bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties and martensitic transition in annealed Ni50Mn30Al20
Authors: Mañosa Lluís , Planes Antoni , Acet Mehmet , Duman Eyup , Wassermann Eberhard F.
Published: May 2003

We have studied the effect of heat treatment on the magnetic properties and on the martensitic transition of the Ni50Mn30Al20 alloy. A mixed L21+B2 state is obtained in the as-prepared sample, while no L21 order is retained in the sample quenched from high temperature. For the two heat treatments, the samples order antiferromagnetically, but there is evidence of coexisting ferromagnetic interactions. A martensitic transition occurs below the magnetic one for quenched samples. However, the martensitic transition is inhibited in the as-prepared sample.
Dynamic magnetomechanical properties of [112]-oriented Terfenol-D/epoxy 1–3 magnetostrictive particulate composites
Authors: Or S. W. , Nersessian N. , McKnight G. P. , Carman G. P.
Published: May 2003

The dynamic magnetomechanical properties of a Terfenol-D/epoxy 1–3 magnetostrictive particulate composite fabricated using 49% volume fraction of needle-shaped, [112]-oriented Terfenol-D particles were investigated as a function of magnetic bias field (HBias). A nonoriented composite with 51% volume fraction of irregular-shaped, ball-milled Terfenol-D particles was also prepared and characterized for comparison. It was found that the composites exhibit a similar qualitative trend in dynamic strain coefficient (d33) and dynamic susceptibility (χ33) with the oriented type possessing much higher values than the nonoriented type for all HBias. Data for the ratio d33/χ33 indicated that these increments in d33 and χ33 in the oriented composite are mainly attributed to [112] particulate crystallographic orientation.
Magnetism, elasticity, and magnetostriction of FeCoGa alloys
Authors: Dai Liyang , Cullen James , Wuttig Manfred , Lograsso T. , Quandt Eckhard
Published: May 2003

It is known that the substitution of Co for Fe gives rise to increases in magnetization and Curie temperature, not only in the bcc metals, but also in intermetallic compounds and alloys as well. With the expectation that this is the case in Co-substituted FeGa, we measured magnetization, Curie temperature, magnetostriction and elastic constants of a series of polycrystalline FeCoGa ternary alloys with up to 17% Ga and up to 10% Co. The magnetostriction at saturation for Fe0.93−xCo.07Gax increases to 90 ppm for x=0.17. For larger percentages of Co, the rise in magnetostriction is not as sharp as it is in the 7% case. The shear elastic modulus decreases with Ga, again in keeping with the results for FeGa. The magnetostriction and the elastic constants are sensitive to sample preparation for the high-Ga material. We conclude that the substitution of small (<0.10) percentages of Co for Fe in bcc FeCoGa alloys enhances the magnetic and magnetostrictive properties of the parent FeGa material.
Influence of submonolayers of sodium on the spin polarization of iron outmost surfaces
Authors: Yamauchi Yasushi , Kurahashi Mitsunori , Suzuki Taku , Ju Xin
Published: May 2003

Spin-polarized metastable deexcitation spectroscopy (SPMDS) is employed to study the electron spin polarization of Na (0.1–0.6 monolayer)/Fe(100) outermost surfaces. At the Fermi level, positive asymmetries of SPMDS spectra, which correspond to negative spin polarizations and are the same as those of the clean Fe(100) surface, are observed. The origin of this positive spin polarization and the drastic decrease in the magnitude of asymmetries of SPMDS spectra are discussed on the basis of the spin density distributions obtained by calculating the electronic structures of Na(c2×2)/Fe(100), which strongly depend on the adsorption sites, using WIEN97, a full-potential linearized augmented plane-wave method.
Improvement of the electromagnetic-noise suppressing features for Fe–Si–Al composite sheets by dc magnetic field biasing
Authors: Ono H. , Yoshida S. , Ando S. , Shimada Y.
Published: May 2003

The electromagnetic-noise suppression sheets made of Fe–Si–Al thin flakes embedded in polymer improve their noise suppressing performance appreciably in the magnetic field. We have already confirmed that the transmission characteristics of a microstrip line exhibit a high-frequency suppressing feature when a small piece of the sheet is placed on it [S. Yoshida et al., IEEE Trans. Magn. 37, 2401 (2001)]. In this article we found that this filtering performance is appreciably improved by a dc magnetic field. The effect becomes explicit in a field with intensity higher than a few hundred Oe and rise of the transmission loss becomes much steeper near the frequency of magnetic resonance. An example is that in the field of 1 kOe the 3 dB width of half to the peak of frequency profile of the transmission loss at resonance is reduced to less than a quarter of the one without magnetic field. This improvement brings about a new research subject to develop the high performance electromagnetic noise absorber that is expected to work under the optimized conditions in various digital electronic devices with operation frequencies up to the GHz band.
Growth and magnetic properties of single crystal Fe1−xCoxS2 (x=0.35–1)
Authors: Cheng S. F. , Woods G. T. , Bussmann K. , Mazin I. I. , Soulen R. J. , Carpenter E. E. , Das B. N. , Lubitz P.
Published: May 2003

The pyrite Fe1−xCoxS2 (0.25⩽x⩽0.9) was predicted to be half metal, insensitive to Fe–Co disorder. To verify its half metallicity, we have grown single crystals of Fe1−xCoxS2 (x=0.35, 0.5, 0.75, 0.9, and 1). Crystals of up to a few mm in size by temperature gradient (923–873 K) solution growth from Te melts, which showed high crystalline quality by scanning electron microscopy, x-ray diffraction, and magnetic measurements. A half-metallic magnetization of 1±0.03μB per Co atom was found for x=0.35–0.9. Point contact Andreev reflection measurements, however, showed spin polarization of 47%–61% with the maximum around x=0.5, well below predictions. Ferromagnetic resonance measurements give g∼2.08 with large intrinsic damping, which indicates a reduced half-metallicity. Inductively coupled plasma and energy dispersive x-ray spectroscopy results confirm a sulfur deficiency of ∼1.5%–10% [(Fe,Co)S2−y,0.03⩽y⩽0.2] and small amounts of Te. Electronic structure calculations show the extra electron provided by Co substitution to FeS2 populates a sulfur-derived conduction band. Consequently, S deficiency and/or S site disorder are expected to affect the transport properties. This is consistent with the low polarization measurements and again indicates the importance of crystalline order in obtaining highly spin-polarized materials.
Ripple field effect on high-frequency measurements of FeTiN films
Authors: Rantschler James O. , Alexander Chester
Published: May 2003

Ferromagnetic resonance and permeability linewidths of high-moment FeTiN thin films have been recorded and analyzed using ripple theory in order to separate inhomogeneous broadening from the intrinsic damping of the material. These results are compared to the analysis of the same phenomenon using a simple but common model of amplitude dispersion. The ripple is also used to analyze the behavior of the resonance frequency of a sample when rotated in low fields.
Microstructure and damping in FeTiN and CoFe films
Authors: Rantschler James , Ding Yunfei , Byeon Soon-Cheon , Alexander Chester
Published: May 2003

Thermally stable films of FeTiN, have been prepared and characterized by ferromagnetic resonance, x-ray diffraction, x-ray photoelecton spectroscopy, and magnetostriction measurements to determine the relationships between the microstructure and the damping constants. The resonance studies were carried out at multiple frequencies to determine the intrinsic damping constant, α, and the extrinsic damping constant, ΔH0, as well as values of the anisotropy field, Hk, the gyromagnetic ratio, γ, and the saturation magnetization value, 4πMs. Data from similar experiments on CoFe films were compared with the FeTiN data. Our results show no relationship between intrinsic damping and the magnetostriction, but a strong dependence of the extrinsic constant on the grain size.
X-ray diffraction and ferromagnetic resonance study of sputtered (110) GaAs/Fe epitaxial films
Authors: Ding Yunfei , Alexander Chester , Klemmer Timothy J.
Published: May 2003

A series of epitaxial (110) Fe films with thicknesses from 5 to 164 nm were deposited on (110) GaAs substrates by rf magnetron sputtering. X-ray diffraction pole figures, in-plane φ-scan measurements, and ferromagnetic resonance linewidths show decreasing crystal quality with increasing thickness. In-plane and out-of-plane θ–2θ scans show a tensile stress decreasing with film thickness. Magnetic crystalline anisotropy and effective in-plane uniaxial anisotropy values were obtained from calculations of the free energy of a (110) cubic crystal and curve fitting of resonance measurements. The quality of the films thinner than 84 nm is close to the reported values of single crystal (110) Fe films deposited by molecular-beam epitaxy systems.
Fabrication of nanocrystalline Fe–Co–Ta–N magnetic films with high saturation magnetization and excellent high-frequency characteristics
Authors: Shin J. M. , Kim Y. M. , Kim J. , Han S. H. , Kim H. J.
Published: May 2003

As-deposited Fe–Co–Ta–N soft magnetic thin films with a thickness of 250 nm were fabricated to achieve high saturation magnetization and excellent high-frequency characteristics. During sputtering, the input power was fixed at 450 W and the nitrogen partial pressure varied from 0% to 10%. In these films, the values of saturation magnetization and coercivity that were obtained were 17–23 kG and 3–6 Oe, respectively. The Fe78Co8Ta9N5 (4% PN2) film exhibits excellent high-frequency characteristics with an effective permeability of about 2000, which is maintained up to 700 MHz. Also, this film has Bs=21 kG, Hc-hard=3 Oe, ρ=100 μΩ cm, and Hk=20 Oe. These high-frequency characteristics could result from the high values of the electrical resistivity and the magnetic anisotropy field. Furthermore, the corrosion resistance of these films was improved by the addition of nitrogen to give characteristics better than those of Co–Ni–Fe and Fe–Hf–N films.
Magnetic properties of fine-grained doubly oriented Si steel sheets
Authors: Tomida T. , Sano N. , Hinotani S.
Published: May 2003

The magnetic properties of fine-grained doubly oriented Si steel sheets of 0.25–0.35 mm in thickness have been investigated. The doubly oriented Si steel sheets with grains of about 0.5 mm in diameter showed a large induction B8 of about 1.9 T as well as a 35% smaller core loss than the previously studied coarse-grained doubly oriented materials. This decrease in core loss associated with the grain size reduction is primarily due to a large decrease in eddy current loss. The core loss was further decreased by applying tensile stresses and by a reduction in sheet thickness. A tensile-stressed 0.25-mm-thick material showed a small core loss of 0.82 W/kg at 1.7 T and 50 Hz. The material also showed relatively small core losses under alternating fields below 500 Hz.
Effect of high-temperature aging on electrical properties of Hiperco® 27, Hiperco® 50, and Hiperco® 50 HS alloys
Authors: Geist B. , Peterson T. , Horwath J. C. , Turgut Z. , Huang M. Q. , Snyder R. A. , Fingers R. T.
Published: May 2003

Some more electric aircraft concepts require soft magnetic FeCo materials to be stable at temperatures as high as 773 K for long periods of time. At this high operating temperature, aging related processes may occur that result in changes in material properties. The material supplier typically specifies only room-temperature properties, and only limited reports are available on properties at elevated temperatures. The change in properties as a function of time at 773 K will give information on the lifetime of the material to assist designers when selecting materials for high-temperature applications. We have conducted a study on the effects of long-term aging on the magnetic, mechanical, and electrical properties of Hiperco® 27, Hiperco® 50, and Hiperco® 50 HS FeCo soft magnetic alloys. Samples of each material were aged in argon for 100, 1000, 2000, and 5000 h at 773 K. Here, we report the changes in electrical resistivity after aging. Of the three alloys, high-temperature aging has the greatest effect on the resistivity of Hiperco® 50. The electrical resistivities for each sample are compared and conclusions are drawn on the relative thermal stability of each alloy. The changes in electrical resistivities for each alloy are also related to changes in other properties, such as total power loss and coercivity, that were observed during this study on aging.
Magnetic properties of Fe–Si steel depending on compressive and tensile stresses under sinusoidal and distorted excitations
Authors: Permiakov V. , Pulnikov A. , Dupré L. , De Wulf M. , Melkebeek J.
Published: May 2003

In this article, the magnetic properties of nonoriented electrical steel under sinusoidal and distorted excitations are investigated for the whole range of unidirectional mechanical stresses. The distorted flux obtained from the tooth tip of 3 kW induction machine at no-load test was put into the measurement system. The total losses increase for compressive stress both under sinusoidal and distorted excitations. For tensile elastic stresses, the total losses first decrease and then increase in a very similar way for both excitations. In contrast, the difference between total losses under sinusoidal and distorted magnetic fluxes becomes smaller with increase of the plastic strain. This work is a serious step toward complete characterization of the magnetic properties of electrical steel in the teeth area of induction machines. A deeper insight of that problem can improve the design of induction machines and other electromagnetic devices.
Electrical transport in locally modulated magnetic field
Authors: Fuse D. , Ono T. , Segi T. , Nasu S. , Kohno H. , Tatara G. , Okuno T. , Shinjo T.
Published: May 2003

Electrical transport of Au50Pd50 films under a periodically modulated magnetic field was investigated. The modulated magnetic field with period of 300 nm was produced by stray fields from surface magnetic charges on a Co film with stripe domains. An increase of resistance proportional to log T was observed over a wide temperature range from 10 to 0.1 K, which is interpreted in terms of an electron–electron interaction effect. No difference was observed between samples under homogeneous magnetic field and the periodically modulated field, indicating that the effect of the periodically modulated magnetic field on electron–electron interaction effect is very weak.
Control of nucleation behavior and high magnetic induction in thin-gauged 3% Si–Fe strips
Authors: Choi Y. S. , Chai K. H. , Kim S. B. , Cho S. S. , Heo N. H.
Published: May 2003

Even in thin-gauged 3% Si–Fe strips with the same final thickness reduction, the strong {110}〈001〉 Goss component at the cold-rolled strip surfaces becomes the {110}〈001〉 texture after final annealing, which results in a magnetic induction (B10, Tesla) higher than 1.9 T. On the other hand, the strips with the {110}〈uvw〉 component deviating from the Goss component show a low magnetic induction (B10, Tesla) of about 1.60 T which results from the final {110}〈uvw〉 texture. The strong dependence of final texture and magnetic induction on the cold-rolling texture at the surfaces of the strip is due to the intrinsic characteristic of diffusionless nucleation that is followed by the surface-energy-induced selective grain growth.
Coercive field and magnetization deficit in Ga1−xMnxAs epilayers
Authors: Potashnik S. J. , Ku K. C. , Wang R. F. , Stone M. B. , Samarth N. , Schiffer P. , Chun S. H.
Published: May 2003

We have studied the field dependence of the magnetization in epilayers of the diluted magnetic semiconductor Ga1−xMnxAs for 0.0135<x<0.083. Measurements of the low temperature magnetization in fields up to 3 T show a significant deficit in the total moment below expected for full saturation of all the Mn spins. These results suggest that the spin state of the nonferromagnetic Mn spins is energetically well separated from the ferromagnetism of the bulk of the spins. We have also studied the coercive field (Hc) as a function of temperature and Mn concentration, finding that Hc decreases with increasing Mn concentration as predicted theoretically.
Magnetic properties of IV–VI compound GeTe based diluted magnetic semiconductors
Authors: Fukuma Y. , Asada H. , Miyashita J. , Nishimura N. , Koyanagi T.
Published: May 2003

Magnetic properties of IV–VI compound GeTe based diluted magnetic semiconductors with 3d transition metals from Ti to Ni have been investigated. Ferromagnetic order is observed for the Cr, Mn, and Fe doped GeTe films, whereas the Ti, V, Co, and Ni doped films are paramagnetic. The ferromagnetic order could give rise to p–d exchange interaction because amplitudes of negative magnetoresistance and the anomalous Hall effect are proportional to that of spontaneous magnetization. The Curie temperatures determined by extrapolating the steep linear part of the temperature dependence of the squared residual magnetization for the Cr, Mn, and Fe doped GeTe films are 12, 47, and 100 K, respectively.
Organic light emitting diodes with spin polarized electrodes
Authors: Arisi E. , Bergenti I. , Dediu V. , Loi M. A. , Muccini M. , Murgia M. , Ruani G. , Taliani C. , Zamboni R.
Published: May 2003

Electrical and optical properties of Alq3 based organic light emitting diodes with normal and spin polarized electrodes are presented. Epitaxial semitransparent highly spin polarized La0.7Sr0.3MnO3 were used as hole injector, substituting the traditional indium tin oxide electrode. A comparison of electroluminescence and IV curves between similar devices with and without spin polarized injection is reported. The results are a first step in realizing an operating device where the light intensity of the emission can be tuned by controlling the spin injection.
Investigation of the cobalt distribution in the room temperature ferromagnet TiO2:Co
Authors: Stampe P. A. , Kennedy R. J. , Xin Yan , Parker J. S.
Published: May 2003

Recent reports of room temperature ferromagnetism in thin films of TiO2 doped with small amounts of cobalt have excited a great deal of interest due to the possible applications of this ferromagnetic, transparent semiconductor to spintronics devices. Ferromagnetism has been reported for TiO2 grown in both the anatase and rutile phases, although a range of magnetic moments has been reported by different groups. We have grown epitaxial thin films of Ti1−xCoxO2, with x=0.01–0.07 by pulsed laser deposition in both the anatase and rutile forms on single crystal substrates of LaAlO3, SrTiO3, and Al2O3. These films are ferromagnetic at room temperature with a magnetic moment of ∼1.7 μB/Co in the anatase phase and ∼0.6 μB/Co in the rutile phase. Detailed transmission electron microscopy measurements show a variation in the cobalt distribution in these materials that corresponds to the different magnetic moments. The cobalt does not appear to enter the anatase phase of TiO2, but rather forms crystallites of cobalt metal on the surface of anatase films. This results in a magnetic moment similar to that of bulk cobalt. In the rutile phase the cobalt has substituted uniformly throughout the lattice. We present the morphology and magnetization of TiO2:Co as a function of the TiO2 growth phase and substrate material. Preliminary electrical measurements are also mentioned.
On the room temperature ferromagnetism in Co-doped TiO2 films
Authors: Punnoose A. , Seehra M. S. , Park W. K. , Moodera J. S.
Published: May 2003

We report detailed studies of magnetization (M) as a function of magnetic field H (up to 50 kOe) and temperature T (5–380 K) in x% Co/TiO2 (rutile) films for x=1, 4, 6, 10, and 12. These films, prepared by sputtering, show room temperature ferromagnetism (RTFM). Measurements of M vs T at H=50 Oe reported here in zero-field-cooled (ZFC) and field-cooled (FC) cases show M peaking at Tp≃30 K for 1% Co to Tp≃125 K for 12% Co doped films whereas bifurcation of the FC and ZFC data is observed near 300 K. For T<Tp, the coercivity Hc rises sharply. These observations and the electron magnetic resonance data suggest that the observed RTFM is at least partly due to magnetic nanoparticles, most likely of Co, that are undetected in standard X-ray diffraction (XRD) for lightly doped samples. XRD studies show that a fraction of Co does substitute for Ti in CoxTi1−xO2. However, because of interference from Co nanoparticles, the RTFM of CoxTi1−xO2 in these samples could not be established.
Ferromagnetism and transport properties of Fe-doped reduced-rutile TiO2−δ thin films
Authors: Wang Zhenjun , Tang Jinke , Tung Le Duc , Zhou Weilie , Spinu Leonard
Published: May 2003

We have investigated FexTi1−xO2−δ (x=0.02, 0.06, and 0.08) thin films grown on α-Al2O3 substrates by pulsed-laser deposition. X-ray diffraction results indicate that the films are single phase and of reduced-rutile type. Detailed microstructural observations reveal no measurable magnetic impurities in the films. Vibrating sample magnetometer measurements show the films are ferromagnetic at room temperature with coercivity ranging from 340 to 770 Oe. The temperature dependence of the resistivity shows nearly metallic behavior at room temperature but semiconducting behavior at lower temperatures. The extraordinary Hall effect with coercivities similar to those in magnetic hysteresis curves was observed at room temperature. The carriers are p type with a carrier density of about 1022/cm3.
Magnetic properties of epitaxial Mn-doped ZnO thin films
Authors: Cheng X. M. , Chien C. L.
Published: May 2003

Epitaxial ZnO thin films doped with 7% Mn have been made by reactive rf magnetron sputtering onto (112_0) sapphire substrates at 400 °C. X-ray diffraction measurements reveal that the Zn0.93Mn0.07O film has a (0001) wurtzite single-crystal structure with a rocking curve width of 0.98°. UV–VIS absorption spectra show a band gap of 3.25 eV for pure ZnO films and 3.31 eV for the Zn0.93Mn0.07O film with states extending into the gap. The Auger electron spectroscopy shows homogeneous distribution of Mn in the film. The magnetic properties of the Zn0.93Mn0.07O film have been measured by a superconducting quantum interference device magnetometer at various temperatures with fields up to 5 T. No ferromagnetic ordering has been observed at temperature at 5 K. Instead, paramagnetic characteristics with a Curie–Weiss behavior have been observed.
Electronic and magnetic structure of a 1000 K magnetic semiconductor: α-hematite (Ti)
Authors: Butler W. H. , Bandyopadhyay A. , Srinivasan R.
Published: May 2003

There has been much interest in doping traditional semiconductors such as GaAs with Mn or other transition metals in order to obtain semiconductors that are magnetic at room temperature. Some of the goals of this research have been a Curie temperature that exceeds 400 K and the possibility of both n- and p-type doping. An alternative approach is to investigate nontraditional semiconducting materials that are known to be magnetic at room temperature. An example of such a material is solid solutions of the minerals ilmenite (FeTiO3) and α-hematite (Fe2O3). In this article we investigate the electronic and magnetic structure of Ti doped α-hematite using density functional theory and find within this model: α-hematite is an antiferromagnetic insulator with strong ferromagnetic coupling in the cation planes perpendicular to the c axis and antiferromagnetic coupling between these planes. Substitution of Ti for Fe produces a net moment of 4μB and a negative carrier in one spin channel. The negative carrier resides largely on the second nearest neighbor cation sites. The Ti atoms prefer not to sit on adjacent cation planes. Doping α-hematite with Ti atoms on alternate cation layers should lead to a ferrimagnetic semiconductor with a magnetic transition temperature of nearly 1000 K.
Universal scaling of magnetoconductance in magnetic nanocontacts (invited)
Authors: Chung S. H. , Muñoz M. , Garcı́a N. , Egelhoff W. F. , Gomez R. D.
Published: May 2003

We present results of half-metallic ferromagnets formed by atomic nanocontact of CrO2–CrO2 and CrO2–Ni that show as much as 400% magnetoconductance. Analysis of the magnetoconductance versus conductance data for all materials known to exhibit so-called ballistic magnetoresistance strongly suggests that the magnetoconductance of nanocontacts follows universal scaling. If the maximum magnetoconductance is normalized to unity and the conductance is scaled to the resistivity of the material, then all data points fall into a universal curve that is independent of the contact material and the transport mechanism. The analysis was applied to all available magnetoconductance data of magnetic nanocontacts in the literature, and the results agree with theory that takes into account the spin scattering within a magnetic domain wall.
Finite-temperature spin polarization in half-metallic ferromagnets
Authors: Dowben P. A. , Skomski R.
Published: May 2003

The temperature dependence of the spin polarization of half-metallic ferromagnets is investigated. A unitary spinor transformation shows that the corresponding spin mixing goes beyond finite-temperature smearing of the Fermi level, leading to a nonzero density of states in the gap of the insulating spin channel. As a consequence, the resistance ratio of the two spin channels changes from infinity to some finite value and, in a strict sense, half-metallic ferromagnetism is limited to zero temperature. Bloch-type spin waves and crystal imperfections contribute to the density of states in the gap but only partly explain the pronounced changes at about 0.2 TC observed in various half-metallic magnets. In the case of NiMnSb, the spin structure depends on a nearly dispersionless transverse optical mode that occurs at about 28 meV. In terms of 3 kBT, this corresponds to 103 K—very close to the temperature at which there is a dramatic loss in the Ni and Mn magnetization in NiMnSb. Similar modes exist in other potential half-metallic systems.
Extrinsic magnetoresistance in magnetite nanoparticles
Authors: Liu Kai , Zhao L. , Klavins P. , Osterloh Frank E. , Hiramatsu H.
Published: May 2003

Magnetite (Fe3O4) nanoparticles, 8 to 9 nm in size, have been synthesized using an aqueous precipitation technique. X-ray diffraction and chemical titration confirm a single cubic spinel phase with expected stoichiometry. Superparamagnetic behavior has been observed in pressed pellets of the nanoparticles above 200 K. Spin-dependent tunneling through adjacent particles has led to a negative magnetoresistance, −8.6% at 200 K and −4.5% at 300 K in a 70 kOe field. This is caused by the field-induced alignment of the nanoparticle magnetization directions.
Search for noncollinear moments at Permalloy/copper interfaces
Authors: Vedpathak Mahesh , Kodama R. H.
Published: May 2003

Recent first-principles electronic structure calculations have shown a tendency for atomic moments near interfaces between Permalloy (e.g., Ni80Fe20) and Cu to become noncollinear with the bulk magnetization direction. One signature of noncollinear moments should be a differential susceptibility at high fields (i.e., above the nominal saturation field) corresponding to a twisting of the noncollinear moments against the exchange fields in the material. We have measured the differential susceptibility for a series of sputtered Permalloy/Cu multilayers and compared it with the bulk (thick Permalloy) film. We have identified a magnetic contribution due to noncollinear moments at the interfaces corresponding to 0.1–0.3 monolayers. Further, we show that the temperature dependence of the differential susceptibility is not consistent with paramagnetic moments, supporting the idea that exchange-driven noncollinearity is present.
Micromagnetic behavior of electrodeposited Ni/Cu multilayer nanowires
Authors: Chen M. , Searson P. C. , Chien C. L.
Published: May 2003

Ni/Cu multilayer nanowires have been fabricated by electrodeposition into 6 μm thick nanoporous polycarbonate templates with pore sizes from 30 to 100 nm. The aspect ratio of the magnetic segments was varied from 0.02 (disk shaped) to 50 (rod shaped) with 10–250 Ni/Cu bilayers. The M–H curves show that the magnetic response can be classified in terms of three micromagnetic states depending on the diameter and aspect ratio of the nickel segments. Further, we show that the magnetic behavior is dependent on the thickness of the nonmagnetic layer due to the dipolar interactions between the ferromagnetic segments.
Overlayer and superlattice studies of metal/ceramic interfaces: Fe/TiC
Authors: Shishidou Tatsuya , Lee Joo-Hyoung , Zhao Yu-Jun , Freeman Arthur J. , Olson Gregory B.
Published: May 2003

Adhesion and magnetism at the Fe(001)/TiC(001) interface, studied by first-principles calculations using the full-potential linearized augmented plane wave method, show that the interfacial Fe and C atoms can form significantly strong covalent bonding, which makes the interface structure with Fe sitting on top of C as the most stable structure for both overlayers and superlattices. Due to this strong bonding, the first layer of Fe at the interface shows a considerably reduced magnetic moment (−20%), while the second layer almost recovers its bulk value. The interface C atom has a negative spin polarization, while the interface Ti atom has a positive magnetic moment.
First principles investigation of domain walls and exchange stiffness in ferromagnetic Fe and antiferromagnetic NiMn
Authors: Nakamura Kohji , Ito Tomonori , Freeman A. J. , Zhong Lieping , Fernandez-de-Castro Juan
Published: May 2003

We investigate the domain walls in ferromagnetic Fe and antiferromagnetic NiMn with the first principles full-potential linearized augmented plane-wave method including intra-atomic noncollinear magnetism. In both cases, the self-consistent results demonstrate that the magnetization changes continuously from one orientation to another as seen in a Bloch wall. The formation energy of the domain wall (ΔEDW) significantly decreases when the wall thickness increases, which leads to an exchange stiffness of 1.13×10−11 J/m for Fe and 1.43×10−11 J/m for NiMn. The predictions agree with those determined separately for Fe from a phenomenological calculation.
Electronic structure of heavy fermion superconductor CeMIn5 (M=Co,Rh,Ir)
Authors: Wang J. L. , Zeng Z. , Zheng Q. Q. , Lin H. Q.
Published: May 2003

The electronic structure of heavy fermion superconductor CeMIn5 (M=Co,Rh,Ir) is studied by density functional theory. Our results indicate that the MIn2 layer plays an important role for stabilizing the layered crystal structure and determining the antiferromagnetic or paramagnetic ground state in this series. When the strong correlation effects of 4f electrons beyond the local density approximation (LDA) are taken into account by the LDA+U approach, the calculated total magnetic moment and band structure of CeRhIn5 yield a good agreement with the experiment. The LDA+U calculation shows that the 4f electrons in this series are located on the border between localization and itineracy.
Optical studies of lattice and charge excitations in La1.2(Sr1.8−xCax)Mn2O7
Authors: Liu H. L. , Her J. L. , Shen C. H. , Liu R. S.
Published: May 2003

Optical and Raman-scattering studies of layered La1.2(Sr1.8−xCax)Mn2O7 manganites are presented as a function of temperature and doping (x=0.0, 0.4, 0.6, and 0.8). The substitution of Ca2+ for Sr2+ leads to the suppression of the low-frequency optical spectral weight with decreasing Tc. Moreover, the observed anomalies of the Raman phonon parameters near Tc are most likely due to a strong spin-phonon coupling caused by the oxygen phonon modulation of the Mn–Mn spin exchange interaction. Our results provide important insight into the interplay of lattice, spin, and charge dynamics in these materials.
Theoretical and experimental studies of cyclotron resonance in p-type InAs and InMnAs at ultrahigh magnetic fields
Authors: Sanders G. D. , Sun Y. , Stanton C. J. , Khodaparast G. A. , Kono J. , Matsuda Y. H. , Miura N. , Slupinski T. , Oiwa A. , Munekata H.
Published: May 2003

We report theoretical and experimental ultrahigh magnetic field cyclotron resonance (CR) studies of paramagnetic p-type InAs and InMnAs. Experimental results are compared with an 8 band Pidgeon–Brown model which includes (i) the wave vector dependence of the electronic states along the magnetic field, and (ii) s–d and p–d exchange interactions with Mn ions. CR spectra are computed using Fermi’s golden rule. Results show two strong peaks associated with heavy and light hole transitions. Line shapes of the transitions provide information on the carrier densities.
Magnetic second harmonic generation in centrosymmetric CoO, NiO, and KNiF3
Authors: Fiebig M. , Lottermoser Th. , Pavlov V. V. , Pisarev R. V.
Published: May 2003

Optical second harmonic (SH) spectroscopy in the centrosymmetric antiferromagnets CoO, NiO, and KNiF3 reveals pronounced signals below the Néel temperature which couple quadratically to the magnetic order parameter. The SH process roots in resonance enhanced magnetic-dipole and electric-dipole excitations between the 3d levels of the transition-metal ions in the crystal field. Different magnetic structures and differently oriented T and S domains are distinguished with a high degree of discrimination, thus demonstrating the feasibility of nonlinear optical techniques for a spatially resolved investigation of antiferromagnetic crystals and thin films.
Magnetic phase diagram of CuB2O4
Authors: Fiebig M. , Sänger I. , Pisarev R. V.
Published: May 2003

The magnetic structure of CuB2O4 is investigated by optical second harmonic generation. A rich second harmonic spectrum is observed and at least three different magnetic phases in the magnetic-field/temperature plane are revealed for magnetic fields applied along the principal axes of the compound. In the temperature ranges T<TR and TR<T<TN (with TR=10 K and TN=21 K) antiferromagnetic phases without and with a weak spontaneous ferromagnetic component are observed, respectively. A static magnetic field supports the phase directly below TN and finally suppresses the magnetic reorientation at TR.
Study of magnetic susceptibility of magnetite nanoparticles
Authors: Rodriguez A. F. R. , Oliveira A. C. , Morais P. C. , Rabelo D. , Lima E. C. D.
Published: May 2003

In this study dynamic susceptibility (DS) was used to investigate magnetite nanoparticles dispersed in styrene-divinylbenzene copolymer. Transmission electron microscopy (TEM) data have been used to support the DS data analysis. The field dependence of the peak position of the imaginary component of DS was analyzed using a picture of an asymmetric double well potential for the relaxation of the magnetic moment associated with the magnetite nanoparticle. The size dependence of the magnetic susceptibility was included in the data analysis. Nanoparticle-size parameters obtained from the analysis of the DS data (19.1 and 18.2 nm) are in excellent agreement with the values obtained from the fitting of the TEM data (19.2 and 20.1 nm).
Drastic changes of the domain size in an ultrathin magnetic film
Authors: Kisielewski M. , Maziewski A. , Zablotskii V. , Polyakova T. , Garcia J. M. , Wawro A. , Baczewski L. T.
Published: May 2003

A general framework for the domain size in any ultrathin film with perpendicular magnetic anisotropy is here discussed. The domain structure is analyzed by using the classical theory taking into consideration the demagnetization field contribution to the domain wall energy. A sinusoidal model is considered to describe the domain structure while approaching, in two different cases, the monodomain state with in-plane magnetization. The first case is realized applying a large enough in-plane magnetic field. The second one is obtained by decreasing the perpendicular magnetic anisotropy, which is connected in many ultrathin systems with the increase of film thickness. A change in the domain size of several orders of magnitude is obtained while approaching the magnetization reorientation region. The minimal stripe domain period p=8πlex2/d is calculated from the sinusoidal model, where lex is the exchange length and d is the thickness of the film. The range of possible domain size changes in ultrathin films is predicted. The domain size has been experimentally studied in a 1 nm Co film characterized by a square hysteresis loop. The investigations have been performed by polar Kerr based microscopy and magnetic force microscopy. The domain structure of two remnant states generated by applying an in-plane and a perpendicular magnetic field has been compared. Drastically, the smallest domain size has been observed for the former.
Noncollinearity of the magnetic structure of TbFe10V2
Authors: Cadogan J. M. , Ryan D. H. , Moze O. , Swainson I. P. , Suzuki K.
Published: May 2003

We have studied the ThMn12-type compound TbFe10V2 by magnetometry and high-resolution neutron powder diffraction. Previous workers claimed that TbFe10V2 undergoes a spin reorientation away from the tetragonal c axis at around 200 K, with the collinear magnetization eventually reaching an angle of 50° at 4 K. We have reinvestigated TbFe10V2 due to the unusual temperature dependence of its magnetization. We show that this behavior cannot be explained by a compensation effect and we suggest that a canted, noncollinear magnetic structure develops below the spin-reorientation temperature.
Magnetic properties of Fe-doped organic–inorganic nanohybrids
Authors: Silva N. J. O. , Amaral V. S. , Carlos L. D. , de Zea Bermudez V.
Published: May 2003

We present a magnetic study of Fe-doped diureasils (siloxane-based networks to which poly(ethylene oxide)-based chains are grafted by urea cross linkages doped with Fe(II) or Fe(III) ions. Structural studies show that the Fe(II) ions interact mainly with the organic chain, whereas the incorporation of Fe(III) leads to the formation of iron-based nanoclusters, with radius increasing from 20 to 40 Å. Fe(II)-doped samples behave as simple paramagnets, with μeff=5.32 μB. Fe(III)-doped hybrids present antiferromagnetic interactions, with TN increasing with Fe(III) concentration up to 13.6 K for 6% doping. Thermal irreversibility was observed below ∼40 K and is stronger for higher concentrations. The coercive fields (HC) are of the order of 1000 Oe at 5 K. Hysteresis cycles are shifted to negative fields, revealing the presence of exchange anisotropy interactions with exchange fields (HE) of the order of 100 Oe. Both fields decrease rapidly with increasing temperature. We analyze this behavior in terms of the contribution of surface spin disorder to exchange anisotropy.
Multiple magnetic transitions and magnetoresistance anomalies in the Er0.9Tb0.1Mn6Sn6 compound
Authors: Yao Jin-lei , Zang Shao-ying , Li Lu , Zhu Tao , Yan Mi , Yang De-ren , Shen Bao-gen
Published: May 2003

The magnetic and transport properties of the Er0.9Tb0.1Mn6Sn6 compound have been investigated in the temperature range of 5–375 K. The compound shows paramagnetism, ferrimagnetism, antiferromagnetism, and reentrant ferrimagnetism with decreasing temperature. Around 60 K, a spin orientation takes place, the easy magnetization direction changing from the c axis to the ab plane. The antiferroferrimagnetic transition is accompanied by a large magnetoresistance (MR) effect of about −5.5% at 200 K in a magnetic field of 50 kOe. It is observed that the sign of MR reverses to positive below 25 K.
Ferromagnetic and ferroelectric behaviors of A-site substituted YMnO3-based epitaxial thin films
Authors: Fujimura N. , Sakata H. , Ito D. , Yoshimura T. , Yokota T. , Ito T.
Published: May 2003

Dielectric and magnetic properties of A-site substituted YMnO3 epitaxial films were studied. Stoichiometric epitaxial YMnO3 films clearly show ferroelectric behavior in P–E and C–V measurements. The I–V property is well explained by the Pool–Frenkel-type carrier emission with p-type conduction due to the existence of Mn4+, and the activation energy is calculated to be 0.58 eV. The leakage current decreases by substituting Y for Zr and increases by Li or Mg substitution. Although YMnO3 films exhibit antiferromagnetic magnetization behavior regardless of the crystallographic orientation and the carrier concentration, Li-doped sample displays parasitic ferromagnetic behavior (weak ferromagnetism). Substituting Y for Yb enhances the ferromagnetic interaction.
Magnetic properties of highly resistive BaFeO3 thin films epitaxially grown on SrTiO3 single-crystal substrates
Authors: Matsui T. , Taketani E. , Fujimura N. , Ito T. , Morii K.
Published: May 2003

We have synthesized single-crystalline films of BaFeO3 (BFO), which may contain unusual tetravalent Fe ions, on (100) and (111) SrTiO3 substrates by pulsed laser-beam deposition. The epitaxially grown BFO is considered to have a pseudocubic perovskite-type crystal structure with some oxygen vacancies. The films were found to be highly insulating, and showed a high value of dielectric constant of ε=59. The magnetization curve of the films exhibited hysteresis, as well as small remanent magnetization. The origin of the observed small magnetization can be ascribed to the mixed valence state of the Fe4+ and Fe3+ ions. The present epitaxially grown BFO apparently had some different magnetic and dielectric properties from those for bulk BFO as well as for the previously reported other Fe4+ oxides: coexisting high resistivity and spontaneous magnetization at room temperature.
Effects of step decoration by oxygen on ultrathin film magnetic anisotropy; p(1×1)Fe on vicinal W(100)
Authors: Mireles Hector C. , Erskine J. L.
Published: May 2003

The mechanisms responsible for surface-step-induced magnetic anisotropy in ultrathin films on vicinal surfaces were explored by studying the effects resulting from surface oxygen adsorption. Magnetic hysteresis loops produced by ultrathin (1–4 ML) Fe films on a variable-step-density W(100) surface were measured using the magneto-optic Kerr effect. Auger electron spectroscopy was used to determine surface oxygen coverage. Significant reductions of the switching fields that characterize the uniaxial surface-step-induced anisotropy were observed. The oxygen-coverage dependencies were found to be consistent with step decoration (preferential chemisorption at steps) and support the highly localized nature of magnetic anisotropy energies associated with the Néel pair-bonding model of surface-step-induced magnetic anisotropy.
Scanning tunneling microscopy studies of the Fe3O4(001) surface using antiferromagnetic probes
Authors: Mariotto G. , Ceballos S. F. , Murphy S. , Shvets I. V.
Published: May 2003

We have studied the (001) surface of a Fe3O4 single crystal using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM). The STM measurements were performed using a novel tip of antiferromagnetic MnNi alloy. Atomically resolved STM images provide evidence of a surface terminated at the octahedral plane, with rows of Fe cations running along the 〈110〉 crystallographic axes. Two different kinds of Fe cations with a separation of 6 Å were imaged, while the periodicity between Fe cations of the same kind is about 12 Å. We propose an interpretation of the anomalous corrugation observed in terms of a spin polarized effect, resulting in magnetic contrast between Fe2+ and Fe3+ ions in octahedral coordination.
Electronic structure calculations of hexagonal and cubic phases of Co3Pt
Authors: Willoughby S. D. , Stern R. A. , Duplessis R. , MacLaren J. M. , McHenry M. E. , Laughlin D. E.
Published: May 2003

Using first principles electronic structure calculations we investigated structural and magnetic properties of three distinct phases of Co3Pt. Relaxed lattice constants, total energies, magnetocrystalline anisotropies, and density of states were calculated for each phase at their equilibrium lattice constants, as well as under expansion and contraction stresses. These computations may help clarify the results of some recent but ambiguous experiments on Co3Pt.
Role of domain and interface spin structure on exchange bias in CoNi/Gd/CoNi trilayers
Authors: Altuncevahir B. , Demirtaş S. , Koymen A. R.
Published: May 2003

In this study, dc remanence measurements were performed on a sputter deposited CoNi(top)/Gd/CoNi trilayers. The remanence state of the CoNi(top)/Gd bilayer, which is the hard layer, determines the exchange bias field strength. If the sample is cooled from room temperature at the remanence state corresponding to the hard layer coercive field, the exchange bias becomes zero. Domains form in the hard layer at this remanence state. The angular dependence of the coercive field does not indicate magnetization reversal by domain wall motion. The bottom soft CoNi layer exchange couples to each domain in the hard layer at the interface. This causes the exchange bias field to become zero on the average. If the trilayer is cooled at its full remanence state, the formation of Hb anisotropy is observed in the angular dependence of coercivity.
Cell manipulation using magnetic nanowires
Authors: Hultgren A. , Tanase M. , Chen C. S. , Meyer G. J. , Reich D. H.
Published: May 2003

The use of magnetic nanowires is demonstrated as a method for the application of force to mammalian cells. Magnetic separations were carried out on populations of NIH-3T3 mouse fibroblast cells using ferromagnetic Ni wires 350 nm in diameter and 35 μm long. Separation purities in excess of 90% and yields of 49% are obtained. The nanowires are shown to outperform magnetic beads of comparable volume.
Magnetotransport properties of bent ferromagnetic nanowires
Authors: Tanase M. , Silevitch D. M. , Chien C. L. , Reich D. H.
Published: May 2003

Magnetotransport measurements were performed on individual multisegmented Pt–Ni–Pt nanowires fabricated by electrochemical deposition in nanoporous alumina templates. The nanowires were removed from the template, and precipitated onto substrates from liquid suspension. The Pt end segments provide an oxide-free interface to the magnetic central segment of interest. Centrifugation prior to precipitation induces sharp bends in the nanowires. The angular dependence of the magnetoresistance of both straight and bent nanowires was used to observe domain switching. The magnetic response of straight nanowires is well described by the curling model of domain reversal. In the case of the bent nanowires, the general behavior of each individual straight segment is also consistent with this model, but evidence for interactions between the segments is also observed.
Structure and magnetic properties of a neutral dimeric copper (II) complex of N-(2-hydroxybenzyl)glycinamide ligand
Authors: Wang Xiaobai , Ding Jun , Ranford John D. , Vittal Jagadese J.
Published: May 2003

A copper (II) complex ([Cu2(sglym)2(NO3)2]) of tridentate reduced Schiff base ligands, namely, (N-(2-hydroxybenzyl)-glycinamide (Hsglym) was synthesized and characterized in the solid state by single crystal x-ray diffraction techniques. The two Cu(II) atoms are bridged by two phenolate oxygen atoms in the neutral dimers and the geometry of Cu(II) can be described as a distorted square pyramid. The Cu–Cu distances are 3.020(2) Å. The magnetic properties of the complex were studied at variable temperatures. Transition of spin state (from spin zero to spin one) was observed due to thermal excitation. This transition of spin state observed in the temperature range 100–400 K was accompanied by magnetic viscosity.