Mechanical and magnetocaloric adjustable properties of Fe3O4/PET deformed nanoparticle film

The flexibility of nanoparticle films is a topic of rapidly growing interest in both scientific and engineering researches due to their numerous potential applications in a broad range of wearable electronics and biomedical devices.This article presents the elucidation of the properties of nanoparticle films.Here,a flexible film is fabricated based on polyethylene terephthalate(PET)and magnetic iron oxide at the nanoscale using layer-by-layer technology.The 2D thin flexible film material can be bent at different angles from 0°to 360°.With an increase in elastic deformation angles,the magnetocaloric effect of the film gradually increases in the alternating magnetic field.The test results from a vibrating sample magnetometer and a low-frequency impedance analyzer demonstrate that the film has a good magnetic response and anisotropy.The magnetocaloric effect and magnetic induction effect are controlled by deformation,providing a new idea for the application of elastic films.It combines the flexibility of the nanoparticle PET substrate and,in the future,it may be used for skin adhesion for administration and magnetic stimulation control.

Effects of Ag layers on the microstructure and magnetic properties of CoPt/BN multilayer films

Ag/[BN/CoPt]5/Ag and [BN/Ag/CoPt]5/Ag thin films were deposited on glass substrates by magnetron sputtering and then annealed in vac- uum at 600 ℃ for 30 min. The structures and magnetic properties of CoPt/BN multilayer films were investigated as a function of Ag layer thickness. It was found that the face-centered tetragonal （fct） （001） texture of CoPt was improved greatly by introducing the Ag toplayer or sublayer together with an Ag underlayer. Good （001）-oriented growth, low intergrain interactions as well as high perpendicular anisotropy can be obtained in the Ag（3 nm）/[BN（2.5 nm）/CoPt（3 nm）]5/Ag（7 nm） and [BN（2.5 nm）/Ag（2 nm）/CoPt（3 nm）]5/Ag（10 nm） films, which become potential candidates for ultrahigh density magnetic recording media.

Optical and magnetic properties of porous anodic alumina films embedded with Co nanowires

A simple method to tune the optical properties of porous anodic alumina （PAA） films embedded with Co nanowires （PAA@Co nanocomposite films） is reported in this paper. The films exhibit vivid structural colors and magnetic properties. The optical properties of the films can be effectively tuned by adjusting the thickness of the PAA template. The deposition of Co nanowires greatly increases the color saturation of the PAA films. The theoretical results of the changes in structural color according to the Bragg-Snell formula are consistent with the experimental results. PAA@Co films can be used in many areas, including decoration, display, and multifunctional anti-counterfeiting applications.

Microstructure and magnetic properties of electrodeposited Gd-Co alloy films

Gd-Co alloy films were synthesized by potentiostatic electrolysis on Cu substrates in urea-acetamide-NaBr-KBr melt at 353 K. The electroreduction of Co^2＋ and Gd^3＋ was investigated by cyclic voltammetry. The reduction of Co^2＋ is an irreversible process. Gd^3＋ cannot be reduced alone, but it can be inductively co-deposited with Co^2＋. Both the Gd content and microstructure of the prepared Gd-Co alloy films can be controlled by the deposited potential. The content of Gd was analyzed using an inductively coupled plasma emission spectrometer （ICPES）, and the microstructure was observed by scanning electron micrograph （SEM）. The films were crystallized by heat-treatment at 823 K for 30 s in Ar atmosphere, and then were investigated by XRD. The hysteresis loops of the Gd-Co alloy films were measured by a vibrating sample magnetometer （VSM）. The experimental results reveal that the deposited Gd-Co alloy films are amorphous, while the annealing causes the samples to change from amorphous to polycrystalline, thus enhancing their magnetocrystalline anisotropy and coercivity. Moreover, the magnetic properties of the Gd-Co alloy films depend strongly on the Gd content.

Magnetic Properties and Heat-Treatment of Electrodeposited Sm-Co Alloy Films

Dense, adhesive and uniform Sm-Co alloy films were prepared by potentiostatic electrolysis on copper substrates in urea-acetamide-NaBr-KBr melt at 353 K, which were observed by SEM. The electroreduction of Co2+ and Sm3+ was investigated by cyclic voltammetry. The reduction of Co2+ is an irreversible process. Sm3+ can not be reduced alone, but Sm-Co can be co-deposited by induced deposition. The films could be crystallized by heat-treatment at different temperature from 723 to 923 K under Ar atmosphere. The annealed time was chosen as 30 s. The phases of deposited and annealed films were investigated by XRD. The content of Sm was analyzed by Inductive Coupled Plasma Emission Spectrometer (ICPES). The hysteresis loops of the Sm-Co alloy films have been measured by Vibrating Sample Magnetometer (VSM). The experimental results reveal that, the heat-treatment has important influence on coercive field Hc and remanent squareness S of Sm-Co alloy films; the deposited Sm-Co alloy films are amorphous, while the annealed those become polycrystalline; in addition, the magnetocrystalline anisotropy and preferring orientation of films depend strongly on the contents of crystal phases.

Influence of Bath Composition on Magnetic Properties of Electrodeposited Co-Pt-W Thin Films

Effect of bath composition （[Co^2＋]/[-Pt^Ⅳ ] and [-WO4^2- ], [cit^-]） and pH on the magnetic properties of electrodeposited Co-Pt-W thin films has been investigated. Electrodeposited Co-Pt-W thin films exhibited strong perpendicular magnetic anisotropy when the ratio of [-Co^2＋ ] to [-Pt^Ⅳ ] was 10 ; cathode current efficiency and perpendicular magnetic anisotropy showed little variations when [WO4^2- ] was lower than 0. 1 mol/L, but perpendicular magnetic anisotropy had strengthened when [WO4^2-] was over 0. 1 mol/L, which could be explained by the fact that the hydrogen evolution could produce pores as magnetic domain pinnings; citrate as complexing reagent can promote the polarization of [Co^2＋] and [Pt^Ⅳ]. As a result, the equilibrium electrode potentials of cobalt and platinum moved to negative direction, which led to the co-deposition of Co, Pt, and W. It was also found out that the as-deposited Co- Pt-W hard magnetic thin films were very homogeneous, smooth, and had the maximum coercivity for the bath pH 8. 5 and the concentration of citrate 0. 26 mol/L.

Preparation and Effect of Oxygen Annealing on the Electrical and Magnetic Properties of Epitaxial (0001) Zn_(1-x)Co_xO Thin Films

Epitaxial （0001）-oriented Zn1-xCoxO （x= 0.01, 0.05 and 0.1） thin films were grown on c-sapphire substrates by pulsed laser deposition. The XRD analysis, optical transmittance and XPS measurements revealed that the Co2＋ substituted Zn2＋ ions were incorporated into the lattice of ZnO in Zn1-xCoxO thin films. The electrical properties measurements revealed that the Co concentration had a non- monotonic influence on the electrical properties of the Zn1-xCoxO thin films due to the defects resulted from imperfections induced by Co substitution. The resistivity remarkably increased and the carrier concentration remarkably decreased in Zn1-x CoxO thin films after oxygen annealing at 600 ℃ under 15 Pa O2 pressure for 60 mins. Room-temperature ferromagnetic was observed and the ferromagnetic Co amount was smaller than the nominal Co concentration for Zn1-xCoxO samples before oxygen annealing. After oxygen annealing, the Zn1-x CoxO thin films exhibited paramagnetic behavior. It is suggested that the room-temperature ferromagnetic ofZn1-x CoxO thin films may attribute to defects or carriers induced mechanism.

Fabrication and Magnetic Properties of Highly Oriented ZnO:Eu Films by Sol-Gel Process

A series of Eu-doped ZnO films were prepared by a sol-gel method. Precursor and films were characterized by thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscope (SEM), UV-vis spectra, as well as the magnetism measurement. The wurtzite structure of obtained films presents an extreme high c-orientation character. The film susceptibility resembles a Curie-Weiss behavior at high temperature, and presents an obvious enhancement at low temperature, indicating the presence of antiferromagnetic interactions in the Zn0.9Eu0.1O films.

EFFECTS OF TREATMENT TEMPERATURE ON THE MICROSTRUCTURE AND MAGNETIC PROPERTIES OF Fe-N THIN FILMS

Fe-N thin films were fabricated on both 100Si and NaCl substrates by RF magnetron sputtering under low nitrogen partial pressure. The microstructure and magnetic properties of Fe-N thin films were investigated with the increase of the substrate temperature （Ts） and the annealing temperature （Ta）. It is more difficult for nitrogen atoms to enter the Fe lattice under higher Ts above 150℃. The phase evolution is visible at higher Ta above 200℃. The phase transformation of α＇＇-Fe16N2 occurred at 400℃. The change of crystal size with Ta was clearly visible from bright and dark field images. The clear high-resolution electron microscope （HREM） images of 110α, 111γ＇, 112α＇＇, and 200α＇＇ phases were observed. The interplanar distances from TEM （transmission electron microscope） and HREM match the calculated values very well. From the results of the vibrating sample magnetometer （VSM）, the good magnetic properties of Fe-N films were obtained at 150℃ of Ts and 200℃ of Ta, respectively.

Soft magnetic properties of (Ni_(50)Fe_(50)) SiO_2 granular thin films for high frequency application

A series of (Ni50Fe50)x(SiO2)(1-x) films with different volume fraction x was fabricated by magnetron co-sputtering technique. The microstructure, magnetic and electrical properties were investigated systematically by using X-ray diffraction, transmission electronic microscope, vibrating sample magnetometer and the traditional four point measurement method of resistivity. The results show that the samples consist of nano-scaled Ni50Fe50 metallic particles with fcc structure uniformly embedded in amorphous insulating SiO2 matrix, and the particle size decreases with the decrease of x. The rapid change of coercivity with x is observed, and a minimum value 160 A·m-1 of Hc was obtained for the sample of x=0.83 with film thickness of 180 nm, which can be contributed to the exchange coupling between nano-scaled Ni50Fe50 particles. At the frequency lower than 1 GHz, the real part μ′ of complex permeability keeps about 110 and the image part μ″ is less than 15. Besides, this film exhibits high resistivity ρ=263 μΩ·cm, high saturation magnetization 4πMs=1.25 T, high in-plane magnetic anisotropy field Hk=6.37 kA·m-1, and the ferromagnetic resonance (FMR) frequency is estimated to be 2.8 GHz. Therefore, this film can be used in high frequency devices operating over 2 GHz.

Low temperature ferromagnetic properties of CdS and CdTe thin films

The magnetic property in a material is induced by the unpaired electrons. This can occur due to defect states which can enhance the magnetic moment and the spin polarization. In this report, CdS and CdTe thin films are grown on FTO glass substrates by chemical bath deposition and close-spaced sublimation, respectively. The magnetic properties, which are introduced from oxygen states, are found in CdS and CdTe thin films. From the hysteresis loop of magnetic moment it is revealed that CdS and CdTe thin films have different kinds of magnetic moments at different temperatures. The M–H curves indicate that from 100 K to 350 K, CdS and CdTe thin films show paramagnetism and diamagnetism, respectively.A superparamagnetic or a weakly ferromagnetic response is found at 5 K. It is also observed from ZFC/FC curves that magnetic moments decrease with temperature increasing. Spin polarized density functional calculation for spin magnetic moment is also carried out.

Magnetic properties and structure of Ni_80Fe_20/Ni_48Fe_12Cr_40 bilayer films deposited on SiO_2/Si(100) by electron beam evaporation

Ni80Fe20/Ni48Fe12Cr40 bilayer films and Ni80Fe20 monolayer films were deposited at room temperature on SiO2/Si（100） substrates by electron beam evaporation. The influence of the thickness of the Ni48Fe12Cr40 underlayer on the structure, magnetization, and magnetoresistance of the Ni80Fe20/Ni48Fe12Cr40 bilayer film was investigated. The thickness of the Ni48Fe12Cr40 layer varied from about 1 nm to 18 nm while the Ni80Fe20 layer thickness was fixed at 45 nm. For the as-deposited bilayer films the introducing of the Ni48Fe12Cr40 underlayer promotes both the （111） texture and grain growth in the Ni80Fe20 layer. The Ni48Fe12Cr40 underlayer has no significant influence on the magnetic moment of the Ni80Fe20/Ni48Fe12Cr40 bilayer film. However, the coercivity of the bilayer film changes with the thickness of the Ni48Fe12Cr40 undedayer. The optimum thickness of the Ni48Fe12Cr40 underlayer for improving the anisotropic magnetoresistance effect of the Ni80Fe20/Ni48Fe12Cr40 bilayer film is about 5 nm. With a decrease in temperature from 300 K to 81 K, the anisotropic magnetoresistance ratio of the Ni80Fe20 （45 nm）/Ni48Fe12Cr40 （5 nm） bilayer film increases linearly from 2.1% to 4.8% compared with that of the Ni80Fe20 monolayer film from 1.7% to 4.0%.

Preparation and magnetic properties of Co-P thin films

Magnetic Co-P thin films were prepared by electroless deposition. The experiment results show that the film thickness has a significant influence on the coercivity. While the film thickness varied from 300 nm to 5 μm,the coercivity dropped sharply from 45.36 to 22.28 kA/m. As the film thickness increased further,the coercivity varied slowly. When the thickness of the film was 300 nm,the deposited film could realize the coercivity as high as 45.36 kA/m,and the remanent magnetization as high as 800 kA/m .The Co-P films were deposited on the surface of magnetic drums of encoders,whose diameter was 40 mm,and then 512 magnetic poles were recorded,meaning that the magnetizing pitch was 0.245 mm. The testing results indicate that the output signals are perfect,the output waveforms are steady and the pulses account is integral. Compared with the γ-Fe2O3 coating,the Co-P thin film is suitable to be the magnetic recording media for the high resolution magnetic rotary encoder.

Deposition and Magnetic Properties of Fe_3O_4/Fe/Fe_3O_4 Tri-layer Films

The Fe_3O_4/Fe/Fe_3O_4 (MIM) tri-layer films (200 nm/12-93 nm/200 um) were prepared on Si(100) by DC-magnetron reactive-sputtering followed by air- or vacuum-annealing at 280-400℃ for 1.5 h, respectively. Magnetic properties and phases under different sandwich and annealing conditions were studied. In MIM structure, the incorporation of the interlayer iron does increase the magnetization measured under 8 kOe (M_8K), but reduce coercivity (H_c). The H_c of asdeposited films decreases from 354 Oe to 74 Oe; while M_8K increases from 254 to 392 emu/cc. By annealing in air, the whole MIM tri-layer film becomes γ-F_e2O_3, H_c is about 550 O_e and M_8K is around 250 emu/cc. The coercivity mechanism of as-deposited and annealed MIM trilayer films belongs to domain-wall pinning type. δM plots show that when the interlayer Fe thickness is 12 um, the Fe and Fe_3O_4 layers are decoupled in the as-deposited and annealed states; while it is coupled in the as deposited state when the Fe thickness increases to 23 um. Vacuum annealing of the MIM films leads to increase in both coercivity and magnetization, and to enhance the exchange coupling between layers.

Flexible rGO/Fe3O4 NPs/polyurethane film with excellent electromagnetic properties

Large-area and flexible reduced graphene oxide(rGO)/Fe3O4 NPs/polyurethane(PU) composite films are fabricated by a facile solution-processable method. The monolayer assembly of Fe3O4 nanoparticles with a high particle-stacking density on the graphene oxide(GO) sheets is achieved by mixing two immiscible solutions of Fe3O4 nanoparticles in hexane and GO in dimethylformide(DMF) by a mild sonication. The x-ray diffraction and Raman spectrum confirm the reduced process of rGO by a simple thermal treatment. The permittivity value of the composite in a frequency range of 0.1 GHz-18 GHz increases with annealing temperature of GO increasing. For 5-wt% rGO/Fe3O4 NPs/PU, the maximum refection loss(RL) of over-35 dB appears at 4.5 GHz when the thickness of film increases to 5 mm. The rGO/Fe3O4 NPs/PU film, exhibiting good electromagnetic properties over GHz frequency range, could be a potential candidate as one of microwave absorption materials in flexible electronic devices.

Influence of vacuum annealing and irradiation on magnetic properties of Fe-3% Y_2O_3 films

Yttria （Y） dispersed ferrum （Fe） films were prepared by a double-target magnetron co-sputtering method. Vacuum annealing and xenon ion irradiation were conducted to investigate the influence on the magnetic and mechanical properties of the films. The crystal grain growth mechanism and second phase precipitation mechanism were conducted simultaneously in the vacuum annealing process. These two effects led to an opposite variation of nano-hardness and coercivity in the films. Xenon ion irradiation played a role in rapid annealing, which also affected the magnetic performance of the yttria dispersed ferrum films.

Phase diagrams and magnetic properties of the mixed spin-1 and spin-3/2 Ising ferromagnetic thin film: Monte Carlo treatment

Phase diagrams and magnetic properties of the mixed spin-1 and spin-3/2 Ising film with different single-ion anisotropies are investigated, by the use of Monte Carlo simulation based on heat bath algorithms. The effects of the crystal-fields and the surface coupling on the phase diagrams are investigated in detail and the obtained phase diagrams are presented. Depending on the Hamiltonian parameters, the system exhibits both second-and first-order phase transitions besides tricritical point, triple point, and isolated critical end point.

Microwave properties and surface topography of soft magnetic films with high resistivity

A single layer of CoFeB and a multilayer of CoFeB MgO films are prepared by means of DC/RF magnetron sputter deposition. The excellent microwave properties and high electrical resistivity are simultaneously achieved in the discontinuous multilayer structure of [Co44Fe44B12（0.7nm）/MgO（0.4nm）]40 film. This film has a high permeability （μ′） （larger than 100 below 2.1 GHz）, a high magnetic loss （μ″） （larger than 100 in a range from 1.5 to 3.3GHz）, a resistivity of 3.3 × 10^3μΩ. cm, a saturation magnetization of 1.2 T, and an in-plane uniaxial anisotropy field of 5.5 kA/m. The microstructure and the surface topography of the film are also analysed. The relatively large surface roughness for the discontinuous film is responsible for the wide frequency band of magnetic loss. The magnetic loss and the high resistivity indicate that the discontinuous CoFeB MgO multilayer film has potential applications in microwave absorbers and electromagnetic interference （EMI） shielding materials in a GHz frequency range.

Effect of Post Annealing on the Microstructure and Magnetic Properties of NdFeB/α-Fe/NdFeB Thin Films

A series of nanocomposite thin films, composed of Nd2Fe14B and α-Fe, has been prepared by DC-magnetron sputtering combined ion beam sputtering onto Si (100) substrates. The effects of post annealing on the microstructure and magnetic properties of [NdFeB/α-Fe/NdFeB]-type thin films have been investigated. The X-ray diffraction (XRD) study showed that annealing of the films for 30 min at temperatures 550, 600, 650, 700 ℃ resulted in the appearance of diffraction peaks, characteristic for Nd2Fe14B tetragonal structure, α-Fe and Nd2O3 phases. The investigation using the Vibrating Sample Magnetometer (VSM) with a maximum applied field of 2 T indicated that with the increase of the annealing temperature, the magnetic properties of the multilayer films were improved and reached peak value at 650 ℃ (Hci=41.72 kA·m-1, Mr/Ms=0.4, (BH)max=30.35 kJ·m-3), after which the magnetic properties were decreased greatly. Along with the increase of the thickness of α-Fe layer from Tα-Fe>16 nm, the coercivity Hci, saturation magnetization Ms, and remanence ratio Mr/Ms all declined. As the Atomic Force Microscope (AFM) indicated, after being annealed at 650 ℃ for 30 min, the sample was showed fine surface morphology with grain size 60 nm≤dα-Fe≤80 nm and 100 nm≤dNdFeB≤150 nm.

PREPARATION OF NANO-CRYSTALLINE Fe-Cu THIN FILMS AND THEIR MAGNETIC PROPERTIES

Fe-Cu thin films of 0.2 mum in thickness with different Cu contents wereprepared by using r.f. magnetron sputtering onto glass substrate. The effect of sputteringparameters, including Ar gas pressure and input rf power, on the structure and magnetic propertieswas investigated. It was found that when the power is lower than 70W, the structure of the filmsremained single bcc-Fe phase with Cu solubility of up to 50at. percent. TEM observations for thebcc-Fe phase showed that the grain size was in the nanometer range of less than 20nm. The coercivityof Fe- Cu films was largely affected by not only Ar gas pressure but also rf power, and reachedabout 2.5Oe in the pressure of 0.67-6.67Pa and in the power of less than 100W. In addition,saturation magnetization, with Cu content less than 60at. percent, was about proportional to thecontent of bcc-Fe. When Cu content was at 60at. percent, however, saturation magnetization was muchsmaller than its calculation value.