bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetization of two-dimensional XY magnets with symmetry breaking fields: Relevance to ultrathin magnetic films (abstract)
Authors: Rothman J. , Holdsworth P. C. W. , Bramwell S. T.
Published: July 2002

The magnetization of ultrathin films shows a power law dependence on temperature with an exponent β that depends on the spin anisotropy. Experimentally it is found that films with easy-axis anisotropy show β=1/8, characteristic of the two-dimensional Ising model, while those with dominant easy-plane anisotropy show β=0.23. We recently discussed the finite size magnetization of the XY model and showed that this system has universal behavior which leads to the exponent β=0.23. A number of authors have therefore interpreted their results in terms of the finite size two-dimensional XY model. The success of these explanations implies that the four- and sixfold anisotropy fields present in real films are irrelevant in determining the critical behavior of the magnetization. In the sixfold case this observation agrees with theoretical expectations, while in the fourfold case the situation is unclear, as the renormalization group analysis of José et al. shows the fourfold field to be a marginally relevant variable which gives rise to nonuniversal exponents. This theoretical result, however, pertains to the thermodynamic limit and is not necessarily relevant to real finite systems. We investigate the effect of symmetry breaking fields on the magnetic behavior of idealized finite size XY models by means of Monte Carlo simulation. We find that the fourfold field is indeed irrelevant for the system sizes of interest, and may only become relevant for system sizes beyond the physical domain. We also confirm that the sixfold field is both qualitatively and quantitatively irrelevant, and notice a number of novel features connected with the behavior of finite size models which cannot be observed in the thermodynamic limit.
Preparation and the magnetic properties of Co-γ-Fe2O3 perpendicular magnetic films on NiO underlayer
Authors: Doi T. , Tamari K.
Published: July 2002

The NiO underlayer, which had 〈100〉 orientation, with NaCl-like structure could be prepared onto the glass substrate by reactive rf sputtering at ambient temperature. The CoO/Fe3O4 multilayers were grown epitaxially on the underlayer at 200 °C; the Fe3O4 and CoO on the NiO grew along the 〈100〉 axis independent of the bilayer thickness Λ, though those on the glass substrate did not show the 〈100〉 orientation for Λ≳100 Å. Followed by annealing of the multilayers in air at 280–350 °C, the 〈100〉-oriented Co-γ-Fe2O3 perpendicular magnetic films were obtained. The (400) of the Co-γ-Fe2O3 on the (200) of the NiO has tensile stress at the interface because of the smaller (400) spacing than the (200) spacing normal to the film plane. Therefore, the (400) spacing measured parallel to the film plane (2.072 Å) was smaller than that of bulk, 2.086 Å. The magnetic properties of the Co-γ-Fe2O3 films on the NiO, Co-γ-Fe2O3/NiO, obtained above were evaluated. The squareness compensated by a demagnetization coefficient of Co-γ-Fe2O3/NiO were more than 0.94, though those of the Co-γ-Fe2O3 on the glass substrate, Co-γ-Fe2O3/glass, were about 0.85. The anisotropy energy of Co-γ-Fe2O3/NiO was estimated 3.3×106 ergs/cm3, which value was larger than that of Co-γ-Fe2O3/glass (2.5×106 ergs/cm3). Coercivity of the perpendicular hysteresis loop of Co-γ-Fe2O3/NiO increased with Co contents and could be controlled in the region of 0.8–5.0 kOe, although Hc of Co-γ-Fe2O3/glass were 5.0 kOe constantly. The columnar grains of the Co-γ-Fe2O3, whose diameter is 300–500 Å, grew continuously along the columnar grains of NiO.
Cu spin reorientation in Tl(BaSr)PrCu2O7
Authors: Li W.-H. , Lin Y. F. , Wu S. Y. , Hsieh W. T. , Lee K. C. , Lynn J. W. , Lai C. C. , Ku H. C.
Published: July 2002

The Cu spins in TlBa2PrCu2O7 order at TN≊370 K with a spin structure that is collinear and is characterized by the {1/21/21} wave vector, where the nearest neighbor spins are aligned antiparallel along all three crystallographic directions. If 50% of the Ba atoms are randomly replaced by the smaller Sr atoms to form Tl(BaSr)PrCu2O7, the TN of the Cu spins reduces to 350 K but the magnetic structure that forms below TN is the same. However, at T≊20 K the Cu spins undergo a change in structure, and the spin arrangement is then characterized by the {1/21/21/2} wave vector below T≊12 K. The ground state spin structure of the Cu ions in Tl(BaSr)PrCu2O7 is hence noncollinear, where the spin directions of the nearest neighbor Cu ions in the ab plane remain collinear and antiparallel while along the c axis they are orthogonal. These results demonstrate that the atoms in the BaO layers are also actively participating in the coupling between the Cu ions.
New spin glass Fe0.67Cr1.33Sn0.67S4 with magnetic ions in tetrahedral and octahedral sublattices (abstract)
Authors: Koroleva L. I. , Lukina L. N. , Odintsov A. G. , Virovets T. V.
Published: July 2002

To date, spin glass state is observed in chalcogenide spinels with magnetic ions either in tetrahedral A sublattice or in octahedral B sublattice. The possibility of spin glass state in chalcospinels with magnetic ions in both of A and B sublattices is not evident because the intersublattice antiferromagnetic superexhange is more higher than intrasublattice ferromagnetic superexhange. In the present paper the magnetic and electrical properties of first produced spinel Fe0.67Cr1.33Sn0.67S4 are studied. This sample is p-type semiconductor. Here B sublattice is diluted of diamagnetic Sn4+ ions and Fe2+ ions deficiency exists in A sublattice. The isotherms of the magnetization σ are not saturated in investigation region of magnetic field H≤35 kOe and of temperatures 4.2≤T≤120 K. At the same time, this sample possesses magnetic properties typical of spin glass. Thus a maximum on the temperature dependence of the magnetic susceptibility measured in a weak ac field is founded at the freezing temperature Tf. (The frequency region is 0.3≤ω≤2 kHz, H∼=0.3 Oe.) The maximum is lowered under a static magnetic field which is applied parallel to the ac field. Low-temperature magnetization in the weak field depends on the cooling process (with or without field). The Tf(ω) dependence obeys the power law and Tf(H,T) dependence obeys the Almeida–Touless relation; these facts attest that phase transition spin glass–paramagnetic exists in this sample. This is a first spin glass among chalcospinels with magnetic ions in A and B sublattices.
Morin-like spin reorientation in BiPb-2201 ferrates with iron in octahedral oxygen coordination
Authors: Rosenberg M. , Sinnemann Th. , Filoti G. , Kemmler-Sack S.
Published: July 2002

From a Mössbauer spectroscopy study of the BiPbSrCaFe6+z ferrate, prepared under different conditions, strong evidence for a variety of Morin-like spin-reorientation processes similar to the ones occuring in hematite was found. The phase evolution, their energetical and dynamical Mössbauer parameters as well as the spin-rotational process are described in detail and finally correlated with a proposed mechanism.
Raman heterodyne detection of magnetic resonance in a phosphate glass
Authors: Liu G. K. , Loong C.-K. , Beitz James V. , Cao Ruoxin , Chen Y. H. , Suzuya K.
Published: July 2002

A Raman heterodyne detection of magnetic resonance has been performed for probing the local structure of a sodium phosphate glass doped with trivalent europium. High resolution rf modulation spectra between 0.5 and 10 MHz were observed without the laser field in resonance with electronic transitions of the glass. The intensity of the observed Raman heterodyne signal depends on the external static magnetic field and sample temperature as well as the intensity of the laser and rf fields. The ability of monitoring the rf resonance spectra with micrometer spatial resolution may offer a potentially important means to probe the variation of local structure in disordered solid state materials.
Modeling the stress dependence of Barkhausen phenomena for stress axis linear and noncollinear with applied magnetic field (abstract)
Authors: Sablik M. J. , Augustyniak B. , Chmielewski M.
Published: July 2002

The almost linear dependence of the maximum Barkhausen noise signal amplitude on stress has made it a tool for nondestructive evaluation of residual stress. Recently, a model has been developed to account for the stress dependence of the Barkhausen noise signal. The model uses the development of Alessandro et al. who use coupled Langevin equations to derive an expression for the Barkhausen noise power spectrum. The model joins this expression to the magnetomechanical hysteresis model of Sablik et al., obtaining both a hysteretic and stress-dependent result for the magnetic-field-dependent Barkhausen noise envelope and obtaining specifically the almost linear stress dependence of the Barkhausen noise maximum experimentally. In this paper, we extend the model to derive the angular dependence observed by Kwun of the Barkhausen noise amplitude when stress axis is taken at different angles relative to magnetic field. We also apply the model to the experimental observation that in XC10 French steel, there is an apparent almost linear correlation with stress of hysteresis loss and of the integral of the Barkhausen noise signal over applied field H. Further, the two quantities, Barkhausen noise integral and hysteresis loss, are linearly correlated with each other. The model shows how that behavior is to be expected for the measured steel because of its sharply rising hysteresis curve.
Circumferential magnetization processes in CoFeBSi wires
Authors: Domínguez L. , Blanco J. M. , Aragoneses P. , González J. , Valenzuela R. , Vázquez M. , Hernando A.
Published: July 2002

The total impedance, Z, of low magnetostriction wires (Co0.94Fe0.06)72.5B15Si12.5 was measured at 100 kHz under ac currents of various amplitudes, i, for as-cast and current annealed samples. We show that curves Z vs i can represent circumferential permeability curves and that the features observed on these curves as a consequence of annealing can be interpreted due to the induced magnetic anisotropy by the effect of the current annealing.
Superconducting properties of Hg-1223 prepared by using fluorides
Authors: Jönsson B. J. , Turkki T. , Ström V. , Iqbal Z. , Rao K. V.
Published: July 2002

A new approach involving the use of fluorides has been adopted to synthesize phase-pure Pb-substituted Hg-1223 superconductors under ambient conditions. A representative sample is characterized using x-ray, SQUID magnetometer, and ac susceptibility techniques. In a measuring field of 1 G, a sharp diamagnetic onset is observed at 132 K and perfect flux screening persists up to 122 K. On approaching Tc the irreversibility line follows a power law with exponent α=2.2. From the ac susceptibility data, in the context of the Bean critical state model, the critical current density at helium temperatures is estimated to be 1.5×106 A/cm2.
Vortex gliding between Cu–O planes in an anisotropic high temperature superconductor (abstract)
Authors: Durán C. A. , Gammel P. L. , Bishop D. J.
Published: July 2002

The magnetooptical technique was used to directly observe the magnetic flux penetration in single crystals of the La–Sr–Cu–O superconductor. The large size of the crystals (several millimeters along the three axes) allows for observations to be made along the different crystalline orientations. In a previous study, we reported on direct measurements of critical currents and the dependence of their anisotropy on the amount of Sr doping. When looking at the behavior of vortices which are parallel to the Cu–O planes, we observed that the roughness of the flux fronts was greatly magnified for the highly anisotropic samples. This suggested that the vortices were moving between the planes, as if they were in independent channels. In this communication, we report on observations made when an additional field component is applied along the c axis. Our experiments show that this additional component strongly suppresses the vortex penetration, drastically reducing the apparent anisotropy of the critical currents. We argue that this behavior is consistent with a picture in which the vortices easily move (‘‘glide’’) between the Cu–O planes, and only feel the pinning potential when they are tilted by the additional field component, and thus forced to ‘‘puncture’’ the planes.
The magnetic response at the metal–insulator transition in La1−xSrxTiO3 (abstract)
Authors: Osborn R. , Aronson M. C. , Goremychkin E. A. , Greedan J. E.
Published: July 2002

We report on recent inelastic neutron scattering measurements of the magnetic response close to the metal–insulator transition in La1−xSrxTiO3. Specific heat and susceptibility data from Tokura et al. give evidence for a divergent effective mass at the critical concentration xc=0.05 in agreement with recent mean-field theories of the transition. The mass enhancement is believed to arise from the formation of a d-electron resonance at the Fermi energy close to the transition. The aim of this investigation is to look for evidence of this resonance in the dynamic magnetic susceptibility. We studied samples with x=0, 0.05, and 0.2 using incident energies between 25 and 200 meV. After correction for the phonon scattering, we observe a broad response above a threshold of 20–30 meV extending to over 100 meV. In addition, the Mott insulating antiferromagnet (x=0) has a peak at 40 meV, consistent with the estimated activation energy derived from resistivity measurements. This feature becomes washed out with temperature and doping. Possible origins for this peak are discussed.
Temperature and field-induced spin reorientations in NdFe10−xCoxMo2 single crystals
Authors: Mendoza W. A. , Shaheen S. A.
Published: July 2002

Single crystals of the NdFe10−xCoxMo2 alloy system (x=0,1,3,5,7,10) have been prepared by the Czochralski technique and studied by x-ray and magnetometry techniques. All of the compounds in this series crystallize in the tetragonal ThMn12-type structure. The single-crystal data support the previous findings on polycrystalline samples, namely, that (1) with increasing Co content, the easy direction of magnetization at 300 K appears to deviate from the c axis for x≤3, and becomes axial for x≥5; (2) temperature-induced spin reorientations are observed for x<3; and (3) for x≥5, no temperature-induced but field-induced spin reorientations are observed. Single-crystal data also clarify the anomalies observed in the temperature-dependent magnetization data on polycrystalline samples.
Aspects of sintering barium hexaferrite with SiO2, Al2O3, CaCO3, and Y6Fe10O24 additions for microwave applications (abstract)
Authors: Fagan J. G. , Snyder R. L. , Hach C. , Jones L. , Ings J. B. , May J. , Simmins J. J.
Published: July 2002

Results are presented regarding the sintering mechanisms of barium hexaferrite (BaFe12O19) and modification thereof via secondary phase additions. Additional studies are presented concerning the effect of additives and microstructural development on the resultant microwave frequency magnetic and dielectric loss properties. The increasing demands on materials for microwave application has required development of barium hexaferrites to achieve fine grain size (i.e., ≤1 μm), a high degree of c axis alignment, high density and a minimum in dielectric loss. To accomplish such a task one area of interest is that of incorporating secondary phases. Additions of SiO2, Al2O3 and CaCO3 are examined in terms of grain size, magnetic, and dielectric loss properties. Thermal analysis methods revealed a redox reaction associated with the sintering process in barium hexaferrite. The use of yttrium iron garnet (Y6Fe10O24) indicated an enhanced densification behavior in comparison to undoped barium hexaferrite which was associated to a decreased redox reaction temperature. The inclusion of the SiO2, Al2O3, and CaCO3 additions were seen to inhibit the redox reaction as measured via thermal analysis while liquid phase sintering occurred.
Kondo behavior in CeNi0.4Cu0.6
Authors: Espeso J. I. , García Soldevilla J. , Gómez Sal J. C. , Reiffers M. , Blanco J. A.
Published: July 2002

The effect of the substitution of Ni by Cu on the CeNi compound is analyzed by means of susceptibility, magnetization, and magnetoresistance measurements on the pseudobinary CeNi0.4Cu0.6 compound. Down to 2 K, the lowest investigated temperature, the compound does not present any magnetic order, but magnetic measurements suggest an ordering temperature (TC) not far below 2 K. Magnetization and magnetoresistance data show an important Kondo interaction leading to a Kondo temperature (TK) higher than TC. The results are discussed considering the Kondo, magnetic exchange, and crystalline electric field interactions.
Currents at angle to the planes of the layers (abstract)
Authors: Levy P. M. , Zhang S. , Ono T. , Shinjo T.
Published: July 2002

A new class of corrugated multilayers has been grown on silicon substrates which have (111) faceted grooves etched on their surface. These structures can be probed by conventional means with current at an angle to the plane of layers (CAP) as well as CIP. This angle is fixed by: the depth to width ratio of the grooves (which determines the angle θ), and the angle φ of the current probes with respect to the grooves. We have prepared multilayers of [Co(12 Å) Cu(t)NiFe(12 Å) Cu(t)]y with t=58 and 116 Å, and y=167 and 91 repeats, respectively; and have varied φ from 0 and 90° while θ is held fixed at 54.7°. We find the data is very well fit to the theoretical expression for CAP resistivity in terms of the more conventional CIP and CPP resistivities. From measurements of the CIP and CAP–MR’s on these corrugated multilayers we are able to predict the CPP–MR for these structures.
Giant magnetoresistance and magnetic phase diagram of UNiGa
Authors: Prokeš K. , Brück E. , de Boer F. R. , Mihálik M. , Menovsky A. , Burlet P. , Mignot J. M. , Havela L. , Sechovský V.
Published: July 2002

As a result of combined magnetization, specific heat, electrical resistivity, and neutron-scattering studies on single crystals, we present a complex magnetic phase diagram of UNiGa that exhibits several antiferromagnetic (AF) phases below TN=39 K. A relatively low magnetic field (∼1–1.5 T) applied along the c-axis induces metamagnetic transitions from the zero-field AF structures to an uncompensated AF and/or to a ferromagnetic (F) phase. All the magnetic structures are collinear (uranium magnetic moments parallel to the c-axis of the hexagonal structure). They consist of F basal-plane sheets which are coupled along c in various ways. The strongly anisotropic magnetism in UNiGa causes anisotropy of the electrical resistivity. The magnetic phase transitions are reflected in pronounced resistivity anomalies especially for current along the c-axis. The metamagnetic transitions are accompanied by giant magnetoresistance (GMR) effects which can be correlated with respective changes of the magnetic periodicity. This implies an important feature of the mechanism responsible for GMR phenomena in UNiGa. The strong resistance enhancement in the paramagnetic range when approaching TN is connected with AF short-range ordering with propagation along the c-axis.
Ferromagnetic resonance of sputtered Co/Mn multilayers (abstract)
Authors: Spoddig D. , Schreiber F. , Pflaum J. , Wang Q. , Zabel H. , Pelzl J.
Published: July 2002

Co/Mn multilayers were prepared by rf sputtering onto single-crystal MgO and sapphire substrates resulting in, respectively, (001)- and (111)-oriented layers. The structure was thoroughly analyzed by x-ray scattering in various geometries (Q. Wang et al. to be published). For the magnetic investigations, ferromagnetic resonance (FMR) was applied. Complementary measurements employed the magneto-optical Kerr-effect (MOKE) and Faraday balance magnetometry. Results for the in-plane anisotropy, the surface anisotropy, the magnetization, and the FMR linewidth are presented. The comparison with other Co-based multilayer systems indicates that both the structural and the magnetic properties of the Co/Mn system are more complicated than in the case of systems with a presumably weaker electronic interaction at the interface [see also K. Ounadjela et al., Phys. Rev. B 49, 8561 (1994)].
Studies of Fe/Cr multilayer and trilayer films
Authors: Ho E. M. , Daykin A. C. , Petford-Long A. K.
Published: July 2002

Series of sputter-deposited Fe3 nm/Crx multilayer and Fe/Cr/Fe trilayer films have been analyzed. The small magnetoresistance exhibited by the multilayer films is attributed to very rough interfaces and poor Cr layer quality. The hysteresis loop data show the interlayer exchange coupling to be predominantly antiferromagnetic. In situ magnetizing of the trilayer films in a Lorentz TEM showed that for a 1.2 nm thick Cr layer the moments of the Fe layers lie approximately parallel at remanence rotating to antiparallel only when the field is increased. The magnetic moments in an Fe12 /Cr0.6 nm/Fe12 nm trilayer film were found to be parallel aligned under an applied field whereas the hysteresis loop for the multilayer films with the same Cr thickness suggest the existence of antiferromagnetic interlayer exchange coupling.
Criticality of the fully frustrated XY model: A study using Monte Carlo hard-spin mean-field theory (abstract)
Authors: Tesiero James E. , McKay Susan R.
Published: July 2002

The number and types of phase transitions occurring in the two-dimensional fully frustrated XY model have remained controversial in spite of over a decade of attention. In this study, we have developed a Monte Carlo hard-spin mean-field approach for models with a continuous spin variable and applied it to this system. From our calculations of the chirality, helicity modulus, specific heat, and sublattice magnetizations, we find that reflection and rotational symmetries are broken at the same temperature. The chirality, order parameter for the reflection symmetry breaking, exhibits power-law dependence on T−Tc with a critical exponent of 0.246±0.006. This result is decisively different from the mean-field value of 0.500, which would be obtained for a transition in the Ising universality class using this method. This finding enables us to rule out the possibility of two separate transitions, too closely spaced in temperature to be resolved by our calculation. The magnitude of the magnetization on each sublattice also shows power-law behavior as a function of temperature in the critical region, with a critical exponent of 0.126±0.002.
Theory of nonlinear magneto-optics (invited)
Authors: Pustogowa U. , Luce T. A. , Hübner W. , Bennemann K. H.
Published: July 2002

Nonlinear magneto-optics is a very sensitive fingerprint of the electronic, magnetic, and atomic structure of surfaces, interfaces, and thin ferromagnetic films. Analyzing theoretically the nonlinear magneto-optical Kerr effect for thin films of Fe(001) and at Fe surfaces we demonstrate exemplarily how various electronic material properties of ferromagnets, such as the d-bandwidth, the magnetization, the substrate lattice constant, and the film-thickness dependence can be extracted from the calculated nonlinear Kerr spectra. Furthermore, we show how the substrate d electrons [Cu(001)] affect the nonlinear Kerr spectra even without being themselves spin-polarized and without film-substrate hybridization. We show that the Kerr rotation angle in second-harmonic generation is enhanced by one to two orders of magnitude compared to the linear Kerr angle and how symmetry can be used to obtain the direction of magnetization in thin films and at buried interfaces from nonlinear magneto-optics.
Periodic breathing oscillations and instabilities in ferrofluids (abstract)
Authors: Luo Weili , Du Tengda
Published: July 2002

Periodic breathing oscillations and instabilities are observed in diffraction patterns of ferrofluids in the presence of a magnetic thermal lens effect. The results crucially depend on (1) the boundary conditions, (2) the strength of external magnetic field, (3) the concentration of magnetic particles, and (4) the thickness of the sample layer. There is a critical field above which instabilities occur. Under a semifree surface boundary condition, the observed oscillation frequency ω is found to vary with external magnetic field according to ω∼H1/2 for small field. In the confined geometry, diffraction patterns show random rotation of various shapes between Hc1 and Hc2. The mechanisms responsible for these phenomena will be discussed.
Effects of surface condition on Barkhausen emissions from steel
Authors: Parakka A. P. , Jiles D. C. , Gupta H. , Jalics S.
Published: July 2002

Temperature changes during mechanical processing such as grinding of steel parts can cause phase changes in the microstructure. Thermal shock during the process can give rise to localized surface residual stress. The net result can be reduced wear resistance and fatigue life leading to early failure during service. Effective methods for the detection of such damage are necessary. Barkhausen emissions, which arise from discontinuous motion of domain walls, are sensitive to microstructual changes that affect domain dynamics. Detected Barkhausen signals are predominantly from a surface layer about 200 μm thick, those from deeper being attenuated due to eddy currents. An analysis of the detected signals can provide an indication of the surface condition of the material. Barkhausen signals from parts ground under controlled conditions were found to be dependent on the grinding process conditions. The signal changes were consistent with residual stress measured by x-ray diffraction and with hardness measurements that are indicative of changes in microstructure.
Simultaneous Barkhausen discontinuities of multiple die-drawn Fe-Si-B amorphous wires connected with amorphous ribbons (abstract)
Authors: Soeda M. , Yamasaki J.
Published: July 2002

In-rotating water quenched Fe-Si-B amorphous wire exhibits the Barkhausen discontinuities (BD) in the as-cast state. Its minimum length to exhibit the BD depends on the demagnetizing effect. The minimum length is around 9 cm for the as-cast wire with 120 μm diameter. For sensor application of the wire as a pulse voltage generator, small size sensor elements are needed. Die-drawn wires with reduced diameter and minimum length of up to 2 cm exhibit BD1 and are expected for such use. But the pulse voltage induced in the sense coil by the BD decreases because of decreased volume of the wire. In this study, an attempt was made successfully to develop a small size BD sensor element with higher pulse voltage using multiple Fe77.5Si7.5B15 die-drawn wires having 30 μm diameter and 4 cm long. Three die-drawn wires were put together closely in parallel and two pieces of Co74.26Fe4.74Si2.1B18.9 amorphous ribbon (5 mm×2 mm×25 μm) were attached to the wire ends. It was found that the BD of the three wires occur simultaneously at the same threshold field. Domain change of ribbon before and after the BD was observed with a Kerr microscope. It was found that the amorphous ribbons were magnetized by the stray field from the ends of the wires in the direction opposite to the magnetization of the wire and that the magnetization of the ribbon changes discontinuously synchronizing with the magnetization of the wire. So it is likely that the magnetizations of the multiple wires and ribbon form stabilized flux closure and that the simultaneous BD of multiple wires is triggered by the flux jump of the wire having the lowest threshold field.
The influence of domain activities on MR head performance
Authors: Ye Weichun , Yu Jinyue , Cai Bingchu
Published: July 2002

The relation of signal distortion of MR heads to the domain structure and the domain activities was studied in this paper. Several kinds of MR elements were fabricated and a measurement system was set up to measure magnetoresistivity. A large drop near the peak of the output wave form was found for some MR elements. And the magnetic structure of the MR element was investigated by the ‘‘Bitter pattern.’’ It was seen that there existed multidomain in the part of the lead without gold coating. Furthermore, it was also found that the multidomain existed in the junction of leads and the MR element, and the new domain looked like a hook. The appearance of this hook-shaped multidomain has not been reported up to now in literature. The design of the MR element was modified to eliminate the drop in the output wave form and the drop was reduced substantially. Our study shows that suitable geometric dimensions and structures of leads are also very important to high performance of MR head in head design in addition to select the optimum biasing conditions.
Iron whisker domain patterns imaged by garnet films
Authors: Lee J.-G. , Govorkov S. A. , Arrott A. S.
Published: July 2002

Bismuth doped yttrium iron garnet thin films formed on the surfaces of a gadolinium gallium garnet substrate are used as magneto-optical indicators for quantitative studies of the micromagnetics of an iron whisker. The method does not require image processing. A field applied perpendicular to the whisker axis splits a 180° domain wall into two 90° sections slightly separated by a section magnetized in the direction of the perpendicular field. A field along the axis of the whisker has a similar effect. Where the region between the two split 90° sections intersect the surface, there is a magnetic charge that strongly affects the domain pattern of the indicator film. More generally, domain walls become visible because the local internal susceptibility is greater at the walls than in the domains. The magneto-optical indicator can be used to measure both susceptibilities.
Magneto-optical indicator film (MOIF) microscopy of granular and layer structures (abstract)
Authors: Nikitenko V. I. , Gornakov V. S. , Dedukh L. M. , Khapikov A. F. , Bennett L. H. , McMichael R. D. , Swartzendruber L. J. , Shapiro A. J. , Donahue M. J. , Matveev V. N. , Levashov V. I.
Published: July 2002

We report on the possibilities of application of magneto-optical indicator film (MOIF) technique for visualization and direct experimental study in real time of the magnetization processes and nondestructive characterization of the quality of magnetic thin granular films and multilayers. The technique utilizes a transparent indicator film, a Bi-substituted iron garnet with in-plane anisotropy, placed on the top of a sample. Polarized light passes through the indicator film and is reflected back by an Al underlayer. Magnetic stray fields with a component perpendicular to the film plane are observed through the magneto-optic Faraday effect created in the garnet film. An investigation of the magnetic moment distribution in granular single films and multilayers was carried out using this method. Some examples of magnetic stray field images of domain walls of different types obtained by MOIF technique and magnetic force microscopy are described. The experimental data are compared with theoretical estimations. The detailed information is obtained on the spin rotation processes as well as on the domain wall nucleation and motion during the remagnetization of these materials. Peculiarities of the magnetization reversal of multilayers with different types of exchange interlayer coupling have been revealed and discussed.
Quantum dynamical calculations in clusters of spin 1/2 particles: Resonant coherent quantum tunneling on the magnetization reversal
Authors: García-Pablos D. , García N. , Serena P. A. , De Raedt H.
Published: July 2002

We investigate the reversal of magnetization and the coherence of tunneling when an external magnetic field is rotated instantaneously in systems of a few (N) spin 1/2 particles described by an anisotropic Heisenberg Hamiltonian at T=0. The temporal evolution is calculated by a numerically exact solution of the time-dependent Schrödinger equation, and the mean value in time of each spin component is computed as a function of the magnetic field. The correlation function and the spectrum are analyzed in terms of the macroscopic quantum coherence. Our calculations demonstrate that this model for small (N<11) magnetic particles exhibit collective tunneling of the magnetization only for some specific resonant values of the applied magnetic field, at variance with the Stoner–Wohlfarth model.
Low temperature magnetic relaxation and quantum tunneling in nanocrystalline particles (abstract)
Authors: Zhang X. X. , Hernandez J. M. , Kroll E. C. , Ziolo R. , Tejada J.
Published: July 2002

We report measurements of the magnetic relaxation rate versus temperature for ferrofluid and magnetic-glass samples, which are formed by a modification of nanocomposite material consisting of nanocrystalline CoFe2O4 and polymer. The magnetic properties of the samples have also been studied by using SHE-SQUID at different temperatures (1.8–300 K) with low and high applied magnetic field (−5 T to 5 T). The magnetic relaxation in two samples show a perfect logarithmic dependence on the time, i.e., M(t)=M(t0)[1−S ln(t/t0)], in accordance with the ZFC-FC results which indicate that there is wide energy distribution. The temperature independence of magnetic viscosity S≡[1/M(t0)dM/d]ln t below several Kelvin for the two samples gives clear evidence of macroscopic quantum tunneling of magnetization, in accordance with current theories of quantum tunneling of magnetization.
Characterization of Fe17R2 phases (R=Pr and Sm) oxidized at 200 °C
Authors: Gama S. , Ribeiro C. A. , Cabral F. A. O. , Colucci C. C. , de Morais E. , Sanjurjo N. L. , Campos C. , Ardisson J. D. , Persiano A. I. C.
Published: July 2002

The results of oxygen absorption in temperatures ranging from 200 to 500 °C are reported for the phases Fe17R2, R=Pr and Sm. It was observed that the oxygen saturation limit is temperature dependent, being of 3 at/fu at 200 °C, 12.8 at/fu at 300 °C, 20.3 at/fu at 400 °C, and 28.5 at/fu at 500 °C. This implies that above 200 °C the phase is deeply altered by oxygen absorption. Samples with absorption at 200 °C were studied as prepared and heat treated at 500 °C/40 h. The results show that the heat-treated samples consist of Fe17R2, Fe, and R2O3. Metallographic examination, susceptibility, and Mössbauer spectroscopy data support the hypothesis that the as-prepared samples consist of a mixture of Fe17R2 and ordered interstitial Fe17R2Ox.
Magneto-optical properties of (BiGdY) iron garnets for optical magnetic field sensors
Authors: Kamada O.
Published: July 2002

The influence of the magnetization process of the stripe domain both on the linearity error and the temperature dependence of the sensitivity in (BiGdY)3Fe5O12 films for optical magnetic field sensors are studied. By measuring the dc applied field dependence of the light beam diffraction angle by the periodic magnetic domain structure, the domain period and the reduced thickness τ were determined. The magnetization curves calculated for the measured τ parameter show good agreement with the experimental results on the output characteristics. The linearity error of the ac Faraday output were within ±1% in the external field ranging of 10–300 Oe. However, a large linearity error was observed in the small field range. It was also found that the sensitivity is not affected by the temperature dependence of the τ parameter.
Computer simulation of microstructure and interaction effects in fine particle systems (abstract)
Authors: Coverdale G. N. , Chantrell R. W. , El-Hilo M. , O’Grady K.
Published: July 2002

The behavior of the magnetization of a fine particle system is partly determined by the interaction effects between the grains. In a previous study by El-Hilo et al., the magnetic particles were considered to be randomly distributed. Many fine particle systems are expected to exhibit a microstructure that has been influenced by intergrain interactions. This effect on the microstructure will be important during the formation of the solid where the magnetic particles exhibit significant mobility. We have developed a 3D Monte Carlo model of a fluid dispersion which after reaching equilibrium is then allowed to ‘‘freeze’’ to produce a fine particle system with microstructures which vary from clusters in the case of zero field to chains of particles in the saturated field case. This provides an excellent model system for the study of interaction effects. Our previous model is then used to study the resulting magnetic properties of the materials. These include the remanence curves in addition to the hysteresis loops. The local microstructure is shown to have a significant effect on the δI plots which are often used to characterize interaction effects. The simulation of the systems in a solid matrix exhibits an interaction dependent magnetic after effect. Because of the interaction fields, the magnetic configuration also changes with time following a change in temperature leading to a ‘‘waiting time’’ dependence of magnetic properties, an effect also found in spin glasses.
Influence of the crystalline electric field on the magnetic properties of Ga-doped NdBa2Cu3Ox (abstract)
Authors: Allenspach P. , Niraimathi A. M. , Gmelin E.
Published: July 2002

Crystal electric field (CEF) effects are of essential importance for the magnetic properties of rare-earth ions. For NdBa2Cu3Ox the variation of the CEF due to a reduction of oxygen directly influences the character of the magnetic ordering and partially explains the peculiar magnetic behavior of this system: Oxygen reduction transforms the 2D-Ising system just below x=6.9 into a (short-range) 2D-Heisenberg system due to a reduction of the single-ion anisotropy. Since, magnetic specific heat data for Ga-doped NdBa2Cu3Ox resemble very much the oxygen reduced data, neutron CEF spectroscopy of Nd3+ in NdBa2(Cu3−yGay)Ox was performed to deduce the behavior of the single-ion anisotropy. These neutron data in conjunction with paramagnetic susceptibility and specific heat data confirm the strong influence of the CEF on the magnetic ordering of the Nd ions.
Synthesis and superconductivity of intermetallic compounds Y2NixB8−xC2, YNixCu2−xB2C, and YNixCu2−xSi2C
Authors: Zhao Wei , Tang Jinke , Lee Young-sook , O’Connor Charles J.
Published: July 2002

Borocarbide and silicocarbide intermetallic Y2NixB8−xC2 (x=1, 2, 3, 5), YNiCuB2C, and YNixCu2−xSi2C (x=0, 2) were prepared and their superconductivity was studied. The results indicated that with the change of the ratio of Ni to B in Y2NixB8−xC2, secondary phases were introduced into YNi2B2C phase. A Tc of 15.0 K was observed for the compounds x=2, 3, and 5, which originated from the major phase YNi2B2C in these samples. Partial substitution of Ni by Cu reduced the Tc to 11.0 K for YNiCuB2C. For Si substitution system, no bulk superconductivity was found in YNi2Si2C and YCu2Si2C. But a minor superconducting phase (Tc∼4 K) with a volume fraction of the order of near 1% was observed in them. It was noticed that for the temperature-dependent magnetization of superconducting compounds containing Ni, a significant difference between zero-field cooling and field cooling curves before Tc was always observed, which was tentatively attributed to Ni-containing impurity.
Transient response of ultralow flying sliders over contaminated and textured surfaces
Authors: Peck Paul R. , Park Ki-Ook , Jhon Myung S. , Kang Soo-Choon , Shih Tom I.-P.
Published: July 2002

The transient flying dynamics of positive and negative pressure sliders over nonsmooth surfaces were investigated. Surface roughness was modeled by variously oriented sinusoidal waves, and contaminated surfaces were modeled as series of asperities and pits. A finite element algorithm was used which incorporates a generalized form of the Reynolds equation based upon the linearized Boltzmann equation. A new kinetic equation descriptive of ultralow flying was also discussed. Spectral analysis using fast Fourier transformation was adopted to explore the transient behavior of sliders in the frequency domain.
The effect of additives on MSR performance of GdFeCoM/TbFeCo (M=Ta, Pt) double layer
Authors: Moritani Isao , Takahashi Koyata , Kondo Akio , Suzuki Takao
Published: July 2002

Magnetically induced super-resolution performance for a center aperture detection scheme in a double layered magneto-optical storage is discussed. In order to make a readout layer thinner for better media lifetime, the effect of Ta and Pt additive elements in a readout layer GdFeCo on recording performance is systematically studied. Ta is found to be most effective in making it possible to reduce the readout layer thickness for an acceptable recording performance. For the mark length of 0.5 μm, the thickness can be reduced to 60 nm with Ta (1.9 at. %) from 80 nm without Ta for carrier-to-noise ratio (CNR)≥42 dB.
Magnetic circular x-ray dichroism in Fe7S8 and Fe7Se8 (abstract)
Authors: Koide T. , Miyauchi H. , Shidara T. , Nakajima N. , Kawabe H. , Fukutani H. , Shimada K. , Fujimori A. , Iio K. , Kamimura T.
Published: July 2002

Magnetic circular dichroism (MCD) in core-level absorption provides insights into the element-specific and site-selective magnetic states of various magnetic materials. Fe7S8 and Fe7Se8 have the pseudo-NiAs-type crystal structure and are ferrimagnetic below 578 and ∼450 K, respectively. We have measured MCD spectra in the Fe 2p (L2,3) and Fe 3p (M2,3) core-level absorption of these compounds. The L2,3 MCD spectra were taken at ∼80 K with the total electron yield method. The M2,3 MCD spectra were measured at room temperature with the reflection method using the magnetic-field modulation technique. Both experiments were made using circularly polarized undulator radiation. The L2,3 MCD spectra were found to exhibit a negative peak at the L3 edge with a maximum intensity of ∼10−2 and a weaker positive peak at the L2 edge. The MCD spectrum of Fe7S8 showed sideband features near the L3 edge. Utilization of the magnetic-field modulation method allowed a detection of small MCD signals around the M2,3 edges; the maximum signal intensity was of the order of ∼3×10−3. The M2,3 MCD spectrum of Fe7S8 showed a MCD signal for a prethreshold multiplet, while that of Fe7Se8 exhibited no appreciable MCD signal for a prethreshold multiplet. The features observed in the L2,3 MCD and M2,3 MCD are consistent with an electronic band-structure calculation reported recently.
Mössbauer and x-ray diffraction studies of the phase composition of crystallized NdxFe81.5−xB18.5 alloys with 7≤x≤16 (abstract)
Authors: Cheng Zhao-Hua , Shen Bao-gen , Zhang Jun-Xian , Mao Ming-xi , Sun Ji-jun , Li Fa-shen , Zhang Yi-de
Published: July 2002

In previous work, the phase composition of melt-spun Nd-Fe-B with a low Nd concentration (X≤6 at. %) have been extensively investigated by means of x-ray diffraction, spin echo nuclear magnetic resonance, and Mössbauer spectra. However, the phase composition of melt-spun Nd-Fe-B with intermediate and high Nd concentration has not been studied by Mössbauer effect. Based on the knowledge of the 57Fe hyperfine parameters for Nd2Fe14B, Nd1.1Fe4B4 and Nd2Fe23B3, the phases produced during annealing Nd-Fe-B amorphous alloys can be identified with greater sensitivity by Mössbauer spectroscopy than by x-ray diffraction. In the present work, a combination of x-ray diffraction experiments and Mössbauer spectroscopy has been performed on annealed NdxFe81.5B18.5 (7≤x≤16). It is found that the samples with 7≤x≤9 contain Nd2Fe23B3 metastable phase and Nd1.1Fe4B4 paramagnetic phase. The body-centered-cubic structure of Nd2Fe23B3 cannot generate the hard magnetic properties. The samples with 12≤x≤16 consist of Nd2Fe14B magnetically hard phase and Nd1.1Fe4B4 paramagnetic phase. The large coercivity for the high Nd content Nd-Fe-B originates from the very fine size of Nd2Fe14B crystallites below the critical size of single domain particle, which has a pinning domain wall effect.
Magnetic multipole cylinders from mould-injection Nd2Fe14B plastic bonded magnets (abstract)
Authors: Nicolaides G. K. , Niarchos D. , Tsamakis D. , Koubouros I. , Mitsis A.
Published: July 2002

Mould injection Nd2Fe14B magnetic material of density ρ∼4 g/cc and of an energy product (BH)max∼4 MGOe, has been pressed into the form of cylindrical segments in order to investigate the possibility of preparing cylindrical magnetic multipoles which could be used as magnetic gears. The obtained cylindrical bonded magnet segments have a length of 3 cm and an angle width of φ=90° or φ=45°. These segments are easily magnetized along a radial direction at the angle φ/2, using a conventional electromagnet at a magnetic field of 2 T. Subsequently, the opposite magnetized segments are combined and bonded together with ultrasonic technique. The final result of the above procedure is the formation of a magnetic multipole cylinder which could be used as a magnetic gear. Here, except the preparation technique, we report the maximum torque applied versus the magnetization M of the poles and the distance between the gears. The dependence of the applied torque on the rotational frequency is also examined.
Magnetic x-ray linear dichroism in the photoelectron spectroscopy of ultrathin magnetic alloy films
Authors: Tobin J. G. , Goodman K. W. , Mankey G. J. , Willis R. F. , Denlinger J. D. , Rotenberg E. , Warwick A.
Published: July 2002

The magnetic structure of nanoscale alloy films has been probed using the magnetic x-ray linear dichroism in photoelectron spectroscopy. FeNi and CoFe epitaxial films were grown on Cu(001), in situ and using molecular beam epitaxy techniques. The magnetic x-ray linear dichroism measurements were made at the Spectromicroscopy Facility of the Third Generation Advanced Light Source. Because soft x-rays were used to generate photoemission from the 3p core levels, both elemental selectivity and magnetic sensitivity were achieved simultaneously.
Track-width dependence of transition jitter
Authors: Dhagat P. , Glavinas E. , Jander A. , Porter D. G. , Indeck R. S. , Muller M. W.
Published: July 2002

A simple model that represents the microstructure of magnetic medium as a rectangular tesselation predicts that the mean-square jitter is inversely proportional to the track width. We test this prediction using different width heads as well as creating different track widths by partially erasing the original track. We also simulate these experiments using a micromagnetic model. Our experimental and simulation results are found to be in agreement with the prediction.
Trilayer media for high track density longitudinal recording
Authors: Akiyama J. , Ohinata Y. , Hikosaka T. , Taguchi T. , Tanaka Y.
Published: July 2002

This paper introduces a new recording method using a trilayer medium (recording layer/nonmagnetic layer/soft magnetic layer/substrate) to diminish the side written band width (ΔW). Magnetostatic coupling between the soft magnetic layer in the media and the write head poles decreases the side fringing field off the track edges. Off-track overwrite experiments revealed that the trilayer media reduced ΔW by 40%–60% compared to the monolayer medium while maintaining the effective write track width and the linear resolution.
Evolution from soft to hard magnetic behavior in Co-based devitrified glassy alloy
Authors: Bottoni G. , Candolfo D. , Cecchetti A.
Published: July 2002

From the amorphous alloy 6030V having the composition Co71.5Fe1.5Mo1Mn4Si13B9, a series of devitrified specimens with increasingly coarser microstructure and magnetic hardening is produced by annealing. From the features of the coercivity, the squareness ratio, the rotational hysteresis integral, and the magnetic interactions we infer that the magnetic hardening is due initially (Ta<600 °C) to a strengthening of the pinning effect of the precipitates on the domain walls, and then (Ta≳600 °C) to the formation of single-domain Co crystallites where the magnetization reversal mode is of incoherent type.