bluuebunny/crossref_metadata_2025 huggingface dataset:
Chinese Area Positioning System With Wide Area Augmentation
Authors: Xuan Cheng , ZhiGang Li , XuHai Yang , WenJun Wu , Hui Lei , ChuGang Feng
Published: March 2012

The Chinese Area Positioning System (CAPS) is a regional satellite navigation system; its space segment consists of some Geostationary Earth Orbit (GEO) satellites and 2∼3 Inclined Geo-Synchronous Orbit (IGSO) satellites. Only a few satellites are needed to provide good area coverage and hence it is an ideal space segment for a regional navigation system. A time transfer mode is used to transmit navigation signals, so no high-precision atomic clocks are required onboard the satellites; all of the transferred navigation signals are generated by the same atomic clock at the master control station on the ground. By using virtual clock technology, the time of emission of signals from the ground control station is transformed to the time of transfer of signals at the phase centre of the satellite antenna; thus the impact of ephemeris errors of satellite on positioning accuracy is greatly decreased, enabling the CAPS to have the capability of wide area augmentation. A novel technology of orbit determination, called Paired Observation Combination for Both Stations (POCBS), proposed by the National Time Service Centre, is used in CAPS. The generation and measurement of ranging signals for the orbit survey are carried out in the ground station and the instrument errors are corrected in real-time. The determination of the clock offset is completely independent of the determination of satellite orbit, so the error of the clock offset has no impact on orbit determination. Therefore, a very high precision of satellite orbits, better than 4·2 cm (1 drms) can be obtained by the stations under regional distribution.
Existing medications among non-pregnancy-related listeriosis patients in England, 2007–2009
Authors: MOOK P. , JENKINS J. M. , O'BRIEN S. J. , GILLESPIE I. A.
Published: March 2012

To identify which medications were most commonly taken by non-pregnancy-related listeriosis patients prior to illness, we compared the medications reported by 512 cases identified via national surveillance in England between 2007 and 2009 with national prescription data, using British National Formulary (BNF) coding. Relative risks and corresponding confidence intervals were calculated, as appropriate, for BNF chapters and sections. Among listeriosis cases, the rates for cytotoxic drugs, drugs affecting the immune response and corticosteroids were significantly higher than for other medications. However, interactions between medications and how medications might confound or be confounded by concurrent medical conditions need to be investigated further. Nevertheless our findings suggest that targeting food-safety advice to prevent this foodborne disease in certain treatment groups is warranted.
Conceptualizing Treatment Nonadherence in Patients with Bipolar Disorder and PTSD
Authors: Rakofsky Jeffrey J. , Levy Steven T. , Dunlop Boadie W.
Published: March 2012

Treatment nonadherence is a concern among patients with bipolar disorder and posttraumatic stress disorder (PTSD). PTSD is common among patients with bipolar disorder and those with this comorbidity often have a more severe course of illness. While many factors have been associated with nonadherence in bipolar disorder patients and in PTSD patients, almost no research has focused on the factors associated with non-adherence in bipolar disorder patients with comorbid PTSD. Studies in primary bipolar disorder samples reveal patient, illness, drug and clinician characteristics associated with nonadherence while studies in primary PTSD samples reveal a significantly shorter list of patient, illness and drug characteristics. Shared risk factors between these two populations and the characteristics that predict noncompliance in only one population but often present in the other, suggest a high likelihood of nonadherence in the bipolar disorder-PTSD population. For bipolar disorder-PTSD patients with early childhood trauma, noncompliance may be related to the trauma-related meanings attributed to interactions with their physicians and their prescribed medications. Given the high side effect burden of bipolar disorder treatments and the importance of lifelong adherence, clinicians should vigilantly monitor for nonadherence in their bipolar disorder-PTSD patients and be particularly aware of patient-physician psychodynamics that might contribute to this behavior.
A G-band cryogenic MMIC heterodyne receiver module for astronomical applications
Authors: Voll Patricia , Samoska Lorene , Church Sarah , Lau Judy M. , Sieth Matthew , Gaier Todd , Kangaslahti Pekka , Soria Mary , Tantawi Sami , Van Winkle Dan
Published: March 2012

We report cryogenic noise temperature and gain measurements of a prototype heterodyne receiver module designed to operate in the atmospheric window centered on 150 GHz. The module utilizes monolithic microwave integrated circuit (MMIC) InP high electron mobility transistor (HEMT) amplifiers, a second harmonic mixer, and bandpass filters. Swept local oscillator (LO) measurements show an average gain of 22 dB and an average noise temperature of 87 K over a 40 GHz band from 140 to 180 GHz when the module is cooled to 22 K. A spot noise temperature of 58 K was measured at 166 GHz and is a record for cryogenic noise from HEMT amplifiers at this frequency. Intermediate frequency (IF) sweep measurements show a 20 GHz IF band with less than 94 K receiver noise temperature for a fixed LO of 83 GHz. The compact housing features a split-block design that facilitates quick assembly and a condensed arrangement of the MMIC components and bias circuitry. DC feedthroughs and nano-miniature connectors also contribute to the compact design, so that the dimensions of the moduleare approximately 2.5 cm per side.
Type II radio bursts: 1. New entirely analytic formalism for the electron beams, Langmuir waves, and radio emission
Authors: Schmidt J. M. , Cairns Iver H.
Published: March 2012

Type II radio bursts drift in frequency as shock waves and coronal mass ejections (CMEs) move through the Sun's corona and the solar wind. This paper extends the theoretical models for type II radio bursts of Knock et al. (2001, 2003), Knock and Cairns (2005), Cairns and Knock (2006) and Schmidt and Gopalswamy (2008). The theory treats the acceleration of electrons at the shock, formation of electron beams, growth of Langmuir waves, and conversion of Langmuir energy into radiation. An entirely analytical and more general formalism is developed, which includes kappa electron velocity distribution functions for the plasma electrons and the shock‐reflected electron beam. The radiation model also includes the plateauing of the electron beam, which releases energy for the Langmuir waves. This paper has two parts. First, the new entirely analytical formalism is presented. Second, first numerical results for synthetic radio images and synthetic dynamic spectra are discussed, gained by applying our radiation model to MHD simulations of a shock driven by a CME. The results are compared with earlier analytic approaches. This work is also applicable to other shock‐related emissions in space and astrophysical plasmas.
Locating earthquakes with surface waves and centroid moment tensor estimation
Authors: Wei Shengji , Zhan Zhongwen , Tan Ying , Ni Sidao , Helmberger Don
Published: March 2012

Traditionally, P wave arrival times have been used to locate regional earthquakes. In contrast, the travel times of surface waves dependent on source excitation and the source parameters and depth must be determined independently. Thus surface wave path delays need to be known before such data can be used for location. These delays can be estimated from previous earthquakes using the cut‐and‐paste technique, Ambient Seismic Noise tomography, and from 3D models. Taking the Chino Hills event as an example, we show consistency of path corrections for (>10 s) Love and Rayleigh waves to within about 1 s obtained from these methods. We then use these empirically derived delay maps to determine centroid locations of 138 Southern California moderate‐sized (3.5 > Mw> 5.7) earthquakes using surface waves alone. It appears that these methods are capable of locating the main zone of rupture within a few (∼3) km accuracy relative to Southern California Seismic Network locations with 5 stations that are well distributed in azimuth. We also address the timing accuracy required to resolve non‐double‐couple source parameters which trades‐off with location with less than a km error required for a 10% Compensated Linear Vector Dipole resolution.
Cyclone‐induced hyperpycnal turbidity currents in a submarine canyon
Authors: Liu James T. , Wang Yu‐Huai , Yang Rick J. , Hsu Ray T. , Kao Shuh‐Ji , Lin Hui‐Ling , Kuo Fang Hsu
Published: March 2012

Density currents such as turbidity currents are major transport agents in various terrestrial, lacustrine, and marine environments worldwide. However, a gap exists between those who study the deposits by turbidity currents (turbidite) on a field scale, and those who study turbidity currents using small‐scale laboratory experiments and theoretical/numerical models. We report two typhoon‐triggered hyperpycnal turbidity current events observed in a submarine canyon. Our findings verify turbidite sequences with the characteristics of suspended sediment carried by passing turbidity currents that displayed distinct waxing and waning phases. Our study also confirms the direct link between typhoon‐triggered hyperpycnal flows in a small mountainous river and turbidity currents in a nearby submarine canyon that transport sediment to the deep‐sea efficiently.
U.S. Geological Survey budget would increase but includes targeted cuts to some key programs
Authors: Showstack Randy
Published: March 2012

The Obama administration's proposed budget for the U.S. Geological Survey (USGS) for fiscal year (FY) 2013 is $1.1 billion, $34.5 million (3.2%) above the Agency's 2012 enacted level. The budget includes $73.2 million in targeted increases but also has $49.5 million in proposed reductions, including cuts to some water and minerals programs and other areas. Funding for the budget was prioritized to maintain programs that are legislatively mandated, that are important for protecting lives and human property, and that are among the Obama administration's key emphases. These include research and development, which the administration believes will help end the economic recession, USGS director Marcia McNutt said at a 14 February briefing.
Tough choices in proposed budget for Environmental Protection Agency
Authors: Balcerak Ernie
Published: March 2012

President Obama's proposed budget for the Environmental Protection Agency (EPA) for fiscal year (FY) 2013 is $8.34 billion, a 1.2% decrease from the agency's 2012 enacted budget. “This budget is focused on fulfilling EPA's core mission to protect health and the environment for millions of American families. It demonstrates the fiscal responsibility called for at this moment, while still supporting clean air, healthy waters, and innovative safeguards that are essential to an America built to last,” said EPA administrator Lisa Jackson in a 13 February briefing announcing the budget proposal. Balancing tight funding environments with EPA's goals “has required taking a step back from programs we have worked on for years, programs were we have had great success,” she said. “There are difficult choices throughout this budget, but they enable us to do what is required for our immediate priorities as well as challenges down the road.”
Weather‐ and climate‐related extreme events: teachable moments
Authors: Wallace John M.
Published: March 2012

It is difficult for the public to grasp the significance of global warming because the mildness of its early symptoms belies the gravity of its long‐term consequences. Mindful of the human tendency to discount the importance of events seen as occurring far in the future, many scientists and science writers have come to regard newsworthy weather‐ and climate‐related extreme events as “teachable moments” that serve to illustrate the importance and immediacy of the impacts of human‐induced climate change. The problem with this approach is that the attribution of extreme events to human‐induced climate change is often viewed as gratuitous and labeled as fear mongering. A more effective communications strategy, in my view, is to use these events to illuminate society's increasing vulnerability to natural disasters in the face of our deteriorating planetary life‐support system.
AGU awarded grant to establish program on engaging 2‐year‐college students in research
Authors: Asher Pranoti , Adamec Bethany Holm
Published: March 2012

Students at 2‐year colleges are a critical part of the future Earth and space science workforce, and undergraduate research experiences provide a hook to retain and ultimately to graduate students in the field. AGU was awarded a planning grant by the U.S. National Science Foundation Directorate for Geosciences (Opportunities for Enhancing Diversity in the Geosciences award 1201578) to help launch a new initiative concerning these issues; education and public outreach staff are the principal investigators. This new initiative, titled Unique Research Experiences for Two‐Year College Faculty and Students (URECAS), will begin with a planning workshop this summer (11–13 July). The workshop will bring together faculty from 2‐year colleges, 4‐year colleges and universities, and representatives from professional societies and federal organizations to learn more about how to support 2‐year‐college faculty and students engaged in Earth and space science research and to discuss the development of a program to strengthen the role of 2‐year‐college Earth and space science students in the future workforce
East African long rains declined abruptly
Authors: Balcerak Ernie
Published: March 2012

In 2010–2011 the East African region suffered a severe drought that affected millions of people. The drought was a consequence of the failure of both the seasonal “short rains,” which typically run from October to December, and the following “long rains,” which typically run from March to May. The failure of the short rains was predictable given a well‐established connection with La Niña, but the failure of the long rains was not. In a new study, Lyon and DeWitt show that the most recent long rains failure is consistent with a recurrent large‐scale precipitation pattern that began with an abrupt shift around 1999. The authors used observations and climate model simulations to show that the abrupt decline in the East African long rains was linked to similarly abrupt changes in sea surface temperatures, mainly in the tropical Pacific basin. (Geophysical Research Letters, doi:10.1029/2011GL050337, 2012) —EB
Capsizing icebergs release earthquake‐sized energies
Authors: Schultz Colin
Published: March 2012

A large iceberg can carry a tremendous amount of gravitational potential energy. While all icebergs float with the bulk of their mass submerged beneath the water's surface, some drift around in precarious orientations—they are temporarily stable, but an outside push would send them tumbling over. Large icebergs, like those that split from the Jakobshavn Isbræ glacier in Greenland, can release the energy equivalent to a magnitude 6 or 7 earthquake when they capsize. A 1995 event demonstrated the potential for destruction, as a tsunami spawned from a capsizing iceberg devastated a coastal Greenland community. Measuring how energy is dispersed during capsizing is crucial to understanding the risk associated with these events but is also key to determining their larger role in surface ocean dynamics
In Japan, seismic waves slower after rain, large earthquakes
Authors: Schultz Colin
Published: March 2012

An earthquake is first detected by the abrupt side‐to‐side jolt of a passing primary wave. Lagging only slightly behind are shear waves, which radiate out from the earthquake's epicenter and are seen at the surface as a rolling wave of vertical motion. Also known as secondary or S waves, shear waves cause the lifting and twisting motions that are particularly effective at collapsing surface structures. With their capacity to cause damage, making sense of anything that can influence shear wave vertical velocities is important from both theoretical and engineering perspectives.
Photochemical reactions a sink for dissolved organic carbon
Authors: Balcerak Ernie
Published: March 2012

Dissolved organic matter is transported from inland sources through rivers to seas, where it provides a major source of carbon and nitrogen in aquatic ecosystems. Solar radiation can break down dissolved organic matter into a form that is more readily used by bacteria. Photochemical reactions can also transform dissolved organic carbon into forms of dissolved inorganic carbon, including carbon dioxide, and convert dissolved organic nitrogen into ammonium, which encourages bacterial and algal growth. Quantifying these photoreactions could help scientists better understand the role of photochemistry and dissolved organic matter in aquatic ecosystems
Effects of sea spray geoengineering
Authors: Balcerak Ernie
Published: March 2012

Anthropogenic climate warming is leading to consideration of options for geoengineering to offset rising carbon dioxide levels. One potential technique involves injecting artificial sea spray into the atmosphere. The sea salt particles would affect Earth's radiation budget directly, by scattering incoming solar radiation, and indirectly, by acting as cloud condensation nuclei, which could lead to whiter clouds that reflect more radiation. However, the potential effects of this method, especially the direct effects, are not fully known. Partanen et al. studied the effects of artificial sea spray using climate model simulations. They found that outside of the most heavily clouded regions the direct effect of scattering of radiation was an important part of the total effect. They also examined the effect of particle size and found that decreasing the size of injected particles could improve the efficiency of the geoengineering technique.
The effect of wind mixing on the vertical distribution of buoyant plastic debris
Authors: Kukulka T. , Proskurowski G. , Morét‐Ferguson S. , Meyer D. W. , Law K. L.
Published: March 2012

Micro‐plastic marine debris is widely distributed in vast regions of the subtropical gyres and has emerged as a major open ocean pollutant. The fate and transport of plastic marine debris is governed by poorly understood geophysical processes, such as ocean mixing within the surface boundary layer. Based on profile observations and a one‐dimensional column model, we demonstrate that plastic debris is vertically distributed within the upper water column due to wind‐driven mixing. These results suggest that total oceanic plastics concentrations are significantly underestimated by traditional surface measurements, requiring a reinterpretation of existing plastic marine debris data sets. A geophysical approach must be taken in order to properly quantify and manage this form of marine pollution.
Large converse magnetoelectric effect in Na0.5Bi0.5TiO3-CoFe2O4 lead-free multiferroic composites
Authors: Narendra Babu S. , Malkinski Leszek
Published: March 2012

Lead-free multiferroic composites of ferroelectric, Na0.5Bi0.5TiO3 (NBT) and ferrimagnetic, CoFe2O4 (CFO) were synthesized by the solid-state sintering method and a systematic study of structural, magnetic, and magnetoelectric properties was undertaken. X-ray diffraction and field emission scanning electron microscopy displayed the formation of single phase for parent phases and the presence of both phases in the composites. Magnetic properties were investigated using a vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) measurements at room temperature. Strong magnetoelectric (ME) coupling was demonstrated by an electric field tunable FMR field shift. A large value of converse ME coefficient 109 Oe-cm kV−1 was observed for NBT/CFO 70/30 composite. Furthermore, these lead-free multiferroic composites exhibiting a large converse magnetoelectric effect at room temperature provide great opportunities for electrostatically tunable devices at microwave frequencies.
Carrier-mediated interaction of magnetic moments in oxygen vacancy–controlled epitaxial Mn-doped ZnO thin films
Authors: Mukherjee Devajyoti , Mukherjee Pritish , Srikanth Hariharan , Witanachchi Sarath
Published: March 2012

Epitaxial Zn0.98Mn0.02O thin films were grown on c-cut sapphire substrates under various ambient oxygen pressures (pO2) using pulsed laser deposition. The variation of pO2 during the growth process allowed for the control of intrinsic oxygen vacancies and resulting carrier densities in the films. While no impurity phase contributions were detected, a strong correlation between the effective carrier densities and the observed ferromagnetism (FM) was established. The magnetic data was consistent with a Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange mechanism. The average spin-spin interaction energy for RKKY at 10 K was found to be smaller than the thermal energy, ensuring the availability of carriers to mediate RKKY-type FM, even at low temperatures.
Effect of rounded corners on the magnetic properties of pyramidal-shaped shell structures
Authors: Knittel Andreas , Franchin Matteo , Nasirpouri Farzad , Bending Simon J. , Fangohr Hans
Published: March 2012

In recent years, the advance of novel chemical growth techniques has led to the fabrication of complex, three-dimensional magnetic nanostructures. The corners and edges of such realistic geometries are generally not sharp but rounded. In a previous article we have argued that high demagnetization fields in the vicinity of sharp edges lead to the formation of an asymmetric vortex state in pyramidal-shaped magnetic shell structures. The asymmetric vortex state is potentially interesting with respect to future magnetic memory devices. In this work a micromagnetic model is used to investigate the effect of rounded corners and edges on the magnetic reversal process within these pyramidal-shaped magnetic shell structures. In particular, we explore the degree of rounding, which has to be introduced in order to suppress the asymmetric vortex state. Another emphasis is placed on the magnetic reversal of (quasi-)homogeneous states within these structures. We demonstrate that the rounding of corners significantly reduces the coercivity. This complies with former studies on cuboidal structures, which suggest the important effect of corners on the magnetic reversal of homogeneous magnetic states. The present study uses a finite-element discretization for the numerical solution of the micromagnetic equations, which provides flexibility with respect to the modeling of complex shapes. In particular, this method is very accurate with respect to structures with a smooth surface.
One-step fabrication of L1 FePt nanocubes and rods by cluster beam deposition
Authors: Akdogan O. , Li W. , Hadjipanayis G. C. , Skomski R. , Sellmyer D. J.
Published: March 2012

In this work, single crystal L10 FePt nanocubes have been successfully produced by a cluster beam deposition technique without the need of post annealing. Particles have been deposited by dc magnetron sputtering using high Ar pressures on both single crystal Si substrates and Au grids for the measurement of magnetic and structural properties, respectively. The nanocubes have a uniform size distribution with an average size of 5 nm. At 1 Torr, the particles have the L10 structure with an order parameter of 0.5 and a RT coercivity of 2 kOe with high switching fields observed in the hysteresis loop. Further annealing increased the particle size to 20 nm and the RT coercivity to 10.2 kOe with perfect chemical ordering. In addition to these nanocubes, micron size rods with the L10 structure have been observed near the cluster gun. SEM analysis showed that these rods consist of nanoparticles with 20 nm average size. Surfactant assisted high-energy ball milling has been used to separate the nanoparticles from the rods. After one hour of milling, these 20 nm particles showed a room temperature coercivity of 9 kOe with an order parameter of 0.85. These FePt nanocubes have a potential for use in the development of future high-density magnetic recording media because of their high coercivity, good shape and very narrow size distribution.
Aligned and exchange-coupled L1 (Fe,Co)Pt-based magnetic films
Authors: Liu Y. , George T. A. , Skomski R. , Sellmyer D. J.
Published: March 2012

Films of aligned L10-structure (Fe,Co)Pt with fcc Fe(Co,Pt) are synthesized by co-sputtering Fe, Co, and Pt on an (001) MgO substrate with in situ heating at 830 °C. The nanostructures and magnetic properties of the films are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID). The compositions of the samples (Fe,Co)xPt1-x are designed to maintain an atomic Fe: Co ratio of 65: 35 while increasing the Fe,Co content in each successive sample. In samples with low Fe and Co concentration, the XRD patterns exhibit three strong peaks, namely L10 (Fe,Co)Pt (001), L10 (Fe,Co)Pt (002), and MgO (002). A fourth peak is observed in samples with high Fe and Co concentration and identified as fcc (002). The XRD patterns confirm the formation of L10-ordered (Fe,Co)Pt and its epitaxial growth on MgO. TEM shows that the (Fe,Co)Pt films form isolated magnetic grains of about 100 nm in diameter. Hysteresis-loop measurements show that the increase of the Fe,Co concentration from 57.3 to 68.3 at % enhances the saturation magnetization Ms from 1245 emu/cm3 to 1416 emu/cm3, and the coercivity decreases from 32 kOe to 8.9 kOe. The nominal maximum energy product per grain is 64 MGOe.
Characterization of interlayer interactions in magnetic random access memory layer stacks using ferromagnetic resonance
Authors: Backes D. , Bedau D. , Liu H. , Langer J. , Kent A. D.
Published: March 2012

Ferromagnetic resonance spectroscopy is used to determine magnetic interactions in layer stacks designed for orthogonal spin-transfer magnetic random memory devices. The stacks have layers with different anisotropy directions and coupling, consisting of a perpendicularly magnetized polarizer, an in-plane magnetized free layer, and an in-plane magnetized exchange biased synthetic antiferromagnetic layer. The oscillatory exchange coupling strength in the synthetic antiferromagnet was measured along with its exchange bias. The free layer properties were also determined. It is demonstrated that this one integrated measurement technique is able to provide quantitative measurements of key magnetic parameters in a complex layer stack, which is a prerequisite for high turn-around device materials characterization and optimization.
Write field asymmetry in perpendicular magnetic recording
Authors: Li Zhanjie , Bai Daniel Z. , Lin Ed , Mao Sining
Published: March 2012

We present a systematic study of write field asymmetry by using micromagnetic modeling for a perpendicular magnetic recording (PMR) writer structure. Parameters investigated include initial magnetization condition, write current amplitude, write current frequency, and initial write current polarity. It is found that the write current amplitude and frequency (data rate) are the dominant factors that impact the field asymmetry. Lower write current amplitude and higher write current frequency will deteriorate the write field asymmetry, causing recording performance (such as bit error rate) degradation.
Application of the grain flipping probability model to heat assisted magnetic recording
Authors: Binte Shafiee Sari Shafidah , Elidrissi Moulay Rachid , Wang Hong Tao , Eason Kwaku , Radhakrishnan Rathna Kumar , Sann Chan Kheong , Liang Guan Yong
Published: March 2012

Heat assisted magnetic recording (HAMR) is often lauded as one of the key technologies poised to replace conventional granular magnetic recording (CGMR). Conventional recording is expected to eventually fail because as the information-bearing grains continue to shrink, they become thermally unstable and will spontaneously flip due to excitations from the ambient temperature. HAMR grains are smaller and have larger anisotropies making them thermally stable, but unwritable at room temperature. Heat from a laser is applied to assist during the writing. The grain flipping probability (GFP) model has been proposed to model and predict the densities achievable in conventional recording systems. In this work we modify the GFP to include a circular hot-spot of a laser as a 2 D Gaussian and predict the expected densities that might be achieved on HAMR media with 4 nm grains. In this work we examine the effect of varying the hot-spot diameter, the hot-spot peak, and the alignment of the hot-spot to the magnetic footprint profile.
Unusual crystallite growth and modification of ferromagnetism due to aging in pure and doped ZnO nanoparticles
Authors: Thurber Aaron P. , Alanko Gordon , Beausoleil Geoffrey L. , Dodge Kelsey N. , Hanna C. B. , Punnoose Alex
Published: March 2012

We report the unusual growth of pure and Fe-doped ZnO nanoparticles prepared by forced hydrolysis and the weakening of ferromagnetism due to aging in ambient conditions. More than four dozen nanoparticle samples in the size range of 4–20 nm were studied over 1 to 4 years. The as-prepared samples had significant changes in their crystallite sizes and magnetization as they aged in ambient conditions. Detailed studies using x ray diffraction and transmission electron microscopy (TEM) demonstrated that the crystallite size increased by as much as 1.4 times. Lattice parameters and strain also showed interesting changes. Magnetometry studies of Zn1−xFexO with x = 0–0.2 showed ferromagnetism at room temperature; however, keeping the samples in ambient conditions for one year resulted in modifications in the crystallite size and magnetization. For the Zn0.95Fe0.05O sample, the size changed from 7.9 nm to 9.0 nm, while the magnetization decreased from 1×10–3emu/g (memu/g) to 0.2 memu/g. Both magnetic and structural changes due to aging varied with the environment in which they were stored, indicating that these changes are related to the aging conditions.
Magnetic and superconducting properties of spin-fluctuation-limited superconducting nanoscale VNx
Authors: Zeng R. , Liu J. , Du G. D. , Li W. X. , Wang J. L. , Horvat J. , Dou S. X.
Published: March 2012

VNx nanoparticles and nanowires have been prepared by nitrifying V2O5 nanoparticles (NP) and nanowires (NW). The V2O5 NP and NW were synthesized by a facile hydrothermal method. Magnetic susceptibility (χ) and magnetization measurements showed long range superconducting ordering (LRSO) at the temperature of 5.8 K for NW, but there was no observation of LRSO (at least down to 2 K) for the NP sample, which is a much lower temperature than for the corresponding bulk, while both NP and NW showed the absence of long range magnetic ordering, at least down to 2 K. However, the χ data showed that both samples possess a high Pauli-like component, χ0, in their susceptibility (χ0 ≈ 2.22 × 10−4 emu/mol for NP and 5 × 10−4 emu/mol for NW). Moreover, for the NW samples, χ has a strong magnetic field dependence and presents a non-linear field-polarization feature, suggesting strong spin-orbit coupling.
Multi-step ion beam etching of sub-30 nm magnetic tunnel junctions for reducing leakage and MgO barrier damage
Authors: Chun Sung-woo , Kim Daehong , Kwon Jihun , Kim Bongho , Choi Seonjun , Lee Seung-Beck
Published: March 2012

We have demonstrated the fabrication of sub 30 nm magnetic tunnel junctions (MTJs) with perpendicular magnetic anisotropy. The multi-step ion beam etching (IBE) process performed for 18 min between 45° and 30°, at 500 V combined ion supply voltage, resulted in a 55 nm tall MTJ with 28 nm diameter. We used a negative tone electron beam resist as the hard mask, which maintained its lateral dimension during the IBE, allowing almost vertical pillar side profiles. The measurement results showed a tunnel magneto-resistance ratio of 13% at 1 kΩ junction resistance. With further optimization in IBE energy and multi-step etching process, it will be possible to fabricate perpendicularly oriented MTJs for future sub 30 nm non-volatile magnetic memory applications.
Cyclical magnetic field flow fractionation
Authors: Tasci T. O. , Johnson W. P. , Gale B. K.
Published: March 2012

In this study, a new magnetic field flow fractionation (FFF) system was designed and modeled by using finite element simulations. Other than current magnetic FFF systems, which use static magnetic fields, our system uses cyclical magnetic fields. Results of the simulations show that our cyclical magnetic FFF system can be used effectively for the separation of magnetic nanoparticles. Cyclical magnetic FFF system is composed of a microfluidic channel (length = 5 cm, height = 30 μm) and 2 coils. Square wave currents of 1 Hz (with 90 deg of phase difference) were applied to the coils. By using Comsol Multiphysics 3.5a, magnetic field profile and corresponding magnetic force exerted on the magnetite nanoparticles were calculated. The magnetic force data were exported from Comsol to Matlab. In Matlab, a parabolic flow profile with maximum flow speed of 0.4 mL/h was defined. Particle trajectories were obtained by the calculation of the particle speeds resulted from both magnetic and hydrodynamic forces. Particle trajectories of the particles with sizes ranging from 10 to 50 nm were simulated and elution times of the particles were calculated. Results show that there is a significant difference between the elution times of the particles so that baseline separation of the particles can be obtained. In this work, it is shown that by the application of cyclical magnetic fields, the separation of magnetic nanoparticles can be done efficiently.
Effects of Ga addition on structural and magnetic properties of nanocomposite Nd-Fe-B-Ti-C thick ribbons
Authors: Wu Q. , Yu T. , Guo S. , Feng X. C. , Pan M. X. , Zhang P. Y. , Han B. S. , Ge H. L. , Yan A. R.
Published: March 2012

Rapidly solidified Nd9Fe73B12.6C1.4Ti4-xGax (x = 0, 0.5, 1) thick ribbons were prepared by melt spinning technique at a surface speed (vs) of 5 m/s. The influences of Gallium doping on the glass-forming ability (GFA), microstructure and magnetic properties of alloys were investigated. The coercivity of Nd-Fe-B-Ti-C nanocomposite alloy thick ribbons can be dramatically enhanced by 0.5 at. % Ga addition in a low cooling-rate regime, attributing to the weakened exchange coupling interaction and grain refinement. The results of XRD showed that the GFA of Nd-Fe-B-Ti-C alloy was enhanced by the Ga addition. Therefore, Gallium addition is effective to refine grain and improve the glass-forming ability, which provides the possibility to obtain the high performance of magnetic properties by using strip casting (SC) method.
Analysis and design of shingled magnetic recording systems
Authors: Keng Teo Kim , Elidrissi Moulay Rachid , Chan Kheong Sann , Kanai Yasushi
Published: March 2012

Shingled magnetic recording (SMR) is an upcoming technology that will extend the life of conventional granular magnetic recording (CGMR). SMR differs from conventional recording in that the tracks are written in a raster scan format, in one direction only, leaving tracks that are overlapped like the shingles on a roof. This simple change means that adjacent track overwrite only occurs from one side, and tracks need to survive this overwrite only once. In contrast, conventional recording needs to survive thousands of overwrites from both sides. This work performs analysis of SMR from three perspectives. First, an analysis of how much gain one might expect for SMR based on the assumptions for the magnetic write width (MWW), magnetic read width (MRW), and erase bandwidth (EBW) is performed. Second, this analysis is corroborated via simulated 747 curves using the grain flipping probability (GFP) model. The third part validates the 747 curves from the model with results from the spinstand.
Atomistic simulation method in head-disk interface of magnetic data storage systems
Authors: Smith Robert L. , Chung Pil Seung , Hari Vemuri Sesha , Yeom Geun-Young , Biegler Lorenz T. , Jhon Myung S.
Published: March 2012

The conventional modeling paradigm of head-disk interface (HDI) in magnetic data storage systems was based on meso/macro scale modeling. We investigate inter-molecular interaction energy for four sets of model PFPE dimers and elucidate the importance of hydrogen bonding between the hydroxylated functional endgroups in interaction strength. We found that for these model dimers representing PFPEs, the DDPA-DDPA (non-hydroxylated) dimer demonstrates the least stable interaction. We further investigated binary blends of hydroxylated and non-hydroxylated model PFPE lubricant and observed diminished interaction strength as compared to pure hydroxylated dimers. Our atomistic interaction energy study reported here will provide insight for tuning physiochemical properties of lubricant film by controlling blending ratios and chain end functionality to obtain desired lubricant performance.
Magnetocaloric effect in Sm-Co2-xFex alloys
Authors: Burrola-Gándara L. A. , Grijalva-Castillo M. C. , Santillán-Rodríguez C. R. , Matutes-Aquino J. A.
Published: March 2012

SmCo2 and SmFe2 magnetic cubic Laves phases have Curie temperatures of 220 and 669 K, respectively. Aiming to increase the Curie temperature of SmCo2 for potential room temperature magnetic refrigeration Co was partially replaced by Fe. The fundamental magnetic entropy change of the SmCo2 compound, ΔSM = 3.61 J/kg·K, for an applied magnetic field of µoH = 1.5 T was observed at TSR = 175 K, where a spin reorientation transition occurs; furthermore a refrigerant capacity of 37 J/kg was calculated. Interestingly the addition of Fe practically suppressed the spin reorientation transition, shifting the magnetic entropy change maximum to the Curie temperature in the SmCo1.8Fe0.2 sample. The magnetic entropy change maximum at Curie temperature TC = 300 K and the refrigerant capacity for the doped compound decreased to ΔSM = 0.20 J/kg·K and 13.5 J/kg, respectively, for an applied magnetic field of µoH = 1.5 T. After an homogenization heat treatment at 773 K during 50 h, the SmCo1.8Fe0.2 compound showed an increase of the maximum magnetic entropy change, ΔSM = 0.28 J/kg·K, and the refrigerant capacity remains 13.5 J/kg, for an applied magnetic field of µoH = 1.5 T.
Enhancement of perpendicular magnetic anisotropy in FeB free layers using a thin MgO cap layer
Authors: Kubota Hitoshi , Ishibashi Shota , Saruya Takeshi , Nozaki Takayuki , Fukushima Akio , Yakushiji Kay , Ando Koji , Suzuki Yoshishige , Yuasa Shinji
Published: March 2012

We prepared magnetic tunnel junction films with PtMn/CoFe/Ru/CoFeB/MgO tunnel barrier/FeB free layer/MgO cap layer/Ta multilayers using sputtering and measured magnetic and magnetoresistive properties of the films at room temperature. The magnetization curves of the FeB plane film measured under perpendicular-to-plane magnetic fields showed much smaller saturation fields (Hs) than those expected from the demagnetizing field. Hs decreased from 4 to 0.4 kOe with increasing MgO cap layer thickness. The small Hs is due to the perpendicular magnetic anisotropy (PMA) induced at both MgO barrier–FeB and FeB–MgO cap interfaces. After microfabrication, the small free layer cells having a 1.6 nm thick MgO cap layer showed a magnetization easy axis in the perpendicular-to-plane direction. By inducing PMA from both upper and lower interfaces, we can stabilize the magnetization of the relatively thick (2 nm) FeB free layer in the perpendicular-to-plane direction.
Crystallographic alignment evolution and magnetic properties of Nd-Fe-B nanoflakes prepared by surfactant-assisted ball milling
Authors: Yue M. , Pan R. , Liu R. M. , Liu W. Q. , Zhang D. T. , Zhang J. X. , Zhang X. F. , Guo Z. H. , Li W.
Published: March 2012

The microstructure, crystal structure, and magnetic properties were studied for Nd-Fe-B nanoflakes prepared by surfactant-assisted high-energy ball milling (HEBM) with heptane and oleic acid as the milling medium. The microstructure, crystal structure, and magnetic properties of the nanoflakes were examined with scanning electronic microscopy, x ray diffraction, and vibrating sample magnetometer, respectively. Effect of ball-milling time on the c-axis crystallographic alignment and coercivity of Nd-Fe-B nanoflakes were systematically investigated. Microstructure observation shows that the Nd-Fe-B nanoflakes have an average thickness of tens of nanometers, an average diameter in the range of 500 ∼ 1000 nm, and an aspect ratio as high as 100. As the ball-milling time increases from 2 h to 12 h, the intensity ratio between (006) and (105) reflection peaks, which indicates the degree of c-axis crystal texture of the Nd2Fe14B phase, drops gradually, indicating that the long time-milling process undermines the c-axis crystal texture of Nd2Fe14B phase in the nanoflakes. On the other hand, the coercivity of the nanoflakes firstly increases, peaks at 3.8 kOe for 8 h, and then decreases again along with the ball milling.
Spin-torque diode spectrum of ferromagnetically coupled (FeB/CoFe)/Ru/(CoFe/FeB) synthetic free layer
Authors: Bang Do , Taniguchi Tomohiro , Kubota Hitoshi , Yorozu Takehiko , Imamura Hiroshi , Yakushiji Kay , Fukushima Akio , Yuasa Shinji , Ando Koji
Published: March 2012

We investigated systematically the spin torque diode spectrum of a ferromagnetically coupled (FeB/CoFe)/Ru/(CoFe/FeB) synthetic free layer in an MgO-based magnetic tunnel junction. In the spectra, we observed single peaks shifted to higher frequency with increasing the in-plane magnetic fields, as expected from the ferromagnetic resonance of the FeB/CoFe adjacent to the MgO tunnel barrier. On the other hand, under the perpendicular fields, we observed several peaks below 6 GHz and around 10 GHz, which were rather insensitive to the field. These behaviors are different from our simple calculation taking account the interlayer coupling, suggesting that the excitation of magnetizations occurs in a complicated manner for the synthetic free layers.
Magnetic micro-structural uniformity of die-upset Nd-Fe-B magnets
Authors: Fang Yikun , Yin Xiaolu , Zhao Rui , Valloppilly Shah , Li Wei , Zhu Minggang , Liou Sy-Hwang
Published: March 2012

Die-upset Nd13.62Fe75.70Co4.45B5.76Ga0.47 magnets have been prepared with height reduction (h) in the range of 60 to 88%. The energy product as high as 50.4 MGOe was obtained in the sample with h ∼ 70%. The magnetic domains of the samples are revealed by using magnetic force microscopy (MFM). The average domain widths of the die-upset samples with surface normal parallel (//) and perpendicular (⊥) to the loading direction are in the range of w//: 0.4-0.6 μm; w⊥: 0.9-3.8 μm, respectively. These interaction domains are formed due to the strong inter-granular exchange interaction and magnetostatic interaction between grains. It was found that the ratio of φrms// to φrms⊥ is a good indicator for the quality of the magnet, where the φrms// and φrms⊥ are defined as the root-mean-square values of phase shift for the MFM images. The microstructures have been investigated by scanning electron microscopy (SEM), MFM and SEM results indicate the magnetic and crystalline microstructures are uniform for the sample with h ∼ 70%, giving rise to the highest magnetic performance among these samples.
Textured Nd2Fe14B flakes with enhanced coercivity
Authors: Cui B. Z. , Zheng L. Y. , Marinescu M. , Liu J. F. , Hadjipanayis G. C.
Published: March 2012

Morphology, structure, and magnetic properties of the [001] textured Nd2Fe14B nanocrystalline flakes prepared by surfactant-assisted high energy ball milling (HEBM) and subsequent annealing were studied. These flakes have a thickness of 80–200 nm, a length of 0.5–10 μm, and an average grain size of 10–14 nm. The addition of some amount of Dy, Nd70Cu30 alloy, and an appropriate post annealing increased the coercivity iHc of the Nd2Fe14B flakes. iHc was 3.7, 4.3, and 5.7 kOe for the Nd15.5Fe78.5B6, Nd14Dy1.5Fe78.5B6 and 83.3 wt.% Nd14Dy1.5Fe78.5B6 + 16.7 wt.% Nd70Cu30 flakes prepared by HEBM for 5 h in heptane with 20 wt.% oleylamine, respectively. After annealing at 450 °C for 0.5 h, their iHc increased to 5.1, 6.2, and 7.0 kOe, respectively. Anisotropic magnetic behavior was found in all of the as-milled and annealed flakes. Both, the thickening of Nd-rich phase at grain boundaries via diffusion of Nd70Cu30 and the surface modification of the Nd2Fe14B flake could be the main reasons for the coercivity enhancement in the as-milled and annealed Nd70Cu30-added Nd2Fe14B flakes.
Perpendicular magnetic tunnel junctions based on thin CoFeB free layer and Co-based multilayer synthetic antiferromagnet pinned layers
Authors: Natarajarathinam A. , Zhu R. , Visscher P. B. , Gupta S.
Published: March 2012

We have previously reported on fully perpendicular Co/Pd multilayer (ML)-based CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs). However, Co/Pd ML-based MTJs have rarely exhibited tunneling magnetoresistance (TMR) ratios greater than 10%. This has been attributed to the inability to pull a sufficiently thick CoFeB layer perpendicular on top of MgO, as well as the incomplete bcc templating of CoFeB from MgO owing to the adjacent fcc Co/Pd MLs. Other researchers have used amorphous thin Ta bridge layers to transition between the bcc and fcc layers. Thin CoFeB with various seed or capping layers have also shown fully perpendicular anisotropy, and thus have gained interest in use as a free layer. Here we report on fully perpendicular MTJs of this type, with a thin CoFeB free layer and a Co/Pd ML-based SAF pinned layer with a thin amorphous Ta bridge layer to transition from bcc CoFeB to the fcc multilayers. The experimentally measured M-H loops show excellent agreement with micromagnetic simulations. Current-in-plane tunneling measurements indicated TMR values of nearly 40% for fully perpendicular stacks annealed at 150 °C for 2 h. Annealing at higher temperatures degraded the magnetoresistance for these Co/Pd ML based SAF pinned MTJs.
Multiscale micromagnetism of Co-Pd multilayers
Authors: Manchanda P. , Skomski R. , Sahota P. K. , Franchin M. , Fangohr H. , Kashyap A.
Published: March 2012

The interplay between atomic and micromagnetic effects in Co-Pd multilayers is investigated by model calculations and numerical simulations. By minimizing the total exchange energy, an effective exchange stiffness is obtained. The stiffness depends on the superlattice periodicity, on the wave vector of the magnetization variation, and on the exchange coupling through the Pd, which is calculated from first principles (J = 7.66 mJ/m2). The net magnetic anisotropy, Keff = 0.71 MJ/m3, which is also obtained from first principles, contains two parts, namely the Pd-Co interface anisotropy Kif = 0.45 mJ/m2 and the bulk anisotropy KCo = −0.28 MJ/m3 of the strained fcc Co. For vertical and lateral magnetization variations, we find domain-wall thicknesses of 5.1 nm and 6.9 nm and domain-wall energies of 5.94 mJ/m2 and 6.66 mJ/m2, respectively.