Alternating Gradient Field Magnetometer Research Articles

FeCuNbSiB thin films with sub-Oersted coercivity

We investigated the microstructural and magnetic properties of nanocrystalline FeCuNbSiB thin films produced through magnetron sputtering followed by heat treatment. Our research focused on film thicknesses (80 nm and 160 nm) and heat treatment temperatures (490 °C–520 °C) that resulted in samples characterized by low coercivity and high effective magnetization. Conducting a comprehensive microstructural examination, we employed X-ray diffraction and transmission electron microscopy techniques, including selected area electron diffraction, high-resolution imaging and Fourier transform analysis. Magnetic properties were investigated using an alternating gradient field magnetometer and broadband ferromagnetic resonance. Structural analysis revealed, for all our heat-treated films, a well-defined microstructure characterized by nanograins, with a Fe3Si ferromagnetic phase, embedded within an amorphous matrix. Our films exhibit sub-Oe coercivity, reaching as low as 0.51 Oe, along with an increase in effective magnetization from 1170 emu/cm3 for the amorphous phase to a maximum of 1260 emu/cm3 in the nanocrystalline phase.

Fabrication and magnetic properties of Co based thin films synthesized by physical vapor deposition under vacuum

We used thermal heating process, under a pressure of 10−7 mbar, to fabricate thin films of cobalt on monocrystalline silicon Si (100) substrates. The incident beam strikes the substrates under normal and oblique incidences within a home-made evaporation chamber. The thickness of the deposited films ranges from 18 to 400 nm. Microscopic characterizations of the films are performed with X-ray diffraction (XRD) measurements and infer that all the samples are polycrystalline, with an hexagonal close packed (h.c.p.) structure and exhibit a <0001> preferred orientation, for the perpendicularly evaporated films. The grain size is found to increase with the thickness of the magnetic layer. The values of the computed parameters allow concluding to a compressive stress for the thinnest films. The static magnetic properties have been performed by means of magnetic force microscopy (M.F.M.) and Alternating Gradient Field Magnetometer (A.G.F.M.) tools. The dynamic magnetic properties have been investigated using Brillouin Light Scattering (B.L.S.) measurements. The M.F.M. observations were performed after in-plane ac demagnetization, and stripe patterns are only observed for the thickest films, showing the weaker perpendicular anisotropies. We used the experimental results provided by these tools to compute the effective magnetic anisotropy factors Ku . Values of Ku anisotropy constants, higher than 13 × 106 erg.cm−3, have been found.

The effects of thickness on magnetic properties of FeCuNbSiB sputtered thin films

Thin films of Fe73.1Cu1Nb3.1Si14.7B8.2 alloy having thickness of 200, 500 and 800 nm have been deposited by RF sputtering. Their magnetic properties have been characterized using alternating gradient field magnetometer (AGFM) and vibrating sample magnetometer (VSM). The effects of residual stresses investigated by nanoindentation experiments were conducted on as-deposited samples. It is observed that the coercivity of as-deposited films is inversely proportional to the thickness in relation with the residual stress induced during sputtering.

Anisotropy Factors of Co-Based Thin Films Computed from FMR and AGFM Studies

We deposited Co x Cr100−x thin films, under vacuum, onto Si (100) substrates; x is the cobalt proportion. The hysteresis loops in the longitudinal and the polar configurations are obtained by means of an alternating gradient field magnetometer (AGFM) at room temperature. The magnetic force microscopy technique is used to observe domain configurations, especially for the thickest films. The magnetic anisotropy of the films is investigated using ferromagnetic resonance (FMR) techniques. The thinnest films do not present any domain configuration whereas the thickest films exhibit clear stripe domains with a period sensibly equal to the film thickness. The magnetic anisotropy constants are computed using the static and the dynamic magnetic studies. The K i values, issued from these techniques, are compared. These results and others are presented and discussed.

Structural and Magnetic Properties of Annealed Vapor Deposited Co&lt;sub&gt;x&lt;/sub&gt;Cr&lt;sub&gt;1-x&lt;/sub&gt; Thin Films&lt;sub&gt;&lt;/sub&gt;

Abstract. We prepared, under vacuum and onto monocrystalline silicone and glass substrates, series of CoxCr1-x thin films, with x ranging from 0.80 to 0.88. The structural and magnetic properties of the as deposited films have been performed using Rutherford backscattering spectrometry (R.B.S.), X-ray diffraction (X.R.D.), Alternating Gradient Field Magnetometer (A.G.F.M.), and Brillouin Light Spectrometry (B.L.S.) techniques. Once the films being annealed under vacuum, for 1 h at 700°C, in a pre-heated furnace, their structural and magnetic properties have been performed, by these tools, as well. Significant results have been found. The as deposited films present only an HCP structure and show a preferred orientation. The annealed films present both HCP and FCC structures. The annealed films possess cell parameters greater than the bulk ones which infer that they are under a tensile stress. The cell parameters of the as deposited films are lower than the bulk ones which infer that they are under a compressive stress. Up to the annealing temperature the films are still ferromagnetic and some decrease of the magnetic moment is noticed. In addition, coercivity and squareness have been strongly improved in the annealed films comparatively to the as deposited films. Moreover, the stiffness constant, computed using Brillouin light scattering measurements and after adjustment of theoretical and experimental results, is found to be far lesser than pure Co one. These results and others will be presented and discussed.

A Comparison of Magnetometry and Relaxometry Measures of Magnetic Nanoparticles Deposited in Biological Samples

The Alternating Gradient Field Magnetometer (AGFM) is an instrument whose high sensitivity (10-8 emu) allows the detection of small amounts of magnetic nanoparticles (MNPs) with high accuracy. Over the last few years, different magnetic techniques have been used for in vitro measurements of magnetic nanostructures inside biological tissues. However, in vivo studies about their distribution within the body are very scarce because their dispersion, after being delivered, reduces their magnetic signal and hinders detection. In this paper we compare the longitudinal relaxation time (T1) and magnetization measurements in mice's biological tissues for the tracking of MNPs after of an injection of iron oxide nanoparticles. Furthermore, we have correlated the AGFM data with Fast Field Cycling NMR Relaxometry (FFCNMR Relaxometry) measurements with histological analysis. The results have demonstrated that these techniques are useful for detecting minute amounts of MNPs in excised organs after in-vivo comparable to other more conventional techniques for the measurement of MNPs biodistribution and clearance. Details about the preparation of the in vivo samples, measurement protocol and statistical data processing are given.

Magnetic properties of obliquely evaporated Co thin films

The magnetic properties of Co thin films obliquely evaporated under silicon and glass substrates are investigated using alternating gradient field magnetometer (AGFM) and magnetic force microscopy (MFM) techniques. The effects of the magnetic layer thickness and the deposition angle are studied. As results, it is found a decrease of the coercive field from 250 Oe, for t = 20 nm, to 95 Oe, for t = 400 nm, and a decrease of the anisotropy field from 1.6 kOe for 20 nm Co thick film, to 0.95 kOe for 200 nm Co thick film. An increase of these fields with the increase of the deposition angle is also found. The easy axis of the saturation magnetization lies in the film plane, whatever is the substrate nature. MFM images reveal well-defined stripe patterns, particularly for the thickest films, where the magnetocrystalline anisotropy is dominant. These results, and others, are presented and discussed.

Magnetic Properties of Co Thin Films Evaporated under Normal and Oblique Incidence

We have evaporated series of Co thin films under vacuum onto silicon and glass substrates at a perpendicular and oblique incidence. The thickness of the magnetic layer ranges from 20 to 400 nm. The static magnetic properties have been performed by means of magnetic force microscopy (M.F.M.) and Alternating Gradient Field Magnetometer (A.G.F.M.) techniques. The influence of the magnetic layer thickness and the deposition angle are studied. As results, it is found a decrease of the coercive field from 250 Oe, for t = 20 nm, to 95 Oe, for t = 400 nm. TheseHcvalues for obliquely evaporated cobalt films are larger than those measured for cobalt films evaporated at normal incidence, found to be equal to a few Oe. It is also found a decrease of the anisotropy field, from 1.6 kOe for the 20 nm Co thick film to 0.95 kOe for the 200 nm Co thick film. Furthermore, an increase of these fields with the increase of the deposition angle is found, as well. The easy axis of the saturation magnetization lies in the film plane, irrespective of the substrate nature. These results, and others, are presented and discussed.

Structural, magnetic and electrical properties of FexNi100−x/Si(100) films

A series of FexNi100−x (2≤x≤100) thin films with thicknesses between 110 and 150nm were evaporated on Si(100) substrates. The structural, magnetic and electrical properties of the films were studied by means of X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Alternating Gradient Field Magnetometer (AGFM) and four probe-point techniques. It was found that the films are polycrystalline and grow with 〈111〉 and 〈110〉 textures in the nickel-rich and iron-rich regions, respectively. The crystallite size and the internal strain rate ε were computed vs. the at% Fe using the line profile analysis of a single peak. The study of the magnetization curves shows that all films have an in-plane easy magnetization axis. The saturation magnetization and the coercive field have been studied as a function of the iron atomic percentage. The electric measurements indicate a maximum electrical resistivity of 45µΩcm near the Anyster composition.

Microstructural evolution and magnetic properties in Fe50Pd50 sputtered thin films submitted to post-deposition annealing

Fe50Pd50 thin films (t=50nm) have been deposited on Si substrates covered with a native oxide layer by sputtering technique. As-prepared films consist of a disordered Fe–Pd A1 phase, being deposited without heating the substrate. The order–disorder transformation towards the L10-ordered tetragonal phase has been induced by post deposition annealing in vacuum (annealing temperature ranging in the interval Ta=550–625°C for 1200s). Samples microstructure has been studied by means of X-ray diffraction, SEM and AFM microscopy. Room-temperature hysteresis loops have been measured by AGFM (Alternating Gradient Field Magnetometer) in parallel and perpendicular configuration. All produced systems have been observed to display tunable microstructure and, consequently, various magnetic properties. To study the magnetic properties evolution with annealing temperature, magnetic domain patterns have been measured by MFM. In particular, the domain-period dependence on the magnetocrystalline anisotropy constant has been analyzed.

Structural and Magnetic Studies of CoCr Thin Films Prepared by Physical Vapor Deposition

We use physical vapor deposition (PVD) to produce, under vacuum, CoCr thin films onto Si (100) and glass substrates. The thicknesses of the samples were measured with a DEKTAK 150 profilometer and the micro structural properties were studied using a Siemens D500 X-ray diffractometer. The static magnetic characterization was done by means of an Alternating Gradient Field Magnetometer (A.G.F.M.) 2900 MicroMag. The films deposited on Corning glass are amorphous. Among all the samples deposited on Si(100) with thickness ranging from 100 nm to 340 nm, only those with thickness 163 nm, 178 nm and 340 nm are polycrystalline and present a hexagonal close-packed (h.c.p.) structure with 〈0001〉 texture. The magnetization curve study infers that all the samples present a planar ferromagnetic anisotropy. The maximum saturation magnetization M s value being 400 emu/cm3, the coercive field decreases vs. thickness beyond a maximum value (178 nm). All these results will be presented and discussed.

Room-temperature organic ferromagnetism in the crystalline poly(3-hexylthiophene): Phenyl-C61-butyric acid methyl ester blend film

Pronounced ferromagnetism was observed in a crystalline blend film of conjugated polymer poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) by using magnetic force microscopy measurements. A substantial room-temperature saturation magnetization of about 0.65 emu g−1 was measured by an alternating gradient field magnetometer. Multiple experimental evidences demonstrate the charge transfer from the P3HT to the PCBM and the formation of P3HT crystal domain are expected to be two critical factors for the originals of room-temperature organic ferromagnetism.

Magnetic anisotropy factors of vapor deposited CoCr thin films on Si and glass substrates

Series of CoxCr1−x thin films have been evaporated under vacuum onto Si (100) and glass substrates. An alternating gradient field magnetometer is used to characterize the static magnetic properties of the samples and Brillouin light scattering is used to study their dynamic magnetic properties. The in-plane easy magnetization axis is found for all samples. Using these results, we computed the first, second and uniaxial magnetic anisotropy factors by several methods. Values of the computed effective magnetic anisotropy factors higher than 106ergcm−3 have been found. The results are discussed and correlated.

Large-area patterned magnetic nanostructures by self-assembling of polystyrene nanospheres

ABSTRACTIn this work, dot and anti-dot structures in Co, Ni, Ni80Fe20, Fe50Pd50, Fe73.5Cu1Nb3Si13.5B9 and Fe78B13Si9 thin films have been produced by means of nanosphere lithography. Two multi-step processes have been followed and will be here described. The first one directly exploits polystyrene nanosheres (PN) as a mask to fabricate arrays of magnetic nanoholes and dots. In the second case, the nanospheres are used to design a polymeric mask of a photoresist subsequently used to pattern a magnetic nanostructure on a film. Advantages and disadvantages of the two lithographical techniques will be here highlighted. In both processes, the dimension and mutual distance of the patterns are dependent on the starting PN diameter (in the interval 500-800 nm). Samples microstructure has been studied by means of SEM and AFM microscopy. Room-temperature hysteresis loops have been measured by an AGFM (Alternating Gradient Field Magnetometer). MFM microscopy has been exploited to study the magnetic domain pattern. All produced systems have been observed to display tunable microstructure and, consequently, various magnetic properties for application.

Nucleation, growth and properties of Co nanostructures electrodeposited on n-Si(1 1 1)

In the present work, cobalt thin films deposited directly on n-Si(111) surfaces by electrodeposition in Watts bath have been investigated. The electrochemical deposition and properties of deposits were studied using cyclic voltammetry (CV), chronoamperometry (CA), ex situ atomic force microscopy (AFM), X-ray diffraction (XRD) and alternating gradient field magnetometer (AGFM) techniques. The nucleation and growth kinetics at the initial stages of Co studied by current transients indicate a 3D island growth (Volmer–Weber); it is characterized by an instantaneous nucleation mechanism followed by diffusion limited growth. According to this model, the estimated nucleus density and diffusion coefficient are on the order of magnitude of 106cm−2 and 10−5cm2s−1, respectively. AFM characterization of the deposits shows a granular structure of the electrodeposited layers. XRD measurements indicate a small grain size with the presence of a mixture of hcp and fcc Co structures. The hysteresis loops with a magnetic field in the parallel and perpendicular direction and showed that the easy magnetization axis of Co thin film is in the film plane.

Magnetic Properties of Cu Nanoclusters Embedded in ZnO Thin Films

Cu nonmagnetic metallic nanoclusters were embedded in the ZnO thin film by using nanocluster beam deposition. No presence of secondary phase was detected in X-ray diffraction (XRD) analysis, but secondary phases CuO and Cu2O nanoclusters were detected in films by transmission electron microscopy (TEM). Cu nanoclusters embedded in ZnO films have the average particle size around 8-10 nm. Cu atoms were surrounded by ZnO matrix, and the interface effect caused overlapping of p-orbital from O contributed by ZnO and d-orbital contributed by Cu as suggested by XPS and UV-Vis absorbance results. Alternating gradient field magnetometer (AGM) results show that the embedment of nonmagnetic Cu nanoclusters in ferromagnetic ZnO thin films can enhance the room temperature ferromagnetism of ZnO thin film up to maximum Ms = 2.64 emu/cc with small coercivities lower than 70 Oe. The saturation magnetization (Ms) value increases with Cu volume fraction in ZnO and decreases with Cu volume fraction after certain volume fractions of Cu were achieved. Based on the clues given by XPS results, +1 valence state of Cu is in the ferromagnetism favorable state, indicating possible spin polarization occurred and ferromagnetism induced in the system.

Fabrication of thin films for a small alternating gradient field magnetometer for biomedical magnetic sensing applications

Thin film alternating gradient field magnetometers (AGFM) have potential for measuring magnetic moments of minerals in extraterrestrial soil samples. AGFM sensors offer increased spatial resolution required to detect magnetic nanoparticles for biosensing applications. We have fabricated a patterned thin film with the properties necessary for use in a small AGFM system. Hexagonal-close-packed CoCrPt thin films of 20 and 500 nm were sputtered (nominal composition of Co66Cr15Pt19), showing a high magnetic moment and large out-of-plane anisotropy. The films showed a Δθ50 of better than 3° for the (002) CoCrPt peak for all films, which improves with thickness. The texture is partly due to the NiW and Ru underlayers. The films showed an out-of-plane easy axis, indicating a strong uniaxial anisotropy that exceeds the shape demagnetization energy. This is due to the addition of Cr, which decreases the magnetic moment of the films; magnetoelastic coupling and film stresses may also aid in achieving a perpendicular anisotropy. The first-order uniaxial anisotropy constants were calculated as a function of temperature, ranging from 3.7 × 106 ergs/cm3 at room temperature to 6.8 × 105 ergs/cm3 at 500 °C, and the T dependence agrees with Akulov’s theory for uniaxial materials. The thickest film was etched with a checkerboard pattern to decrease the demagnetization effects, which are seen more influentially in the thicker films. This opened up the hysteresis loop, and decreased the amount of field necessary to overcome the thin film geometry.

Deposition of thin cobalt films onto silicon by galvanostatic and potentiostatic techniques

In this study, thin cobalt films were electrodeposited directly onto n-Si (100) using two different electrodeposition techniques: galvanostatic and potentiostatic. The morphological difference between galvanostatic and potentiostatic deposits was observed by atomic force microscopy (AFM) and X-ray diffraction (XRD). Analysis of the deposits by an alternating gradient field magnetometer (AGFM) showed the influence of the electrodeposition process on the magnetic properties of the film.

Structural, static and dynamic magnetic studies of evaporated CoxCr1x/Si (100) and CoxCr1x/glass thin films

We have evaporated a series of CoxCr1-x thin films under vacuum onto Si (100) and glass substrates, with a perpendicular incidence. The thickness of the magnetic layer ranged from 17 to 220 nm, and the content chromium, from 0.12 to 0.20, values determined by means of Rutherford Backscattering Spectrometry (R.B.S.) spectra using SIMNRA programme. Microscopic characterizations of the films were done with X-ray diffraction (XRD) measurements and infer that all the samples were polycrystalline, with an hcp structure and show a <0001> preferred orientation, and with the grain size increasing with the chromium content decrease. Atomic force microscopy (A.F.M.) observations reveal very smooth film surfaces. The static and dynamic magnetic properties have been investigated by means of Alternating Gradient Field Magnetometer (A.G.F.M.), and Brillouin Light Scattering (B.L.S.) measurements. The saturation magnetization MB was found to decrease from 1200 emu/cm3 to 220 emu/cm3 as the chromium content increases from 12%at. to 20%at, whatever the thickness is.From the fit of the B.L.S. spectra, we have computed effective magnetic anisotropy factors, as well. All the results are discussed and correlated.

Effect of Cr on the magnetic 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. Thickness ranges from 17 to 220 nm, and x from 0.80 to 0.88. Alternating gradient field magnetometer (AGFM) measurements provided saturation magnetization values ranging from 220 to 1200 emu/cm 3. Values of squareness exceeding 0.8 have been measured. Coercive field may reach values up to 700 Oe, depending on the percentage of chromium, as well as the substrate nature and the direction of the applied magnetic field. The saturation magnetization value decreases as the Cr content increases. In order to study their dynamical magnetic properties, Brillouin Light Scattering (BLS) measurements have been performed on these samples. Stiffness constant value and anisotropy magnetic field were adjusted to fit the experimental BLS spectra. These results are analyzed and correlated.