bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties and crystal structure of FeTaAIN soft magnetic materials for MIG head (abstract)
Authors: Li Yiqun , Cai Bingchu , Zeng Xianglin , Xu Dong
Published: July 2002

Fe-based nitride films have been expected as promising head core materials used for high-density magnetic recording MIG head due to their large saturation flux density combined with excellent soft magnetic properties. Recent studies found that the addition of 8–13 at. % Ta in Fe–N resulted in a remarkable improvement of thermal stability. It was also reported that small amount of Al appeared to inhibit the formation of γ′-Fe4N phase and to prevent the grain growth during annealing. In this paper, the magnetic properties and crystal structure of a new Fe–M–N soft magnetic film, FeTaAlN, has been reported. FeTaAlN films about 3 μm thick were prepared on glass substrate by dc magnetron sputtering method in Ar+N2 plasma and then annealed in vaccum. The films generally present high 4πMs (15–20 kG). X-ray diffraction results show that both as-deposited and annealed films have only two phases, an α-Fe phase with perfered (110) axis orientation and a Ta3N5 phase. Annealing is essential in lowering Hc without seriously diminishing 4πMs of the films; the film with the lowest Hc (about 0.5 Oe) has a 4πMs of above 15 kG. The peak broadenings of both the α-Fe phase and the Ta3N5 phase are observed as annealing temperature increases. Meanwhile, the (110) peaks of α-Fe shift slightly to higher 2θ value. This indicates that the interstitial nitrogen atoms come out of α-Fe lattice when the films are annealed and a part of b.c.t. α-Fe is transferred into b.c.c. α-Fe, which causes the broadening of α-Fe peak. On the other hand, the segregated nitrogen atoms may react with Ta atoms that dissolved substitutionally in α-Fe to form fine Ta3N5 particles and make the Ta3N5 peak broadened.

Thus, it is thought that the decrease of Hc is mainly due to the reduction of internal stress. The magnetostrictions of the films are on the order of 10−6. FeTaAIN film presents high saturation flux density and good soft magnetic properties even after annealing at 500 °C, and it is potentially a superior substitute for the core materials of high-density recording MIG head.
Magnetic scattering of neutrons (invited) (abstract)
Authors: Moon R. M.
Published: July 2002

Ever since the pioneering work of C. G. Shull and E. O. Wollan in the early 1950s, neutron scattering has played a crucial role in expanding our understanding of magnetic materials. Neutrons have been the preferred tool to reveal the most detailed information on the magnetic structure and dynamics of the full range of materials exhibiting magnetic properties. Some highlights of the substantial body of work during the first 45 years of magnetic scattering will be presented. Topics include magnetic structures, magnetic form factors, magnetic phase transitions, and magnetic excitations.
Strong magnetic fluctuations in transition metal oxides (invited)
Authors: Broholm C. , Aeppli G. , Lee S.-H. , Bao W. , DiTusa J. F.
Published: July 2002

Most magnets have long-range magnetic order when the thermal energy is less than the local magnetic exchange energy (T<‖ΘCW‖). Effects such as reduced dimensionality and frustration, however, can suppress the ordering transition and lead to unusual cooperative paramagnetic phases at low temperatures. We review neutron scattering experiments exploring such short-range-ordered phases in insulating transition metal oxides. We discuss (V1−xCrx)2O3, in which orbital fluctuations appear to limit spin correlations to within small ‘‘molecular’’ clusters, SrCr9pGa12−9pO19, in which geometrical frustration allows local anitferromagnetic constraints to be fulfilled without long-ranged order, and Y2BaNiO5, in which magnetic interactions occur only within chains of spins which are unable to order because of the Haldane effect. Emphasis is placed on the common features of exchange interactions in these oxides and the important role which magnetic neutron scattering has played in understanding the unusual magnetic phenomena.
Ultramicro fabrications on Fe-Ni alloy films using electron-beam writing and reactive-ion etching (abstract)
Authors: Nakatani I.
Published: July 2002

Microfabrication techniques are successfully used for semiconducting materials, while they are limited for the application to magnetic materials. For the magnetic materials, useful RIE (reactive-ion-etching) process that is essential for high-resolution microlithography has not yet been successful. In this work, RIE method useful for permalloy (80%Ni-4.5%Mo-Fe) has been newly constructed. High-resolution electron-beam writing was followed by the RIE process, leading to 250 nm line and space patterns in the permalloy film with 10 nm accuracy. In order to achieve a high-resolution electron-beam writing, amorphous carbon film was use between the resist layer and SiO2 film overlaid on the permalloy film. There are four levels in the process. Most critical step in the fabrication of magnetic material is RIE process using a rf discharged plasma of NH3-CO mixed gas. Maximum etching rate of 35 nm/min and highly anisotropic etching for the permalloy was obtained at the composition of 50 mol % NH3-CO at the pressure of 2.4×10−3 Torr. The etching selectivity ratio of permalloy to SiO2 employed as a mask was about 10. By this method, nanostructures of permalloy with highly anisotropic profile were fabricated. This method shows prominent features still for Co-Cr alloy films.
Low-energy ion beam-assisted deposition of giant magnetoresistive thin films
Authors: Guilfoyle S. J. , Pollard R. J. , Grundy P. J.
Published: July 2002

Granular and multilayer Co-Ag and NiFe-Ag thin films have been prepared by magnetron sputtering and by concurrent low-energy (0–500 eV) ion radiation-assisted deposition. The ion beam bombardment slightly increased the giant magnetoresistance of granular films and then progressively decreased it. X-ray data revealed a change in the crystalline structure of these films, dependent on the energy of the beam. Examination using transmission electron microscopy (TEM) also highlighted differences between the as-sputtered and the ion beam-assisted films. For multilayer films, TEM and x-ray analysis shows changes in the interfacial and crystal structure induced by the ion beam.
Complex anisotropies in sputtered Co90Fe10 alloy thin films (abstract)
Authors: Yun E. J. , Win W. , Walser R. M.
Published: July 2002

Among all the known magnetic materials with vanishingly small magnetostriction, alloys with the composition Co90Fe10 have the highest magnetization at 300 K. Despite this combination of useful properties, thin films of these alloys have been little studied. This study investigated the magnetic characteristics of Co90Fe10 alloy thin films deposited by rf diode sputtering. The hysteresis loops of nominal 1000-Å-thick Co90Fe10 films deposited in ≊150 Oe planar field exhibited complex biaxiality. Two, orthogonal easy axis loops with different coercivities were observed. The direction corresponding to the hysteresis loops with the smallest (largest) coercivity are referred to as the soft (easy) axis. Dual hard axes were found at ±68° on either side of the easy axis. Similar biaxial hysteresis loops were observed in Co90Fe10 films deposited by sequential sputtering from pure Co and Fe targets on static or rotating substrates, and in films deposited from a Co90Fe10 alloy target on stationary substrates. The magnetization and resistivity of the sequentially sputtered films were 19.66 kG and 18.4 μΩ cm, while those deposited from the alloy target were 19.00 kG and 14.5 μΩ cm. The biaxiality was sensitive to a number of parameters which appeared to destabilize the soft axis state compared to the hard axis states. With increasing film thickness (to 3400 Å), the biaxiality disappeared, and films deposited under similar conditions exhibited rotatable anisotropy. The biaxiality could also be reduced, and the coercivity increased, by increasing the magnetic bias applied during deposition. Films annealed at 370 °C became uniaxial when a 1.3 kOe field was applied parallel to the easy axis, and became isotropic when the field was parallel to the hard axis.

The biaxiality was enhanced, and Hc reduced, by depositing 1000-Å-thick Co90Fe10 films onto a 500 Å 80Ni20Fe underlayer. In all cases, whenever the biaxiality was eliminated, the films exhibited a rotatable uniaxial anisotropy. The biaxiality of these films likely has its origin in the coupling of two uniaxial anisotropies as previously analyzed. The deposited films are highly polycrystalline. In addition, the symmetries of the planar magnetic state obtained were the same for crystalline and amorphous substrates. Thus, it is unlikely that either uniaxial anisotropy is due to magnetocrystallinity, but are probably induced. The experimental trends observed in the study can in principle be understood in terms of a two layer model in which a rotatable, stress induced uniaxial anisotropy in an underlayer, is exchange coupled to the field induced uniaxial anisotropy of an overlayer. In this model the complex biaxiality is modified by experimental parameters which modify the relative strength and coupling strength of these anisotropies.
Characterization of iron-oxide films grown on Cu(001) and Ag(001) (abstract)
Authors: Scipioni L. , Sinkovic B.
Published: July 2002

Ultrathin films of different phases of iron oxide have been grown in UHV on Cu(001) and Ag(001) substrates by reactive evaporation and their structural and magnetic properties measured. By varying the oxygen partial pressure during growth, the oxide stoichiometry was varied from Fe/O=2/3 (fully oxidized) to Fe/O=3.5, as measured by AES and XPS, spanning: FeO, α-Fe2O3, Fe3O4, and oxide+metal films. LEED patterns and STM images reveal that all of the films grow with a (111) surface orientation with two domains rotated 90° from each other. Films with Fe/O≳1 exhibit a 16×1 superstructure induced by the presence of Fe-metal atoms localized at oxide/substrate interface, as found by XPD measurements. Their net magnetization is perpendicular to the film plane, while the films without an interfacial Fe-metal layer exhibit in-plane magnetization. The fully oxidized films (α-Fe2O3) exhibit an antiferromagnetic behavior. Temperature dependences of MOKE signal from thin Fe3O4 films indicate enhancement of Verwey transition.
Melt-spun Pr2Co14B/Co nanocomposite magnets
Authors: Withanawasam L. , Panagiotopoulos I. , Hadjipanayis G. C.
Published: July 2002

We have successfully prepared a new nanocomposite magnet consisting of a mixture of a magnetically hard Pr2Co14B phase and a soft Co phase using the technique of melt spinning. The final microstructure with the above phases is formed after annealing the melt-spun ribbons through an intermediate transformation to the metastable TbCu7-type structure. Optimum coercivity of 4.3 kOe was observed in a sample with the composition Pr8Co83Nb1B8 after heating above 775 °C.
Recording characteristics of Co-γFe2O3 perpendicular magnetic recording media
Authors: Yamamoto S. , Andou T. , Kurisu H. , Matsuura M. , Doi T. , Tamari K.
Published: July 2002

The recording characteristics of Co-γFe2O3 perpendicular magnetic recording hard disk media were investigated. Sliding contact recording was performed to evaluate the intrinsic high-density recording performance of the media with using a metal-in-gap-type ring head. The half-voltage density D50 of 176 kFRPI and low-density reproduced voltage Ep of 143 nVp-p/[turn μm (m/s)] were obtained for the optimal medium whose Co-γFe2O3 layer thickness was 0.13 μm and perpendicular coercivity was 1800 Oe. The pass wear durability test was performed at 2 m/s, or at a disk rotation of 830 rpm. The reproduced voltage did not decrease with time, and scratches and damage were not observed on the tested track even after 18 000 000 passes. The Co-γFe2O3 medium is one of the candidates for ultrahigh-density recording media because of its specific advantages; superior high density recording performance and hardness tolerable for sliding contact use.
Application of Barkhausen effect measurements for detection of near surface stress (abstract)
Authors: Kaminski D. A. , Jiles D. C.
Published: July 2002

Barkhausen effect emissions have been shown to be dependent on stress in previous work. This paper shows how the technique has been applied to evaluation of stress in automobile crankshafts. These components often fail prematurely due to residual tensile stress in the surface of the components, which leads to cracking and sudden fatigue failure. The measurements were made using an excitation frequency of 8 or 128 Hz with signal detection bandwidths of 3–15, 20–70, and 70–200 kHz. These corresponded to nominal magnetic field penetrations of 0.2, 0.07, and 0.02 mm. Results showed that measurements from the near surface (0.02 mm) were most sensitive to stress. A number of calibration experiments on different materials confirmed this result. In addition, it was found that low values of the root-mean-square Barkhausen voltage correlated with low tensile strength of the material. This measurement could, therefore, be used for detection of components that were likely to encounter early failure. A calibration of the Barkhausen voltage signal as a function of stress was obtained and this was in accordance with earlier theoretical calculations.
A two-dimensional single sheet tester incorporating controlled magnetization direction
Authors: Dalton J. J. , Liu J. , Moses A. J. , Horrocks D. H. , Basak A.
Published: July 2002

The existence of magnetic anisotropy in electrical steels has long been known to designers of electrical machines. However the effect of this anisotropy in real devices has not to date been studied in any great depth. Finite element modeling software is proving useful for designing such electrical machines, however, the material models which form the heart of the process are based on limited data and indeed often make incorrect assumptions regarding the anisotropic nature of the machine core. This article discusses shortcomings of present anisotropic material models, suggests what is needed to overcome these shortcomings and presents one such two-dimensional magnetic test system capable of generating the materials data required. The method by which the data is obtained is described and measured results are presented, indicating some of the features of the system.
Magnetic and phase transformation studies in Nd15DyFe75(C,B)9 cast alloys
Authors: Murthy A. S. , Panagiotopoulos I. , Hadjipanayis G. C.
Published: July 2002

Previous studies have shown that high coercivities can be achieved in cast Nd–Fe–C alloys through an annealing heat treatment at 900 °C, which causes a peritectoidal transformation from Nd2Fe17Cx to Nd2Fe14Cx. We have studied the characteristics of this transformation in cast Nd15DyFe75(C,B)9 alloys. Optimum coercivities were obtained by annealing for 6 h at 900 °C. A highly faulted carbide phase was identified in samples annealed for 5 min at 900 °C. From electron diffraction investigations, this phase was identified to be hexagonal with lattice parameters, a=0.48 nm and c=0.81 nm. The development of coercivity in the various stages of transformation is related to the crystal structure and microstructure developed in the transformation. The presence of α-Fe in samples with increased Fe content leads to reduced coercivities.
Homogeneous magnetization dynamics below T
c of EuO: Effects of spin waves and anisotropy
Authors: Flosdorff A. , Görlitz D. , Kötzler J.
Published: July 2002

Using a broadband reflectometer, the dynamic susceptibility χ(ω) of a EuO sphere has been measured from 0.3 to 20 GHz at temperatures ranging between 4.2 K and Tc=69.5 K. For fields applied parallel to the hard [100] direction one heavily damped Lorentzian is observed which for internal fields H larger and smaller than the anisotropy field arises from the dynamics of the homogeneous and the wall magnetization, respectively. For fields near HA applied along one of the easy [111] axes, both processes contribute to χ(ω) but with increased and decreased values of the resonances and damping frequencies of the homogeneous and wall processes, respectively. The homogeneous process is identified by the static susceptibility χz(0) which obeys the H−1/2 divergence due to spin waves. Its line shape is explained by a frequency variation of the kinetic coefficient of the relaxation damping, Lz(ω)=Lz(0)/[1+(iω/ωc)]. The characteristic frequency, ωc/2π=18 GHz, turns out to be independent of temperature and magnetic field, and is related to the relaxation rate of the long-wavelength longitudinal magnetization fluctuations. The field and temperature variation of the kinetic coefficient of the relaxation can be described by the same scaling function, Lz(χz(T,H)), as previously observed above Tc. Based on results of numerical mode-coupling work, this behavior is associated with the dipolar anisotropy of the magnetic fluctuations.
Concentration-dependent critical behavior in dilute ferromagnetic Fe1−xAsx[S2CN(C2H5)2]2Cl
Authors: DeFotis G. C. , Coffey G. A. , Coker G. S. , Marmorino J. L. , Beers K. L. , Chandarlapaty S. , Brubaker W. W. , Pugh V. J. , Carling S. A. , Day P.
Published: July 2002

The dilute insulating ferromagnet Fe1−xAsx[S2CN(C2H5)2]2Cl is examined in single crystal form for several compositions spanning the range x=0.014 to x=0.040. For x=0.0143 and x=0.0162 crystals, the inverse molar susceptibility along the [101] ferromagnetic easy axis is quite linear in temperature for T greater than a few times Tc. In the case of x=0.0313 and x=0.0402 crystals, in contrast, significant curvature appears in χ−1vs T throughout the 20–80 K temperature range. The initial (low-field) susceptibility along [101] for each crystal is measured in the critical region and analyzed via a standard power law form χ0=Γt−γ, where t=(T−Tc)/Tc. Tc decreases with increasing x, but somewhat slowly. The critical exponent γ increases with increasing x, from 1.19±0.01 near x=0.014 to 1.22±0.01 near x=0.040. The prefactor Γ is significantly smaller for the two higher As crystals, probably due to increased disorder. The variation in γ is not entirely unexpected, since the pure material, which is a candidate Z2xS1 system, has an unusual set of critical exponents, including a large positive α. Thus new critical behavior on dilution can occur by the Harris criterion.
Resolution of conflicts concerning Fe16N2 (abstract)
Authors: Arrott A. S.
Published: July 2002

The 1994 3M-Intermag meeting featured an invited session on Fe16N2 in which many of the research workers in this exciting field put forth apparently conflicting views on the nature and possibilities for the use of, perhaps, the most promising transition metal based alloy for magnetic applications. The debate centers on the promise of 3μB per atom at transition metal densities if pure Fe16N2 could be made. A particularly compelling resolution of the conflicts was not mentioned at the meeting, even though it has been in the past. The conflict arises primarily from the original classification of Fe16N2 as a phase denoted by α″ to distinguish it from Fe8N classified as a phase denoted by α′ and the substitutional alloy α-Fe(N). The conflicts arise because data are interpreted as a mixture of two phases α′ and α″. For any measured property, it is then sufficient to know the ratio of the two component phases for two different compositions to deduce the apparent properties of the individual phases. But this is not the case. The distinction between α″ and α′ is not that of two separate phases but, rather, the end points of a continuum characterized by the degree of order. This makes it necessary to produce the fully ordered state in order to determine its properties, unless it is possible to have enough data about those properties for various degrees of order to justify extrapolation to the fully ordered state. The most ordered Fe16N2 is produced using molecular beam epitaxy. It also shows the highest magnetic moments. The high magnetic moments are supported by Mössbauer measurements of large hyperfine fields in bulk materials (not the molecular beam epitaxy material) and by some of the theoretical calculations for the ordered state.

One of the criticisms of the molecular beam epitaxy work is that those thin films do not decompose into Fe4N and Fe(N) on heating as do bulk alloys of the same composition. (The implication is that the thin films contain something else.) But this criticism is not valid, simply because one cannot predict the stability of a highly ordered state from observations of a weakly ordered state. This is particularly the case where the ordering is accompanied by large lattice distortions. The existing literature is analyzed to extract the dependence of magnetic moment on the degree of order. These considerations lend support to those who are pursuing Fe16N2 for its potential for producing a magnetic material with 3μB per atom at transition metal densities. How to increase the degree of order in bulk materials becomes a central concern.
Synthesis of nanometer-scale boron phosphide whiskers by vapor–liquid–solid chemical vapor deposition
Authors: Schroten E. , Goossens A. , Schoonman J.
Published: July 2002

Densely packed layers of boron phosphide whiskers have been grown on quartz, tungsten, and graphite substrates by chemical vapor deposition. Nickel and silver acted as liquid forming agents in a vapor–liquid–solid growth mechanism. The formed whiskers have diameters typically between 10 and 5000 nm, depending on the substrate material, the seeding metal, and the synthesis temperature. The length of the whiskers can be as large as 0.1 mm. High-resolution transmission electron microscopy imaging revealed that the whiskers are single crystalline with a large number of twin faces.
Suppression of biquadratic coupling at the Cr Néel temperature in Fe/Cr(001) superlattices (invited) (abstract)
Authors: Fullerton Eric E. , Adenwalla S. , Felcher G. , Sowers C. H. , Bader S. D. , Robertson J. L. , Berger A.
Published: July 2002

We present the effects of antiferromagnetic (AF) order of the Cr spacers in Fe/Cr(001) superlattices on the interlayer coupling of the Fe layers. AF order of the Cr spacers is suppressed for layer thicknesses less than 42 Å. For ≳42 Å of Cr, the Néel temperature (TN) increases rapidly and asymptotically approaches the bulk value for thick Cr spacers as characterized by a transition-temperature shift exponent λ=1.4±0.3. Neutron diffraction confirms both the AF order of the Cr layers in superlattices with 62, 100, and 200 Å thick Cr layers, and the existence of the incommensurate, transverse spin-density-wave magnetic structure whose nesting wave vector is equal to that of bulk Cr. The AF ordering of the Cr results in anomalies in a variety of magnetic properties, including the interlayer coupling, remanent magnetization, coercivity, and magnetoresistance. Most strikingly, the 90° or ‘‘biquadratic’’ coupling of the Fe layers observed for T≳TN is suppressed below TN as confirmed by polarized neutron reflectivity. This behavior can be understood in terms of the combination of finite-size and spin frustration effects at rough Fe/Cr interfaces.
Intrinsic broadening of the modulation-related reflections in a high-quality Bi2Sr2CaCu2Oy crystal
Authors: Wu Wenbin , Zhu Jingsheng , Sun Xuefeng , Zhao Xiaoru , Zhou Guien , Li Xiao-Guang , Zhang Yuheng
Published: July 2002

The intensity distribution of the satellites from the incommensurate modulation 0.21b*+c* and the additional modulation-related reflections, described by 0.21b* and incompatible with the generally accepted Bbmb symmetry, have been studied in exactly the b*c* plane by means of x-ray diffraction for a high-quality Bi2Sr2CaCu2Oy crystal. The mosaic spread of this crystal, with only a single large domain, is as small as 0.15°. Broadening solely along the c* direction of the satellites, especially the additional modulation-related reflections, was clearly observed and further confirmed by a monochromatized x-ray Laue photograph, which should be intrinsic to the superstructure in bulk Bi2Sr2CaCu2Oy crystals. Apart from the broadening relative to the Bragg reflections, for the first time a weak diffuse feature fundamental to the satellites was also clearly detected.
Calorimetric single particle detection in high magnetic fields at low temperatures
Authors: De Moor P. , Camps J. , Schuurmans P. , Severijns N. , Vanderpoorten W. , Van Geert A. , Vanhellemont Y. , Vanneste L. , Wouters J. , Coron N. , Jegoudez G. , Leblanc J.
Published: July 2002

High resolution calorimetric detection of single particles in magnetic fields up to 8 T at temperatures <0.1 K is reported. A careful study of heavily doped Si and Ge thermistors reveals an extremely large positive magnetoresistance in the variable range hopping conductivity regime. This phenomenon is used to optimize the impedance and the temperature sensitivity of a calorimetric detector. Initial experiments show an energy resolution full width at half maximum of 800 eV for 62.5 keV conversion electrons and an energy threshold of <400 eV.
Frequency upshifting with power intensification of a whistler wave by a collapsing plasma medium
Authors: Kalluri D. K.
Published: July 2002

A source wave is assumed to be present in an unbounded magnetoplasma medium. The parameters are such that the refractive index is greater than one. A wave propagating in the ‘‘whistler mode’’ is an example of such a wave. By collapsing the ionization, it is possible to obtain a frequency upshifted wave with power intensification. Two limiting cases of (i) sudden collapse and (ii) slow decay are considered. In either case, it is shown that the final upshifted frequency is the source frequency multiplied by the refractive index. When the source frequency is much less than electron gyrofrequency the refractive index nw is quite large and the electric field is intensified by a factor of nw/2 for the case of sudden collapse and by a factor of nw/√2 for the case of slow decay. The corresponding intensification factors for the power density are nw/4 and nw/2. A physical explanation of the results, based on energy balance, is offered.
Coimplantation of silver and halogens in thin SiO2 films
Authors: Pham M. T. , Möller D. , Hüller J. , Albrecht J.
Published: July 2002

Silver and halogens, Br and Cl, were coimplanted into thin SiO2 films sandwiched on a field-effect structure. Compositional depth distribution and chemical states of the implants were measured by means of Auger electron spectroscopy and x-ray photoelectron spectroscopy. Ion sensitivity of the surface layer was measured using a capacitive field-effect structure, electrolyte–insulator– semiconductor. Silver halides were found to be incorporated in SiO2 in addition to metallic silver. The distribution of the implanted silver sensitively responds to the reactive halogens subsequently implanted into a silver-containing surface. The solid phase of silver halides with a concentration of less than 10 at. % delivers a distinct ion sensing characteristic toward halide ions in an electrolyte solution, comparable to that of bulk material.
Giant magnetoresistance as a probe of interfacial electronic character (invited) (abstract)
Authors: Parkin S. S. P.
Published: July 2002

The giant magnetoresistance (GMR) effect exhibited by magnetic multilayers and related structures is very sensitive to the nature of the interfaces between the magnetic and nonmagnetic layers. We have explored the dependence of GMR on the electronic character of these interfaces by inserting additional thin magnetic layers at the interfaces. Insertion of thin Co layers in Ni–Fe/Cu/Ni–Fe or thin Ni–Fe layers in Co/Cu/Cu exchange biased sandwiches leads to an increase or decrease, respectively, in the magnitude of the GMR effect; the variation is monotonic with thickness of the inserted layer. In contrast, insertion of thin layers of Fe at the Ni–Fe/Cu interfaces in Ni–Fe/Cu/Ni–Fe exchange biased sandwich structure results in a nonmonotonic variation of GMR with Fe layer thickness; for intermediate thicknesses in particular the GMR is substantially reduced. The magnetism and structure of the Fe layers is explored in related sputter-deposited single-crystalline Ni/Fe/Cu thin-film structures prepared using thin Fe/Pt seed layers grown at high temperatures on single crystalline polished wafers of MgO(100), MgO(110), and (0001)Al2O3. The magnetism of the Ni, Fe, and Cu layers is examined using x-ray magnetic circular dichroism (XMCD) and the structure of the Fe is analyzed using extended x-ray absorption fine structure (EXAFS) studies. These experiments show that the Fe moment varies nonmonotonically with thickness resulting from a structural phase transition from fcc to bcc Fe with increasing thickness.

The Fe displays a very small magnetic moment for an intermediate range of Fe thickness for which the Fe structure is fcc. This range of thickness depends on the crystalline orientation of the Fe. It is within this same range of thickness that the GMR is suppressed in related exchange biased sandwich structures. Interestingly we find that such nonferromagnetic layers of fcc Fe can be used as spacer layers in magnetic multilayers of, for example, Ni/Fe. These multilayers display both antiferromagnetic interlayer coupling of the Ni layers and giant magnetoresistance, which each oscillate as a function of Fe thickness.
Quantized writing processes in quantum magnetic disks (abstract)
Authors: Suriono Usman , Chou Stephen Y.
Published: July 2002

It has been suggested that the writing process in quantum magnetic disks (QMDs) is quantized: a write head either writes perfectly the entire bit which is a discrete single-domain element isolated from other bits with nonmagnetic materials, or it does not write the bit at all. This article presents the micromagnetics demonstration of this quantized writing process. In the simulation, each QMD bit is assumed to be a polycrystalline cobalt bar of 700 nm long, 50 nm wide, and 30 nm thick, and to be oriented parallel to the disk surface. To obtain the dynamic motion of the magnetization structure of the bit, iterative energy minimization algorithm and the Landau–Lifshitz–Gilbert equation were used. The write head field is assumed to be parallel to the long axis of the bar and uniform with a strength of 2.5 times the bar coercivity. The write field has a width the same as that of the bar but a length that is only three-quarters of the cobalt bar length. It was found that even though the writing field size was smaller than the size of the bar, the magnetic moment of the entire single-domain bar can be switched from one direction to another, giving a perfect writing. The switching process occurred roughly in two stages. First, the magnetic moments got reversed in the region where the write field was applied. Second, driven by exchange force and shape anisotropy, the reversal propagated out of the write field region and reached the entire bit.

It was also found that if the overlap of the writing field with the bar was less than one-quarter of the bar length in the bar long axis or four-fifths of the bar width in the bar short axis, the writing field would only temporarily perturbs the magnetic moment distribution of the bar. When the write field was removed from the bar, the magnetic moment of the bar would return to its original state. The quantized writing process in the QMD will allow the use of a smaller and therefore faster write head, can avoid the errors due to misplacement and fringing field, hence is suitable for ultrahigh-density storage.
Anomalous temperature dependence of interlayer coupling in Fe/Si multilayers (abstract)
Authors: Michel R. P. , Chaiken A. , Wall M. A. , Dykes J. W. , Ankner J. F. , Kaiser H.
Published: July 2002

The magnetic coupling of the Fe layers in Fe/Si multilayers strongly depends on the morphology of the iron-silicide interlayer that forms during deposition. Antiferromagnetic interlayer coupling is only observed in Fe/Si multilayers with crystalline interlayers in the CsCl structure. Recently, it has been shown that single layers of Fe–Si in the CsCl structure can be grown epitaxially on Si over a range of stoichiometries. FeSi films are reported to be Kondo insulators below 50 K. We find evidence of a magnetic phase transition in antiferromagnetically coupled Fe/Si multilayers. Ms measured in a constant applied field of 50 kOe shows T3/2 behavior down to 10 K. However, M(T) at a lower constant field peaks around 50 K and decreases at lower temperature, indicating enhanced antiferromagnetic coupling or a phase transition. The remanent magnetization increases monotonically with decreasing temperature and has been explained by invoking thermally activated coupling. However, the saturation field also increases with decreasing temperature, indicating a stronger antiferromagnetic interaction. We explore the suggestion that the interlayer coupling is biquadratic in nature. Polarized neutron reflectometry has also been used to get a clearer picture of the complicated magnetic behavior of this multilayer system.
Nuclear magnetic resonance study of expanded lattice permanent magnet nitrides and carbides at high pressure
Authors: Kapusta Cz. , Lord J. S. , Tomka G. J. , Riedi P. C. , Buschow K. H. J.
Published: July 2002

The nuclear magnetic resonance spin-echo spectra of 89Y and 147Sm for Y2Fe17, Y2Fe17C0.4, Y2Fe17C1.5, Y2Fe17N2.5, Y2Fe17CN1.5, Y2Fe17H1.6, and Sm2Fe17 have been measured at pressures up to 10 kbar at 4.2 K. A reduction of the magnitude of the valence electron polarization contribution to the effective field Be at Y and Sm sites with pressure is observed. The effect is strongly related to the nearest neighbor environment of the site. A significant reduction of ∂B/∂p is observed for the sites with nitrogen neighbors. Carbon increases (decreases) ∂B/∂p in the rhombohedral (hexagonal) structure of the compound. A decrease of the lattice electric field gradient at the Sm site in Sm2Fe17 with pressure is observed. A corresponding decrease of the crystal electric field coefficient A02 at the Sm site with pressure of 0.7% per kbar is derived, indicating an anisotropic compressibility of the material.
Reorientational transition of the magnetic anisotropy and antiferromagnetic coupling of Co/Cr(001) superlattices
Authors: Zeidler Th. , Schreiber F. , Zabel H.
Published: July 2002

We have measured the magnetic anisotropy of high quality Co/Cr(001) superlattices as a function of the Co thickness using the magneto-optical Kerr effect (MOKE) and a torsion magnetometer. The samples grown by molecular beam epitaxy exhibit a reorientational transition of the easy axis from in-plane for large Co thicknesses (tCo≥14 Å) to out-of-plane for 10 Å≤tCo≤14 Å and back again to the in-plane orientation for tCo≤10 Å. We provide evidence that this reorientational transition of the magnetization direction is due to a sign change of the interface anisotropy constant induced by a concomitant structural phase transition of the Co layers from hcp to bcc with decreasing Co layer thickness. We have observed antiferromagnetic alignment of the Co layer magnetization both for in-plane and perpendicular magnetic anisotropy. The first maximum of the antiferromagnetic interlayer interaction occurs at tCr=6 Å, which is in a good agreement with the results for Fe/Cr(001). In order to theoretically describe the spin structure of the antiferromagnetic coupled multilayers we have performed absolute minima calculations of the angle dependent anisotropy energy. In contrast to trilayer systems we found highly asymmetric spin structures in the superlattices during the remagnetization process.
Effect of stoichiometry on the dominant deep levels in liquid phase epitaxially grown n-type Al0.3Ga0.7As doped with Te
Authors: Murai Akihiko , Nishizawa Jun-ichi , Oyama Yutaka , Suto Ken , Chubachi Noriyoshi
Published: July 2002

Photocapacitance (PHCAP), deep level photoluminescence (PL), and Hall effect measurements are applied to the liquid phase epitaxially grown n-Al0.3Ga0.7As crystals followed by an annealing at 900 °C for 1 h under controlled arsenic vapor pressure. Photocapacitance measurements reveal the dominant deep level at Ec−0.5 eV. The Ec−0.5 eV level density increases with increasing applied arsenic vapor pressure during annealing. Deep level PL bands at ∼1.21 and ∼1.36 eV are also detected and the PL band intensity increases with increasing arsenic vapor pressure and the content of doped impurity Te. In conjunction with the results of Hall effect measurements, the origin of the native defects in n-AlGaAs is discussed in view of the deviation from the stoichiometric composition of the AlGaAs ternary alloy system.
Identification of a high-temperature magnetic phase transition in ball-milled and compacted nanocrystalline Fe-Cu alloys
Authors: Shull R. D. , Cline J. P. , Baker I. , Liu F.
Published: July 2002

Fex–Cu100−x alloys (40≤x≤90) prepared by ball milling nominally pure (99%) Fe and Cu powders and warm compacted (at ∼300 °C) were investigated by differential scanning calorimetry, scanning electron microscopy, x-ray diffraction, and magnetic susceptibility measurements. Both fcc and bcc diffraction peaks (indicative of pure Fe and Cu) showed that the mixtures were still two phase even after milling for 400 h, and that they were comprised of 6–10 nm diameter grains. Surprisingly, however, calorimetric measurements indicate the presence of a large endothermic peak for these nanocrystalline composites on heating near 600 °C and an exothermic peak near 400 °C on cooling. Magnetic measurements show that these materials are ferromagnetic at room temperature and remain so (with decreasing saturation magnetization) up to near the Curie point of α-Fe, 770 °C. However, near 600 °C on heating (and also near 400 °C on cooling), the magnetic susceptibility indicates the existence of a magnetic phase change. High-temperature x-ray diffraction data show these effects are due to the oxidation of Fe to form magnetite which subsequently decomposes into wustite. The thermal hysteresis observed in the magnetic and thermal data is due to the sluggishness of the latter transformation. Furthermore, heating to temperatures in excess of 600 °C results in the dissolution of Cu into the iron oxides which does not reprecipitate on cooling.
Small-angle neutron scattering behavior of Fe91Zr9 glass under magnetic field
Authors: Barquín L. Fernández , Sal J. C. Gómez , Kaul S. N. , Barandiarán J. M. , Gorría P. , Pedersen J. S. , Heenan R.
Published: July 2002

Zero-field and in-field small-angle neutron scattering measurements over a wide Q range are presented for the Fe91Zr9 metallic glass in the 10–290 K range. Two transitions observed at 210 K and around 60 K are related to Tc and reentrant transition temperature, respectively. The spectra (0.003 Å−1<Q<0.5 Å−1) reveal the existence of an important contribution at the lowest Q values and at least two humps in the entire curves. The application of the magnetic field results in an anisotropic signal, and a global decrease of intensity. The magnetic field drastically reduces I(Q) in the region for Q<0.04 Å−1, but not so strongly at larger Q values (even at H=4 T), becoming more evident a remaining hump. Its origin can so far be uniquely explained by the models dealing with the existence of clusters embedded in a ferromagnetic matrix.
Lanthanide and boron oxide-coated α-Fe particles
Authors: Li Feiyue , Bao Xiaohua , Metzger Robert M. , Carbucicchio Massimo
Published: July 2002

To increase the coercivity of α-Fe particles, needlelike goethite crystals were first coated with different Ln3+ ions (Ln=La,Nd,Sm,Gd,Dy,Eu) plus B3+, then reduced to α-Fe under H2. The magnetic moment of the particles depends upon the Ln and B contents and temperature. Both powder x-ray diffraction and Mössbauer spectra indicate the existence of a crystalline FeO phase; the FeO content decreased as the reduction temperature increased. A phase with no hyperfine splitting was also detected in the Mössbauer spectra, which may be superparamagnetic α-Fe or amorphous iron oxide; the amount of this phase decreased as the reduction temperature increased. The temperature dependence of the coercivity of these B- and Ln-coated particles was steeper than for particles coated with silica: this suggests a coercivity mechanism other than shape anisotropy.
Magnetic and electrical properties of CoFeSiB:O thin films near the percolation threshold
Authors: Banerjee R. , Valanju A. P. , Choe G. , Walser R. M.
Published: July 2002

Nanocomposite thin films with coexisting magnetic metal and magnetic nonmetal amorphous phases were synthesized by reactively sputtering CoFeSiB:O thin films with a large silicon (15 at.%), and varying oxygen concentrations. The microstructure, magnetization, and hysteresis loops were measured for films with resistivities near the metal–nonmetal transition. These data revealed that, below the metal–nonmetal transition, conductive transport was along the soft magnetic, metallic backbone of the percolation network; the nonmetal phase was a discontinuous, randomly distributed, hard magnetic oxide. The metallic resistivity and exchange anisotropy were both maximized in a nanocomposite with a resistivity at the metal–nonmetal transition.
Magnetic properties of polycrystalline Sm2−xCexCuO4−y at high magnetic fields
Authors: Jardim R. F. , Westphal C. H. , Cohenca C. H. , Ben-Dor L. , Maple M. B.
Published: July 2002

We have performed measurements of ac magnetic susceptibility χac as a function of temperature and magnetic field on polycrystalline specimens of Sm2−xCexCuO4−y (0.15≤x≤0.18) prepared from a sol-gel precursor. All the samples studied show a striking double resistive superconducting transition. One of the resistive transitions occurs at a higher temperature Tci and the other one at a lower Josephson-coupling temperature Tcj. Magnetic measurements reveal the appearance of superconductivity below Tcj which is evident from the resistive component χ″ which peaks only at Tcj. Measurements made on pellets and crushed samples with average grain size ∼1 μm show essentially the same features. This suggests that Josephson coupling occurs inside physical grains with dimensions close to 5 μm. We have also utilized the behavior of the peak in the χ″ component as a function of applied magnetic fields to build a H vs T phase diagram for these compounds. Some interesting features were observed in this H vs T phase diagram: (1) a Hα, α=2/3, dependence at low applied magnetic fields (H≤2 kOe) and high temperatures, and (2) an abrupt increase in the magnitude of the exponent at high fields and low temperatures. The behavior at low fields and high temperatures suggests that the magnetic response of the system is mainly controlled by a disordered Josephson network. Possible connections between these two different behaviors are discussed.
Alternating current susceptibility studies of Tb ordering in Pb2Sr2TbCu3O8
Authors: Wu S. Y. , Li W.-H. , Lee K. C. , Meen T. H. , Yang H. D.
Published: July 2002

The magnetic response of the Tb spins in Pb2Sr2TbCu3O7 to the applied magnetic field have been studied by ac susceptibility measurements. Both the in-phase component χ′ and the out-of-phase component χ″ of ac susceptibility are found to be sensitive to the frequency but not to the strength of the driving field. At high temperatures χ′ exhibits Curie–Weiss behavior, it departs from this behavior as the magnetic correlations between the Tb spins develop, and a cusp which is typical of antiferromagnetic ordering is clearly revealed at lower temperatures. The correlated Tb spins respond ‘‘better’’ to a driving magnetic field which has a lower frequency. The relative maximum of the dχ′/dT versus T plot matches to the TN determined using neutron diffraction measurements. This relative maximum continues to occur at the same temperature as the frequency of the driving field is varied. It, however, shifts to a lower temperature as a dc external field is applied, indicating the antiferromagnetic coupling between the Tb spins are weaken by the dc field. Moreover, the thermal behavior of χ″ exhibits a well-defined peak around the transition temperature, and a dc field of strength 5 kOe smears the peak.
‘‘Standing’’ diffusion of electromagnetic fields in superconductors with gradual resistive transitions
Authors: Mayergoyz I. D. , Neely M.
Published: July 2002

Electromagnetic field diffusion in superconductors with gradual resistive transitions may exhibit a peculiar (anomalous) mode which does not exist in superconductors with sharp (ideal) resistive transitions. This is a ‘‘standing’’ mode. In the case of this mode, the electromagnetic field on a superconductor boundary increases with time, while the region occupied by the electromagnetic field within the superconductor does not expand. In this paper, an exact analytical solution to the appropriate nonlinear diffusion equation is derived. It is demonstrated that this solution can be physically interpreted as the standing mode. The standing mode solution is also obtained by using a ‘‘rectangular profile’’ approximation and these two results are compared.
Direct observation of domain walls in NiFe films using high-resolution Lorentz microscopy
Authors: Wong Bunsen Y. , Laughlin David E.
Published: July 2002

A novel approach to observe the interaction between magnetic domain wall and nanoscale microstructural features is demonstrated. The method is based on Focault mode Lorentz microscopy and utilizes a Gatan energy image filter to provide additional magnification. A postexperimental image processing technique was applied to separate lattice diffraction from that induced by magnetic domains. The effect of NiFe thickness on the width of a 180° Néel wall has been studied. It was found that the thickness dependence has a similar profile to the theoretically predicted trend but the actual wall thickness is smaller than the calculated values.
Determination of the energy dependence of the off-diagonal terms of the dielectric tensor by means of M2,3 reflection MCD measurements (abstract)
Authors: Höchst Hartmut , Zhao Dai , Huber David
Published: July 2002

We present the first magnetic circular dichroism (MCD) measurements around the M edges of 3d metals utilizing SRCs recently developed quadruple reflection polarizer system. The reflection polarizer converts linearly polarized light by means of the phase shift between s- and p-reflections into either left or right circular polarized radiation. The concept of the phase shifter has been tested at a bending magnet beam line at the Aladdin storage ring using the M2,3 absorptions of magnetically ordered thin films of Fe, Co and Ni. The normalized MCD signal e.g., (IR−IL)/0.5*(IR+IL) is on the order of several % from peak to peak and scales linearly with the magnetic moments. The shape of the reflection MCD signals has a very pronounced angular dependence with a maximum around a reflection angle of θ=60°–65°. The main trends in the angular dependence of the reflection MCD signal can be verified by model calculations. The model also allows us to extract the energy dependence of the off-diagonal terms in the dielectric tensor from the experimental data. The potential use and high sensitivity to variations in the local magnetic environment will be demonstrated with high resolution measurements of several ferrimagnetic compounds.
Finite element modeling of powder aligning and multipole magnetizing systems for anisotropic bonded permanent magnets
Authors: Riley C. D. , Jewell G. W. , Howe D.
Published: July 2002

The manufacture of anisotropic bonded permanent magnets involves the application of an aligning field during the moulding of the magnet, and in most cases, particularly those involving anisotropic NdFeB powder, the subsequent application of a considerably larger magnitude magnetizing field, which in turn is usually produced by a capacitor discharge magnetizer and a geometry specific fixture. A finite element based method for modeling both of the production stages is presented, and the method is validated by a case study, which includes extensive material characterization on a four-pole anisotropic NdFeB cylinder.