes

Domain observations using the Kerr effect have been made on 50-percent Ni-Fe grain oriented tapes of 50-μm (2-mil) and 100-μm (4-mil) thickness. The surface domain patterns differ depending on sample preparation, which is described in detail. When the tape samples were annealed and then electrochemically polished, complex patterns, suggestive of surface stresses, appeared. When the tape samples were annealed after electrochemical polishing, the patterns observed were in close agreement with previously postulated models for flux reversal in 50-percent Ni-Fe tapes. Correlations of surface domain structure with net magnetization were also made by inductive pickup, and data on the observed coercive forces are included.

A further investigation of factors influencing domain configurations in yttrium iron garnet

The domain patterns exhibited by flux-grown crystals of yttrium iron garnet are described and interpreted in terms of oriented strains resulting from the growth process. Thin sections that are carefully prepared and have as one surface a well-defined growth pyramid show domain patterns consisting of parallel bands when observed by transmitted polarized light. The bands are symmetrically arranged around the growth center responsible for the pyramid to form a system of concentric diamonds. The directions of magnetization within the bands are not parallel to the 〈111〉 easy directions of magnetization in the plane of the sample but rather cross each quadrant formed by the growth pyramid at an angle of about 45°. Surface domain patterns, formed by deposition of colloidal magnetite, are also symmetrical with respect to the growth pyramids and can be correlated with the transmission patterns. Surface tree patterns are observed and interpreted as arrays of compensating domains resulting from the presence of weak magnetic poles on the crystal faces. The effects of annealing and silicon incorporation on the domain patterns of yttrium iron garnet are described and discussed in terms of strain reduction.