Regular Domain Pattern Research Articles

Enhanced piezoelectric and dielectric properties of Pb(Yb1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals by combining alternating and direct current poling

As one of domain engineering methods, alternating current poling (ACP) has been proved a convenient, effective, economical method for the enhancement of the dielectric and piezoelectric properties of relaxor–PbTiO3 (PT) ferroelectric crystals. However, a shortcoming of ACP is that there are some non-rotational domains. To further improve the potential piezoelectric properties of relaxor–PT crystals, a modified poling method, combining alternating and direct current poling (ACP + DCP), was used for improving the piezoelectric properties of Pb(Yb1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3 (PYbN–PMN)–PT ferroelectric crystals. Compared with separate DCP and ACP, the piezoelectric coefficient d33 of [001]-oriented PYbN–PMN–PT crystals increased by 51% and 15% using ACP + DCP, respectively, indicating that applying an appropriate DCP on ACP samples is beneficial to further improve the piezoelectric properties. The domain analysis reveals that the full rotation of polarization, regular domain patterns, and domain boundaries are the key factors for the enhancement of piezoelectric and dielectric properties. We established the relationship between the position of the (300)c peaks, reflecting the degree of the stretch of the lattice, and piezoelectric properties. This work indicates that combining alternating and direct current poling methods is a better poling strategy for enhancing the piezoelectric properties of relaxor–PT ferroelectric crystals compared with separate DCP and ACP methods.

Magnetic microstructure in a stress-annealed Fe73.5Si15.5B7Nb3Cu1 soft magnetic alloy observed using off-axis electron holography and Lorentz microscopy

Fe-Si-B-Nb-Cu alloys are attractive for high frequency applications due to their low coercivity and high saturation magnetization. Here, we study the effect of stress annealing on magnetic microstructure in Fe73.5Si15.5B7Nb3Cu1 using off-axis electron holography and the Fresnel mode of Lorentz transmission electron microscopy. A stress of 50 MPa was applied to selected samples during rapid annealing for 4 s, resulting in uniaxial anisotropy perpendicular to the stress direction. The examination of focused ion beam milled lamellae prepared from each sample revealed a random magnetic domain pattern in the sample that had been rapidly annealed in the absence of stress, whereas a highly regular domain pattern was observed in the stress-annealed sample. We also measured a decrease in domain wall width from ∼ 94 nm in the sample annealed without stress to ∼ 80 nm in the stress-annealed sample.

Binding of Short Cationic Peptides (KX)4K to Negatively Charged DPPG Monolayers: Competition between Electrostatic and Hydrophobic Interactions.

The influence of the peptide sequence on the binding of short cationic peptides composed of five lysines alternating with uncharged amino acids within the series (KX)4K to negatively charged monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) was investigated by adsorption experiments in combination with epifluorescence microscopy. To evaluate the impact of electrostatic and hydrophobic contributions, different uncharged amino acids X with increasing hydrophobicity, where X = G (glycine), A (alanine), Abu (α-aminobutyric acid), V (valine), or L (leucine) were introduced into the peptide sequence to tune the peptide hydrophobicity. The adsorption kinetics of these peptides to a DPPG monolayer always showed two superimposed processes, one leading to an increase and another to a decrease of the surface pressure Π. Thus, the plots of the change in Π after peptide binding vs initial surface pressure of the monolayer showed an unusual behavior with maxima and negative changes in Π at high initial Π values. Epifluorescence microscopy confirmed that electrostatic binding of the peptides with a concomitant decrease in Π leads to a condensation of the lipid monolayer and the formation of liquid-condensed (LC) domains even at Π values where the monolayer is supposedly in the liquid-expanded (LE) state. An increase in hydrophobicity of the amino acid X was found to counteract the condensation and an increase in Π upon peptide binding is observed at low Π values, also concomitant with the formation of LC-domains. Compression of monolayers after peptide adsorption at low surface pressure for 4 h leads to a change of the isotherms compared to pure DPPG isotherms. The phase transition of DPPG from LE to LC state is smeared out or is shifted to higher surface pressure. Considerable changes in the shapes of LC-domains were observed after peptide binding. Growth of the LC-domains was hindered in most cases and regular domain patterns were formed. Binding of (KL)4K leads to a decrease in line tension and the formation of extended filaments protruding from initially circular domains.

Magnetostatic behaviour of antidot arrays under the local influence of nanopillars

We fabricated highly ordered patterned Permalloy nanometric structures by means of ion beam sputtering on top of an anodic aluminium oxide nanoporous template. First-order reversal curve (FORC) results and micromagnetic simulations indicate the presence of Permalloy inside one side of the pores, leading to a nanopillar array anisotropically arranged combined with an antidot array. The strong shape anisotropy of the pillar forces it to maintain the magnetization along its axis, even for a large in-plane applied field. This phenomenon induces out-of-plane hysteresis, as well as in-plane anisotropic behaviour. Depending on the in-plane applied field direction, the presence of nanopillars differently modifies the regular domain pattern, and therefore they could act as a new parameter for tailoring of magnetic anisotropy in antidot arrays.

Magnetic domain patterns in Co2MnGe Heusler nanostripes

We have prepared thin films of the ferromagnetic Heusler alloy Co2MnGe on a-plane Al2O3 substrates exhibiting growth-induced, superimposed fourfold and uniaxial magnetic anisotropies, the symmetry being determined by the single-crystalline Al2O3 substrate. The magnitude of the uniaxial anisotropy compared to the cubic anisotropy can be tuned over a wide range by the film thickness and the growth conditions. On submicrometer-wide stripes of Co2MnGe prepared by electron beam lithography we studied magnetic domain patterns by magnetic force microscopy. For stripes with a sufficiently large uniaxial anisotropy and with the easy axis oriented perpendicular to the stripe axis, we find perfectly regular domain patterns with the magnetization direction perpendicular to the stripe axis and alternating from domain to domain. The highly regular and controllable domain patterns in Co2MnGe nanostripes could be useful for magnetic storage devices and applications related to spin transfer torque.

Polarization inscription in ferroelectric (111) PZT and (100) SBT films

Abstract Ferroelectric thin films form an equilibrium domain structure compatible with their respective crystallographic symmetry. In tetragonal (111) PZT, 90° domains prevail; in (pseudo-tetragonal) (100) SBT both 90° and 180° domains are present. The size of 90° domains has been measured for e.g., PZT as slabs of ∼15 nm width. Domain size is a result of stress minimization in the film during the paraelectric (PE) → ferroelectric (FE) transition. A precise and regular domain pattern for (111) PZT and (100) SBT films has been investigated in detail by TMSFM. Single domains can be addressed mechanically with the tip of an AFM. Such single domain switching corresponds to a data storage density of ∼200 Gbit/inch 2 . Applications of ferroelectric and high- ɛ paraelectric materials for e.g., non-volatile data storage replacing DRAM devices or as sensors in infrared cameras are increasingly becoming popular.

Temperature-dependent domain investigations on exchange-biased IrMn-NiFe and IrMn-CoFe systems

The magnetic microstructure and magnetization processes of sputtered IrMn-NiFe exchange-biased films were studied by Kerr microscopy and magneto-optical magnetometry in a temperature range from room temperature to 200/spl deg/C. A ferromagnetic film in the exchange-biased state (as created by cooling a regular domain pattern or a saturated state from above the blocking temperature) is reversed in a patch-like way in applied magnetic fields, indicating inhomogeneities in the coupling. The domain processes are reversible far below the blocking temperature T/sub B/ and get increasingly irreversible within a range of some 10 K around T/sub B/. Magnetic anisotropies in the ferromagnetic layer, though clearly visible above the blocking temperature, have no significant influence on exchange bias. A granular frozen-in domain pattern is observed in as-deposited bilayers, indicating the presence of local exchange bias even without annealing.

Observation of recorded tracks in Co-Cr media by magnetic force microscopy

Tracks recorded on two Co-Cr layers having coercivities of 15 kA/m and 45 kA/m were investigated by magnetic force microscopy. Different wavelengths were recorded, corresponding to bit lengths between 0.125 and 0.5 mu m. In the case of the layer with the low coercivity, the bits in a track recorded with a wavelength of 0.5 mu m were obscured by the meandering nature of the transitions, something which is not observed for the high coercivity layer. This is consistent with a higher noise level and a lower signal level for the low coercivity layer in recording experiments. A more detailed observation of the tracks in the high layer revealed the presence of subdomains in the recorded bits. The extent to which regular domain patterns (recorded bits) or more detailed magnetic structures can be observed depends on the size of the magnetic tip and the distance between tip and layer. The observed width of the intrinsic domains in these layers agrees well with calculated values.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Microstructure and domain effects in ferroelectric ceramics

Abstract In tetragonally distorted ferroelectric ceramics a regular domain pattern develops, which allows the grain to keep its shape according to its clamping condition. In coarse grained ceramic the adjustment of the shape is possible in three dimensions, in fine grained ceramic and in thin films a two dimensional adjustment is adequate. Using these rules of 90°-twinning and the minimization of the free energy the domain width decreases with grain size. Irregular domain configurations in small regions of the grain indicate local stress regions. 90°-domain walls can contribute considerably to the dielectric behavior of the ceramic. Aging of the dielectric, elastic and piezoelectric constants result from various processes which are not well known. One of these processes is the clamping of the 90°-domain walls by oriented dipolar defects in the adjacent domains.

Domains in Liquid Crystals

A regular domain pattern has been observed to form in nematic liquid crystals when an electric field is applied. The domains are visible in unpolarized light by either transmission or reflection. Both ac and dc fields produce similar domain patterns and these appear at a rather sharp threshold field of about 1000 V/cm. The general features of the phenomenon have been investigated. It is believed that the domains are due to ordering in the liquid of a kind which has not previously been recognized.