bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetization reversal of individual Fe nanowires in alumites studied by magnetic force microscopy
Authors: Sorop T. G. , Untiedt C. , Luis F. , de Jongh L. J. , Kröll M. , Raşa M.
Published: May 2003

We have studied the magnetization reversal of two-dimensional (2D) arrays of parallel ferromagnetic Fe nanowires in nanoporous alumina templates. Combining bulk magnetization measurements using a superconducting quantum interference device with field-dependent magnetic force microscopy (MFM), we decomposed the macroscopic hysteresis loop in terms of irreversible magnetic responses of individual nanowires. The field-dependent MFM provides a microscopic method by which to obtain the hysteresis curve by registering the fraction of upward and downward magnetized wires for each field. The nanowire system proves to be an excellent example of the 2D classical Preisach model, well-known from the field of hysteresis modeling and micromagnetism.
Zero magnetization states in electrodeposited Co0.45Fe0.55 nanowire arrays
Authors: Fodor P. S. , Tsoi G. M. , Wenger L. E.
Published: May 2003

Co 0.45 Fe 0.55 alloy nanowires with 12 to 35 nm diameter and 12 μm length were fabricated by electrodeposition in porous anodic alumina templates. The initial magnetization curves reveal that the zero magnetization state is not unique and is determined by the field history (ac demagnetization process) leading to the zero average moment state. For ac demagnetization processes with the field applied parallel to the nanowire axis, the subsequent magnetization curves suggest that an individual nanowire behaves as a single domain with neighboring nanowires being antiparallel to each other in the zero magnetization state. However, for a demagnetization process with the field applied perpendicular to the nanowires, a different zero magnetization state is created in which the individual nanowires consist of multidomains having opposite axial orientations. These results are consistent with the asymmetric (symmetric) behavior found in the minor hysteresis loops measured after perpendicular (parallel) ac demagnetization on these nanowire arrays.
Adjacent track encroachment analysis at high track density
Authors: Li Zhihao , Schaff Mike , Munson Rolf , Jurisch Mark , Noonon Ted , Li Shaoping , Zhou Yuming
Published: May 2003

The issue of adjacent track encroachment (ATE) has been studied for high track density (TPI) situations. Several techniques and methods have been utilized to determine the root cause of the adjacent track erasure. The new encroachment mechanisms, differing from those reported previously, have been identified for several different cases. It was found that the write-head gap edge corner or shoulder can generate a sizable fringing field, leading to measurable adjacent track encroachment problems in certain conditions. This type of side-erasure problem is not only associated with the amplitude and frequency of the writing current, but is also skew sensitive, depending upon both skew angle and skew polarity. Furthermore, finite element calculations confirm that in the vicinity of the notch corner, the fringing field strength could be as much as 4000 Oe. Experimentally it was also found that the side-erasure process induced by the notch shoulder was asymmetric in some situations.
Effects of focused-ion-beam irradiation on perpendicular write head performance
Authors: Park Chang-Min , Bain James A. , Clinton Thomas W. , van der Heijden Paul A. A.
Published: May 2003

The effects of focused-ion-beam (FIB) irradiation on writer performance were examined on a perpendicular recording system. The entire top pole was irradiated by FIB with ion doses from 0 to 300 pC/μm2. PW50 and signal to noise ratio (SNR) were characterized using a spin stand before and after FIB irradiation. It was found that there is degradation of PW50 and SNR due to FIB irradiation. At the maximum dose (300 pC/μm2), PW50 increased by 33 nm (>30%) and SNR decreased by 5 dB (>25%). The degradation was attributed to the physical pole tip recession and the formation of a magnetic dead layer. The thickness of the magnetic dead layer was estimated by analyzing the write spacing loss. Using atomic force microscopy and stage current change monitored during FIB process, it was found that the entire 4-nm protective carbon layer was etched away with a dose of 25 pC/μm2. This result implies that the degradation with ion doses <25 pC/μm2 is exclusively due to damage to the magnetic layer at the pole surface due to Ga implantation. It was found that our experimental results are consistent with the conventional write spacing loss behavior.
Influence of underlayers on the soft properties of high magnetization FeCo films
Authors: Jung H. S. , Doyle W. D. , Matsunuma S.
Published: May 2003

A remarkable reduction in coercivity Hc was found in sputtered Fe65Co35(=FeCo) films on Cu, NiFe, Ru, Ta/Cu, Ta/NiFe, or Cu/IrMn underlayers. A decrease in Hc from 120 to 7–12 Oe was observed for Cu, NiFe, and Ru underlayers as thin as 2.5 nm but less for Ta. A Cu underlayer significantly reduced the maximum anisotropy fields from 2 kOe to 40 Oe, resulting in a well-defined in-plane average uniaxial anisotropy field Hk∼30 Oe. The saturation magnetostriction with Cu was (47±4)×10−6, independent of Cu and FeCo thicknesses. In-plane tensile film stress decreased with underlayer thickness tUL from 2 to 0.2 GPa but much less rapidly than the reduction in Hc. All underlayers induced a (110) texture in FeCo, which was strongest with Ta. Transmission electron microscopy of cross-sections showed an unusually long range coherence with low angle grain boundaries in the FeCo without an underlayer. Clear columnar grains were visible with all underlayers with an average grain size of ∼50 nm with Ta dropping to 9–10 nm for Cu, NiFe, and Ru. This alone is sufficient to explain quantitatively the reduction in Hc using Hoffmann’s ripple theory.
Scaling of head response function in spin-stand imaging
Authors: Mayergoyz I. D. , Tse C. , Mircea D. I. , Krafft C.
Published: May 2003

Scaling of head response function in spin-stand imaging is proposed. This scaling is performed in order to improve the accuracy of the measured head response function. This response function is measured by imaging a small spot of magnetic charges formed as a result of dc-trimming of isolated transitions. The theoretical justification for the scaling is the “nearly” self-similar nature of the measured response function with respect to the cross-track dimension of the charged spot. This scaling technique has been tested experimentally. It is demonstrated that the scaling of head response function allows one to reconstruct magnetization images of overwritten data that cannot be discerned otherwise.
High linear density in perpendicular recording
Authors: Guarisco Davide , Nguy Hai
Published: May 2003

Two kinds of perpendicular oxide media are compared with a conventional, boron-alloy media. Using an integrated, 245 nm wide, single-pole, high-Bsat writer with trapezoidal write pole, a linear density of 760 kfci at a BER of 10−5 was achieved at the ID radius of an oxide disk at 5400 RPM. MFM images of written tracks show higher-quality transitions up to a higher linear density on the oxide media. Furthermore, transitions on the B-alloy media exhibit a high degree of curvature. Finally, room temperature measurements of thermal decay on an improved oxide media, with only slightly degraded recording performance, showed the oxide media to be thermally stable.
Cross-track noise profile measurement for adjacent-track interference study and write-current optimization in perpendicular recording
Authors: Jiang Wen , Khera Gautam , Wood Roger , Williams Mason , Smith Neil , Ikeda Yoshihiro
Published: May 2003

A cross-track noise profile measurement is developed for identifying the source of adjacent-track interference (ATI) fields in perpendicular recording systems. The noise amplitude as a function of cross-track position and write current clearly delineates the extent, magnitude, and polarity of stray fields under different portions of the head. Experimentally obtained stray field strength relative to writing field is in good agreement with finite element modeling. For given head and disk components, the composite picture of noise amplitude for both writing field and stray fields as a function of write current also provides a way of selecting an optimal write current with respect to the medium dynamic coercivity, saturation, and ATI threshold. Further investigation on the asymmetries in the noise profiles have led to two interesting discoveries. The first is an asymmetry in ATI field that can be attributed to the polarity of the radially oriented magnetization in the soft underlayer. The second is an artifact associated with the change in read head sensitivity around track edges due to fields from the dc-erased hard recording layer.
Experimental study of playback giant magnetic resonance head nonlinearity in perpendicular recording
Authors: Luo P. , Stoev K. , Liu F. , Vadde A. , Gibbons M. , Lederman M. , Re M.
Published: May 2003

In this article, nonlinear distortions of the playback giant magnetic resonance (GMR) sensor in perpendicular recording are characterized in both time and frequency domains. We use three perpendicular media with different Mrt (0.46, 0.6, and 0.8 emu/cm2) and two groups of similar magnetic-read width (MRW) but different junction type [contiguous junction (CJ) and lead-over-lay (LOL)] GMR heads. Square-wave patterns at moderate densities are recorded to minimize NLTS, partial erasure, and transition broadening effects. Both time- and frequency-domain measurements indicate that the LOL-type GMR heads show playback nonlinearity (7%–23%), while the CJ-type GMR heads do not. Micromagnetic simulation is utilized to understand the hard bias field with different junction designs. The result indicates that the hard bias (HB) field in LOL type (HB field ∼6.9 Oe) at the air bearing surface (ABS) and stripe center is much lower than that in CJ type (HB field ∼54.0 Oe). Therefore, the free layer with large HB–HB distance will be more susceptible to saturation.
Laminated nanocrystalline soft underlayers for perpendicular recording
Authors: Tanahashi Kiwamu , Kikukawa Atsushi , Takahashi Yoshio , Hosoe Yuzuru
Published: May 2003

Media with laminated [Fe(Ta,Ti,Nb)C/Ta]n=2–4 soft magnetic underlayers (SULs) were prepared, and the effect of lamination on spike noise was investigated. Cross-sectional transmission electron microscopy observation revealed that nanocrystalline layers, composed of α-Fe grains with three-dimensional random orientation, were physically separated by 2.5-nm-thick Ta layers. Laminated SULs had low coercivities, i.e., less than 0.2 Oe, when the total thickness of the SUL ranged from 200 to 400 nm and the thickness of each nanocrystalline layer was more than 50 nm. These low coercivities are probably due to magnetostatic interaction between adjacent nanocrystalline layers. The medium with a laminated SUL showed much lower spike noise than the medium with a single-layer SUL. It is thought that magnetostatic interaction can reduce the stray field from the SUL, and result in a decrease in spike noise.
Oxide seed layer with low surface energy to attain fine grains in magnetic layers
Authors: Kong S. H. , Mizuno K. , Okamoto T. , Nakagawa S.
Published: May 2003

The relationship of surface energy γs to the seed layers, grain size, and crystallite orientation of the recording layer is discussed. The oxide seed layer with lower γs is effective in attaining fine grains in magnetic upper layers. The grain size of a Co–Cr–Ta recording layer deposited on an oxide seed layer with lower γs is about 50% that of a recording layer deposited on a metallic seed layer with higher γs. The reduction in grain size in the recording layer with a Ni–Fe–O seed layer led to suppression of the noise level in the high recording density region. Furthermore, the grain size of the Fe–Co–B soft magnetic layer on the oxide seed layer with 27 mN/m γs, which corresponds to 75%–50% that of metallic films, also reduced to about 70% that of the Fe–Co–B single layer. The material of the magnetic upper layer on the seed layer with low γs may consist of very small dense island grains in the region of initial film growth, due to its high diffusion energy. These small dense nucleation sites in the region of initial growth may reduce the grain size.
Influence of thermal relaxation on the irreversible magnetization processes for perpendicular recording media
Authors: Papusoi Cristian , Suzuki Takao
Published: May 2003

The influence of grain interaction and thermal relaxation on the rotational hysteresis loss (RHL) for perpendicular recording media is investigated using Landau-Lifshitz-Gilbert and Monte Carlo simulations. The results indicate that both thermal relaxation and grain exchange interactions decrease the applied field value HM, corresponding to a vanishing RHL, with respect to the grain intrinsic anisotropy field HK(=2K/MS). In the case of weak grain exchange coupling, the thermal decrease of HM is scarcely affected by grain magnetostatic interactions. In this case, the ratio HM/HK can deliver the maximum grain size. This statement is checked on two samples of hard disk media with perpendicular (CoPtCrO) and longitudinal anisotropy (CoCrPtB).
Reverse dc erase medium noise analysis on exchange-coupling effect in coupled granular/continuous perpendicular recording media
Authors: Sonobe Y. , Supper N. , Takano K. , Yen B. K. , Ikeda Y. , Do H. , Muraoka H. , Nakamura Y.
Published: May 2003

The role of intergranular exchange coupling was experimentally investigated in a coupled granular/continuous (CGC) perpendicular medium structure. By changing the number of Co/Pt bilayers in the continuous layer, the degree of exchange coupling can be systematically controlled. The switching field distribution (SFD) was roughly estimated from Kerr loops. The SFD became narrower for media with a thicker continuous layer. Using a head with a single-pole writer and an 80 nm gap giant magnetoresistance reader, reverse dc erase noise was measured as a function of the reverse dc erase current. The media showed a clear positive noise peak with an increase in reverse erase current. Narrowing of the SFD was reflected by narrowing of the noise peak width. However, the peak value of the medium’s noise also increased with an increase in the thickness of the continuous layer. Although exchange coupling increases the average magnetic cluster size in the demagnetization condition, CGC media with moderate exchange coupling showed no degradation of the signal to noise ratio compared to the base granular medium.
Linear and nonlinear magneto-optical diffraction from one-dimensional periodic structures
Authors: Lazarenko S. V. , Kirilyuk A. , Rasing Th. , Lodder J. C.
Published: May 2003

Nonlinear magneto-optical diffraction from periodically structured samples has been studied using magnetization-induced second harmonic generation (MSHG). Several orders of diffraction were clearly observable in MSHG, along with a strong dependence on the magnetization. Sizeable asymmetry between the MSHG signal measured in positive and negative diffraction peaks, especially visible in second order, are explained by Fresnel factors. It was found that first-order diffraction hysteresis loops differ from all others by showing an “overshoot” at magnetization reversal, both in MSHG and in the linear magneto-optical Kerr effect. Tentatively this behavior is explained as due to inhomogeneous reversal of the magnetization in the stripes.
Energy absorption in Ni-Mn-Ga-polymer composites
Authors: Feuchtwanger Jorge , Michael Sadie , Juang Jiankang , Bono David , O’Handley Robert C. , Allen Samuel M. , Jenkins Catherine , Goldie James , Berkowitz Ami
Published: May 2003

Martensitic Ni-Mn-Ga single crystals are easily twinned and the twin boundaries can be displaced by applying a mechanical stress or magnetic field. Twin boundary motion is a highly dissipative process. Composites of aligned Ni-Mn-Ga particles in a polymer matrix show evidence of stress-induced twin boundary motion that results in stress-strain curves with significantly greater hysteresis than for Fe-polymer composites or polymer samples.
Pulsed field magnetometery for high coercivity permanent magnets
Authors: Kim Yoonbae , Kim Hyoungtae , Cho Sungho , Kapustin G. A.
Published: May 2003

A high sensitivity pulsed field magnetometer for the measurement of thin films or small volume of high coercive rare earth permanent magnets has been constructed. The pickup coil designed in principle of 3-axis compensation has the sensitivity of 5×10−4 emu at tested field of 76 kOe. The compensation has been repeatable within 4×10−4–10×10−4 emu, which is enough for measurement within 2% accuracy for the materials with magnetic moment as small as 5×10−2 emu. Measurements on NdFeB magnet show excellent repeatability within 0.3% discrepancy for remanence and coercivity. The magnetic hysteresis loop of a NdFeB thin film (1050 nm) was measured satisfactorily. Estimation of the eddy current effect, by measuring the similar dimensioned but lower resistive nonmagnetic metals, has also been investigated.
Experimental study of signal dependent noise in perpendicular recording
Authors: Zhu Wenzhong , Chen Jian , Kaiser David , Judy Jack , Palmer Dean
Published: May 2003

The extracted dipulse technique, or pseudorandom sequence method, has been used to determine the dependence of the noise upon the signal. Four main types of echo are identified. A simple model is developed and the simulated waveforms are used to substantiate the physical interpretation of the noise echo pulse. The model takes into account the most significant eigenmodes of noise obtained from experimental dibit data at different linear densities using a Karhunen–Loeve expansion. The calculations and experimental data agree very well from low linear density up to high linear density where the supralinear noise occurs.
FEM analysis on the effects of soft magnetic film as a noise suppressor at GHz range
Authors: Kim Ki Hyeon , Ikeda Shinji , Yamaguchi Masahiro , Arai Ken-Ichi
Published: May 2003

To investigate the rf electromagnetic noise attenuation properties by soft magnetic films, the finite element method is applied to analyze electromagnetic field and loss generation in a coplanar transmission line with soft magnetic thin film at GHz range. The coplanar transmission line is with the total width of 400 μm and 50 μm width of signal line, 3 μm thickness, respectively, and has 50 Ω characteristic impedance. The change of the magnetic field distribution, the induced surface current density on the coplanar transmission line and hence the rf noise suppression by magnetic films are significant as a function of the magnetic film width/slit width (10/3, 20/3, and 50/3 μm) and magnetic film thickness (0.1, 0.3, 0.5, and 1 μm).
Effect of interfacial coupling on the magnetic ordering in ferro-antiferromagnetic bilayers
Authors: Tsai Shan-Ho , Landau D. P. , Schulthess Thomas C.
Published: May 2003

Monte Carlo simulations have been used to study magnetic ordering in coupled anisotropic ferro/antiferromagnetic (FM/AFM) films of classical Heisenberg spins. We consider films with flat interfaces that are fully uncompensated as well as rough interfaces that are compensated on average. For both types of interfaces above the “Néel temperature” we observed order in the AFM with the AFM spins aligning collinearly with the FM moments. In the case of rough interfaces there is a transition from collinear to perpendicular alignment of the FM and AFM spins at a lower temperature.
Numerical simulation of unidirectional anisotropy in ferro(F)/antiferromagnetic(AF) exchange coupled layers with a compensated AF-interface
Authors: Sakurai Yutaka , Fujiwara Hideo
Published: May 2003

We have performed a Zero-K Monte Carlo simulation for F/AF coupled systems of simple cubic structure. No combination of parameters, JF-AF/JF-F and JAF-AF/JF-F (JF-F, JAF-AF and JF-AF are exchange constant between F-F, AF-AF, and F-AF spins, respectively) ranging between 0.1 and 1 has been found, assuming Ku/JF-F=0.01 (Ku: uniaxial anisotropy coefficient), which gives unidirectional anisotropy in the sense that the energy exhibits 360° symmetry dependence on the F-magnetization direction. However, by assuming the existence of a plane in the AF-layer across which the AF-spins couple loosely with each other, it is demonstrated that a typical 360° symmetry anisotropy appears without assuming any AF-spin constraint in the plane.
Stationary antiferromagnetic domains during magnetization reversal in an exchange-biased FeMn/Fe76Mn6C18 bilayer
Authors: Shull R. D. , Shapiro A. J. , Gornakov V. S. , Nikitenko V. I. , Zhao Hong-Wu
Published: May 2003

Domain processes were observed at 300 K using the magneto-optic indicator film technique (MOIF) in an exchange-coupled ferromagnet (FM)/antiferromagnet (AF) bilayer Fe76Mn6C18 (150 Å)/FeMn (100 Å) deposited under the presence of a 0.4 mT magnetic field (H) applied in the plane of the sample. The hysteresis loop for this sample was comprised of two half-loops symmetrically shifted in opposite directions from the origin. At H=0, MOIF observations showed the presence of domains in the FM with magnetization (M) vectors along the axis of the preparation field separated by 180° walls. Upon field application along that axis, saturation of the FM was achieved by the nucleation and growth of domains. In this state, at not very high fields, it was possible to observe an unusual MOIF contrast at the location of the original FM domain walls in the as-prepared ground state, associated with the intersection of domain walls in the AF with the FM. Upon field reduction M reversed only in regions which had reversed during the prior field application, so that at H=0 the domain structure was the same as that in the original ground state. If H was off-axis, during the original field application domain growth occurred in that same direction; upon field reduction, the preferred domain growth direction was at an angle with reversed sign. These results prove the AF domain walls do not move during the motion of FM domain walls, and that an exchange spring is created parallel to the AF/FM interface as the ferromagnetic layer reverses.
Rigorous micromagnetic computation of configurational anisotropy energies in nanoelements
Authors: Dittrich Rok , Thiaville André , Miltat Jacques , Schrefl Thomas
Published: May 2003

A method combining the nudged elastic band method with finite element micromagnetics is used to calculate minimum energy paths, global minima, metastable states and, most importantly, saddle points between energy minima. We study configurational anisotropy effects in thin permalloy elements, e.g., 5 nm thick squares. For squares with the size of 15–200 nm the ground states are so-called “leaf” states with the average magnetization along one of the diagonals. However a second state (“buckle”) becomes stable with the average magnetization along one edge at sizes larger than ∼80 nm. The superposition of the four easy axes leads to a combination of four and eightfold anisotropy. At ∼200 nm size both states have about the same energy so that the overall picture becomes that of an effective eightfold anisotropy.
Effect of a high magnetic field on the bioactivity of apatite-based biomaterials
Authors: Nakahira A. , Konishi S. , Nishimura F. , Iwasaka M. , Ueno S.
Published: May 2003

The effect of a high magnetic field on the bioactivity of biomaterials was evaluated using simulated body fluid (SBF) immersion tests. After immersion in SBF at 37 °C for 4 days 14 T, many large bone-like hydroxyapatite crystals thickly precipitated for carbonate hydroxyapatite sintered samples with NaCaPO4 as a second phase, compared to samples without applying a magnetic field (0 T). On the other hand, little difference in hydroxyapatite-like crystal growth between 14 and 0 T for monolithic hydroxyapatite samples without an additive was observed. In this study, the possibility of bioactivity enhancement of hydroxyapatites applying a high magnetic field of 14 T has been confirmed for certain hydroxyapatite-based biomaterials.
Design of an integrated microspeaker and vibration motor used for mobile phones
Authors: Lee Hong-Joo , Hwang Sang-Moon , Hwang Gun-Yong , Jeung Seung-Kyu , Kang Beom-Soo
Published: May 2003

Electromechanical parts, such as microspeakers and vibration motors, are essential components for mobile phones in order to come up with advance in the communication industry. The size reduction of mobile phones still remains the most prominent trend in the marketplace and demands a continual effort for the size reduction of components. The most realistic approach for the reduction of size is accompanied by integrating at least two parts within a structure. In this article, design of an integrated microspeaker and vibration motor is introduced and compared with the conventional type. For sound pressure level analysis of the microspeaker, electromagnetic, mechanical, acoustical, and their coupling effects is considered for the analysis. For the vibration analysis, structural and output torque analysis is also followed to predict vibration quantity. Results show that the proposed design shows better performance compared to the conventional type.
Performance comparison between inner and outer permanent magnet type microspeakers used for mobile phones
Authors: Hwang Gun-Yong , Lee Hong-Joo , Hwang Sang-Moon , Kang Beom-Soo , Jeung Seung-Kyu
Published: May 2003

In mobile phones of the multimedia era, microspeakers of high quality sound are essential parts to generate the human voice in speaker phones and MP3 song players. In this article two types of microspeakers, inner permanent magnet (PM) and outer PM type, are analyzed using electromagnetic, mechanical, acoustical, and their coupling analysis. For performance comparison, a voice coil diameter is chosen as a design parameter to change magnet volume and excitation position for both types. With the decreased voice coil diameter of the outer type, magnet volume is increased to produce higher sound pressure level (SPL) and the first resonant mode of the diaphragm is more efficiently excited due to concentrative excitation, resulting in lower and broader frequency range.
Magnetic softening of switching field of magnetic garnet films by controlling groove depth
Authors: Park Jae-Hyuk , Takagi H. , Nishimura K. , Uchida H. , Inoue M. , Lee Dong-Hoon , Cho Jae-Kyeong
Published: May 2003

We magneto-optically investigate the switching properties of the grooved pixels. The switching field of the 70%-grooved pixel achieves a factor of over two reductions more than that of the 100%-grooved pixel. The switching properties of the geometric pixel arrays for the magneto-optic spatial light modulators are very sensitive to the depth of the pixel groove, and also depend on the state of individual pixel, in additions to the state of the neighbors in two-dimensional pixel arrays. Optimally grooved pixels can allow high amounts of bismuth in the iron garnet film, and actually reduce the driving current of the magneto-optic spatial light modulator due to a low switching threshold field.
Comparison of methods for the determination of dc-magnetic properties of laminated SiFe alloys
Authors: De Wulf Marc , Makaveev Dimitre , Dupré Luc , Permiakov Viatcheslav , Melkebeek Jan
Published: May 2003

A comparative study was performed of the different techniques for determination of dc-magnetic properties of laminated SiFe alloys. Three characterization methods are considered: (1) the point-by-point method (PbPM) for the construction of magnetization loops; (2) the slow time-varying excitation in which a low-frequent periodic magnetic field excitation is used; and (3) fitting of the dc properties based on the statistical power loss model of Bertotti. All experiments are performed on the Epstein frame using the same excitation source and the same electronic flux integrator. Both grain-oriented, in both the rolling direction (RD) and transverse direction (TD), and non-oriented (NO-RD) materials are considered. In the low induction range, fitting by the Steinmetz formula is used to compare the methods. Under slow time-varying excitation, the loss in energy observed when samples are magnetized at constant dB/dt is always lower than at constant dH/dt excitation for the same frequency. It is also observed that the PbPM for the low induction range gives a lower value of hysteresis loss than the other methods (approximately 30% for GO-RD, 10% for GO-TD and 5% for NO-RD).
Ferromagnetic resonance in tunnel junctions: Mag-noise and complex impedance analysis
Authors: Synogatch Valeri , Smith Neil , Childress J. R.
Published: May 2003

Ferromagnetic resonance (FMR) in the Co80Fe20/Ni80Fe20 free (sense) layer of micron-sized, magnetic tunnel junction (MTJ) devices is studied by two different techniques. The first method employs the MTJ device’s magnetoresistance, and measures thermally excited magnetization fluctuations (mag-noise) as a resistance noise spectrum. Correlations between magnetoresistance and FMR frequency versus in-plane magnetic field have been observed for different devices. The FMR frequencies agreed well with calculations when including substantial out-of-plane magnetic anisotropy fields. The second method detects the change in the complex impedance of the MTJ before and after applying a dc current, as measured by a vector network analyzer. The latter method seems to be very sensitive to internal nonuniform states of the free layer magnetization.
Micromagnetic calculations of bias field and coercivity of compensated ferromagnetic antiferromagnetic bilayers
Authors: Suess Dieter , Kirschner Markus , Schrefl Thomas , Scholz Werner , Dittrich Rok , Forster Hermann , Fidler Josef
Published: May 2003

Exchange bias in polycrystalline IrMn/NiFe was found at perfectly compensated interfaces. The energy associated with unidirectional anisotropy is stored in lateral domain walls in the antiferromagnet. In addition to exchange bias, this mechanism leads to a training effect. The bias field shows a maximum of μ0Hb=4 mT at an antiferromagnetic layer thickness of 22 nm. The coercivities are on the order of μ0Hc=10 mT. The coercive field increases with decreasing intergrain exchange interactions within the ferromagnet.
Stitched pole-tip design with enhanced head field for perpendicular recording
Authors: Bai Daniel Z. , Zhu Jian-Gang
Published: May 2003

A perpendicular write head with a stitched pole tip and side yoke recessed from the air-bearing surface is proposed and investigated using three-dimensional micromagnetic modeling. The design yields an increase of head field magnitude by 30% over the conventional single pole head. It is found that the optimal flare angle at the bottom of the yoke is 45°, for maximizing the on-track field magnitude and getting the minimum off-track field at the same time. Reducing the throat height significantly increases on-track field, while the off-track field increases as well. Lamination of the pole tip is necessary for producing robust zero remanent field for deep-submicron track widths. Introducing adequate transverse anisotropy in the head will significantly shorten the relaxation time of the magnetic moments after writing with little degradation on write efficiency.
New servo pattern for hard disk storage using pattern media
Authors: Hughes Eric C. , Messner William C.
Published: May 2003

This article compares three patterns for position error signal generation in hard disk drives: the conventional amplitude pattern, the chevron phase pattern, and the frequency pattern. The three approaches were evaluated for sensitivity to fabrication variation and noise using simulations. The motivation was to determine which of the approaches would be most suitable for preformatted media. The study showed that the phase approach was least sensitive to the dominant forms of variation in preformatting. However, the performance of the frequency pattern was only slightly worse than that of the phase, while the performance of the amplitude pattern was significantly worse.
Neutron diffraction and Mössbauer studies of CoAlxFe2−xO4
Authors: Kim Sam Jin , Myoung Bo Ra , Kim Chul Sung
Published: May 2003

Al substituted CoAlxFe2−xO4 powders were fabricated using the sol-gel method, and their magnetic and structural properties were studied with thermal analysis, x-ray, neutron diffraction, Mössbauer spectroscopy, and magnetization measurements. The crystals of the samples x=0.1 and 0.2 were found to have a cubic spinel structure with lattice constants a0=8.3864 and 8.3784 Å, at room temperature, respectively. Neutron diffraction patterns on CoAl0.1Fe1.9O4 were obtained at various temperature ranges from 10 to 816 K. Neutron diffraction at 10 K revealed a cubic spinel structure of ferrimagnetic ordering, with the effective magnetic moments of Fe3+(A)(−4.18 μB), Fe3+(B)(4.81μB), and Co2+(B)(2.98μB), respectively. The temperature dependence of the magnetic hyperfine field in Fe57 nuclei at the tetrahedral (A) and octahedral (B) sites was analyzed based on the Néel theory of magnetism. For the sample CoAl0.1Fe1.9O4, the intersublattice A–B interaction and intrasublattice A–A superexchange interaction were antiferromagnetic with strengths of JA–B=−23.3kB and JA–A=−18.0kB, respectively, while the intrasublattice B–B superexchange interaction was found to be ferromagnetic with a strength of JB–B=5.6kB. It is interpreted that the unusual reduction of magnetic moment in Fe3+(A) and a noticeable strength of the A–A interaction are closely related to the covalency effects.
Surface spin-flop transition in epitaxial Co/Re superlattices
Authors: Charlton T. , Lederman D.
Published: May 2003

Two hcp [Co/Re]x superlattices were grown simultaneously on (112̄0) Al2O3 single crystal substrates, where the number of bilayers x=20 and 21. The film growth was epitaxial in nature with the [0001] of the substrate aligned with the [0001] of the superlattice. The film interface roughness and thickness were determined by x-ray reflectivity to be σ=4.4 Å, tRe=8 Å, tCo=20 Å for x=20 and tCo=16 Å for x=21. The Co layers were antiferromagnetically coupled with an easy axis along the [0001]. As expected, the 20-bilayer superlattice exhibited both surface and bulk spin-flop transitions, while in the 21-bilayer superlattice only the bulk spin-flop transition was observed by magneto-optic Kerr effect measurements. The magnetoresistance (MR) with H∥[0001] shows an extended plateau around H=0 with H⊥I, where H is the applied magnetic field and I the sensing current. The layer-by-layer magnetization profile was found using energy minimization techniques and the MR was calculated using an empirical model. The calculations compare favorably with the MR data allowing the separation of anisotropic magnetoresistance and giant magnetoresistance components to the MR.
Magnetic field-induced degradation of magnetic properties in molecular beam epitaxy grown FeMn/NiFe exchange-coupled bilayers
Authors: Choi Y. S. , Petford-Long A. K. , Ward R. C. C.
Published: May 2003

Degradation of magnetic properties has been observed in molecular beam epitaxy grown Si(111)/Cu 2 nm/NiFe 6 nm/FeMn (2–12)nm/Cu 5 nm exchange-biased bilayers during magnetic field sweeping. When the samples are subjected to several magnetic field sweeps, there is blister-shaped deterioration of the film surface quality and the magnetometry data suggest an increasing fraction of the NiFe moments become unpinned from the FeMn layer. Comprehensive characterization using high resolution electron microscopy and electron probe microanalysis revealed that this degradation has been initiated by delamination between the NiFe and FeMn layers and crack formation as a result of magnetostrictive stress buildup during the magnetic field sweeps. Further degradation can then be attributed to the formation of the nonmagnetic FeMn oxide by oxidation of the bare FeMn around the delaminated area.
Exchange bias of NiO/NiFe: Linewidth broadening and anomalous spin-wave damping
Authors: Kuanr Bijoy K. , Camley R. E. , Celinski Z.
Published: May 2003

We studied sputtered NiO(150 nm)/NiFe exchange-biased films using Network Analyzer ferromagnetic resonance spectroscopy (NA-FMR) and Brilliouin light scattering (BLS) techniques. The complex permeability spectra were obtained for NiO/NiFe films and were fitted to the Landau–Lifshitz–Gilbert equation to determine intrinsic and extrinsic contribution to Gilbert damping, in addition to other magnetic parameters. The exchange anisotropy (HEX) was determined from the field variation data of NA-FMR resonance frequency (fres) and BLS mode frequency (fm). HEX was observed to decreases as 1/thickness, from where we derive macroscopic interfacial exchange energy JE=0.021 erg/cm2. Second, we investigated the relaxation mechanism in NiO/NiFe films from NA-FMR linewidth (Δfres) for wave vector k=0 mode and from BLS mode linewidth (Δfm) for k≠0 modes. Interestingly, we observed Δfres to increase with increasing magnetic field but Δfm was observed to decrease with increasing magnetic field. Therefore, it is confirmed that, the relaxation rate measured by FMR and BLS techniques is different. Δfres was observed to increase with decreasing NiFe thickness and follows a t−2 fit function, from which we determine the local interfacial exchange energy J1=3.3 erg/cm2.
Effects of CrMo spacer layer on thermal stability and magnetic properties in an antiferromagnetically coupled medium
Authors: Oh S. C. , Tahk Y. W. , Hong S. Y. , Lee H. J. , Lee T. D.
Published: May 2003

In this work, magnetic properties and thermal stability of antiferromagnetically coupled AFC medium with a CrMo spacer layer instead of the conventional Ru spacer layer were studied. It was found that a reduction of Mr/Ms could also be obtained in the AFC medium with a CrMo spacer layer due to the antiferromagnetic coupling, similar to the conventional AFC medium with a Ru spacer layer. Thermal stability ratio, KUV/kBT for the proposed medium was slightly smaller than that of the conventional AFC medium with a Ru spacer layer, but larger than that of a single magnetic layer medium. By a comparison of the switching field distribution and ΔM of the AFC medium with those of the conventional AFC medium, it is conjectured that the intergranular exchange coupling decreases when a CrMo is used as a spacer layer.
Effect of radio-frequency noise suppression on the coplanar transmission line using soft magnetic thin films
Authors: Kim Ki Hyeon , Yamaguchi Masahiro , Arai Ken-Ichi , Nagura Hideaki , Ohnuma Shigehiro
Published: May 2003

We demonstrated the radio-frequency (rf) noise suppressor using soft magnetic films on a coplanar transmission line from 0.1 to 20 GHz. The coplanar transmission line is composed of magnetic film/polyimide/Cu transmission line/seed layer (Cu/Ti)/glass substrate with the dimension of 50 μm width of the signal line and 3 μm thickness (characteristic impedance: 50 Ω). The magnetic films (CoPdAlO, CoZrO, and CoNbZr) as a noise suppressor are prepared by rf sputtering. The saturation magnetization of each magnetic film is about 10 kG. The magnetic anisotropy field and the ferromagnetic resonance frequency are 230, 89, and 6 Oe and 4.2, 2.5, and 0.7 GHz, respectively. The power loss of the coplanar line with magnetic films is significantly larger than without magnetic and nonmagnetic films due to ferromagnetic resonance losses.
Explosion compacted FeCo particles coated with ferrites: A possible route to achieve artificial soft ferrites
Authors: Zhao Y.-W. , Zhang Tao , Xiao John Q.
Published: May 2003

A simple and effective method has been developed to coat soft ferromagnetic particles (e.g., FeCo alloy) with a thin (1–3 nm) CoFe2O4 or NiFe2O4 layer. A general tendency of coercivity enhancement after the ferrites coating has been observed, which we ascribe to the exchange coupling between the ferromagnetic core and the ferrimagnetic coating shell. Using explosion compaction technique, the ferrite-coated particles were compacted into fully dense bulk material with density very close to the ideal value. The impedance of the compacted sample was measured in the frequency range of 1 kHz–100 MHz. The real part of measured impedance for our compacted sample is very high and decreases with increasing frequency much slower than a standard ferrite sample in the range of 35 kHz–4.2 MHz. While the hysteresis loops at 5 K for free-standing ferrite-coated particles cooled under 5 T field show a few tens Oe shift in the negative field direction indicating a typical antiferromagnetic-like exchange coupling behavior, the compacted bulk materials give symmetrical hysteresis loops in both field or zero-field cooling. This may be understood in the context of exchange coupling in random anisotropic systems. Our results are promising for high frequency magnetic devices applications.
Improvement of magnetocrystalline anisotropy of columnar structure for epitaxially grown CoCr-based perpendicular media
Authors: Saito Shin , Itagaki Norikazu , Hoshi Fumikazu , Takahashi Migaku
Published: May 2003

To improve uniaxial magnetic anisotropy Kugrain of c-plane-oriented columnar grains for CoCr-based perpendicular recording media, an epitaxial growth technique has been applied. The main results are as follows. (1) Using a Ru(3 nm) or Co60Cr40(20 nm)/C(1 nm) intermediate layer, Kugrain for a Co69Cr19Pt8B4 medium was enhanced from 2.04×106 erg/cm3 to 2.53×106 erg/cm3 or to 2.76×106 erg/cm3, respectively. (2) The enhancement of Kugrain depends on the composition of the magnetic layer when using the Co60Cr40/C intermediate layer. (3) The epitaxial growth technique is also effective to increase KugrainVact/kT. Especially, in the media with a high concentration of B or Cr, the thermal stability is improved mainly due to an increase of Kugrain rather than an enlargement of Vact.
Dependence of signal-to-noise ratio on excitation current and signal frequency in spin valve sensors
Authors: Bei Y. , Hill E. W.
Published: May 2003

Spin valves are widely used as magnetic microsensors. Their performance is limited by the presence of noise. In this article, signal and noise responses of microfabricated spin valve sensors are investigated in the linear region and in the nonlinear region close to saturation where peaks in noise output have been reported. The anisotropy of the free layer and the pinned layer are in a cross configuration. The noise of the sensor is of 1/f type at low frequency. The signal-to-noise ratio (SNR) as a function of signal frequency was measured near saturation. It is found that below 300 Hz the SNR increases almost linearly as the signal frequency increases. The variation of SNR with excitation current, measured at different frequencies, is shown. The SNR shows a nonlinear characteristic. At low frequency the increase in signal power is matched by that in noise. The SNR curve at 35 Hz shows a maximum as the current increases. The slope of other curves increases with increasing frequency. We explain these curves in a model with thermal excitation.
Exchange-biased spin valves with perpendicular magnetic anisotropy based on (Co/Pt) multilayers
Authors: Garcia F. , Fettar F. , Auffret S. , Rodmacq B. , Dieny B.
Published: May 2003

We have prepared spin valves exhibiting perpendicular magnetic anisotropy [perpendicular spin valves (PSVs)] by sputtering. These PSVs associate a “free” (Co/Pt) multilayer with a “pinned” (Co/Pt)/FeMn multilayer separated by various spacer materials (Pt, Cu, Al2O3). We carried out a comprehensive study of the magnetic and magnetotransport properties of the biased multilayers and of the complete spin valves. When the number of repeats in the (Co/Pt) exchange-biased multilayer is larger than 3, the samples present 100% remnant magnetization in the perpendicular configuration. The major hysteresis cycles exhibit two well-separated loops associated with the free and the exchange-biased (Pt/Co) multilayers. When optimized, the exchange-bias field can be larger than the coercivity of the pinned layer. Metallic PSVs with Cu spacers exhibit giant magnetoresistance but the amplitude is only of the order of 1% due to significant current shunting. In contrast, perpendicularly magnetized tunnel junctions are very promising.
Effect of grain size on the properties of the CoFe–NiFe/NiMn top spin valve
Authors: Vas’ko V. A. , Kief M. T.
Published: May 2003

The top spin valve (TSV) of NiFe 60 Å/CoFe 20Å/Cu 29 Å/CoFe 20Å/NiFe 20Å/NiMn 200 Å has been deposited on a NiFeCr seed layer on a Si/SiO2 substrate using magnetron sputtering. After deposition, the samples were subjected to ex situ magnetic annealing at 270 °C to establish the pinning field of the CoFe–NiFe pinned layer. The structure, magnetic, and magnetoresistive properties of the TSV were characterized by x-ray diffraction (XRD) and magnetic and magnetotransport measurements. It was found that the grain size of the CoFe–NiFe and NiMn layers of the TSV, as determined from XRD using Scherrer’s equation, can be controlled by changing the composition and thickness of the NiFeCr seed layer. It was also found that the grain size of the NiMn layer, and especially the CoFe–NiFe layer of the TSV, correlates with both the giant magnetoresistance (GMR) ratio (ΔR/Rmin) and pinning field of the CoFe–NiFe pinned layer. The GMR ratio increases from 3% to 12% and the pinning field decreases from 800 to 50 Oe as the CoFe–NiFe grain size increases from 90 to 210 Å.
Biquadratic coupling through nano-oxide layers in pinned layers of IrMn-based spin valves
Authors: Lai Chih-Huang , Lu K. H.
Published: May 2003

We have investigated the coupling between top and bottom pinned layers through various nano-oxide layers (NOLs) in IrMn-based spin valves. The NOLs were formed by using oxygen-plasma oxidation or natural oxidation on 1 nm metallic layers. By inserting naturally oxidized Co-NOLs in the pinned layer, strong ferromagnetic coupling through NOLs and high specularity at the NOL interface were achieved. In contrast, when the plasma-oxidized Co-NOLs were inserted, ferromagnetic coupling through NOLs disappeared, plausibly due to the formation of nonferromagnetic oxides, which led to a low magnetoresistance (MR). Insertion of naturally oxidized Ni80Fe20-NOLs showed the same results as that of naturally oxidized Co-NOLs. On the other hand, biquadratic coupling between top and bottom pinned-Co90Fe10 layers was observed by inserting plasma-oxidized Ni80Fe20-NOLs. The highest MR was obtained when the field was applied along the direction perpendicular to the field-annealing direction. Similar biquadratic coupling was also found with naturally oxidized or plasma-oxidized Fe-NOLs. We suggest that the biquadratic coupling between pinned Co90Fe10 layers through NOLs results from the coupling between Fe (or Co90Fe10) and Fe+3 oxides
Effect of very thin Cr-based seedlayer material with different affinity for oxygen on thin film media microstructure and recording properties
Authors: Yoshimura S. , Djayaprawira D. D. , Takakuwa Y. , Takahashi M.
Published: May 2003

To reduce the grain size and the media noise in longitudinal media, a sputtering process which includes the exposure of oxygen onto the surface of Cr-based seedlayers (CrTi15, Cr100, WCr75, WCr50, WCr25, and W100) with the thickness of 0.5 nm have been utilized. It is found that to effectively reduce the media grain size and improve the media signal-to-noise ratio, it is essential to utilize a very thin Cr-based seedlayer with a high melting point, a high affinity for oxygen, and which forms an island-like structure. A physical guideline for seedlayer material that is effective in reducing the grain size and the media noise is proposed.
Effects of alloying additions in the CrMo underlayer on the grain size and magnetic properties of CoCrPt longitudinal media
Authors: Lai Chih-Huang , Chen Wei-Chuan , Tsai P. H. , Ding I. P.
Published: May 2003

The alloy doping effects of the CrMo underlayer were investigated on the texture, grain size, and magnetic properties of CoCrPt longitudinal media. 5% Mn dissolving into CrMo lattices enhanced the texture of the recording layer and significantly raised the coercivity from 2200 (on the CrMo underlayer) to 3200 Oe. Further increases in the Mn content resulted in the grain growth of the recording layer, and less enhanced coercivity. The doped Zr, Ag, and Nb atoms into CrMo underlayers were segregated and led to reduction of grain size. Among them, Zr doping exhibited the most pronounced effects.