Helicity-Preserving Metasurfaces for Magneto-Optical Enhancement in Ferromagnetic [Pt/Co] N Films
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Engineering strain, densification, order parameter and magnetic properties of FePt thin films by dense electronic excitations
FePt films prepared by DC sputtering on Si 〈100〉 substrates when annealed at 600 °C for 1 h exhibited a structurally ordered and magnetically hard L1{sub 0} phase. These FePt films were exposed to dense electronic excitations by using 100 MeV oxygen ions as a function of increasing fluences. Such excitations induce pressure and result in the enhancement of order parameter by increasing strain on the FePt films. Apart from this, the surface morphological images from field emission scanning electron microscopy reveal a densification of the films consequent to irradiation and are correlated with the details obtained from Rutherford back scattering analysis. The variation in the values of coercivity correlates well with the change in volume percentage of face centered tetragonal and face centered cubic phase. A coercivity of 14.7 kOe with order parameter 0.92 is achieved at a fluence of 5 × 10{sup 12} ions/cm{sup 2}. The theoretical simulation of the demagnetization curve shows a strong correlation of coercivity and order parameter between the experimentally obtained values with that of simulation. The effect of irradiation induced strain, the structural ordering and coercivity of FePt films as a function of fluences have been discussed.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
In situ measurement of the bonded film thickness of Z-Tetraol lubricant on magnetic recording media
Currently, the bonded film thickness of perfluoropolyether lubricant on top of magnetic recording media is measured by a two-step process. First, the media disk has to be rinsed thoroughly using a fluorocarbon solvent (for instance, Vetrel) to remove the mobile lubricant. Second, the thickness of the remaining lubricant on the media surface which is regarded as the bonded lubricant thickness is then measured either by Fourier transform infrared spectroscopy (FTIR) or electron spectroscopy for chemical analysis. As the total lubricant thickness approaches single molecular dimension ({approx}10 A), current methods face tremendous challenge on the accuracy and sensitivity of the measurement. We studied the spectral characteristics responding to the lubricant bonding with the carbon overcoat by the time-of-flight secondary ion mass spectra and proposed to use the peak area ratio (C{sub 3}H{sub 2}F/C{sub 3}H{sub 5}O and C{sub 4}H{sub 10}O/C{sub 3}H{sub 6}O{sub 2}) to characterize the bonded Z-Tetraol lubricant that produces a direct bonded lubricant thickness measurement without the need to remove the mobile lubricant with a solvent. After taking the background signal of disks prior to bonding by UV irradiation into account, this method becomes independent of the total lubricant thickness as well as shows good correlation linearity (R{sup 2{approx}}87%) with the current FTIR method for the ratio of C{sub 4}H{sub 10}O/C{sub 3}H{sub 6}O{sub 2}.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Improvement of thermal stability of amorphous CoFeSiB thin films
The excellent soft magnetic properties of amorphous (a-) CoFeSiB films make it suited for use in the yoke of granular-in-gap sensors, but only if their thermal stability can be improved. To this end, this study investigated the effects of adding small amounts of other metals on the magnetic and structural properties of a-CoFeSiB films. It was found that adding metals with relatively large atomic radii is an effective way to increase thermal stability, with both Ta and Hf showing good thermal stability after annealing at temperatures of 473 to 573 K. Indeed, a -(CoFeSiB){sub 96.2}Hf{sub 3.8} film was found to maintain its initial coercivity of 0.2 Oe without very little decrease in magnetization after annealing at 623 K. Furthermore, even after annealing at 673 K a -(CoFeSiB){sub 93.0}Hf{sub 7.0} film still had a relatively low coercivity of approximately 0.5 Oe.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Electron microscopy of phase and structural transformations in soft magnetic nanocrystalline Fe-Zr-N films
The effect of deposition conditions (film thickness) on the structure of soft magnetic Fe{sub 80-78}Zr{sub 10}N{sub 10-12} films formed by reactive magnetron deposition on a heat-resistant glass substrate has been investigated by analytical transmission electron microscopy, high-resolution electron microscopy, and diffraction analysis. The processes of evolution of the phase and structural state of films and the film-substrate interface upon annealing in the temperature range of 200-650 Degree-Sign C have been analyzed taking into account the thermodynamic, kinetic, and structural factors and the specific features of the nanocrystalline state.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Magnetometry of single ferromagnetic nanoparticles using magneto-optical indicator films with spatial amplification
We present a magneto-optical technique to spatially amplify and image fringe fields from single ferromagnetic nanorods. The fringe fields nucleate magnetic domains in a low-coercivity, perpendicularly magnetized indicator film, which are expanded by an applied out-of-plane field from the nanoscale to the microscale for measurement with polar Kerr microscopy. The nucleation location and therefore magnetic orientation of the sample nanorod are detected as spatially dependent field biases in locally measured hysteresis loops of the indicator film. We first discuss our method to fabricate the high-sensitivity indicator film with low energy argon ion irradiation. We then present a map of the amplified signal produced from a single nanorod as measured by the indicator film and compare it with a simultaneously obtained, unamplified fringe field map. The comparison demonstrates the advantage of the amplification mechanism and the capability of the technique to be performed with single-spot magneto-optical Kerr effect magnetometers. Our signal-to-noise ratio determines a minimum measureable particle diameter of tens of nanometers for typical transition metals. We finally use our method to obtain hysteresis loops from multiple nanorods in parallel. Our technique is unperturbed by applied in-plane fields for magnetic manipulation of nanoparticles, is robust against many common noise sources, and is applicable in a variety of test environments. We conclude with a discussion of the future optimization and application of our indicator film technique.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Asymmetric crossing of the attractive and repulsive magnetic potential by Abrikosov vortices
Here, we present studies of Abrikosov vortex motion across the magnetically charged edges of long thin ferromagnetic stripes placed above or under a thin superconducting film. The magnetic charges at the stripe edges form attractive or repulsive potential wells for vortices. Using a relatively small in-plane magnetic field to polarize the stripe edges and normal-to-plane magnetic field to induce up or down polarized vortices, we tune the attractive or repulsive stripe-vortex interactions. Imaging of the vortex dynamics reveals that the repulsive magnetic potential U m + acts as a robust vortex pinning barrier, while the attractive U m - has practically no effect on the vortex motion irrespective of the position of the stripes located above or underneath the superconducting film. We analyze the observed asymmetry using equations of the overdamped vortex motion. The formal analytical solution yields an asymmetry, but the numerical modeling with and without noise terms does not confirm it. Instead, we find that the asymmetry is caused by the creation of spontaneous vortices at the maxima of U m , which depends on the edge polarity and suppress U m - . Furthermore, our experiment and time-dependent Ginzburg-Landau simulations demonstrate that magnetic pinning dominates over vortex pinning due to corrugations of the superconducting layer deposited on top of the ferromagnetic stripes.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Magnetic ac susceptibility of superconducting Ta films for quantum computing
Recently, breakthroughs were reported in the long coherence time (>0.5 ms) transmon qubit using tantalum films (Ta). Identifying the loss mechanism in Ta films will help further improve the performance of Ta-based superconducting qubits. We report a study of superconducting properties in two sets of Ta films grown on c-cut and a-cut sapphires respectively using contact transport and noncontact magnetic ac susceptibility measurements. Although the resistive transition appears to be similar in both films, we found strikingly different responses in their complex magnetic susceptibilities χ' + iχ'$^{'}$ .χ'$^{'}$ in the c-cut films exhibits a sharp peak at superconducting transition Tc and becomes featureless below Tc indicating a strongly coupled superconducting state. In contrast, χ'$^{'}$ \ in the a-cut films exhibits a broad peak near Tc and a second peak appears below Tc, indicating granular superconductivity behavior. This second peak χ'$^{'}$ in is associated with the hysteresis loss at weak-link-type grain boundaries, which is believed to be a leading source of decoherence in the a-cut Ta films. The derived magnetic loss tangent in the a-cut films is about one order of magnitude higher than in the c-cut films. This study demonstrates that ac susceptibility is an excellent probe for characterizing bulk superconducting properties of the constituent superconducting materials used in qubits.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Phase transitions and magnetic domain coexistence in Nd0.5Sr0.5MnO3 thin films
We present a study of the physical properties of perovskite oxide Nd 0.5 Sr 0.5 MnO 3 (NSMO) thin films grown on (110)-oriented SrTiO 3 substrates. In bulk form, NSMO displays coupled magnetic and electronic transitions from paramagnetic/insulator to ferromagnetic (FM)/metal and then to antiferromagnetic (AFM)/charge-ordered insulator with decreasing temperature. In thin films, the AFM ordering only occurs when the films exist in an anisotropic strain state such as those obtained on (110)-oriented cubic substrates. In this work, resonant X-ray reflectivity, soft X-ray photoemission electron microscopy (X-PEEM), and magnetometry measurements showed that the NSMO film displays both vertical and lateral magnetic phase separation. Specifically, the film consists of three layers with different density and magnetic properties. The FM and AFM properties of the main NSMO layer were probed as a function of temperature using soft X-ray magnetic spectroscopy, and the coexistence of lateral FM and AFM domains was demonstrated at 110 K using X-PEEM.
36 MATERIALS SCIENCE↗
Tailoring of magnetic properties of ultrathin epitaxial Fe films by Dy doping
We report on the controlled modification of relaxation parameters and magnetic moments of epitaxial Fe thin films through Dy doping. Ferromagnetic resonance measurements show that an increase of Dy doping from 0.1% to 5% gives a tripling in Gilbert damping, and more importantly a strongly enhanced anisotropic damping that can be qualitatively understood through the slow-relaxing impurity model. X-ray magnetic circular dichroism measurements show a pronounced suppression of the orbital moment of the Fe with Dy doping, leading to an almost threefold drop in the orbital to spin moment ratio, m{sub l}/m{sub s}. Doping with Dy can therefore be used to control both dynamic and static properties of thin ferromagnetic films for improved performance in spintronics device applications, mediated through the antiferromagnetic interaction of the 4f and 3d states.
36 MATERIALS SCIENCE↗
Long-range magnetic order and relaxor ferroelectricity in a hexagonal high-entropy ferrite
Multiferroics that combine ferroelectricity and magnetic order are attractive for electronic and spintronic technologies, yet chemical disorder that promotes relaxor ferroelectricity usually suppresses long-range magnetic order. Here, we report entropy-stabilized relaxor multiferroicity in epitaxial hexagonal (Tb0.2Dy0.2Ho0.2Lu0.2Yb0.2)FeO3 thin films. Structural, magnetic, dielectric, and synchrotron spectroscopic measurements show the coexistence of relaxor ferroelectricity and long-range ferromagnetic order. We find that improper ferroelectricity remains robust against A-site configurational disorder, while the Fe sublattice preserves magnetic exchange. This separation of the microscopic origins of the polar and magnetic responses enables chemically disordered multiferroicity. Our results establish entropy engineering in hexagonal ferrites as a route toward multifunctional oxide thin films and provide a general design strategy for high-entropy multiferroics.
Miertschin, Duncan [Baylor University]↗
Combined Technology Fabrication of Spin-Valve Magnetoresistive Elements and Micromagnets
We present the research results of the fabrication technology of magnetoresistive (MR) elements based on the multilayer spin-valve magnetoresistive (SVMR) Ta–FeNiCo–CoFe–Cu–CoFe–FeNiCo–FeMn–Та nanostructures and CoNi micromagnets for the construction of digital galvanic interchanges and the magnetic field sensors. The results of experimental studies of test elements based on multilayer SVMR nanostructures with an MR effect from 7 to 8% and films of magnetically hard materials with a coercive force of up to 95 Oe formed on a single silicon die are presented.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Magnetic and high frequency properties of nanogranular CoFe-TiO{sub 2} films
A series of soft magnetic nanogranular CoFe-TiO{sub 2} films with different thicknesses were fabricated on Si substrates by co-sputtering CoFe and TiO{sub 2}, and the magnetic and high frequency properties were studied in details. X-ray diffraction analysis confirmed that the films were nanocrystalline/amorphous composites. A saturation magnetization as high as 21 kGs and a ferromagnetic resonance (FMR) frequency above 3 GHz were obtained. It was found that the coercivity decreased steeply with the increase of film thickness and its minimum value was about 6 Oe. In addition, the variations of FMR peak broadness of the imaginary part and damping factor were also presented and discussed as functions of film thickness.
36 MATERIALS SCIENCE↗
X-ray magnetic circular dichroism study of epitaxial magnetite ultrathin film on MgO(100)
The spin and orbital magnetic moments of the Fe{sub 3}O{sub 4} epitaxial ultrathin film synthesized by plasma assisted simultaneous oxidization on MgO(100) have been studied with X-ray magnetic circular dichroism. The ultrathin film retains a rather large total magnetic moment, i.e., (2.73 ± 0.15) μ{sub B}/f.u., which is ∼70% of that for the bulk-like Fe{sub 3}O{sub 4}. A significant unquenched orbital moment up to 0.54 ± 0.05 μ{sub B}/f.u. was observed, which could come from the symmetry breaking at the Fe{sub 3}O{sub 4}/MgO interface. Such sizable orbital moment will add capacities to the Fe{sub 3}O{sub 4}-based spintronics devices in the magnetization reversal by the electric field.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Effect of oxygen pressure on structural and magnetic properties of YIG thin films
The effect of oxygen pressure (P{sub O2}) on the Yttrium Iron Garnet (YIG) thin films were grown on silicon substrate by rf sputtering method was studied. The as-deposited films at 300K were amorphous in nature. The crystallization of these films was achieved by annealing at a temperature of 800 deg. C/1hr in air. The structural, microstructural and magnetic properties were found to be dependent on P{sub O2}.
36 MATERIALS SCIENCE↗
Electronic and Magnetic Structure of Intercalated Graphene Films
Ab initio calculations of the electron spectrum of the graphene–cobalt–nickel system were performed in the slope of the spin density functional theory (SDFT). Dispersion curves E{sub σn}(k) are presented; they were used to determine partial and total densities of valence electron states, and also magnetic moments of all atoms in the supercell. Energy position of the “Dirac cone” defined by p{sub z} states in graphene is shown to depend only slightly on the number of Co layers intercalated into the gap between the cobalt and graphene layers.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Transport properties of heteroepitaxial films based on bismuth telluride in strong magnetic fields
The temperature and magnetic-field dependences of the galvanomagnetic properties of n-Bi{sub 2}Te{sub 3} heteroepitaxial films in magnetic fields to 14 T at low temperatures are studied. It is shown that steps in the magnetic-field dependences of the quantum Hall effect and the plateau in the temperature dependences of the magnetoresistance of films are caused by topological surface states of Dirac fermions.
36 MATERIALS SCIENCE↗