Magnetic Stripe Domains Research Articles

Magnetic Properties of Hexagonally Ordered Arrays of Fe Antidots by Vacuum Thermal Evaporation on Nanoporous Alumina Templates

Highly ordered arrays of Fe antidot films were fabricated by thermal vapor deposition technique using nanoporous alumina templates. The film thickness varies from 20 up to 100 nm, and the antidots array has about 50 nm in diameter and 105 nm of periodic interspacing. Scanning electron microscopy and atomic force microscopy measurements confirmed that the Fe antidots film retains the well-ordered hexagonal structure of the nanoporous alumina template. Meanwhile, the micromagnetic structure was studied by magnetic force microscopy and SQUID measurements. A stripe magnetic domain pattern featuring a large out-of-plane magnetization component is found in the films. Noteworthily, the magnetic domains are not pinned by the nanopores but, on the contrary, several antidots are included in each magnetic domain. According to the magnetic measurements, the easy magnetization axis of the Fe antidot array remains in the film plane, while the hard one lies perpendicular to the plane, which can be explained on the basis of the different contributions of the nanoholes to the total magnetic anisotropy of the antidots film.

Adjustable superconducting anisotropy in MoGe-Permalloy hybrids

We studied the magneto-transport properties of magnetically coupled superconducto ferromagnet MoGe/Permalloy bilayers. The rotatable anisotropy Permalloy ferromagnet with stripe domain structure induces in-plane anisotropy in superconducting order parameter. Superconducting phase diagram shows that near the superconductor-normal state phase boundary the superconductivity is localized in narrow mesoscopic channels just above the magnetic domain walls. By changing the in-plane direction of magnetic stripe domains it is possible to re-configure the direction of the superconducting channels and controllably rotate the direction of the in-plane anisotropy axis in the superconductor.

Magnetron sputtering deposition of Pr12.5Fe77.5B10 thin films and substrate temperature dependence of the magnetic properties

Thin films of Pr12.5Fe77.5B10 have been successfully fabricated on thermally oxidized Si substrates by magnetron sputtering deposition. The microstructure and magnetic properties were altered by controlling the substrate temperature during the deposition. The stripe magnetic domain structure arising from the perpendicular magnetic anisotropy was observed by a magnetic force microscope in the uniform amorphous film deposited at room temperature. In contrast, the exchange coupled magnetic domain leading to the magnetic hardening was evidenced in the film deposited at 600 °C. These results suggest the great possibility of Pr12.5Fe77.5B10 thin films for electromagnetically actuated microelectromechanical applications.

Direct and simultaneous observation of ferroelectric and magnetic domains

Abstract The ferroelectric/magnetic domain structure in a magnetoelectric binding BaTiO 3 /Fe 81 Ga 19 and the ferroelectric/crystallographic domain structure in a magnetoelectric binding PMN-34PT/Mn 50 Ni 28 Ga 22 were observed successfully by scanning electron acoustic microscopy (SEAM). Both the stripe ferroelectric domains in single crystals and the stripe magnetic domains in polycrystalline grains are obtained simultaneously, which exhibits that the scanning electron acoustic microscopy is a unique imaging technique. In addition, the experimental results show that the SEAM technique may be used in multiferroics to character two or more ferroic domains simultaneously. The imaging mechanisms of ferroelectric domains, magnetic domains, and crystallographic domains are attributed to piezoelectric coupling mechanism, magneto–elastic coupling mechanism, and thermo–wave coupling mechanism, respectively.

Tunable transport in magnetically coupled MoGe/Permalloy hybrids

We demonstrate controlled magnetotransport anisotropy of magnetically coupled superconductor-ferromagnet MoGe/Permalloy hybrids. The rotatable anisotropy Permalloy ferromagnet with stripe domain structure induces in-plane anisotropy in superconducting order parameter. We show that near the superconductor-normal state phase boundary the superconductivity in MoGe is localized in narrow mesoscopic channels just above the magnetic domain walls. Changing the in-plane direction of magnetic stripe domains it is possible to reconfigure the direction of the superconducting channels and controllably rotate the direction of the in-plane anisotropy axis in the superconductor.

Temperature dependence of the exchange stiffness in FePd(001) thin films: Deviation from the empirical lawA(T)∝MS2at intermediate temperatures

We study the temperature dependence of the exchange stiffness $A(T)$ of a thin FePd(001) film, which exhibits well-ordered magnetic stripe domains. We employed two different methods: (i) applying an exact micromagnetic model of the nucleation point and (ii) a detailed analysis of the temperature dependence of the saturation magnetization. The experimental data needed as input for the theoretical model are the stripe domain width and the nucleation field, and these were obtained as a function of temperature using soft x-ray magnetic scattering and superconducting quantum interference device (SQUID) magnetometry, respectively. The temperature independence of the domain width is very important from the point of view of the energetics of the FePd film, i.e., the number of magnetic domains remains constant per unit area. From this experimental finding we infer that the exchange stiffness must vary as a function of the temperature. We show that the $A(T)$ dependence obtained with the two procedures are consistent but different from the phenomenological law $A(T)\ensuremath{\propto}{M}_{S}^{2}(T)$, normally assumed to be valid in the temperature range examined $(T=50\char21{}250\text{ }\text{K})$, an intermediate temperature range for which there is no known expression of the magnetization as a function of the temperature. We have also investigated the $\text{Fe}\text{ }3s$ core level and valence band of FePd using hard x-ray photoemission spectroscopy. The $\text{Fe}\text{ }3s$ spectra exhibit negligible changes in the temperature range investigated, while small changes occurring over large energy scales are observed in the valence-band spectra. Based on the lack of consistency of the magnetometry and scattering results compared to local-moment theories, these results favor an itinerant magnetism picture for FePd.

Magnetization and Domain Patterns in Martensitic NiMnGa Films on Si(100) Wafer

A series of Ni51.4Mn28.3Ga20.3 films sputter-deposited on Si(100) wafer (with 500 nm thick buffer layer of SiNx) and annealed at 800 oC for 1h. are investigated with respect to their transformation behavior and magnetic properties. The film thickness, d, varies from 0.1 to 5.0 μm. Resistivity measurements reveal martensitic transformation above room temperature for all the films except for 0.1μm-thick film which is transforming at much lower temperature. The magnetic characteristics of martensitic films such as susceptibility and anisotropy field extracted from the inplane and out-of-plane magnetization curves show film thickness dependence likewise Curie temperature obtained from the resistivity curves. The surface topography and micromagnetic structure are studied by scanning probe microscopy. A stripe magnetic domain pattern featuring a large out-of-plane magnetization component is found in the films. The domain width, δ, depends on the film thickness, d, as δ ~ d .

Superconductor/ferromagnet bilayers: Influence of magnetic domain structure on vortex dynamics

We study the magnetically coupled superconductor-ferromagnet bilayers comprised of a ferromagnet with a rotatable periodic stripelike magnetic domain structure with alternating out-of-plane component of magnetization and a MoGe superconductor. We demonstrate a prominent difference in critical current density between cases when magnetic domain stripes are oriented parallel and perpendicular to the superconducting current. The bilayer exhibits pronounced commensurability features that are related to the matching periodicities of the Abrikosov vortex lattice and the magnetic stripe domains.

Spin reorientation transition and magnetic domain structure of Co ultrathin films grown on a faceted Au(455) surface

The spin reorientation transition (SRT) and magnetic domain structure of Co ultrathin films on faceted Au(455) surfaces have been investigated as a function of thickness by using magneto-optic Kerr effect and x-ray photoemission electron microscopy in combination with x-ray magnetic circular dichroism. The magnetization easy axis of the Co films is found to rotate from an out-of-plane to an in-plane orientation perpendicular to the atomic steps of the substrate due to the dominant contribution of the step-induced magnetic anisotropy. Moreover, magnetic stripe domains are observed to replicate the underlying periodic facets of the Au surface. Depending on the facet, the SRT occurs at a well-defined critical thickness and proceeds via a different mechanism: a state of uniform canted magnetization is formed for (233) facets, while the SRT involves continuous magnetization rotation followed by the nucleation of small in-plane magnetic domains for (677) facets.

Reversible magnetic domain-wall motion under an electric field in a magnetoelectric thin film

We report direct microscopic measurements that confirm the magnetic stripe-domain patterns can be reversibly changed under an electric field due to the converse magnetoelectric effect in a bilayer thin film ferromagnetic-Ni/ferroelectric-lead zirconate titanate (100nm∕1.28μm) heterostructure. Electric field-induced curving, bending, branching, and elongation of magnetic stripe-domain patterns in the Ni layer are observed with the use of magnetic force microscopy. Upon removal of the electric field, the magnetic stripe-domain patterns return to their original configuration, i.e., reversible.

Magnetic force microscopy study of magnetic stripe domains in sputter deposited Permalloy thin films

A magnetic force microscopy based study on the formation of stripe domains in Permalloy (Ni80Fe20) thin films is presented. Our results show that the critical thickness for stripe domain initiation depended on the sputtering rate, the substrate temperature, and the film thickness. Beyond the stripe domain formation, an increase of the period of a highly ordered array of stripe domains was evident with increasing film thickness. Thin films sputtered at room temperature with thickness variation between ∼80 and ∼350nm exhibited square-root growth dependency on stripe domains periodicity from ∼150to∼380nm, respectively. Above a certain thickness, the domain period decreased and the periodicity deteriorated with the array becoming more random, which is a strong indicator of relatively high structural perpendicular anisotropy. To illustrate, Permalloy sputtered at 100°C initially showed linear dependence in stripe domain periodicity growth up until ∼650nm thick films. The magnetic stripe domain structure began breaking down for thicker Permalloy films. Our data also suggested that the perpendicular anisotropy responsible for the formation of stripe domains might have resulted from strain-caused magnetostriction and the thin-film microstructure shape effect.

Variable temperature magnetic force microscopy of La<SUB align=right>2/3Sr<SUB align=right>1/3MnO<SUB align=right>3 thin films grown on (LaAlO<SUB align=right>3)<SUB align

The surface magnetic domain patterns of a La2/3Sr1/3MnO3 film grown on a LSAT (001) substrate, where LSAT stands for (LaAlO3)0.3(Sr2AlTaO6)0.7, were observed by magnetic force microscopy (MFM) as a function of the temperature in the 300?360 K range at its remanent state. Magnetic stripe domains showing an up and down magnetic configuration were observed, thus indicating the existence of a small out-of-plane magnetisation component. The domain size was in the order of 300 nm and did not vary with temperature. However the magnetic contrast in the MFM phase images decreased as the temperature increased and vanished as it approached the Curie temperature of the film. MFM measurements were compared with magnetisation vs. temperature curves measured by superconducting quantum interference device magnetometer.

Mechanism of drift of stripe magnetic domains in ferrite-garnet single crystals

The drift of stripe magnetic domains in (111) single-crystal ferrite-garnet plates in an alternating magnetic field (25–1000 Hz) has been investigated. The dependences of the drift velocity of stripe domains on the field frequency and amplitude have been obtained for magnetic fields of different orientations. A dislocation drift mechanism is proposed. Enhanced motion of magnetic dislocations in a system of stripe domains is established.

Soft X-ray resonant magnetic scattering study of magnetization reversal in low dimensional magnetic heterostructures

Soft X-ray resonant magnetic scattering (SXRMS) has been used to investigate the microscopic magnetization reversal behavior of complex magnetic systems. SXRMS is a unique technique, providing chemical, spatial and magnetic sensitivity, which is not affected by external magnetic fields. The study of two selected thin magnetic heterostructures is presented, amorphous rare-earth transition metal alloys and perpendicular exchange coupled antiferromagnetic/ferromagnetic films. In the first system, the internal structure of magnetic stripe domains on nanometer length scales is obtained by measuring bi-dimensional (2D) scattering images. In the second system, the element specificity is exploited to identify the role of the uncompensated spins in the antiferromagnetic layer on the exchange coupling phenomena. Future trends are also discussed.

Domain structure and magnetization reversal of antiferromagnetically coupled perpendicular anisotropy films

We describe experimental and theoretical investigations of the magnetic domain formation and the field reversal behavior in antiferromagnetically coupled perpendicular anisotropy multilayers that mimic A-type antiferromagnet (AF) structures. The samples are sputter deposited Co/Pt multilayers with perpendicular anisotropy that are periodically interleaved with Ru to mediate an antiferromagnetic interlayer exchange. This structure allows precise tuning of the different magnetic energy terms involved. Using various magnetometry and magnetic imaging techniques as well as resonant soft X-ray scattering we provide a comprehensive study of the remanent and demagnetized configurations as well as the corresponding reversal mechanisms. We find that adding AF exchange to perpendicular anisotropy system alters the typical energy balance that controls magnetic stripe domain formation, thus resulting in two competing reversal modes for the composite system. In the AF-exchange dominated regime the magnetization is ferromagnetically ordered within the film plane with the magnetization of adjacent layers anti-parallel thus minimizing the interlayer AF exchange energy. In the dipolar dominated regime the magnetization pattern forms ferromagnetic (FM) stripe domains where adjacent layers are vertically correlated, but laterally anti-correlated thus minimizing the dipolar energy at the expense of the AF interlayer coupling. By tuning the layer thickness or applying a magnetic field, we observed the co-existence of AF domains and FM stripe domains. We find that a FM phase exists at AF domain boundaries, causing complex mesoscopic domain patterns with surprising reversibility during minor loop field cycling.

Analysis of steplike change of impedance for thin-film giant magnetoimpedance element with inclined stripe magnetic domain based on magnetic energy

The phenomenon of steplike impedance change for thin-film giant magnetoimpedance (GMI) element was reported. The steplike change happens simultaneously with the appearance or the disappearance of stripe magnetic domain. This phenomenon is obtained for amorphous Co85Nb12Zr3 soft magnetic thin film in a rectangle shape with an in-plane uniaxial easy axis in the direction nearly 60° against the short-side axis of the element. The steplike change of impedance appears in a certain magnitude of external magnetic field. A high-sensitive magnetic field sensor can be realized by applying this phenomenon. In this study, a mechanism of the appearance or the disappearance of inclined stripe magnetic domain is discussed based on an analysis of magnetic domain energy, for the purpose of applying to a high-sensitivity magnetic field sensor. We assume these extremely different magnetic domains as (I) stripe domain with closure domain and (II) single domain, based on experimentally observed domain structures. The result of analysis shows that the magnetic energy of these two phases intersects each other in a certain external magnetic field, which means that the basis of steplike GMI of thin-film element is revealed as a structural change of magnetic domain based on magnetic energy.

Temperature dependence of magnetic stripe domain period in ultrathin films

In ultrathin films, due to the thermal activation and temperature dependencies of the magnetic parameters, magnetization reversal processes are strongly affected by thermal effects. We analyze changes of domain periods of ultrathin cobalt and L 1 0 films in a wide temperature range. With regard to the temperature dependencies of the film magnetic parameters we calculate the equilibrium stripe period as a function of temperature. It is shown that on film heating the equilibrium domain structure (DS) period decreases and at the reorientation phase transition (RPT) approaches its minimal value corresponding to the temperature independent period of the sinusoidal domain structure. Just below the RPT temperature (or thickness) the stripe domain period was found to exponentially decrease with temperature. Irreversible temperature changes of the domain period affected by coercivity are also discussed.

X-ray resonant magnetic scattering study of magnetic stripe domains ina−GdFethin films

X-ray resonant magnetic scattering (XRMS) has been used to investigate the structure of magnetic stripe domain patterns in thin amorphous GdFe films. Under the influence of a perpendicular magnetic field, the scattered intensity displays a smooth transition from a structure factor of correlated stripes to the form factor of isolated domains. We derive a quite general expression that relates the total scattered intensity of XRMS to the absolute value of the magnetization. Furthermore, we compare our results for the domain period with domain theory. We obtain good agreement for prealigned stripes, but disorder tends to lead to an overestimation of the period measured with XRMS.

Self-assembly of fractal nanowires and stripe magnetic domain on stretchable substrate

Magnetic properties of Ni thin films on polydimethylsiloxane (PDMS) are being studied. The author finds that coercivity of the films grown on PDMS is two to three times higher than their rigid counterpart. Magnetic force microscopy studies show that surface morphology and magnetic domains are quite different on elastic substrate. 5nm thick films do not exhibit planar morphology but rather form very long nanowires. The 50nm thick films exhibit in-plane and canted magnetizations with nonmagnetic disordered regions within the thin films. Study suggests that elastomers coupled with magnetic thin films can give rise to interesting material properties.

Magnetic and structural properties of evaporated Co xCr 1−x/Si(1 0 0) and Co xCr 1−x/glass thin films

Series of Co x Cr 1− x thin films have been evaporated under vacuum onto Si(1 0 0) and glass substrates, where x variations were between 0.51 and 0.61. Thickness ranges from 350 to 4000 Å. DRX measurements show an hcp structure. AGFM measurement gives saturation magnetization ranging from a negligible value to 120 emu/cm 3 . Coercive field may reach values up to 200 Oe, depending on the percentage of chromium. The saturation magnetization decreases as the Cr content increases. Magnetic force microscopy (MFM) study reveals the absence of stripe domains equilibrium magnetization structure. Brillouin light scattering (BLS) measurements were possible only for the 1800 Å thick sample. They confirm, through the derived magnetic parameters, the absence of stripe magnetic domains as observed by MFM on one hand, and, on the other hand, the adjustment of theoretical and experimental results lead to a stiffness constant 10 times lower than pure Co one. These results are analyzed and correlated.