bluuebunny/crossref_metadata_2025 huggingface dataset:
Transition from the thermal activation process to the viscous process in magnetization reversal behavior of the Co/Pd multilayer
Authors: Ryu Kwang-Su , Lee Kyeong-Dong , Choe Sug-Bong , Shin Sung-Chul
Published: May 2004

We have investigated the transition from thermal activation process to viscous process in magnetization reversal behavior of the Co/Pd multilayer from the determination of the wall-motion speed and the nucleation rate via time-resolved domain observation. Interestingly, we find that the field dependencies of two activation volumes in the thermal activation regime are different from each other, which reveals that the wall-motion and nucleation experience completely different interactions. We also find that the wall-mobility in the viscous regime is much smaller than a typical value for the sandwiched Co films, which implies that the Co/Pd interfaces substantially contribute to the dynamic dissipation.
Acoustic assisted, field-induced strain in ferromagnetic shape memory alloys
Authors: Peterson Bradley W. , Feuchtwanger Jorge , Chambers Joshua M. , Bono David , Hall Steven R. , Allen Samuel M. , O’Handley Robert C.
Published: May 2004

A technique has been developed that uses acoustic energy to assist a magnetic field in driving twin boundary motion in a NiMnGa single crystal. Acoustic assisted magnetic-field-induced strain has been observed to increase the magnetic-field-induced strain response by up to one order of magnitude. This effect is most pronounced for magnetic field drives near the twin boundary threshold field. Increasing frequency of the acoustic wave input is shown to increase strain up to about 4 kHz after which there is a small decline in FSMA strain for higher frequencies.
Mn
L
3,2
x-ray absorption from (Ga,Mn)As and (Ga,Mn)N
Authors: Edmonds K. W. , Farley N. R. S. , Johal T. K. , Campion R. P. , Gallagher B. L. , Foxon C. T. , van der Laan G.
Published: May 2004

We present Mn L3,2 x-ray absorption measurements from two dilute magnetic semiconductor systems: p-type (Ga,Mn)As, which is ferromagnetic with TC=140 K; and n-type (Ga,Mn)N, in which the magnetic impurities are predominantly paramagnetic. After removing a Mn-rich oxide surface layer by chemical etching, the Mn L3,2 spectra from (Ga,Mn)As appear less localized than in previous reports, which is ascribed to screening due to p–d hybridization. Our results suggest that previous studies may have been influenced by the quality of the surface. In contrast, in the (Ga,Mn)N film the Mn ground state is closer to pure d5.
Scanning tunneling microscope observation and magnetic anisotropy of molecular beam epitaxy-grown Fe/Pt superlattices with (111) and (001) orientations
Authors: Yamamoto S. , Kato T. , Iwata S. , Tsunashima S. , Uchiyama S.
Published: May 2004

The surface morphology and the perpendicular magnetic anisotropy for (001) and (111) oriented [Pt(nML)/Fe(nML)]10 superlattices were investigated. From in situ scanning tunneling microscope observation, the small grain whose diameter was about 5–10 nm and height was 0.2–0.4 nm, was observed in the Fe(2 ML) surface grown at room temperature on the Pt(111) seed layer, while the surface of the Fe deposited at 150 °C was covered with flat terraces and steps. It is found that the (111) oriented films were all in-plane magnetized. On the other hand, the (001) films were in-plane magnetized at room temperature, perpendicular magnetized at 100 °C and 150 °C.
Comparative studies of the electronic structure of LiFePO4, FePO4, Li3PO4, LiMnPO4, LiCoPO4, and LiNiPO4
Authors: Xu Yong-Nian , Ching W. Y. , Chiang Yet-Ming
Published: May 2004

We report a comparative study of the electronic structures of LiFePO4, FePO4, Li3PO4, LiMnPO4, LiCoPO4, and LiNiPO4. We used the spin-polarized ab initio orthogonalized linear combinations of atomic orbitals method for the calculation. Li3PO4 is a large-band gap insulator with a band gap of 5.75 eV. For other crystals containing the 3d-transition metals (TM), the localized 3d bands of the TM fall within the large insulting gap. In the cases of FePO4 and LiMnPO4, the band gaps between the occupied majority spin band and the unoccupied minority spin band are of the order of 0.27 and 1.91 eV, respectively. For LiFePO4 and LiCoPO4, our calculation shows that they are 100% spin-polarized half metals. In the case of LiNiPO4, the Fermi level is in the small gap separating t2g and eg minority bands. These results are discussed in the context of the number of 3d electrons in the TM series and the possibility of strong electron correlation effects in these crystals.
Penetration of ac magnetic field into bulk high-temperature superconductors: Experiment and simulation
Authors: Sokolovsky Vladimir , Meerovich Victor , Dikovsky Valery , Paperno Eugene
Published: May 2004

To determine the magnetic field inside a superconductor, we have measured the distribution of the ac magnetic field in a narrow gap between two BSCCO superconducting cylinders with a set of Hall probes. Numerical simulations showed a close agreement between the magnetic field distributions inside the superconductor and the gap. Bean’s model was used for setting the current density distribution inside the superconductor. It was found that at low currents, the field distribution inside the superconductors could be described by Bean’s model. Marked difference observed at higher currents can be explained by flux creep and flux flow.
Biquadratic coupling in antiferromagnetically coupled magnetic recording media
Authors: Moser Andreas , Berger Andreas , Margulies David T. , Fullerton Eric E.
Published: May 2004

Using spinstand and magnetometry measurements we have investigated the effective coupling between the two ferromagnetic layers in antiferromagnetically coupled (AFC) longitudinal magnetic recording media. For AFC media with soft-magnetic CoCr and Co lower layers we find that the average equilibrium magnetization direction of the lower layer is a function of transition density in the upper layer. In particular for medium-sized bit cells, biquadratic coupling is observed, for which the average magnetization of the lower layer is perpendicular to that of the upper layer.
Magnetic phase transition and anisotropy of ultrathin Fe films grown on inclined Al2O3(0001) substrates
Authors: Shiratsuchi Yu , Endo Yasushi , Yamamoto Masahiko , Li Dongqi , Bader S. D.
Published: May 2004

We investigated the magnetic properties of ultrathin Fe films grown on inclined Al2O3(0001) substrates at various growth temperatures. We report the evolution of the magnetism with Fe thickness tFe, growth temperature, and the effect of the inclination of the substrate orientation on the magnetic anisotropy. The films are superparamagnetic (tFe≈5 monolayer, ML), ferromagnetic (tFe>15 ML), or coexistent (tFe≈10 ML). The effect of inclination of the substrate is small in the superparamagnetic region and substantial in the ferromagnetic region. Fe thin films grown on the inclined substrate have a uniaxial magnetic anisotropy with the magnetic easy axis parallel to the step edge. This uniaxial magnetic anisotropy might be derived from the effective demagnetizing field due to the magnetic charge distribution at the corrugated surface. The strength of the uniaxial magnetic anisotropy decreases as the growth temperature increases. The dependence of the uniaxial magnetic anisotropy on growth temperature is caused by the change of growth mechanism, from smooth to rough with an increasing of growth temperature.
Magnetization chirality due to asymmetrical structure in Ni-Fe annular dots for high-density memory cells
Authors: Nakatani Ryoichi , Yoshida Tetsuo , Endo Yasushi , Kawamura Yoshio , Yamamoto Masahiko , Takenaga Takashi , Aya Sunao , Kuroiwa Takeharu , Beysen Sadeh , Kobayashi Hiroshi
Published: May 2004

Ni–Fe asymmetric ring dots with partially planed outer sides were investigated as candidates for high-density magnetic memory cells. The magnetic states, which were measured with magnetic force microscopy, show that in-plane magnetic fields can control the chirality, either clockwise or counterclockwise, of vortical magnetizations of the Ni–Fe asymmetric ring dots. This control facilitates applying ring dots to the magnetic random access memories.
Anisotropy of epitaxial Fe films grown on n-type GaAs by electrodeposition
Authors: Liu Y.-K. , Scheck C. , Schad R. , Ding Y. , Alexander C. , Zangari G.
Published: May 2004

We report the epitaxial growth of high quality Fe thin films on both n-type GaAs(001) and GaAs(011) substrates using electrochemical deposition. X-ray diffraction shows Fe(001)[110]//GaAs(001)[110] and Fe(011)[100]//GaAs(011)[100] as the primary epitaxial relations similarly to Fe films grown by molecular-beam epitaxy. The structural quality depends on the composition of the plating solution. The Hc values of these films are around 30–100 Oe. The 4πMs value is about 20–21 kG. In-plane angular ferromagnetic resonance measurements showed crystalline anisotropy for both the Fe(001) and Fe(011) films which is superimposed by a substrate induced uniaxial anisotropy for the Fe(011) layers.
Inverse problem approach to the design of magnetic field pulses for precessional switching
Authors: Mayergoyz I. , Dimian M. , Bertotti G. , Serpico C.
Published: May 2004

The “inverse problem” approach to the analysis of precessional switching of magnetization in thin films is presented. This approach leads to the explicit expressions for magnetic field pulses that guarantee the precessional switching. The effectiveness of the developed technique is illustrated by examples.
Mesoscopic magnetotransport in thin La0.7Ca0.3MnO3/SrTiO3 films
Authors: Rozenberg E. , Markovich V. , Yuzhelevskii Ya. , Gorodetsky G. , Ziese M.
Published: May 2004

DC resistivity (ρ) and differential resistance Rd=dV/dI have been measured as functions of temperature (10⩽T⩽300 K), magnetic field (H⩽1.5 T) and current flow in three epitaxial La0.7Ca0.3MnO3 films grown on (001) SrTiO3 substrates. The films had thickness of 70, 22, and 9 nm, Curie temperatures of 263, 254, and 220 K and were found to be in strain-relaxed, noncoherent, and coherent strain states, respectively. The different strain states induce different magnetic ground states of the above films: homogeneous ferromagnetic metallic-like (FMM), mixed FMM+orbitally ordered (OO) and predominate OO, respectively. It was found that magnetoresistance and electroresistance effects (Rd versus H and I dependences, accordingly) correlate with prevailing magnetic ground states of considered films.
Structure and magnetocaloric effect in the pseudobinary system LaFe11Si2–LaFe11Al2
Authors: Liu X. B. , Altounian Z. , Beath A. D.
Published: May 2004

Structure and magnetocaloric effect (MCE) were investigated by x-ray diffraction and magnetic measurement in the pseudobinary system LaFe11Si2–LaFe11Al2. The compounds have the cubic NaZn13 structure and the lattice constant increases with increasing Al content. The Curie temperature TC decreases from 236 to 186 K with increasing Al content. All compounds exhibited large MCE and the values of magnetic entropy changes ΔS ranged from 10.8 to 8.5 J/kg K for LaFe11Si2–LaFe11Al2 system under an external field change of 7 T. The temperature dependence of the Landau coefficients has been derived by fitting the magnetization M(μ0H) using the Landau expansion of the magnetic free energy. The results indicate the replacement of Si by Al changes the ferromagnetic to paramagnetic transition near TC from first order to second order.
Phase formation, microstructure, and hard magnetic properties of electrodeposited FePt films
Authors: Leistner K. , Backen E. , Schüpp B. , Weisheit M. , Schultz L. , Schlörb H. , Fähler S.
Published: May 2004

FePt films of different compositions have been electrodeposited on Cu coated Si substrates. After deposition films were annealed at temperatures up to 900 °C for 10 min. Phase formation, microstructure, and magnetic properties are analyzed. From these measurements, necessary conditions to obtain good hard magnetic properties are concluded. Remanence reaches a maximum value at 800 °C annealing temperature, while coercivity continuously increases for annealing temperatures up to 900 °C. A coercivity of 0.42 T has been achieved in this case.
Retrieving pulse profiles from pump-probe measurements on magnetization dynamics
Authors: Jozsa C. , Rietjens J. H. H. , van Kampen M. , Smalbrugge E. , Smit M. K. , de Jonge W. J. M. , Koopmans B.
Published: May 2004

A method for back-tracing magnetic field pulses in pump-probe-type magnetization dynamics measurements is presented. Solving vectorially the Landau–Lifshitz–Gilbert equation for our field-induced measurement geometry yields field pulse profiles fulfilling the theoretical expectations on a 100 ps timescale. Applying the method to our earlier, all-optical-type pump-probe measurements, the claim that the optical pulse triggers an ultrafast anisotropy field pulse gets a direct proof: we derive a pulse consisting of a delta-peak type, full width at half maximum <5 ps impulse on top of a very fast rising step-like profile. Application of the method to other, less trivial pump-probe schemes can contribute to the development of novel type magnetic recording technologies.
Synthesis and magnetic properties of CoPt nanoparticles
Authors: Sun Xiangcheng , Jia Z. Y. , Huang Y. H. , Harrell J. W. , Nikles D. E. , Sun K. , Wang L. M.
Published: May 2004

High magnetocrystalline anisotropy CoPt particles with an average size of 8 nm were synthesized by the superhydride reduction of CoCl2 and Pt(acac)2 at a high temperature. As-made particles showed a disordered face-centered cubic lattice and were superparamagnetic. Upon heat treatment at temperatures above 600 °C, the particles transformed to the L10 phase, as indicated by the appearance of the superlattice peaks in the x-ray diffraction and high magnetocrystalline anisotropy. The temperature dependence of the coercivity of nanoparticles annealed at 650 °C was measured from 10 to 300 K and analyzed using a Sharrock formula. After annealing at 650 °C, the anisotropy of the nanoparticles was K∼1.7×107 erg/cm3.
Spin dynamics and spin-glass state in Fe-doped cobaltites
Authors: Phan Manh-Huong , Phan The-Long , Huynh Thanh-Nhan , Yu Seong-Cho , Rhee Jang Roh , Khiem Nguyen Van , Phuc Nguyen Xuan
Published: May 2004

A thorough study of the magnetic and transport properties of La0.5Sr0.5Co1−xFexO3 (0⩽x⩽0.6) compounds has been made. The Fe substitution destroys the metallic state and the resistivity increases by orders of magnitude even with a very small extent of Fe substitution. The charge localization due to Fe substitution is likely to have its origin in the electronic configuration rather than in its ionic size. The hole-poor regions, corresponding to the Fe-rich regions, would also dilute the magnetic lattice and thereby prevent the occurrence of long-range order. Spin-glass behavior was observed for x⩾0.5 compositions and is ascribed to the frustration of random competing exchange interactions, namely the ferromagnetic double-exchange interaction between Co3+ and Co4+, and the antiferromagnetic interactions like Co-O-Fe and Fe-O-Fe. A dynamic scaling analysis of ac susceptibility data using conventional critical slowing down indicates a finite spin-glass phase-transition temperature Tg≈85 K and a dynamic exponent zv≈12.4, for x=0.5 composition.
Micromagnetic simulation of effect of stress-induced anisotropy in soft magnetic thin films
Authors: Bai Daniel Z. , Zhu Jian-Gang , Yu Winnie , Bain James A.
Published: May 2004

The effect of stress in soft magnetic thin films, in particular, on the in-plane anisotropy, has been studied, based on the analysis of the magnetoelastic energy associated with the stress. The easy-axis directions and the effective anisotropy constants have been identified, as functions of the stress, the magnetostriction coefficients of the material, and the growth texture of the film. The magnetoelastic energy has been combined into an existing micromagnetic model to simulate the magnetization of thin films with various materials, stress states, and growth textures. Simulation results of static magnetic domain structures are in agreement with the theoretical predictions.
Ferromagnetic resonance linewidth models for perpendicular media
Authors: McMichael R. D.
Published: May 2004

The extrinsic ferromagnetic resonance linewidth is modeled in a perpendicular recording media with inhomogeneous uniaxial anisotropy field Hu and with tilting of the easy axes from the film normal. The linewidth is calculated using both a local resonance model and a classical equivalent of the two-magnon model. Variations in Hu and easy axis tilting are shown to produce very different angular dependence of the linewidth, and when the two-magnon models are valid, the linewidth is also shown to depend on inter-granular exchange coupling.
Magnetic and electrical transport properties of La0.67Ca0.33MnO3 (LCMO): xSiCN composites
Authors: Das D. , Saha A. , Srivastava C. M. , Raj R. , Russek S. E. , Bahadur D.
Published: May 2004

The magnetic and electrical transport properties of La0.67Ca0.33MnO3 (LCMO): xSiCN (x=0–40 vol %) composites, synthesized by mechanical mixing of citrate gel derived LCMO and polymer derived ceramics SiCN, have been investigated as a function of composition. The ability of SiCN to behave as a sintering additive leads to interesting magnetic and electrical properties. Si+4, being strongly favored for tetrahedral coordination, cannot enter the perovskite lattice. Saturation moment, MS of 68 emu/gm at 5 K and at 5 kOe field of pure LCMO shifts to 79 emu/gm in the sample with x=0.05 and then decreases monotonically as x increases further. The lower MS, TC and high electrical resistivity of the sample with x=0, compared to those which have been reported in the literature, is due to small particle size in nm range. SiCN as a sintering aid increases the particle size of LCMO to 1–2 μm for x=0.10. Three orders of magnitude change in electrical resistivity (204 Ω cm for x=0;0.5 Ω cm for x=0.05) is explained on the basis of the difference in the mobility of the charge carriers, by fitting the experimental transport data with a correlated polaron hopping model.
Influence of point defects on magnetic vortex structures
Authors: Rahm M. , Höllinger R. , Umansky V. , Weiss D.
Published: May 2004

We employed micro-Hall magnetometry and micromagnetic simulations to investigate magnetic vortex pinning at single point defects in individual submicron-sized Permalloy disks. Small ferromagnetic particles containing artificial point defects can be fabricated by using an image reversal electron beam lithography process. Corresponding micromagnetic calculations, modeling the defects within the disks as holes, give reasonable agreement between experimental and simulated pinning and depinning field values.
Effect of the magnetocrystalline anisotropy on the magnetic behavior of ring elements
Authors: Vaz C. A. F. , Kläui M. , Bland J. A. C. , Heyderman L. J. , Nolting F.
Published: May 2004

We systematically compare the magnetic properties of epitaxial and polycrystalline Co disks and rings with varying width (110–730 nm) for a fixed Co thickness and outer diameter (16 nm and ∼1.6 μm, respectively) by magneto-optical Kerr microscopy and photoemission electron microscopy. The magnetic hysteresis loops of the epitaxial (fcc Co) samples exhibit much larger switching fields and broader switching field distributions than the polycrystalline structures. This behavior is attributed to the different origin of the pinning fields in, respectively, the epitaxial and polycrystalline structures. Our results show also that for epitaxial rings, the magnetic global easy axis is along the magnetocrystalline hard axis.
Magnetoresistance and magnetostriction effects in ballistic ferromagnetic nanoconstrictions
Authors: Ozatay O. , Chalsani P. , Emley N. C. , Krivorotov I. N. , Buhrman R. A.
Published: May 2004

Nanofabrication and thin film deposition techniques have been employed to form Ni nanocontacts that have a three-dimensional point contact geometry with a minimum contact diameter in the range of 1–10 nm. The electron transport through these nanocontacts has been demonstrated to be ballistic or at least quasiballistic. Measurements of the magnetoresistance arising from the creation and removal of a domain wall have yielded a small effect, <1%, but one which increases with decreasing contact diameter. Depending upon the substrate preparation, the nanocontacts can exhibit a strong magnetostriction behavior in the presence of an in-plane magnetic field.
Synthesis of ferrite on SiO2 spheres for three-dimensional magneto-photonic crystals
Authors: Nishimura K. , Baryshev A. V. , Kodama T. , Uchida H. , Inoue M.
Published: May 2004

This article reports the preparation of submicrometric magnetic particles which are promising parts for fabrication of three-dimensional magneto-photonic crystals. In our experiments SiO2 spheres with diameter of about 260 nm were coated with Fe3O4 fine particles from an aqueous solution at room temperature. It is found that spheres coated with Fe3O4 fine particles with a diameter of about 20 nm are synthesized when the ratio of Fe3+/Fe2+ is in the range 50%–100% and the pH value is in the range 8–10.
Ferromagnetic resonance study of nanoscale ferromagnetic ring lattices
Authors: Xu Wentao , Watkins D. B. , DeLong L. E. , Rivkin K. , Ketterson J. B. , Metlushko V. V.
Published: May 2004

Square lattices of permalloy rings with different inner diameters (Di) were fabricated by electron beam lithography and investigated by ferromagnetic resonance (FMR). Results reveal that FMR spectra are sensitive to the ring dimensions. A large shift of the uniform mode from 1200 to 1800 Oe, and a dramatic decrease in its intensity are observed as Di increases from 0 to 300 nm. Other resonance peaks at fields slightly below the uniform mode greatly increase in intensity and shift to lower field with increasing Di. An isolated resonance below 200 Oe is also observed. Possible reasons for these variations are discussed.
Giant resistance switching against thermal cycling in twinned La0.65Ca0.35MnO3 films
Authors: Park J. S. , Lee H. K. , Bae H. R. , Lee Y. P. , Prokhorov V. G.
Published: May 2004

The magnetic and transport properties of La0.65Ca0.35MnO3 film grown on LaAlO3 (001) twinned crystal were investigated in a temperature range of 77–300 K. A decrease in transport current in a temperature range below the metal–insulator–transition temperature can be ascribed to a formation of the charge ordered insulating (COI) state. It is found that thermal cycling leads to the formation of a nonequilibrium state in the ensemble of charge-ordered domains and to the appearance of a giant switching in resistance up to 100%. It is suggested that a martensitic transformation of the COI phase plays an important role in this effect.
Magnetic irreversibility in single crystalline UPt2Si2
Authors: Otop A. , Litterst F. J. , Hendrikx R. W. A. , Mydosh J. A. , Süllow S.
Published: May 2004

We present a susceptibility study on single crystalline UPt2Si2. For this material, which orders antiferromagnetically below TN=31 K, we observe irreversibility in susceptibility runs performed in field cooled and zero field cooled modes, respectively. The irreversibility exhibits pronounced anisotropy. While along the c axis it sets in above TN, i.e., at Tirr≃36 K, along the a axis we find a much lower Tirr∼10 K. The observation of magnetic irreversibility indicates the presence of crystallographic disorder in this single crystalline, stoichiometric compound. We discuss possible sources of the crystallographic disorder and unusual irreversibility behavior of this compound.
X-ray diffraction study in high magnetic fields of magnetovolume effect in itinerant-electron metamagnetic La(Fe0.88Si0.12)13 compound
Authors: Fujita A. , Fukamichi K. , Koyama K. , Watanabe K.
Published: May 2004

Magnetovolume effect due to the itinerant-electron metamagnetic (IEM) transition in La(Fe0.88Si0.12)13 has been investigated by x-ray diffraction measurements in high magnetic fields. No crystal structure change was confirmed after the IEM transition. The relative change in the lattice constant measured perpendicular to the magnetic field direction is similar to the longitudinal linear magnetostriction, and hence the volume change due to the IEM transition is isotropic. The volume change in both the ferromagnetic and the paramagnetic states is proportional to the square of the magnetization, though the magnetovolume coupling constant in the former is smaller than that in the latter.
Textured growth of highly coercive L10 ordered FePt thin films on single crystalline and amorphous substrates
Authors: Weisheit M. , Schultz L. , Fähler S.
Published: May 2004

FePt films have been prepared by pulsed laser deposition at a temperature of 800 °C onto (001) oriented single crystalline (MgO, SrTiO3) as well as amorphous substrates (Si3N4, glass) with and without a (001) textured MgO buffer layer. Although all films have been prepared under identical conditions, significant differences in coercivity are observed. Very high values of up to 5.6 T have been measured for the epitaxial films, while on the amorphous substrates the coercivities range between 0.8 and 2.0 T. We analyze whether changes in intrinsic or extrinsic properties due to a modified microstructure are responsible for these differences.
Shape modes in the ferromagnetic resonance of small rectangular elements
Authors: Pardavi-Horvath Martha
Published: May 2004

Ferromagnetic resonance experiments were performed on a series of thick yttrium–iron–garnet films. Due to the finite surface to volume ratio, the distribution of the internal field is bimodal, and distinct “shape” and “volume” modes can be observed. The origin of the shape modes is magnetostatic, and they are localized near the edges, corners, and surfaces. The shape modes are located at a higher field than the main volume mode in parallel, and below the volume mode in perpendicular configuration. A crossover between these modes at a critical angle is observed.
Stress-induced remagnetization in magnetostrictive films
Authors: McCord Jeffrey , Schäfer Rudolf , Frommberger Michael , Glasmachers Stefan , Quandt Eckhard
Published: May 2004

Strictly stress-induced magnetization reversal in magnetostrictive Co50Fe50/Co80B20 multilayers was studied by magneto-optical Kerr microscopy. The remagnetization takes place by rotational processes in externally applied stress in the absence of magnetic fields. Multiple small-angle domains develop at low magnetic anisotropy. Cross-tie and “fir-tree”-like domain structures appear. Magnetoelastic energy contributions in the substrate–film structure are responsible for the low-angle domain wall patterns. Additional effects from the crystalline nature of the films are discussed.
Dynamic anisotropy in amorphous CoZrTa films
Authors: Neudert Andreas , McCord Jeffrey , Schäfer Rudolf , Schultz Ludwig
Published: May 2004

The high-frequency response of amorphous CoZrTa thin films was measured by using a pulsed inductive microwave magnetometer. The anisotropy of the magnetic films was varied by magnetic field annealing. Static anisotropy field values ranging from Hk=100 to 1920 A/m were obtained. The dynamically determined anisotropy field is shifted to higher values compared to the static anisotropy by an additional isotropic internal field Hadd. This internal field is independent of the strength of the static anisotropy field. We determined a value of about Hadd=510 A/m.
Inverted current-driven switching in Fe(Cr)/Cr/Fe(Cr) nanopillars
Authors: AlHajDarwish M. , Fert A. , Pratt W. P. , Bass J.
Published: May 2004

From both theory and experiment, scattering of minority electrons is expected to be weaker than scattering of majority electrons in both dilute Fe(Cr) alloys and at Fe(Cr)/Cr interfaces. We show that Fe(Cr)/Cr/Fe(Cr) trilayer nanopillars display a normal magnetoresistance (largest resistance at low magnetic fields and smallest at high fields), but an inverted current-driven switching (positive current flowing from the fixed to the reversing layer switches the trilayer from higher to lower resistance, and negative current switches it from lower to higher).
Measurement of local magnetization in the buried layer of a pseudo-spin-valve submicron wire
Authors: Choi Y. , Haskel D. , Lee D. R. , Lang J. C. , Srajer G. , Im J. S.
Published: May 2004

A pseudo-spin-valve (PSV) wire [Au(3 nm)/Py(10 nm)/Cu(5 nm)/Co(10 nm)/Si] was patterned by e-beam lithography into two sections with different widths, connected by a narrow part that acts as a domain wall trap. The two sections have different magnetic shape anisotropies and thus different coercive fields. Since the sample has two different magnetic layers (soft and hard) and two different anisotropies (thick and thin widths), this patterned system has more than two magnetic configuration states depending on the applied field strength. To probe local magnetization from the two different sections, x-ray magnetic circular dichroism (XMCD) measurements were done on the PSV wire with a microfocused x-ray beam. Measurements were done on the buried hard layer, from which magnetic information cannot be obtained by surface-sensitive techniques. The XMCD experimental results are compared with micromagnetic simulations.
Effects of patterning on perpendicular exchange bias probed by extraordinary Hall effect
Authors: Menéndez J. L. , Ravelosona D. , Chappert C.
Published: May 2004

In this work, the evolution of the exchange bias in epitaxial CoO/Pt/Co/Pt/Al2O3 structures with perpendicular anisotropy is studied by using extraordinary Hall effect. It is shown that for nonpatterned films, a perpendicular exchange bias is present with a blocking temperature around 150 K. However, when the structures are patterned into 1-μm-wide and 15-μm-long wires, the exchange bias disappears at any temperature.
Current-perpendicular-to-the-plane giant magnetoresistance in structures with half-metal materials laminated between CoFe layers
Authors: Hoshiya Hiroyuki , Hoshino Katsumi
Published: May 2004

A current-perpendicular-to-the-plane spin-valve (CPP-SV) structure having half-metal materials laminated between CoFe layers was investigated. A CPP-SV film having a CoMnGe free layer had a resistance-change-area product ΔRA of 0.9 mΩ μm2, almost the same as that of a CPP-SV film having a simple CoFe free layer. But the ΔRA of a CPP-SV film with a CoFe/CoMnGe/CoFe sandwiched free layer was 1.6 mΩ μm2. CPP-SV films having CoFe/iron-added-magnetite/CoFe sandwiched layers were also investigated and found to have a ΔRA of ≈2 mΩ μm2. We found that a CoFe/half-metal/CoFe sandwiched layer was a stronger source of spin-dependent scattering than a CoFe layer and simple half-metal layer.
Double exchange and charge fluctuations in CrO2
Authors: Schlottmann P.
Published: May 2004

CrO 2 is a half-metallic ferromagnet, whose magnitude of TC, the magnons in the magnetization and specific heat, and the activation energy in the resistivity cannot be explained with the predicted gap of 1.5 eV in the minority spin density of states. Possible double-exchange mechanisms between sites with two electrons in three orbitals subject to strong Hund’s rule correlations are studied. While three itinerant orbitals lead to an antiferromagnetic ground state, one localized and two itinerant orbitals give rise to ferromagnetism. Mechanisms to avoid the Mott–Hubbard limit for the correlated bands are discussed.
Silicide formation and particle size growth in high-temperature-annealed, self-assembled FePt nanoparticles
Authors: Thomson T. , Terris B. D. , Toney M. F. , Raoux S. , Baglin J. E. E. , Lee S. L. , Sun S.
Published: May 2004

L1 0 FePt nanoparticle assemblies consisting of a few layers of 4-nm-diameter particles, are a potential data storage medium beyond 1 Tbit/in2. However, annealing at temperatures >500 °C is required to form the high anisotropy L10 phase. Recent studies have shown a substantial drop in magnetization for Tanneal>650 °C. We show that this reduction in magnetization is due to silicide formation as a result of a chemical reaction with the native oxide or Si substrate. We also show that full L10 ordering is established only after annealing at 725 °C for 60 min and note that particle agglomeration occurs under these conditions.
Nonmagnetic shell in surfactant-coated FePt nanoparticles
Authors: Wu X. W. , Liu C. , Li L. , Jones P. , Chantrell R. W. , Weller D.
Published: May 2004

Self-assemblies of chemically-synthesized 3 nm FePt nanoparticles show a dramatic increase of the saturation magnetization from about 210 emu/cm3 in the as-prepared state to about 850 emu/cm3, when annealed above 400 °C for 30 min. This increase correlates directly with the decomposition of the surfactant coating above 400 °C. The low magnetization state is attributed to the formation of a nonmagnetic shell (dead layer) due to oxygen bonds of the polar end group surfactant of oleic acid/oleylamine with Fe. Magnetic analysis in the superparamagnetic regime suggests a 2.7-nm-diameter FePt particle size with core–shell structure of 1.7-nm-diameter FePt magnetic core and ∼0.5 nm nonmagnetic shell.
Domain wall motion by spin-polarized current: a micromagnetic study
Authors: Thiaville A. , Nakatani Y. , Miltat J. , Vernier N.
Published: May 2004

The effect of a spin-polarized current crossing a domain wall in a thin and narrow Permalloy™ strip is studied by micromagnetic simulations, supported by a one-dimensional model of wall dynamics. We use the simplest way to incorporate the spin-polarized current effect in the micromagnetic formalism; namely, a local momentum transfer under the assumption that the current polarization is in local equilibrium. We predict current influence on wall velocity and mobility under field. However, in order to reach agreement with recent experiments, more than ten times larger currents would be required within this simplest model. Thus, more elaborate models of spin transfer are needed.
Structural and magnetic properties of a series of low-doped Zn1−xCoxO thin films deposited from Zn and Co metal targets on (0001) Al2O3 substrates
Authors: Fouchet A. , Prellier W. , Padhan P. , Simon Ch. , Mercey B. , Kulkarni V. N. , Venkatesan T.
Published: May 2004

We report on the synthesis of low doping Zn1−xCoxO (0<x<0.1) thin films on (0001)-Al2O3 substrates. The films were prepared in an oxidizing atmosphere, using the pulsed-laser deposition technique starting from Zn and Co metallic targets. We first studied the influence of the strains of ZnO and their structural properties. Second, we investigated the structural and the magnetic properties of the Zn1−xCoxO films. We show that at low doping, the lattice parameters and the magnetization of the Zn1−xCoxO films depend strongly on the Co concentration.
Ferromagnetism in chromium-doped reduced-rutile titanium dioxide thin films
Authors: Wang Zhenjun , Tang Jinke , Zhang Hongguo , Golub Vladimir , Spinu Leonard , Tung Le Duc
Published: May 2004

Cr-doped reduced-rutile TiO2 thin films were grown on R-plane sapphire substrates by pulsed-laser deposition. X-ray diffraction and transmission electron microscopy results indicate that the films are single phase and reduced-rutile type. Superconducting quantum interference device magnetometer measurements show the films are ferromagnetic up to 400 K. A large magnetic moment of 2.9 μB per Cr atom is found for 6% Cr-doped reduced films at room temperature, and the saturation magnetization of the films decreases with increasing Cr doping. The temperature dependence of the resistivity shows semiconducting behavior.
Sweep-rate-dependent coercivity simulation of FePt particle arrays
Authors: Feng Xuebing , Visscher P. B.
Published: May 2004

We present a simple method for parameterizing the sweep-rate dependence of the coercivity. We use it to fit data obtained from Landau–Lifshitz dynamic simulation, to extrapolate them to experimental time scales. The method is a generalization of the Sharrock theory in which all the data fall on a single universal curve if the coercivity and sweep rate are scaled properly.
Thermal expansion in a system with nested Fermi surface
Authors: Schlottmann P.
Published: May 2004

The nesting of the Fermi surfaces of an electron pocket and a hole pocket separated by a wave vector Q and the interaction between electrons gives rise to spin- and charge-density waves. The order can gradually be suppressed by mismatching the nesting, and a quantum critical point is obtained as the critical temperature tends to zero. The renormalization group flow leads to a strong coupling fixed point. We study the enhancement of the electron–phonon coupling and the softening of the phonon with wave vector Q. The phonons couple to charge- and spin-density waves, giving rise to a Peierls distorted ground state. The consequences of this phonon softening on the thermal expansion are investigated. The results are discussed in the context of non-Fermi-liquid behavior observed in several heavy fermion compounds.
Magnetic structure of Er5Si4
Authors: Cadogan J. M. , Ryan D. H. , Altounian Z. , Liu X. , Swainson I. P.
Published: May 2004

As part of our ongoing study of giant magnetocaloric compounds, we have determined the magnetic structure of Er5Si4 by high-resolution neutron powder diffraction, ac-susceptibility, and Er166 Mössbauer spectroscopy. The crystal space group is orthorhombic Pnma and the magnetic space group is Pn′ma′. The magnetic ordering temperature is 32(3) K and the magnetic structure is characterized by ferromagnetic order of the three Er sites (4c, 8d1, and 8d2) along [010], together with antiferromagnetic order of the 8d sites in the perpendicular (010) plane. The Er 4c magnetic mode is FY and the 8d magnetic mode is CX+FY+GZ+. At 3.6 K, the Er magnetic moments are 7.4(1), 6.9(2), and 7.6(2) μB at the 4c, 8d1, and 8d2 sites, respectively, and the corresponding Er166 hyperfine magnetic fields, at 5 K, are 715(5), 627(2), and 736(3) T. The neutron diffraction data show tentative evidence of a reorientation of the magnetic structure, most likely involving the development of an antiferromagnetic component at the 4c site, between 14 and 4 K.
Effect of Au spacer layer on L1 phase ordering temperature of CoPt thin films
Authors: Yokota T. , Gao L. , Liou S. H. , Yan M. L. , Sellmyer D. J.
Published: May 2004

We have studied the effect of Au on the ordering temperature of CoPt films. The coercivity of the CoPt multilayer with 2 nm Au inserted is around 5 kOe after annealing at 400 °C. This ordering temperature is about 200 °C lower than that of a pure CoPt film. Crystallographical analysis using x-ray diffraction has also revealed that the lattice constant is drastically changed around the same temperature, which is related to the formation of the L10-ordered structure. Thus, the Au plays an important role in reducing the ordering temperature.
Irregular domain patterns in structured magnetic thick films
Authors: McCord Jeffrey
Published: May 2004

Domain structures in patterned magnetostrictive NixFe1−x films are observed by Kerr microscopy. The micrometer-thick films display different types of domain patterns varying with saturation magnetostriction. In negative magnetostrictive and tensile-stressed films, regular closure domains are replaced by edge curling walls seen for the first time in single layer films. The influence of shape anisotropy is strongly reduced. Small changes in material composition drastically alter the domain structures. For positive magnetostriction films, an “anisotropy structured” pattern is observed. Deviations from a regular Landau state are due to local effective magnetic anisotropy changes induced by stress relaxation at the sample edges.
Ferromagnetic properties of MnAs/Ge multilayers grown by molecular beam epitaxy
Authors: Lee Jaejin , Cui Yongjie , Song Jonghyun , Kim Yunki , Freeman A. J. , Ketterson J. B. , Cho Sunglae
Published: May 2004

MnAs/Ge multilayer structures successfully fabricated using molecular beam epitaxy were grown on (001) GaAs substrates at a growth temperature of 580 °C. The multilayer with a 100 Å period thickness exhibited ferromagnetism up to 345 K with a coercive field of 147 Oe at 300 K and a vanishingly small in-plane magnetic anisotropy, as determined from temperature-dependent magnetization and hysteresis loop measurements. These results indicate the formation of novel ferromagnetic multilayers, which may have spintronic applications.
High spin filtering using multiple magnetoelectric barriers
Authors: Jalil M. B. A. , Tan S. G. , Liew T. , Teo K. L. , Chong T. C.
Published: May 2004

A periodic array of magnetoelectric barriers is modeled to achieve maximum spin polarization (P) at high transmission probability (T). Each double-pair unit of the array consists of four magnetic barriers designed in several ways, such that an electron passing through, in the Landau gauge A=(0,Ay(x),0), acquires zero gain in kinetic energy. This enables multiple double-pairs to be used to enhance P without sacrificing T. By tuning the magnetoelectric barrier heights, a high P of 75%–100% is obtained at 0.8–1.0EF, for a 27 unit array. For antisymmetrical arrays, electrical barriers act as a switch to the polarization capability.
Effect of composition and cooling rate on the structure and magnetic entropy change in Gd5SixGe4−x
Authors: Yan A. , Handstein A. , Kerschl P. , Nenkov K. , Müller K.-H. , Gutfleisch O.
Published: May 2004

The effects of composition and cooling rate on the structure and the magnetic entropy change in Gd5SixGe4−x (x=1.7,2) were investigated. A large magnetic entropy change was obtained in cast and quenched Gd5Si2Ge2, which was attributed to a magnetic field-induced phase transition. This transition is significantly weakened in the slowly cooled sample, leading to a lower magnetic entropy change. The Gd5Si2Ge2-type phase in the Gd5Si2Ge2 alloy is metastable at room temperature, while it is stable in the Gd5Si1.7Ge2.3 alloy. The transition can be induced in the Gd5Si1.7Ge2.3 near room temperature by a pulsed field of 48 T.
Bias dependent tunneling in ferromagnetic junctions and inversion of the tunneling magnetoresistance from a quantum mechanical point of view
Authors: Li Fei-fei , Li Zheng-zhong , Xiao Ming-wen , Du Jun , Xu Wang , Hu An , Xiao John Q.
Published: May 2004

In the framework of the free-electron approximation, we have developed a quantum mechanical treatment for describing the bias dependent tunneling in FM/I/FM ferromagnetic junctions. In our theory, the Slonczewski model is extended to include the bias effect. In the barrier region, the Wentzel–Kramers–Brillouin wave function is used following Harrison. The main point of our treatment is to match the wave functions at both sides of the electrode/barrier interfaces quantum mechanically. We find that apart from the usual density of states effect, there exists a quantum coherent factor D(Ex,V)=κR2(Ex,V)−kR↑(Ex,V)kR↓(Ex,V), which decreases monotonously with the increasing applied bias and could change its sign at a sufficiently high bias. The characteristic of this coherent factor can explain the observed rapid decrease of tunneling magnetoresistance (TMR) with increasing bias and the sign change of TMR in some ferromagnetic junctions. Furthermore, numerical results for asymmetry barrier junctions provide a good understanding to the observed asymmetry of the TMR versus V curve in junctions with composite barrier (e.g., Al2O3/Ta2O5).
Vacancies at Mn-sites in LaMn1−xO3 manganites: Interplay between ferromagnetic interactions and hydrostatic pressure
Authors: Markovich V. , Rozenberg E. , Gorodetsky G. , Jung G. , Fita I. , Puzniak R. , Wisniewski A. , Martin C. , Hebert S. , Raveau B.
Published: May 2004

Magnetic properties of self-doped LaMn1−xO3 manganites (0⩽x⩽0.06) under hydrostatic pressure up to 12 kbar have been investigated. Samples with x=0 and 0.02 are antiferromagnetic insulators with a Néel temperature TN=138 K and 124 K, respectively. Materials with x=0.04 and 0.06 are ferromagnetic with a Curie temperature TC close to 110 K. With increasing self-doping, the ferromagnetic moment at T=5 K increases significantly while the pressure coefficient of TN decreases significantly. Pressure dependences of TC and of spontaneous magnetization are markedly different. For x=0.04, both quantities increase under increasing pressure. However, for x=0.06 transition temperature becomes pressure independent while magnetization markedly decreases with increasing pressure. Suppression of the ferromagnetism under pressure is tentatively attributed to the development of antiferromagnetic domains capable of competing with the ferromagnetic order under pressure.
Stoichiometry–anisotropy connections in epitaxial L10 FePt(001) films
Authors: Barmak Katayun , Kim Jihwan , Lewis Laura H. , Coffey Kevin. R. , Toney Michael F. , Kellock Andrew J. , Thiele Jan-Ulrich
Published: May 2004

The order parameters and anisotropy constants of a series of epitaxial L10 FePt films with compositions in the range of 45–55 at. % Fe and nominal thicknesses of 50 nm have been characterized. The films were made by cosputtering the elements onto single crystal MgO(001) substrates. The substrates were coated with 1 nm Pt/1 nm Fe bilayer seeds prior to alloy deposition. Both the bilayer seed and the alloy film were deposited at 620 °C. Lattice and order parameters were obtained by x-ray diffraction. Film compositions and thicknesses were determined by Rutherford backscattering spectrometry, and room-temperature magnetocrystalline anisotropies were determined with a torque magnetometer. It was found that the order parameter had a maximum for the film composition closest to the equiatomic composition, whereas the magnetocrystalline anisotropy increased as the Fe content increased from below to slightly above the equiatomic composition. These results imply that nonstoichiometric FePt compositions, with a slight excess of Fe, may in fact be preferred for applications that require high anisotropy.
Structural and transport studies of stoichiometric and off-stoichiometric thin films of the full Heusler alloy Co2MnSi
Authors: Singh L. J. , Barber Z. H. , Miyoshi Y. , Branford W. R. , Cohen L. F.
Published: May 2004

Co 2 MnSi Heusler alloy thin films have been grown by cosputtering from three elemental targets. Changes in growth temperature and stoichiometry affect the film texture and the temperature dependence of the resistivity. However, the spin polarization of the transport current is insensitive to these changes, being of the order of 54% as determined by point contact Andreev reflection spectroscopy. Stoichiometric films are single phase, have a strong (110) texture, and a saturation magnetization of 1007 emu/cc (4.95 μB/formula unit) at 10 K.
Room-temperature ferromagnetism in manganese doped reduced rutile titanium dioxide thin films
Authors: Wang Zhenjun , Tang Jinke , Chen Yuxi , Spinu Leonard , Zhou Weilie , Tung Le Duc
Published: May 2004

Mn x Ti 1−x O 2−δ  (x=0.02–0.12) thin films grown on α-Al2O3 substrates by pulsed-laser deposition have been investigated. X-ray diffraction and transmission electron microscopy results indicate that the films are single phase and reduced rutile-type. Superconducting quantum interference device magnetometer measurements show the films are ferromagnetic at room temperature with nonzero coercivity up to 170 Oe. The saturation magnetization of the reduced films is as high as 0.83 μB per Mn atom at room temperature. The temperature dependence of the resistivity shows semiconducting behavior with p-type carriers. The nature of the p-type conduction and its significance to the ferromagnetism are discussed.
Quantifying the thickness of magnetically active layers using x-ray resonant magnetic scattering
Authors: Barnes B. M. , Li Z. , Savage D. E. , Wiedemann E. , Lagally M. G.
Published: May 2004

X-ray resonant magnetic scattering measurements below and above the critical angle for total external reflection allow fitting to extract the magnetically active volume within specific magnetic layers. Uncapped ultrathin Co films deposited onto Ni on Si display more magnetic resonant response than do those grown directly onto the native oxide of Si.