bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of perpendicular media anisotropy field with accurate demagnetization correction
Authors: Ju Ganping , Wu Xiaowei , Zhou Hong , Weller Dieter , Chantrell Roy , Lu Bin , Kubota Yukiko , Yu Jun
Published: May 2003

Magneto-optical measurements have been applied to determine the anisotropy field of perpendicular media with a well-defined demagnetizing state. The rotation of the perpendicular magnetization component is measured as a function of the in-plane field by the Polar Kerr effect. The field range is sufficiently small to avoid domain formation and ensure coherent magnetization rotation. By fitting to a simple response function, the effective anisotropy field (HK1′=HK1−4πMS) with a well-defined 4πMS demagnetization correction can be determined. This also enables accurate determination of the ratio of short-time coercivity H0 over anisotropy field Hk, an important parameter for perpendicular recording. The H0/Hk ratio is found to decrease with increasing intergranular coupling strength, in good agreement with our micromagnetic results. It drops from about 0.8 for weakly coupled media to 0.5 for strongly coupled media. Theoretical studies show that the effects of easy axis angular dispersion are small, about 1% error for 5° dispersion, and the rotation method measures the mean value of Hk for media with anisotropy field distribution.
Effects and microstructures of indium tin oxide seed layers for perpendicular magnetic recording media
Authors: Qi Xiaoyuan , Stadler Bethanie J. , Judy Jack H. , Victora R. H.
Published: May 2003

Co/Pd multilayers have been shown to exhibit fcc structures and they have good recording properties with ITO as a seed layer. The microstructures of extremely thin indium–tin–oxide (ITO) grown in pure Ar, and the effects of this ITO as seed layers for Co/Pd and Co75B25/Pd multilayers, have been studied. The magnetic properties of the multilayers have been correlated with the crystallinity of the ITO. TEM analysis showed that this ITO has a crystalline structure instead of the amorphous structure reported by other researchers. Both heated and unheated films had what appeared to be metallic fcc structures with lattice constants of 4.88 Å. Heating ITO seed layers led to increased coercivity (from 5.5 kOe to 7 kOe) in Co/Pd multilayers that were grown at room temperature.
Magnetic properties of aligned Fe-filled carbon nanotubes
Authors: Mühl T. , Elefant D. , Graff A. , Kozhuharova R. , Leonhardt A. , Mönch I. , Ritschel M. , Simon P. , Groudeva-Zotova S. , Schneider C. M.
Published: May 2003

We report on the magnetic properties of Fe-filled multiwalled carbon nanotubes (MWNTs) grown by chemical vapor deposition (CVD) on Si substrates with ferrocene as precursor. The MWNTs are aligned perpendicularly to the substrate plane. X-ray diffraction analyses indicate the presence of both bcc and fcc iron with a relatively strong texture. Magnetometry measurements show a pronounced magnetic anisotropy with the easy axis perpendicular to the substrate plane and parallel to the axis of the aligned MWNTs, respectively. The low-temperature behavior suggests a negligible coupling between the two iron phases. We accessed the magnetic properties of individual Fe-filled MWNTs by electron holography using a transmission electron microscope (TEM).
Magnetization of Co elements sensed by semiconductor transport magnetometry and transmission electron microscopy
Authors: Kirk K. J. , McVitie S. , Long A. R. , Skuras E.
Published: May 2003

Magnetization reversal in 300 nm Co squares has been investigated by semiconductor transport magnetometry using a Hall bar containing a two-dimensional electron gas. In this technique the local field from a regular array of magnetic elements patterned on top of the Hall bar changes the measured longitudinal magnetoresistance, enabling the magnetization of the elements to be deduced. Hysteresis loops obtained from the magnetoresistance curve showed a zero magnetization state at zero applied field, which was confirmed by transmission electron microscopy imaging and micromagnetic modelling to represent a vortex state. Repeatable fields were found for vortex expulsion and re-entry, with strong dependence on element size but rather weak dependence on film thickness.
Thermal stability of the magnetization of 150 nm×230 nm Ni19Fe81 elements
Authors: Hao Y. , Ross C. A. , Smith Henry I.
Published: May 2003

The time- and temperature-dependencies of the switching fields of arrays of 230 nm×150 nm Ni19Fe81 rectangular elements have been investigated. The elements have thicknesses of 3 nm, 5 nm, and 10 nm. For temperatures from 100 K to 300 K, all three arrays show a linear dependence of switching field on temperature, with similar slopes, but below 100 K, a deviation from linearity occurs, indicating a change in the switching process. The energy barrier for reversal at zero field has been estimated as 70kT300, 125kT300, and 280kT300 for the 3-nm, 5-nm, and 10-nm thick elements, respectively, which suggests that the energy barrier scales approximately linearly with film thickness. For uncoupled permalloy elements with these lateral dimensions, superparamagnetism is expected at room temperature for thicknesses below about 1 nm.
Magnetization reversal of iron nanoparticles studied by submicron Hall magnetometry
Authors: Li Yongqing , Xiong Peng , von Molnár Stephan , Ohno Yuzo , Ohno Hideo
Published: May 2003

Magnetization of an array of 16 elongated iron nanoparticles with diameter of ∼7 nm and height of ∼100 nm has been studied with a submicron semiconductor Hall magnetometer. Details of the magnetization hysteresis curves and the angular dependence of switching fields are examined. The results indicate that the magnetization reversal in these cylindrical nanoparticles cannot be described with a single coherent rotation mode.
Driving the single-electron device with a magnetic field (invited)
Authors: Shimada Hiroshi , Ono Keiji , Ootuka Youiti
Published: May 2003

The single-electron devices some of whose electrodes are composed of ferromagnetic metals can be driven with a magnetic field. It is based on the fact that a ferromagnetic electrode has a function as a magnetochemical or magnetoelectric coupling component in the device through the Zeeman effect on the electron spins in it. Double- and triple-small-junction devices composed of Ni and Co electrodes showed conductance oscillations typical to the single-electron device when the applied magnetic field was swept, illustrating the magnetic-field control of the device operation. A single-electron box and a single-electron pump driven with a magnetic field are described based on the functions of the ferromagnetic electrodes.
Transport in magnetic nanostructures in the presence of Coulomb interaction (invited)
Authors: Martinek J. , Barnaś J. , Fert A. , Maekawa S. , Schön G.
Published: May 2003

Recent experiments on magnetic nanostructured materials revealed new phenomena associated with the interplay of ferromagnetism and discrete charging effects. A typical example is a ferromagnetic single-electron transistor, i.e., a small grain or quantum dot (QD) coupled by tunnel junctions to ferromagnetic electrodes. We investigate the interplay of charge and spin degrees of freedom in these systems in the sequential tunneling, cotunneling and strong coupling regimes. The description is formulated in a two-dimensional space of charge and spin states, and allows us to calculate electric and spin currents, spin and charge accumulation and fluctuations, as well as the tunnel magnetoresistance. For QDs, we find a Kondo resonance at low temperatures, which significantly depends on the spin polarization of conduction electrons in the leads.
Magneto-optic spatial light modulators driven by an electric field
Authors: Park Jae-Hyuk , Takagi H. , Nishimura K. , Uchida H. , Inoue M. , Park Jae-Hak , Cho Jae-Kyeong
Published: May 2003

A magneto-optic spatial light modulator driven by an electric field is fabricated by using the electrostrictive effect of [Pb(Zr0.52Ti0.48)O3] (PZT) thin film. As the stress field induced by the PZT thin film reduces the anisotropy energy of the structured garnet film, we find that the pixels can be easily switched in accordance with or without the small external bias field. When peak-to-peak 8 V at the X and Y conductors is applied with the external bias field of 40 Oe at the fabricated device, the selected pixel is switched independently.
Thermal magnetization noise in submicrometer spin valve sensors
Authors: Tsiantos Vassilios D. , Schrefl Thomas , Scholz Werner , Fidler Josef
Published: May 2003

With decreasing device dimensions thermal fluctuations may ultimately limit the performance of spin valve sensors. Using finite element micromagnetic simulations, we investigate thermal magnetization noise in submicrometer soft magnetic sensor elements within the framework of Langevin simulations. Local random thermal fluctuations lead to a collective motion of the magnetization. The magnetization precesses in the end domains leading to an oscillation of the total magnetization parallel to the long axes with an amplitude in the order of 0.1 Ms at 350 K. The noise power increases linearly with temperature. Irrespective of the bias field, the time averaged total magnetization parallel to the long axes decays approximately by 0.01 Ms as the temperature is raised by 100 K.
Thermally excited ferromagnetic resonance as diagnostic tool for spin valve heads
Authors: Zhou Yuchen , Zhu Jian-Gang , Kim Nayoung
Published: May 2003

Thermally excited ferromagnetic resonance (TEFMR) in a spin valve head gives rise to mag-noise while its power spectral density directly reflects the magnetic field distribution in the sensing layer as well as the corresponding micromagnetic states. In this article, we report an experimental study on utilization of TEFMR spectral characteristics for spin valve head diagnosis and characterization. The study suggests that the variation of the micromagnetic states in the PM layer at the junctions is one of the most important factors causing the head-to-head variations of the recording performance, especially the heads from the same wafer.
Phase control of nonadiabatic parametric amplification of spin wave packets
Authors: Serga A. A. , Demokritov S. O. , Hillebrands B. , Min Seong-Gi , Slavin A. N.
Published: May 2003

The influence of the phase shift between the signal and pumping wave on the process of parametric amplification of microwave spin wave pulses has been examined. The experiment was specifically made in the nonadiabatic regime, where the pumping field is strongly localized in a region on the order of the spin wave carrier wavelength. In this regime all previous experiments exhibited a strong random modulation (beating) of the amplified output signal. For a fixed phase shift between the signal and the pumping carrier waves the output signal was found to be stable, and no beating was observed. The amplitude of the amplified output pulse varies from the maximum value (corresponding to the maximum gain factor of 15 dB) to the minimum value (corresponding to almost no gain) when the phase shift between signal and pumping wave is changed. The measured phase interval between two consecutive minima in the phase dependence of the output power is equal to π.
Iron and Permalloy based magnetic monolithic tunable microwave devices
Authors: Kuanr Bijoy , Malkinski L. , Camley R. E. , Celinski Z. , Kabos P.
Published: May 2003

We fabricated a series of magnetic monolithic tunable microwave notch-filters and phase shifters. In contrast to previous work with molecular beam epitaxy grown metallic ferromagnets, our devices were created by magnetron sputtering. Single crystal GaAs (001) was used as a substrate. Iron and Permalloy were used as magnetic materials in a coplanar waveguide geometry. The transmission characteristics of the filters were observed to depend on substrate quality, film deposition parameters (Argon pressure, growth rate, power, etc.), and grain size. In addition we observed a substantial increase in the resonance frequency for the Fe based notch-filters. This increase in the resonance frequency is due to a growth-induced uniaxial anisotropy field of 40 kA/m in the Fe films. This is an unexpected and important result especially because the observed anisotropy is growth and not field induced. The resonance frequency shifted from 9.3 GHz at zero applied magnetic field to 15 GHz for an applied static magnetic field as low as 72 kA/m (0.9 kOe). The Fe based notch filter attenuation was greater than 35 dB/cm over the whole applied field range at the resonance condition. The phase shift of the Fe structures was up to 100°/cm at 8 GHz. The Permalloy based filters show, over the same magnetic field range, a shift in the resonance frequency from 2 to 9 GHz. The attenuation of the Permalloy filters at resonance (6 dB/cm) is substantially lower than in the Fe based filters.
Microwave signal processing using dipole-exchange spin waves
Authors: Kobljanskyj Yu. V. , Melkov G. A. , Tiberkevich V. S. , Vasyuchka V. I. , Slavin A. N.
Published: May 2003

A microwave signal processor using short (wave number k∼104 cm−1) phase-conjugated dipole-exchange spin waves (DESWs) propagating in yttrium–iron–garnet films has been developed. A DESW pulse having low group velocity (νg∼103 cm/s) and low relaxation parameter (effective linewidth ΔH=0.2 Oe) was excited by a narrow (W=10 μm) strip-line transducer, experienced wave front reversal in a parametric interaction with a double-frequency pumping field created by a dielectric resonator, and was received again at the input transducer. As a result, a controlled delay of an input microwave pulse of more than 1 μs with insertion loss of 40 dB/μs was achieved.
Temperature-induced sign change of the exchange bias in Fe0.82Zn0.18F2/Co bilayers
Authors: Shi Hongtao , Lederman D. , Dilley N. R. , Black R. C. , Diedrichs J. , Jensen K. , Simmonds M. B.
Published: May 2003

A single crystal, (110)-oriented dilute antiferromagnet (AF) Fe0.82Zn0.18F2 film was grown via molecular beam epitaxy on a (110)-MgF2 substrate by codepositing FeF2 and ZnF2, followed by 1.0 nm pure FeF2 and 18 nm Co layers. The exchange bias (HE) and coercivity (HC) of the Co film strongly depend on the cooling field (HCF) and temperature. For 0⩽HCF<2 kOe, HE<0 in the whole temperature range before reaching zero at the blocking temperature (TB). For HCF⩾15 kOe, HE>0 for T<TB. In both cases, HC peaks when T∼TB. For 2 kOe⩽ HCF<15 kOe, HE<0 at low temperatures, and then suddenly becomes positive at a characteristic switching temperature TS(<TB). TS decreases as HCF is increased and HC peaks at both T∼TS and T∼TB. These results indicate that for intermediate HCF unstable domains are created in the AF during the cooling procedure. The domains suddenly disappear as enough thermal energy is available to switch them when perturbed by the rotation of the ferromagnetic magnetization.
Effect of reader saturation on the measurements of NLTS in perpendicular recording
Authors: Chen Jian , Zhu Wenzhong , Fernandez-de-Castro Juan , Palmer Dean
Published: May 2003

In perpendicular recording, the magnetostatic interaction delays the second transition in a dibit, giving rise to a positive nonlinear transition shift (NLTS) in the written magnetization pattern. However, when the reader becomes saturated, the measured NLTS can take on negative values. Two different techniques to measure NLTS are simulated using a self-consistent recording model: (1) the fifth-harmonic cancellation and (2) dipulse extraction from pseudorandom sequence. The measured NLTS from both techniques is shown to be affected by reader saturation.
Experimental demonstration of the nonreciprocity of magnetic composite materials for microwave applications
Authors: Quéffélec Patrick , Konn Anne-Marie , Gelin Philippe , Mallégol Stéphane
Published: May 2003

The purpose of this article is to bring out the nonreciprocity of ferrimagnetic powder loaded composites. We first describe their technology of preparation. Then we briefly recall the principle of the broadband measurement method used to determine the permeability tensor components of magnetized materials. Our experimental results performed at X-band frequencies (8–12 GHz) on two different ferrimagnetic loaded composite samples are presented and discussed. We finally show that for each material under test, the off-diagonal component κ of the permeability tensor, which is at the origin of the nonreciprocal effect, is of a magnitude comparable to the magnitude observed in bulk ferrites. This result proves that powders technology can be used to realize composite materials for nonreciprocal microwave applications.
Temperature dependence of core loss in Co-substituted MnZn ferrites
Authors: Fujita A. , Gotoh S.
Published: May 2003

Substitution of Co2+ for a small part of Fe2+ in (MnZn)Fe2O3 results in much smaller temperature variation in core loss, compared with that of conventional MnZn ferrite used for transformers. This effect appears in the temperature dependence of hysteresis loss rather than two other contributions of loss, eddy current loss, and residual loss. The total loss not exceeding 370 kW/m3 at 100 kHz/200 mT is obtained in the wide temperature range from 0 to 100 °C. However, excess substitution gives rise to a steep increase of loss below room temperature. Both the improvement of temperature dependence and the abrupt changes in loss in a lower-temperature region accompanying Co2+ substitution could result from a change in the magnetocrystalline anisotropy constant K1.
Structure and magnetic properties of rf thermally plasma synthesized Mn and Mn–Zn ferrite nanoparticles
Authors: Son S. , Swaminathan R. , McHenry M. E.
Published: May 2003

Plasma synthesis has previously been shown to be a viable route to producing nanocrystalline magnetite and Ni ferrite nanoparticles. In this work nanocrystalline powders of Mn and Mn–Zn ferrites have been synthesized using a 50 kW–3 MHz rf (radio frequency) induction plasma torch. We investigate these materials for soft magnetic applications. High-energy ball milled Mn + Fe powders and (Mn+Zn) +Fe powders (<10 μm) in the stoichiometric ratio of 1:2 were used as precursors for the ferrite synthesis. Compressed air was used in the oxygen source for oxidation of metal species in the plasma. X-ray diffraction patterns for the plasma-torched Mn ferrite and MnZn ferrite powders were indexed to the spinel ferrite crystal structure. An average grain size of ∼20 nm was determined from Scherrer analysis confirmed by transmission electron microscopy studies. The particles also exhibited faceted polygonal growth forms with the associated truncated cuboctahedral shapes. Room-temperature vibrating sample magnetometer measurements of the hysteretic response revealed saturation magnetization Ms and coercivity Hc of Mn ferrite are 23.65 emu/g and 20 Oe, respectively. The Néel temperatures of Mn ferrite powders before and after annealing (500 °C, 30 min) were determined to be 200 and 360 °C, respectively. Inductively coupled plasma chemical analysis and energy dispersive x-ray analysis data on the plasma-torched powders indicated deviations in the Mn or Zn contents than the ideal stoichiometry. MnZn ferrite was observed to have a Néel temperature increased by almost 400 °C as compared with as-synthesized Mn ferrite but with a larger coercivity of ∼35 Oe.
Magnetization reversal and spin dynamics exchange in biased F/AF bilayers probed with complex permeability spectra
Authors: Spenato David , Youssef Jamal Ben , Le Gall Henri
Published: May 2003

The spin dynamics of the ferromagnetic pinned layer of ferro-antiferromagnetic (FIAE) coupled NiFe/MnNi bilayers is investigated in a broad frequency range (30 MHz–6 GHz). A phenomenological model based on the Landau–Lifshitz equation for the complex permeability of the F/AF bilayer is proposed. The experimental results are compared to theoretical predictions. We show that the resonance frequencies, measured during the magnetization, are likewise hysteretic.
Magnetic cluster size and activation volume in perpendicular recording media
Authors: Shimatsu T. , Uwazumi H. , Oikawa T. , Inaba Y. , Muraoka H. , Nakamura Y.
Published: May 2003

The magnetic cluster size Dcluster of perpendicular recording media, which is a main factor in media noise, is discussed in terms of activation volume, intergranular exchange coupling, and the slope of magnetization curves. It was experimentally shown that the values of Dcluster (observed by magnetic force microscopy in the ac demagnetized state) are ∼55 nm for CoPtCr–SiO2 media of 24 nm thickness, and are several times larger than activation diameter Dact (Dact=Vact/δ, Vact; the activation volume). Dcluster decreases as the film thickness δ decreases, particularly in a series of media with small intergranular exchange coupling, while Dact is nearly constant at ∼10 nm. It was experimentally shown that the slope of the magnetization curve α decreases as the value of Dcluster/δ decreases, and reaches a value of approximately 1 at Dcluster/δ of around 2. The results suggest that reduction of film thickness δ is important in order to realize both small Dcluster and large α values in granular-type perpendicular recording media.
Bicrystal structure of tilted perpendicular media for ultra-high-density recording
Authors: Guan Lijie , Zhu Jian-Gang
Published: May 2003

A modified tilted perpendicular medium has been proposed. With crystalline easy axes oriented randomly at ±45° relative to the perpendicular direction in the cross-track plane, the in-plane magnetic charges in the uniformly tilted perpendicular media can be effectively eliminated. Recording properties of the tilted perpendicular media are studied via micromagnetic simulation. In addition to the advantage of less saturation field, titled perpendicular media also show improved recording performance as compared to the conventional perpendicular media.
Effect of anisotropy field of soft magnetic underlayer on read/write properties in perpendicular recording media
Authors: Nakatani Y. , Hayashi N. , Uesaka Y. , Fukushima H.
Published: May 2003

The change in the read/write properties of double-layered perpendicular recording media with uniaxial anisotropy in the soft layer was investigated by micromagnetic simulation. It was found from the result of calculation that the media signal-to-noise ratio decreases by the soft layers, however, it can be improved by giving larger anisotropy to the soft layer.
Effect of microstructure on the magnetic properties of L1 CoPt–20 at. %C magnetic thin film
Authors: Oh D. Y. , Park J. K.
Published: May 2003

Effect of microstructure on the magnetic properties of monolithic L10 CoPt–20 at. %C granular film was investigated by intercalating the carbon layer in the form of CoPt/Cn (n=1,4) using magnetron sputter deposition. A micromagnetics simulation was also performed to calculate the effect of microstructure on the magnetic hysteresis loop. The carbon was observed to dissolve into the ordered CoPt lattice and to increase the c/a ratio; the amount of dissolution increases with decreasing carbon single layer thickness due to the capillarity effect. The carbon dissolution reduces the effective magneto-crystalline anisotropy constant of the ordered CoPt(C) granular film because of the increasing c/a ratio and of the reduced ordering kinetics. The slope of the hysteresis loop varied with the amount of carbon dissolution, which is primarily related to the grain size variation with the amount of carbon dissolution together with the presence of untransformed disordered phase in the film.
Fabrication of two-dimensional assembly of L1FePt nanoparticles
Authors: Miyazaki T. , Okamoto S. , Kitakami O. , Shimada Y.
Published: May 2003

We searched for an optimum thermal treatment of double or quadruple layers of (Fe 2.5 nm/Pt 2.5 nm) in ordered to obtain a monolayer assembly of ordered FePt particles. It was found that by controlling the thickness, the substrate temperature, and using MgO(100) substrates, monolayer assemblies of ordered FePt particles with the crystal axes [001] aligned vertically can be obtained at relatively low substrate temperatures around 400 °C.
Low-noise antiferromagnetically coupled media through the use of a superparamagnetic CoCrRu intermediate layer
Authors: Zhou J. N. , Choe G. , Acharya B. R. , Johnson K. E.
Published: May 2003

A superparamagnetic CoCrRu alloy is proposed for the intermediate layer (IL) between Ru/M2 in a typical antiferromagnetically coupled media structure M1/Ru/M2 (M2: recording layer). With the presence of the IL, the exchange coupling energy (Jex) initially increases from ∼0.09 to ∼0.10 erg/cm2 and asymptotes to ∼0.056 erg/cm2 when the IL thickness reaches 11 A. Due to its superparamagnetic nature, the CoCrRu IL does not introduce extra medium noise, in contrast to the ferromagnetic CoCrPtTa IL. The vibrating sample magnetometer thermal stability ratio (KV/kT) increases from 52 to 58 with a ∼7 Å CoCrRu IL, in agreement with the improved spin stand signal decay. X-ray diffraction scans indicate an improved epitaxial growth in the M2 layer when a CoCrRu IL is present.
Effect of inserted Cu on current-perpendicular-to-plane-giant magnetoresistance of Fe50Co50 spin valves
Authors: Yuasa H. , Fukuzawa H. , Iwasaki H. , Yoshikawa M. , Takagishi M. , Sahashi M.
Published: May 2003

We have reported that body-centered-cubic (bcc) Fe50Co50 with ultrathin Cu layers has large spin-dependent bulk scattering and enhances AΔR of spin valves. In order to clarify the role of Cu, two series of samples with (Fe50Co50 1 nm/Cu)×5 were prepared by two different sputtering machines. Machine A has a high rate, and machine B has a comparatively low rate. Both of AΔR in series A and B are increased by inserting thin Cu of about 0.1 nm, but they have a significant difference in Cu thickness dependence. While series A keeps high AΔR through the Cu thickness, AΔR in series B decreases when Cu is thickened. In order to find the reason for the difference, we took the extended x-ray absorption structure (EXAFS) spectra. By comparing AΔR and EXAFS, it was found that the very thin Cu of about 0.1 nm in Fe50Co50 takes a body-centered-cubic bcc structure, namely a solid solution state. Cu of 1 nm in spin valves with high AΔR takes a bcc and face-centered-cubic (fcc) evenly, and that with a low AΔR is a fcc structure. These results indicate that the existence of the solid solution Cu in Fe50Co50 is attributable to the enhancement of AΔR and are consistent with the report that Cu impurity in Fe and Co enhances the difference between the subband resistivity of up and down spins.
Magnetic force microscopy and x-ray scattering study of 70×550 nm2 pseudo-spin-valve nanomagnets
Authors: Castaño F. J. , Hao Y. , Haratani S. , Ross C. A. , Vögeli B. , Smith Henry I. , Sánchez-Hanke C. , Kao C.-C. , Zhu X. , Grütter P.
Published: May 2003

The room-temperature magnetic properties of large area arrays of 70×550 nm2 nanoelements made from a NiFe 6 nm/ Cu 3 nm/ Co 4 nm multilayer stack have been investigated using magnetic force microscopy (MFM), alternating gradient magnetometry (AGM), and scattering experiments using synchrotron radiation. MFM measurements on individual elements show square major and minor loops, while the collective magnetization reversal, measured from both AGM and elementally specific hysteresis loops obtained from synchrotron scattering experiments, show a wide distribution of switching fields and interaction fields, due to the variability between the elements.
Micromagnetic characterization of the reversal of Co/Cu/Co thin-film elements
Authors: Redjdal M. , Ruane M. F. , Humphrey F. B. , Castaño F. J. , Ross C. A.
Published: May 2003

The effects of aspect ratio and interlayer coupling on the switching of 50 nm wide Co(5 nm)/Cu(3 nm)/Co(2 nm) rectangular elements with aspect ratios of 10, 5.0, 2.48, and 1.52 were studied using direct integration of the Landau–Lifshitz–Gilbert equation. Hysteresis loops were calculated for both thick and thin layers taking into account both magnetostatic and exchange coupling between the layers. The switching dynamics for aspect ratio 1.52 were, investigated also.
Magnetic and magneto-optical properties of neodymium gallium garnet under “extreme” conditions
Authors: Guillot Maurice , Wei Xing , Hall Donovan , Xu You , Yang Jie Hui , Zhang Fang
Published: May 2003

The magnetization and Faraday rotation (FR) of Nd3 Ga5 O12 (NdGaG) were studied under high magnetic fields up to 33 T and low temperatures down to 4.2 K. No saturation of the magnetization was observed. The magnetic moment of the fundamental doublet was determined to be close to 1.25 μB/ion, with the energy gap with respect to the nearest level of about 132 cm−1. Above 30 K, the magnetic moment, M(H), shows a linear field dependence, even at the maximum field. The reciprocal magnetic susceptibility follows the Curie–Weiss law at temperatures above 100 K, with a Curie constant of about 15% below that of free ions. At 4.2 K, the FR spectrum is strongly field dependent, with very strong signals in the wavelength range from 440 to 720 nm. The FR signal decreases rapidly with increasing wavelengths above 720 nm and retains very small values in the wavelength range from 800 to 850 nm. The results are briefly discussed in light of a recent theoretical analysis of the magnetic and FR properties of the isomorphous ferrimagnetic garnet (Nd:YIG).
Biased FeTaC(N) soft underlayers for perpendicular media
Authors: Lai Chih-Huang , Jiang Ruo-Fan
Published: May 2003

FeTaCN films, prepared by using reactive sputtering, were studied for the application for soft underlayers of perpendicular media. As-deposited FeTaCN nanocrystalline films with a N2/Ar ratio of 5% exhibited high saturation moment (Bs=1.63 T) and low coercivity (1.4 Oe). IrMn/FeTaCN exchange-biased multilayer films and CoSm/FeTaCN hard-biased films were investigated to control the domain structure and magnetization reversal in FeTaCN films. Exchange bias field is inversely proportional to the thickness of FeTaCN films and reaches 11.4 Oe in the laminated sample of [IrMn (8 mm)/FeTaCN (50 nm)]×4. The interfacial coupling energy between IrMn and FeTaCN is 0.09 erg/cm2. The biasing field of CoSm/FeTaCN can reach a maximum value of 10.6 Oe at the FeTaCN thickness of 200 nm. The corresponding interfacial coupling energy of FeTaCN/CoSm is as large as 0.27 erg/cm2.
HITPERM soft-magnetic underlayers for perpendicular thin film media
Authors: Kumar S. , Laughlin D. E.
Published: May 2003

A class of nanocrystalline alloys, HITPERM (Fe, Co)–M–B–Cu (M=Zr,Hf,Nb, etc.) found to exhibit excellent soft-magnetic properties is being studied for use as a soft-magnetic underlayer for perpendicular recording media. Previously, we reported that HITPERM films of ∼100 nm thickness sputtered at room temperature (RT) and at ∼2.3 W/cm2 power density had exhibited an amorphous microstructure, which had turned mixed nanocrystalline when prepared at ∼250 °C. However, nanoparticles of FeCo have now been crystallized even at RT without the application of heat, by increasing the sputtering power density to ∼4.5 W/cm2. This dramatically improved the 4πMs while still maintaining a low coercivity. There was a further slight increase in the 4πMs at ∼6.8 W/cm2. Moreover, these soft-magnetic properties were maintained even when the substrate temperature was subsequently raised to ∼250 °C. Transmission electron microscopy studies showed the presence of relatively small nanocrystals of the ferromagnetic α′-FeCo (or α-FeCo) phase alone, for both sets of films. Previously, we had reported that the CoCrPt magnetic layer grew with a strong (00⋅2) texture on amorphous HITPERM. We have now seen that with a thin Ti intermediate layer (∼5 nm) the CoCrPt layer maintained a strong (00⋅2) texture even on the nanocrystalline HITPERM. Thus, due to their particular nanocrystalline nature, these HITPERM films exhibit much better soft-magnetic properties, while still leading to strong (00⋅2) texture on the CoCrPt magnetic layer.
Reduction of magnetic interaction in CoB/Pd multilayer perpendicular media using a phase-separated Pd–SiO underlayer
Authors: Domon H. , Djayaprawira D. D. , Takahashi M. , Endou T. , Furukawa S.
Published: May 2003

To realize CoB15/Pd multilayer perpendicular media with weak intergranular exchange coupling, we utilize PdSi18 (at. %) alloy, which contains elements that have large difference of affinity for oxygen, as the underlayer. It is clarified that introducing oxygen into Ar atmosphere during deposition of the underlayer substantially reduces the intergranular exchange coupling of the multilayer. Microstructural analysis reveals that the introduction of oxygen has separated the PdSi18 underlayer into two phases and enhances the formation of grain boundaries of the multilayer. It is suggested that the two-phase-separated Pd–SiO underlayer becomes a template for the growth of the multilayer and promotes the formation of grain boundaries in the multilayer, which reduces the exchange coupling through isolation of grains of the multilayer. In addition, independent of the oxygen pressure, coercivity and anisotropy energy maintain values of around 3.5 kOe and 2.3×106 erg/cm3, respectively. It is concluded that the two-phase-separated Pd–SiO underlayer, fabricated by introducing oxygen during sputtering of PdSi18 underlayer, is effective for reducing the magnetic exchange coupling without degrading the magnetic properties.
Structural changes in the nano-oxide layer with annealing in specular spin valves
Authors: Jang S. H. , Kim Y. W. , Kang T. , Kim H. J. , Kim K. Y.
Published: May 2003

We investigated microstructural changes in a nano-oxide layer (NOL) with annealing in specular spin valves (SVs) by cross-sectional transmission electron microscopy and x-ray photoelectron spectroscopy analysis. In the SV annealed at high temperature of 400 °C, an increase in thickness and a local breakdown of the NOL were observed. This local coarsening of the NOL is closely related to the formation of Mn oxides in the oxide-rich part of the NOL through Mn diffusion. Thus, the chemical structure of the NOL changes to the structure with Mn oxide-rich content after annealing.
Seed layer characterization for PtMn bottom spin-filter spin valves
Authors: Lee Chih-Ling , Devasahayam Adrian , Mao Ming , Kools Jacques , Cox Paty , Masaryk Katherine , Mahenthiran Dilip , Munson Jasper
Published: May 2003

The effect of seed layers on the giant magnetoresistance (GMR) response of bottom spin-filter spin valves (SFSVs) of the structure (seed layer)/PtMn/CoFe/Cu/CoFe/NiFe/Cu/Ta have been studied in detail. Four types of seed layers, NiFeCr, Ta/NiFeCr, NiFeCr/NiFe, and Ta/NiFe were used. The GMR response has been found to be very sensitive to the type and the thickness of the seed layers, which determine the crystallographic quality of the films and the degree of the fcc to fct phase transformation of the PtMn crystals in the films. Among the four, Ta/NiFeCr and NiFeCr/NiFe seed layers give the optimal GMR performance at a NiFeCr layer thickness of about 40–45 Å.
Highly deleterious role of small amounts of carbon on the giant magnetoresistance effect
Authors: Yang David X. , Repetski Edward J. , Chopra Harsh Deep , Chen P. J. , Egelhoff W. F.
Published: May 2003

Carbon (in the form of hydrocarbons) is a common contaminant in high and ultra-high-vacuum systems, and easily gets incorporated in films during deposition. This work reports the highly deleterious role of small amounts of carbon on the structure and magnetic properties of “giant” magnetoresistance (GMR) spin valves. Controlled incorporation of 1–3 at. % carbon in Co/Cu layers of NiO–Co–Cu-based spin valves has been found to completely eliminate the GMR effect. Transmission electron microscopy (TEM) shows that carbon promotes highly discontinuous Co/Cu layers, resulting in a large number of pinholes; domain studies corroborate that the “free” layer under the influence of a large pinhole coupling is unable to switch independently of the “pinned” Co layer. These results also have implications for other multilayers and spintronics devices.
Analyses of the effect of head imaging on medium demagnetization field in perpendicular recording
Authors: Zhou Hong , Gao Kaizhong , Bertram H. Neal
Published: May 2003

Poisson’s equation is solved exactly to obtain the medium demagnetization field for both a single pole head and a single pole with a trailing shield (shielded single pole) head designs in perpendicular recording. To write an isolated transition, for the semi-infinite single pole head, head imaging can be neglected when calculating the demagnetization field. To the semi-infinite shielded single pole head, when the pole separation is reduced, perfect imaging from both the head and the soft magnetic underlayer is a good approximation.
Pole tip protrusion study of various magnetic-head designs using finite-element analysis techniques
Authors: Alfoqaha Arshad , Young Kenneth
Published: May 2003

This article delineates the finite-element modeling techniques used in modeling four different magnetic head designs: (1) the flat-top pole, (2) the pedestal-defined-zero-throat, (3) the pedestal-defined-zero-throat-extended and (4) the stitch pole. We discuss the assumptions used in modeling the heads, the boundary conditions, meshing the geometry, and the type of analysis selected to perform the computations. Pole tip protrusion (PTP) results obtained for the heads were compared to see which design performs better under both current heating and ambient heating conditions. Results showed that the nine-turn stitch pole design does not perform as well as the other head designs in terms of PTP for current heating and ambient heating. This is due, among other reasons, to the existence of two layers of high coefficient of thermal expansion (CTE) photoresist material instead of one layer, and due to the fact that the lower photoresist in the apex region of the first insulation layer is very close to the ABS. Given the task of improving the PTP performance of the stitch pole design, we will show results on the implementation of partially or fully replacing the photoresist in the first and second insulation layers with alumina, or any appropriate material that has a low CTE.
Instrumental setup for polarized neutron scattering experiments
Authors: Schmidt W. , Ohl M. , Ruppert H. , Buchenau U.
Published: May 2003

Neutron scattering with polarization analysis is a powerful tool to determine magnetic structures and excitations. A common setup is to mount the sample at the center of a Helmholtz-type coil which can provide a magnetic field of any direction at the sample position and also a guide field along the neutron flight paths around the sample. We have extended the standard setup to a combination of a large vacuum tank surrounded by the electrical coils. The vacuum tank eliminates the air scattering, and we can use the polarization analysis down to the lowest accessible momentum transfers. The coils themselves also show some appealing features: In contrast to the classic (symmetric) coil distribution, we use an asymmetric setup which gives the advantage of a larger scattering window. Due to a more sophisticated current distribution, this modified Helmholtz coil does not need to be rotated for different scattering conditions. The whole setup is currently being constructed at the IN12 instrument, a three-axis spectrometer for cold neutrons, operated by FZ Jülich in collaboration with CEA Grenoble as a CRG-B instrument at the Institut Laue Langevin in Grenoble.
Structural and magnetic properties of nanostructured Ni0.5Zn0.5Fe2O4 films fabricated by thermal spray
Authors: Ge Shihui , Ma Xinqing , Zhang Tony , Wu Mingzhong , Zhang Heng , Zhang Y. D. , Ings J. , Yacaman J.
Published: May 2003

Nanostructured Ni0.5Zn0.5Fe2O4 thick films were fabricated by a high velocity oxygen fuel (HVOF) thermal spray approach with over 98% of the theoretical density and with no cracks, followed by heat treatment under an oxygen atmosphere. Crystallographic, microstructural, as well as static and dynamic magnetic properties of the films were studied by x-ray diffraction, high-resolution transmission electron microscopy, superconducting quantum interference device magnetometer, and high-frequency impedance analyzer. By controlling the nature of the flame, the crystal structure of the ferrite can be retained during thermal spraying while the grain size as small as 10–20 nm can be attained. By controlling the spray conditions and postannealing, the real part of initial complex permeability μ′ reaches 120 while the image part μ″ remains small in the frequency range up to 13 MHz. In comparison with a conventional Ni0.5Zn0.5Fe2O4 (μ′=800, cutoff frequency fc=1.5 MHz), a nanostructured sample possesses a much higher cutoff frequency, a merit for high-frequency application. It is determined that HVOF is a promising approach for the fabrication of nanostructured ferrite films.
Field-induced phase transitions in Sc-substituted ytterbium–iron–garnet under high dc fields
Authors: Ostoréro J. , Guillot M.
Published: May 2003

High magnetic field measurements were performed on Yb3Fe5−xScxO12 (YbIG:Sc), x=0.5, single crystals platelets oriented along the [111] and [100] crystallographic axes, in the 4.2 K–250 K temperature range in a magnetic field up to 230 kOe. When T=4.2 K, a first-order transition is observed at 63 kOe for H applied parallel to [111]. For 4.2 K<T<25 K, an anisotropy of magnetization is observed below 70 kOe, the differential magnetic susceptibility presenting a maximum independent of temperature at H=125 kOe. In this temperature range, [111] is the “easy” magnetic axis in the spontaneous state. For T>25 K, isotherms are linear as usually observed in ferrites. However, isofield curves reveal the presence of a singular point at 60 K that indicates that the field-induced canted magnetic structures remain until this temperature. The magnetic phase diagram is then established. The spontaneous magnetization data are analyzed within the frame of the Dionne-refined Néel model.
Superlattice source and its application in Co/Pd multilayers for perpendicular magnetic recording
Authors: Johnson Paul R. M. , Zheng Min
Published: May 2003

This article reports a sputtering system, the Intevac Superlattice Source (SLS), designed to meet the needs of making perpendicular multilayers for hard disk manufacturing. The SLS is a two-sided sputtering station in which each side is capable of depositing multiple sequential bilayers of two different film materials. Each side of the source contains a magnetron (sharing the same centerline as the substrate) and a rotating cathode on which are mounted two semicircular targets. The two rotating cathodes (one on each side of the source) are synchronized to ensure matched elements sputtering simultaneously and to prevent cross contamination between target materials. The design easily integrates onto standard hard disk manufacturing systems and can deposit up to 5 bilayers per second. Using this source, a series of Co/Pd multilayers has been made. We investigated the effect of different seedlayers, Pd, Ti, and Ru, on the coercivity and microstructure of Co/Pd multilayers. We found that although the crystalline growth is very different for each of the three seed layers studied, all three lead to higher coercivity and unique squareness of Co/Pd multilayers as compared to multilayers made without any seedlayer. The coercivity achieved for a 300 Å thick seedlayer [Co 4 Å/Pd 10 Å]×15 multilayer is 6253, 6871, and 6920 Oe for Pd, Ti, and Ru seedlayers, respectively.
High-frequency transport properties of spin-spray plated Ni–Zn ferrite thin films
Authors: Fu C. M. , Hsu H. S. , Chao Y. C. , Matsushita N. , Abe M.
Published: May 2003

The frequency and temperature variation of magnetoimpedance in Ni–Zn ferrite thin films fabricated by spray plating method were studied. It is observed that the frequency induces a metal–insulator crossover behavior in impedance spectra. The frequency behavior of the electrical properties of the film can be modeled by an equivalent circuit composed of resistance and capacitance. The relaxation time and activation energy of the conductivity were calculated. The result suggests that the high-frequency conductivity of the spin-spray plating of a Ni–Zn ferrite film is predominantly associated with the dielectric, rather than by magnetization, dynamics. Mechanisms underlying high-frequency transport are discussed.
Spin-sprayed Ni–Zn–Co ferrite films with high μr″>100 in extremely wide frequency range 100 MHz–1 GHz
Authors: Matsushita Nobuhiro , Nakamura Tatsuro , Abe Masanori
Published: May 2003

Ni–Zn–Co ferrite films were deposited by the spin-spray ferrite plating from an aqueous solution. Film with optimized Zn and Co contents (i.e., Ni0.22Zn0.52Co0.03Fe2.23O4) exhibited the real permeability μr′ higher than 260 at frequencies up to 130 MHz, and the imaginary permeability μr″ higher than 100 in the extremely wide frequency range from 100 MHz to 1 GHz. Prepared at the very low temperature of 90 °C without postdeposition annealing, these films are promising to be actually applied to electromagnetic noise suppressors which directly cover the noise source elements on printed circuit boards.
Fabrication and magnetoresistive effect of current perpendicular to plane devices using half-metallic Fe3O4 thin films on metallic films
Authors: Takahashi H. , Soeya S. , Hayakawa J. , Ito K. , Kida A. , Yamamoto C. , Asano H. , Matsui M.
Published: May 2003

The current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) devices having half-metallic Fe3O4 for their magnetic layers were investigated along with the fabrication of Fe3O4 films on Au layers at low temperature (523 K). The 10–50-nm-thick Fe3O4 films that were grown on a 100 nm Au (111) layer were Fe3O4 (111) oriented. These films showed Verwey transition at ∼120 K. Using these films, the relation between the magnetoresistive (MR) effect of CPP-GMR and the Fe3O4 layer thickness was examined with 2×2 μm2 samples of Ni80Fe20/Au/Fe3O4 trilayers on Au bottom electrode films. At the Fe3O4 layer thickness of 20 nm, the MR ratio was 0.04% and the area magnetoresistance-change product (ΔRA) was 1.5 mΩ μm2. The MR ratio was increased with decrease in the Fe3O4 thickness. The CPP-GMR of Fe3O4/Au/Fe3O4 on the Au layer showed that the MR ratio was 0.04% and the ΔRA was 3.9 mΩ μm2. This MR ratio was four times larger than that of the NiFe-type CPP-GMR for the same Fe3O4 bottom layer thickness.
Calculation of exchange integrals and electronic structure of manganese ferrite (MnFe2O4)
Authors: Zuo Xu , Vittoria Carmine
Published: May 2003

The exchange integrals of manganese ferrite (MnFe2O4) are calculated with the density functional theory method for both normal and inverse spinel structures. The functional is chosen to be a mixture of Becke exchange and Fock exchange with variable weight (w). The exchange integrals JAB (the exchange integral between the nearest neighbor A and B sites) and JBB (the exchange integral between nearest neighbor B sites) are calculated by substituting the total energies of different magnetic ground states into the Heisenberg model. The calculated value of JAB is in agreement with experimental values measured by neutron diffraction and nuclear magnetic resonance. Also, the parameters U (Coulomb repulsion energy) and Eg (band gap) are extracted from density of states plotted versus w. Our calculated band gap shows that MnFe2O4 is a complex insulator in contrast to previous local spin density approximation and generalized gradient approximation calculations which predicted it to be metallic.