bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of substrates roughness on c-axis preferred orientation of ZnO films deposited by rf magnetron sputtering
Authors: Lee Jae Bin , Kwack Sanghyon , Kim Hyeong Joon 
Published: April 2011

ABSTRACTWe investigated the effect of substrate surface roughness on c-axis preferred orientation of ZnO films deposited by radio frequency (rf) magnetron sputtering. We used as substrates a bare Si(100), evaporated Au/Si(100), evaporated Al/Si(100), and sputtered Al/Si(100), of which rms roughness by atomic force microscope (AFM) were 0.127, 1.71, 2.11, and 6.5∼11.8 nm, respectively. The crystallinity and the c-axis preferred orientation of ZnO films strongly depended on the surface roughness of the used substrates.
The Decomposition of tBAA on the Silicon Surface
Authors: Chang Che-Chen , Huang Ing-Jye 
Published: April 2011

ABSTRACTAmong the copper precursors used, cupric β-diketonate complexes exhibit a high sublimationrate and a low pyrolysis temperature. This work explored the possibility of using a nonfluorinated t-butylacetato complex of Cu(II) as the precursor. Secondary ion mass spectrometry and temperature-program desorption studies on the adsorption and decomposition of the ligand, tert-butyl acetoacetate (tBAA), of this precursor on Si(100) showed that at low doses, all tBAA molecules dissociated readily upon adsorption on the surface at substrate temperatures as low as –160°C. For dissociation through tBAA bonding via the ester oxygen to the surface, the bond scission occurring at the tBu-O bond resulted in the formation of surface tert-butylfragments, which in turn underwent a β-hydride elimination reaction to yield isobutene and surface hydride. In addition, the bond scission occurring at the tBuO-CO bond produced surface tert-butoxy specie, of which the hydrogen atom in the â position can be transferred to the oxygen atom of the butoxy group to yield isobutene and surface hydroxyl species. Its implication in the quality of the copper film generated is discussed.
Exchange Coupling and Spin-Flip Transition of CoFe2O4/α-Fe2O3 Bilayered Films
Authors: Fujii Tatsuo , Yano Takuya , Nakanishi Makoto , Takada Jun 
Published: April 2011

ABSTRACTCoFe2O4/α-Fe2O3 (ferrimagnetic / antiferromagnetic) bilayered films were prepared on α-Al2O3(102) single-crystalline substrates by helicon plasma sputtering. A well-crystallized epitaxial α-Fe2O3(102) layer was formed on the substrate, while CoFe2O4 grown on α-Fe2O3(102) was a polycrystalline layer with a (100)-preferred orientation. The α-Fe2O3(102) films without CoFe2O4 layers clearly showed a spin-flip transition at about 400 K. The spins aligned perpendicular to the film plane at room temperature changed their direction within the film plane above 400 K. However the α-Fe2O3 base layers of CoFe2O4/α-Fe2O3 bilayered films did not show any spin-flip transition. The CoFe2O4 layer on α-Fe2O3 had a large in-plane magnetic anisotropy, while the spin axis of the α-Fe2O3(102) base layer was directed perpendicular to the film plane. The magnetization of ferrimagnetic CoFe2O4 layers was coupled perpendicularly to the spin axis of anitiferromagnetic α-Fe2O3 layers due to the exchange coupling at the interface between CoFe2O4 and α-Fe2O3.
Exchange-Biased Nio-Co Nanofaceted Bilayers Grown on MgO (110)
Authors: Dubourg S. , Bobo J.F. , Warot B. , Snoeck E. , Ousset J.C. 
Published: April 2011

ABSTRACTWe have sputter-grown self-organised faceted NiO-Co epitaxial bilayers on MgO(110). Due to very close lattice parameters, NiO adopts the same NaCl crystallographic structure as the substrate but it minimises its surface energy growing in a stripe-shaped morphology elongated along [001] MgO direction. The Co layers then deposited on NiO adopt a fcc structure. They consist of a set of connected nanowires whose height is about 50 Å, length is near to 1 µm and lateral periodicity ≍ 100 Å. Magnetic properties of the Co layers were investigated by magneto-optical Kerr effect from 10 K to room temperature. They are dominated by a strong shape-induced uniaxial anisotropy and exchange coupling with the antiferromagnetic underlayer. Magnetisation loops recorded along the easy axis exhibit a perfect squareness and switch in a field range smaller than 10 Oe. Transverse measurements indicate that switching occurs by domain nucleation and/or domain wall propagation. On the contrary, close to the [110] hard axis, magnetic switching occurs by coherent rotation. The bi-stable Co magnetisation state along its easy axis has been used for ordering the NiO spins configuration from room temperature to 10 K. Sign and value of exchange bias induced by such a thermal treatment can be modulated thanks to a wide magnetocrystalline or local exchange path energies distributions.
Computational Modeling For Magnetic-Sensor-Based Three-Dimensional Visualization Of Microcracks
Authors: Muratov Leonid , Lederman David , Cooper Bernard R. 
Published: April 2011

ABSTRACTThe presence of cracks, phase segregation, or even submicron-sized grain boundaries creates a disruption of the magnetic field response to an externally applied electrical current running through the material. These effects can be detected through the magnetic field leakage in the external near-surface region. Using a computer model of an array of magnetic tunnel junction detectors, magnetic “signatures” of various faults and/or material borders and domains have been calculated using finite element analysis and portrayed by icons. We have considered a number of typical cracks and flaws, of different dimensions and orientations, within the bulk of the component. The database of “signatures” thus generated allows fast recognition of faults and generation of their images in real time. Significant efforts have been made to provide an adequate three-dimensional visualization of the shape and distribution of microcracks, the magnetic field lines, and delineation of the position of the faults in relation to the surface.
Magneto-Resistance and Induced Domain Structure in Tunnel Junctions
Authors: Hehn M. , Lenoble O. , Lacour D. , Schuhl A. , Tiusan C. , Hrabovsky D. , Bobo J.F. 
Published: April 2011

ABSTRACTMagnetization reversals in sputtered Co electrodes of a magnetic tunnel junction are studied using transport measurements, magneto-optic Kerr magnetometry and microscopy. Using the tunnel magneto-resistive effect as a probe for micromagnetic studies, we first evidence the existence of an unexpected domain structure in the soft Co layer. This domain structure originates from the duplication of the domain structure of the hard Co layer template into the soft layer via ferromagnetic inter-electrode coupling. A detailed analysis of the kerr microscopy images shows that all features appearing in the variation of tunnel resistance as a function of the applied field are associated to the domain phase evolution of each electrode. By tailoring the magnetic properties of the hard Co layer, we have demonstrated that the appearance of the domain duplication is driven by the magnetic anisotropy of the hard layer. Finally, a brief theoretical description of the domain duplication process allows us to extract the main parameters governing the effect.
Multilevel Magnetoresistance in a Structure Consisting of two spin-valves
Authors: Li Kebin , Wu Yihong , Qiu Jinjun , Han Guchang , Guo Zaibing , Chong Towchong 
Published: April 2011

ABSTRACTThe magnetic and electrical properties as well as the structural characteristics have been studied on a series of samples with structure substrate (Sub)/SV(1)/Al2O35nm/SV(2). Here, SV(1) is either CoFe/IrMn based spin-valve (SV) such as Ta5/NiFe2/IrMn8/CoFe2/Cu2.6/CoFe2/Ta5 (thicknesses are in nanometers) bottom SV or Ta5/NiFe2/CoFe1.5/Cu2.6/CoFe2/FeMn10/Ta5 top SV and SV(2) is Ta5/NiFe2/CoFe1.5(or 2)/Cu2.6/CoFe2/IrMn8/Ta5 top SV. SV(1) and SV(2) in the structure are decoupled by a Al2O3 layer with 5nm in the magnetic properties, however, they are in parallel connection in the electrical properties. In a sample with structure Sub/Ta5/NiFe2/IrMn8/CoFe2/Cu2.6/CoFe2/Ta5/Al2O35/Ta5/NiFe2/CoFe2/Cu2.6/CoFe2/IrMn8/Ta5, five magnetoresistance states which are related to five magnetization states have been observed after the sample was annealed at T=220 °C with a field strength of 1T under high vacuum because of different interlayer coupling fields (Hint) in the top and bottom CoFe/IrMn based SVs (Hint is about 12.21 Oe in the top CoFe/IrMn SV and 29.3 Oe in the bottom CoFe/IrMn based SV). In a sample with structure Sub/Ta5/NiFe2/CoFe1.5/Cu2.6/CoFe2/FeMn10/Ta5/Al2O35/Ta5/NiFe2/CoFe1.5/Cu2.6/CoFe2 /IrMn8/Ta5, since the blocking temperature of the CoFe/FeMn based SV (Tb is about 150 °C) is lower than that of CoFe/IrMn based SV (Tb is about 230 °C), the spins can be easily engineered and therefore various magnetoresistance states can be obtained when the sample is magnetically annealed at different temperatures in a proper annealing sequence. By properly selecting materials and controlling the magnetically annealing conditions, multilevel giant magnetoresistance (MR) magnetic random access memory (MRAM) cell can be realized, which will significantly improve the MRAM data storage density without increasing any additional processing complexity.
Microstructure and Magnetic Properties of Co-CoO Nanocomposite Films
Authors: Yi Jae-Young , Hirata G. A. , Rudee M. L. 
Published: April 2011

ABSTRACTThe effect of exchange anisotropy on nanosize Co particles was studied in Co-CoO nanocomposite thin films for possible applications for magnetic storage media. XRD analyses showed nanosize hcp Co particles and (111) textured CoO phase. A broken columnar structure was observed in cross-section TEM images. Very large room temperature coercivity (∼1 kOe) was observed and believed to be due to a shape effect and possible local exchange coupling. Large exchange anisotropy at low temperatures and linear type temperature dependence were explained by finite size effects and thermal relaxation of the CoO particles. A slow decrease of thermoremanent moment (TRM) with temperature and large TRM at room temperature indicated that the exchange anisotropy significantly modified the anisotropy energy barrier of the Co crystallites in the CoO matrix. The results indicated that the exchange anisotropy could be used to stabilize nanosize ferromagnetic particles.
Modification of the magnetic properties of longitudinal thin-film media by ion-beam irradiation
Authors: Wright Jason D. , Krishnan Kannan M. 
Published: April 2011

ABSTRACTThe modification of conventional longitudinal recording media by ion-beam irradiation is of both scientific and technological interest. In particular, patterning by irradiation through a stencil mask at the 50 nm length scale may fulfill the promise of a commercially viable patterned media architecture. In this context, the magnetic properties and microstructural evolution of high-coercivity longitudinal thin film media were investigated after ion-beam irradiation. TRIM simulations were used to calculate the depth profiles and damage distributions as a function of energy and dose for carbon, nitrogen, and chromium ions and three different media (C, Cr, no capping layer). Corresponding implantations were carried out and hysteresis curves were measured using a vibrating sample magnetometer (VSM). Using chromium ion implantation at 20 keV, both remanence and coercivity were reduced to zero, i.e., rendering the ferromagnetic thin film paramagnetic, at doses as low as 1×1016 cm−2. For C+ implantation at 20 keV, remanence and coercivity were also reduced to varying extent up to doses of 5×1016 cm−2 after which further irradiation had no effect. Slight decreases in remanence and coercivity were observed for 20 keV N2+ irradiation. XRD measurements indicate that the hexagonal cobalt alloy phase remains intact after irradiation. The physical and magnetic domain structures at the surface were assessed by atomic force and magnetic force microscopy. Combined with the development of a suitable stencil mask, such chromium ion implantation can be used to develop a viable patterned media with nanoscale dimensions, consisting of locally defined ferromagnetic and paramagnetic regions. This work is in progress.
Chalcopyrite Magnetic Semiconductors: An AB–Initio Study of Their Structural, Electronic and Magnetic Properties
Authors: Picozzi S. , Continenza A. , Geng W. T. , Zhao Y. J. , Freeman A. J. 
Published: April 2011

ABSTRACTStimulated by recent experimental observations of room{temperature ferromagnetism of MnxCd1−xGeP2, we investigate the structural, electronic and magnetic properties of these systems as a function of Mn concentration by means of first–principles density-functional-theory-based codes. Moreover, we investigate the effect of the anion substitution (P vs As) in Mn-rich chalcopyirites. Our calculations indicate that the antiferromagnetic alignment is the most stable ordering for all the systems studied, at variance with that experimentally reported. Moreover, we find that there is a slight reduction of the total magnetic moment per Mn atom from ∼5 µB in all the Cd-rich P-based chalcopyrites to ∼4 µB in the Mn–rich MnGeP2 and MnGeAs2 systems.
Ferromagnetic properties and Nanocrystallization behavior of Amorphous (Fe0.99Mo0.01)78Si9B13 Ribbons
Authors: Sun Xiang-Cheng , Toledo J. A. , Galindo S. , Sun W. S. 
Published: April 2011

ABSTRACTFerromagnetic properties and nanocrystallization process of soft ferromagnetic (Fe0.99Mo0.01)78Si9B13 ribbons are studied by transmission electron microscope (TEM), X-ray diffraction (XRD), Mössbauer spectroscopy (MS), differential scanning calorimeters (DSC) and magnetization measurements. The Curie and crystallization temperature are determined to be TC=665K and Tx = 750K, respectively. The Tx value is in well agreement with DSC measurement results. X-ray diffraction patterns had shown a good reconfirm of two metastable phases (Fe23B6, Fe3B) were formed under in-situ nanocrystallization process. Of which these metastable phases embedded in the amorphous matrix have a significant effect on magnetic ordering. The ultimate nanocrystalline phases of α-Fe (Mo, Si) and Fe2B at optimum annealing temperature had been observed respectively. It is notable that the magnetization of the amorphous phase decreases more rapidly with increasing temperature than those of nanocrystalline ferromagnetism, suggesting the presence of the distribution of exchange interaction in the amorphous phase or high metalloid contents.
Characterization of Softmagnetic Thin Layers using Barkhausen Noise Microscopy
Authors: Hoffmann Jochen , Meyendorf Norbert , Altpeter Iris 
Published: April 2011

ABSTRACTFerromagnetic materials are essential for data recording devices. For inductive or magnetoresistive (MR) sensors softmagnetic thin layer systems are used. Optimal performance of these layers requires homogeneous magnetic properties, especially a pronounced uniaxial magnetic anisotropy. Furthermore, microstructural imperfections and residual stresses influence the magnetic structure in the layer system.Barkhausen Noise Microscopy enables the characterization of such thin layers. By cycling the magnetic hysteresis of ferromagnetic material electrical voltages (the Barkhausen noise) are induced in an inductive sensor. Miniaturization of the sensor and the scanning probe technique provides resolution down to few micrometers. Two materials were examined in terms of their structure, thickness, residual stresses and heat treatment condition: Sendust, used in inductive sensors and nanocrystalline NiFe, used in MR-sensors. In quality correlations to Barkhausen noise parameters were found. For representative sample a quantification of residual stress distribution could be established employing X-ray stress analysis.
Effect of Composition and Processing on the Microstructure and Magnetic Properties of 2:17 High Temperature Magnets
Authors: Tang W. , Zhang Y. , Goll D. , Kronmüller H. , Hadjipanayis G. C. 
Published: April 2011

ABSTRACTA comprehensive and systematic study has been made on Sm(CobalFevCuyZrx)zmagnets to completely understand the effects of composition and processing on their magnetic properties. The homogenized Sm(Co,Fe,Cu,Zr)z magnets have a featureless microstructure. A cellular/lamellar microstructure develops after 2-3 hours of aging at 800-850°C, but the coercivity increases only after a subsequent slow cooling to 400°C. During cooling, diffusion takes place and Cu is concentrated in the 1:5 cell boundaries and Fe in the 2:17R cells. This dilutes the magnetic properties of the 1:5 phase and causes domain wall pinning/nucleation at the cell boundaries. Higher ratio z leads to larger cells as expected due to the larger amount of the 2:17 phase. For a fixed Cu content, this translates to a larger amount of Cu in the 1:5 cell boundaries, and therefore, to a higher coercivity. Magnets without Cu but with Zr have a lamellar and a cellular like microstructure. In Zr free samples, however, a larger amount of Cu is needed to form the cellular microstructure. This cellular microstructure is unstable with prolonged isothermal aging. A uniform and stable cellular/lamellar microstructure is only observed in alloys containing both Cu and Zr. A higher aging temperature Tag leads to larger cells and higher coercivity as explained above. The results of all these studies clearly show that the amount of Cu in the 1:5 cell boundaries controls both the coercivity and its temperature dependence leading to positive and negative temperature coefficients of coercivity in low and high Cu content alloys, respectively.
Magnetic and Microstructural Aspects of the Bulk Metallic Glassy Materials Nd60Fe30Al10
Authors: Dan N. H. , Phuc N. X. , Ky V. H. , Hong N. M. , Chau N. , Luong N. H. , Huu C. X. , Mccallum R. W. , Kramer M. J. , O'Connor A. S. , Dennis K. W. , Lewis L. H. , Tung L. D. 
Published: April 2011

ABSTRACTThe ferromagnetic bulk metallic glass (BMG) Nd60Fe30Al10system exhibits extremely large coercivities at low temperature and moderate coercivities near room temperature. The magnetic hardness, as best evidenced by the onset of magnetic irreversibility, was studied in bulk suction-cast and melt-spun alloys with the nominal composition Nd60Fe30Al10. Systematic x-ray diffraction studies of the degree of crystallinity performed as a function of position within the bulk suction-cast samples is found to correlate with the variation in the room-temperature magnetic hysteresis character. X-ray diffraction data clearly shows the presence of both crystallites and amorphous material on the samples' outmost surfaces; the amorphous phase content increases with distance into the cast sample. These results underscore the importance of solidification conditions and attendant nanophase selection, on the resultant magnetic properties of this class of alloys.
Investigations on the Magnetic Properties of High-Coercivity (Nd1−xFex)90Al10 Bulk Amorphous Alloys
Authors: Lupu N. , Chiriac H. , Takeuchi A. , Inoue A. 
Published: April 2011

ABSTRACTBulk rods with diameters up to 3 mm prepared by suction casting and respectively mould casting and melt-spun amorphous ribbons with thicknesses in the range 25 – 150 μm with compositions Nd90−xFexAl10 (x = 35; 40; 45; 50) were investigated by XRD, DSC and magnetic measurements in the temperature range 5 – 600 K. The microstructure and magnetic properties are strongly dependent on the cooling rate, preparation process and Fe content. The large values of the coercive field, which amount to 320 kA/m in the as-cast state as well as the increase with decrease of the temperature and cooling rate result from the formation of very small metastable or nonequilibrium magnetic clusters.
Influence of Domain Structure on Magnetoresistance in Perovskite Manganite Grain Boundary Junctions
Authors: Gunnarsson Robert , Kadigrobov Anatoli , Ivanov Zdravko 
Published: April 2011

ABSTRACTWe have been able to deduce a temperature dependence of the built-in potential in La2/3Sr1/3MnO3 grain boundary junctions. This has been performed by trimming a single grain boundary down to 1μm width with a focused ion-beam. We can thereby see the impact of single domain walls on the magnetoresistance and the current-voltage characteristics. We have also demonstrated the effect of averaging as we increased the number of junctions.
Magnetic Properties of Self-Assembled Fe Nanoparticle Arrays
Authors: Farrell D. , Yamamuro S. , Majetich S. A. 
Published: April 2011

ABSTRACTThe magnetic properties of multilayer arrays of Fe nanoparticles were compared with those of frozen, dilute suspensions of the same particles. The array sample displayed larger coercivity in both hysteretic and remanent magnetization measurements. However, the derivative of the remanent magnetization curve shows a much broader switching field distribution for the arrays than for the dilute sample. Magnetic relaxation measurements show the convergence of the time dependent properties of the samples at large times, and much more rapid relaxation in the arrays at short times.
Stability of Magnetic States in Patterned Materials
Authors: Pardavi-Horvath Martha 
Published: April 2011

ABSTRACTThe stability of the individual elements of a two-dimensional (2D) regular array of single domain particles is investigated. The variance in the statistical distribution of up- and down switching fields of the elements leads to premature switching for the low coercivity particles, and incomplete overwriting for the high end of the distribution. The distribution of the interaction fields from surrounding elements on a 2D array depends the saturation magnetization of the elements, their packing density, and the recorded information. The non-ellipsoidal shape of the elements leads to reduced switching fields as a result of non-collinear magnetization around the corners and edges. The thermal stability of 2D arrays, switching by (incoherent) rotation of the magnetization, is enhanced compared to bulk/contiguous media, due to the lack of low energy barrier domain wall motion processes. However due to the fast decrease of the anisotropy, stability at elevated temperatures is still a problem. Experimental data for a model 2D square array of single crystalline, strongly uniaxial, single domain garnet particles illustrate the effects on stability of statistics, shape, and thermal excitation.
Synthesis and Self-Assembly of Films Containing FeCoPt Nanoparticles
Authors: Chen Min , Nikles David E. 
Published: April 2011

ABSTRACTFe49Co7Pt44 and Fe40Co17Pt43nanoparticles were synthesized by simultaneous chemical reduction of platinum acetylacetonate and cobalt acetylacetonate and thermal decomposition of iron pentacarbonyl. As-prepared the particles had a disordered face-centered cubic lattice with an average diameter of 3.2 nm and were superparamagnetic. These particles were well dispersed in a 50/50 mixture of hexane and octane. The particles self-assembled into ordered superlattices when deposited onto carbon coated Cu TEM grids or onto single crystal Si (100) substrates. After vacuum annealing (from 500°C to 700 °C), the particles transformed to the tetragonal phase. The coercivity of the film strongly depended on the composition and annealing temperature. For the Fe49Co7Pt44film, coercivity of 8700 Oe and a squareness of 0.75 after annealing at 700 °C for 30 minutes. XPS shows existance of oxidized iron and cobalt on the surface of film.