Magnetic Nanofilms Research Articles

The effect of magnetic nanofilm morphology on spintronic terahertz emission performance

Femtosecond laser-driven spintronic terahertz (THz) emitters based on magnetic nanofilms are poised to be the next-generation mainstream THz radiation devices due to their low cost, high performance, ultra-broadband, and easy integration. The radiation performance of spintronic THz emitters is related to the material characteristics, heterostructure interfaces, pump laser, and magnetic field intensity. Additionally, the THz emission performance is greatly reliant on the material surface morphology. Here, we employed ultrafast THz scattering-type scanning near-field optical microscopy with nanoscale spatial resolution to obtain the static THz scattering nano-imaging of ferromagnetic/antiferromagnetic heterostructures (W/Co20Fe60B20/IrMn3). We established the relationship between surface morphology and THz scattering intensity. Utilizing laser-induced THz emission technology, we achieve injection and detection of nanoscale ultrafast spin current without the external magnetic field. The strong consistency of the THz emission nanoscopy with the atomic force microscopy topography demonstrates that the sample surface morphology is critical to the THz radiation performance. This study serves as a valuable reference for the further optimization of spintronic THz emitters and promotes the development of high-performance, strong-field spintronic THz sources.

Micro-scale aerosol jet printing of superparamagnetic Fe3O4 nanoparticle patterns

The opportunity to create different patterns of magnetic nanoparticles on surfaces is highly desirable across many technological and biomedical applications. In this paper, this ability is demonstrated for the first time using a computer-controlled aerosol jet printing (AJP) technology. AJP is an emerging digitally driven, non-contact and mask-less printing process which has distinguishing advantages over other patterning technologies as it offers high-resolution and versatile direct-write deposition of a wide range of materials onto a variety of substrates. This research demonstrates the ability of AJP to reliably print large-area, fine-feature patterns of superparamagnetic iron oxide nanoparticles (SPIONs) onto both rigid material (glass) and soft and flexible materials (polydimethylsiloxane (PDMS) films and poly-L-lactic acid (PLLA) nanofilms). Investigation identified and controlled influential process variables which permitted feature sizes in the region of 20 μm to be realised. This method could be employed for a wide range of applications that require a flexible and responsive process that permits high yield and rapid patterning of magnetic material over large areas. As a first proof of concept, we present patterned magnetic nanofilms with enhanced manipulability under external magnetic field gradient control and which are capable of performing complex movements such as rotation and bending, with applicability to soft robotics and biomedical engineering applications.

A Microfluidic Platform Equipped With Magnetic Nano Films for Organizing Bio-Particle Arrays and Long-Term Studies

We introduce a microfluidic platform that combines hydrodynamic trapping and magnetic switching techniques for precise manipulating magnetic micro-particles and forming particle and cell arrays, in a massively parallel manner. In the first step, hydrodynamic forces transport and then trap the single particles and cells in a large array. Then, magnetic forces transfer them into adjacent low-shear compartments which are used as single cell culture micro-chambers. Furthermore, using this tool, we run single cell assays and perform drug screening as well as mRNA analysis experiments. The flawless magnetic transport in this work is obtained by growing a non-fouling layer on microchannel surfaces. The chip treatment became possible by a novel microfluidic chip design and a new simple self-aligned fabrication method, based on a silicon substrate, magnetic nano thin-films embedded in the microfluidic walls, and a glass lid. The resulting chip is an innovative tool suitable for long-term single cell phenotypic and genotypic studies, with applications in immunology and medicine.

Exchange bias adjust resonance frequency in FeNi/FeMn nanofilm based on polarized neutron reflectometer

To study the relationship between the exchange bias effect and the resonance frequency of magnetic nanofilms, FeNi and FeNi/FeMn exchange-coupled films were fabricated on a silicon substrate by magnetron sputtering deposition. The static and dynamic magnetic properties of the multilayer films were investigated using a vibrating sample magnetometer (VSM) and a vector network analyzer (VNA). The VSM results indicate that after introducing the FeMn layer, the exchange bias field increased to 62 Oe and the magnetic anisotropy field shifted from 6 to 107 Oe. The VNA results show that the resonance frequency increased from 0.72 to 2.8 GHz, originating from the interface exchange coupling strength. In addition, as a probe for the surface and interface structure, a time-of-flight polarized neutron reflectometer was used to observe the microstructure of the multilayer films. The diffusion with a 2.5 nm thickness between the multilayer films was observed by the polarized neutron reflection experiment, further illustrating that the exchange bias effect is derived from the interaction between the FeNi/FeMn layers. It is concluded that the magnetic induction of a FeNi layer is 0.98 T through fitting the data obtained from the polarized neutron reflection experiment.

Generation of highly efficient terahertz radiation in ferromagnetic heterostructures and its application in spintronic terahertz emission microscopy (STEM)

The laser terahertz emission microscopy (LTEM) technique, which breaks through the resolution limitation of terahertz waves from millimeter to micrometer scales, has been widely used in many real application circumstances, such as contactless chip nondestructive testing, biosensing, imaging, and so on. Recently developed spintronic terahertz emitters featuring many unique properties such as high efficiency, easy integration, low cost, large size and so on, may also have great applications in LTEM, which can be called spintronic terahertz emission microscopy (STEM). To achieve high efficiency and good performance in STEM, we propose and corroborate a remnant magnetization method to radiate continuous and stable terahertz pulses in W/CoFeB/Pt magnetic nanofilms without carrying magnets on the transmitters driven by nJ femtosecond laser pulses. We systematically optimize the incidence angle of the pumping laser and find the emission efficiency is enhanced under oblique incidence, and we finally obtain comparable radiation efficiency and broadband spectrum in W/CoFeB/Pt heterostructures compared with that from 1 mm thick ZnTe nonlinear crystals via optical rectification under the same pumping conditions of 100 fs pulse duration from a Ti:sapphire laser oscillator, which was not previously demonstrated under such long pulse duration. We believe our observations not only benefit for a deep insight into the physics of femtosecond spin dynamics, but also help develop novel and cost-effective broadband spintronic terahertz emitters for the applications in STEM.

Magnetostriction theory of ultrathin freestanding nanofilms

In this paper, a continuum theory for describing the magnetostrictive behavior of magnetic nanofilms is proposed. Surface effects (including surface elastic and surface magnetoelastic effects) as well as symmetry lowering of nanofilms are considered in the theoretical scheme. The spherical symmetry is lowered to the cylindrical one in nearly two-dimensional nanofilms. And then, there are some additional new elastic and magnetoelastic parameters induced by symmetry lowering have to be reckoned into model the magnetostriction of nanofilms rigorously. The application of our theoretical scheme to Fe nanofilms shows good agreement with experiment. The magnetostriction minimum vs film thickness of Fe nanofilms was produced straightforwardly. In addition, the surface elastic and surface magnetoelastic constants are physically reasonable and consistent with most solid surfaces (on the order of 1–10 J/m− 2 for surface elasticity and 10− 2–10− 4 J/m− 2 for surface magnetoelasticity). This fact confirms the great importance of additional new elastic and magnetoelastic parameters in magnetostriction theory of magnetic nanofilms. The relationship (λx = − 2λy = − 2λz) between magnetostrictions breaks down for nanofilms. In addition, when the magnetic field is applied along vertical direction, the magnetostriction of nanofilms behaves different from the case that magnetic field is applied along in-plane direction.

Deposition of Magnetite Nanofilms by Pulsed Injection MOCVD in a Magnetic Field.

This report is on the growth of Fe3O4 nanofilms on Al2O3(0001) and MgO(001) substrates with and without the presence of an external magnetic field using a pulsed injection metallorganic chemical vapour deposition (PI MOCVD) technique. The effects of growing magnetic oxide nanofilms in a 1 T field have been examined using various instrumental methods. It was found that the application of a magnetic field during PI MOCVD does not drastically alter the crystalline texture, surface morphology, and film thickness, but it significantly modifies the Fe3O4 film magnetisation and coercive field. Moreover, it was shown that the application of a 1 T field during the cooling of the sample also improves the magnetic properties. We believe that the large external field orients the magnetic spin structure at high temperatures (during growth or the initial stages of cool down) and that cooling through local magnetic ordering temperatures at Fe3O4 defect sites subsequently favours a ferromagnetic spin alignment. The control of magnetic properties of magnetite nanofilms by the application of magnetic fields during growth opens up new routes towards the fabrication and application of magnetic thin film devices.

On the injectability of free-standing magnetic nanofilms.

Free-standing films with sub-micrometric thickness, composed of soft polymers and functional nanostructures are promising candidates for many potential applications in the biomedical field, such as reduced port abdominal surgery. In this work, freely suspended poly(L-lactic acid) nanofilms with controlled morphology embedding superparamagnetic iron oxide nanoparticles were fabricated by spin-coating deposition. The mechanical properties of magnetic nanofilms were investigated by Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIMM) test. Our results show that these freely suspended nanocomposite nanofilms are highly flexible and deformable, with Young's moduli of few GPa. Since they can be handled in liquid with syringes, a quantitative description of the nanofilms behavior during the manipulation with clinically applicable needles has been also provided. These magnetic nanofilms, remotely controllable by external electromagnetic fields, have potential applications in minimally invasive surgery as injectable nanopatches on inner organs wall. Graphical abstract ᅟ.

Reversal of the Magnetic Nanofilms and Data Recording by Spin Current

Reversal of the Magnetic Nanofilms and Data Recording by Spin Current

CONTROL SPIN CURRENT AND DATA RECORDING ON SPIN STORAGE MEDIUM

The paper presents the results of experimental studies of the physical mechanisms and dynamics of magnetization reversal of the films Al 2 O 3/ Tb 25 Co 5 Fe 70/ Al 2 O 3, Al 2 O 3/ Tb 22 Co 5 Fe 73/ Al 2 O 3, Al 2 O 3/ Tb 19 Co 5 Fe 76/ Al 2 O 3, Al 2 O 3/ Co 30 Fe 70/ Al 2 O 3 with a single magnetic layer and the films Al 2 O 3/ Tb 22 Co 5 Fe 73/ Pr 6 O 11/ Tb 19 Co 5 Fe 76/ Al 2 O 3, Al 2 O 3/ Co 80 Fe 20/ Pr 6 O 11/ Co 30 Fe 70/ Al 2 O 3 with two magnetic layers radiated by picosecond (τi ≈ 80 ps ) and femtosecond (τi ≈ 130 fs ) laser pulses. The experimental samples of spin transistors and data recording devices on the spin storage medium are also described. The results of studies have shown that magnetic switching effects in the nanolayers under femtosecond laser pulses can be used for creation of systems of high-speed controlling of spin currents with the response time τ ≤ 10-11s. Conclusions from the studies are the following: thermomagnetic switching under the influence of an external magnetic field or a demagnetization field, magnetic switching of antiferromagnetic films under the influence of an effective internal field of antiferromagnetic interaction between magnetic sublattices rare-earth and transitive metals, magnetic switching under the influence of a magnetic field of the inverse Faraday effect, or under the influence of a magnetic field of a spin current. The magnetic switching of magnetic layers under action of the magnetic field of a spin current is the most important for practical use in elements of spintronics. This mechanism of magnetic reversal takes place only in multilayer nanofilms and the heterogeneous multilayer magnetic nanofilms are the base material for creation of spintronic devices. The great advantage of the magnetization reversal of magnetic nanolayers of the spin current is that the mechanism of magnetization reversal is working in the films with perpendicular anisotropy and in the films with in-plane anisotropy. The injection of polarized electrons can also be realized using short electrical pulses. That is why the mechanism of magnetization reversal of the control electrodes spin current is the most appropriate for the management of high-spin current in the elements of spintronics. On the basis of this mechanism, we have realized the high-speed recording of information on the spin carrier and the experimental model memory with three magnetic nanolayers. The data recording in this memory cell is realized using an electric nanosecond pulse.

Изменение магнитных характеристик магнитных нанопленок и управление спиновым током с помощью лазерного излучения

Изменение магнитных характеристик магнитных нанопленок и управление спиновым током с помощью лазерного излучения

Tuning of Magnetic Dipolar Interactions of Maghemite Nanoparticles Embedded in Polyelectrolyte Layer-by-Layer Films

In this study we report an experimental approach capable of tuning dipolar interactions in hybrid magnetic nanofilms produced via layer-by-layer assembly of positively-charged maghemite nanoparticles and sodium sulfonated polystyrene onto glass and silicon substrates. Morphological and magnetic properties of the as prepared nanofilms were determined by Raman spectroscopy, atomic force microscopy, conventional and SQUID magnetometry. Maghemite nanoparticles form densely packed layers with voids between particles being filled by polymeric material as observed in atomic force microscopy images. Magnetic hysteresis loops and zero-field-cooled/field-cooled magnetization curves reveal a superparamagnetic behavior at room temperature. The energy barrier for the magnetic moment reversal of the nanofilms has been determined from the frequency dependent ac susceptibility and is related to the gamma-Fe2O3 nanoparticles concentration used in the colloidal dispersion throughout film fabrication. Variations on the interparticle distances have a direct effect on the interparticle dipolar interactions. A less concentrated colloid gives rise to large separated nanoparticles inside the nanofilm with a consequent reduction on the energy barrier for the magnetic moment reversal. The fabrication process exploring the control of the nanoparticle concentration can thus be used to tune the magnetic dipolar interactions in the nanofilms.

Assembly of γ-Fe2O3/polyaniline nanofilms with tuned dipolar interaction

The internal morphology and magnetic properties of layer-by-layer assembled nanofilms of polyaniline (PANI) and maghemite (γ-Fe2O3—7.5-nm diameter) were probed with cross-sectional transmission electron microscopy (TEM) and magnetization measurements (magnetic hysteresis loops, magnetization using zero-field cooled/field-cooled protocols, and ac magnetic susceptibility). Additionally, simulations of the as-produced samples were performed to assess both the nanofilm’s morphology and the corresponding magnetic signatures using the cell dynamic system (CDS) approach and Monte Carlo (MC) through the standard Metropolis algorithm, respectively. Fine control of the film thickness and average maghemite particle–particle within this magnetic structure was accomplished by varying the number of bilayers (PANI/γ-Fe2O3) deposited onto silicon substrates or through changing the concentration of the maghemite particles suspended within the colloidal dispersion sample used for film fabrication. PANI/γ-Fe2O3 nanofilms comprising 5, 10, 25 and 50 deposited bilayers displayed, respectively, blocking temperatures (T B) of 30, 35, 39 and 40 K and effective energy barriers (ΔE/k B) of 1.0 × 103, 2.3 × 103, 2.8 × 103 and 2.9 × 103 K. Simulation of magnetic nanofilms using the CDS model provided the internal morphology to carry on MC simulation of the magnetic properties of the system taking into account the particle–particle dipolar interaction. The simulated (using CDS) surface–surface particle distance of 0.5, 2.5 and 4.5 nm was obtained for nanofilms with thicknesses of 36.0, 33.9 and 27.1 nm, respectively. The simulated (using MC) T B values were 33.0, 30.2 and 29.5 K for nanofilms with thicknesses of 36.0, 33.9 and 27.1 nm, respectively. We found the experimental (TEM and magnetic measurements) and the simulated data (CDS and MC) in very good agreement, falling within the same range and displaying the same systematic trend. Our findings open up new perspectives for fabrication of magnetic nanofilms with pre-established (simulated) morphology and magnetic properties.

Magnetic nanofilms of nickel prepared at the liquid–liquid interface

Thin films of metallic nickel with a thickness of the order of 20 nm have been prepared at the organic–aqueous interface at room temperature by the reaction of nickel cupferronate [Ni(C 6H 5N 2O 2) 2] in toluene medium and sodium borohydride (NaBH 4) in aqueous medium. The films were characterized with transmission electron microscopy, scanning electron microscopy and atomic force microscopy. Thicker Ni films could be prepared by carrying out the reaction at the interface at 60 °C. The Ni nanofilms exhibit superparamagnetic behavior.

Freestanding Functionalized Nanofilms for Biomedical Applications

Polymeric ultra-thin films show peculiar properties making them potentially useful for several applications in biomedicine. Moreover, the possibility to functionalize these films by using different agents opens new and partially unexplored scenarios. In this work we present the more recent advancements we achieved in this field, focusing on freestanding magnetic nanofilms and freestanding conductive nanofilms.

Laser radiation control of the magnetic state of multilayer nanofilms

Physical mechanisms of magnetization reversal of multilayer magnetic nanofilms by laser radiation are examined and the experiments on the effect of the magnetic field and nanosecond and picosecond laser pulses on the conductivity of the Tb19Co5Fe76/Pr6O11/Tb22Co5Fe73 and Co80Fe20/Pr6O11/Co30Fe70 tunnel microcontacts are carried out. It is shown that with the help of such laser pulses, magnetization reversal of magnetic nanolayers is possible in a zero external magnetic field under the action of the spin current magnetic field, induced by the photon pressure of laser radiation, or the magnetic field generated by circularly polarized picosecond laser pulses. A relative change in the resistance upon the laser magnetization reversal of one of the nanolayers in the Co80Fe20/Pr6O11/Co30Fe70 microcontacts reaches a value of ΔR/R = 0.06 for T = 300 K and ΔR/R = 0.25 for T = 80 K, in the Tb19Co5Fe76/Pr6O11/Tb22Co5Fe73 microcontacts, ΔR/R = 0.3 for T = 300 K and ΔR/R = 0.7 for T = 80 K.

Magnetic Nanofilms for Biomedical Applications

Polymeric ultrathin films, also called nanofilms or nanosheets, show peculiar properties making them potentially useful for several applications in biomedicine, e.g., as nanoplasters for localized drug release or as a new solution for closing endoluminal surgical wounds. In this sense, one of most challenging issues is film control in the working environment: the possibility of including magnetic components, such as magnetic nanoparticles or nanotubes, paves the way for the effective use of nanofilms in the human body, by allowing precise positioning by an external magnetic field. State of the art and new perspectives of magnetic nanofilms for biomedical applications are here presented, including fabrication, modeling, characterization and validation.