bluuebunny/crossref_metadata_2025 huggingface dataset:
Transition-metal monoxides: Itinerant versus localized picture of superexchange
Authors: Oguchi T. , Terakura K. , Williams A. R.
Published: February 2003

We demonstrate that energy-band theory based on the local-spin-density-functional treatment of exchange and correlation accounts well for the insulating behavior of MnO, MnS, and NiO. This is true, however, only if the magnetization is allowed to vary in the [111] direction, as is observed experimentally. As a further test of the itinerant picture of these materials, the ‘‘exchange integrals’’ entering a Heisenberg model are calculated, using muffin-tin CPA theory to describe the interaction between two magnetized atoms embedded in a medium of disordered spins. These parameter-free calculations of the coupling strength are the first nonempirical estimates to be in qualitative agreement with measurements. The numerical overestimate of the coupling strength by approximately a factor of three is consistent with the fact that both of the fundamental approximations underlying the estimate act to overestimate the coupling strength; these are: (1) the neglect of magnetic order in the CPA calculations and (2) the neglect of screening effects caused by the response of the electrons to the spin-wave-like perturbations described by a Heisenberg Hamiltonian. The band-theoretic description of superexchange differs qualitatively from the traditional localized-electron picture. Two of the most interesting of these differences concern the observed sharp increase in the coupling strength at the end of the transition series, and the ferromagnetic coupling of nearest Ni neighbors in NiO. The band picture, provides a natural explanation for both observations, whereas the localized picture does not.
Variation of magnetic properties of FezO with nonstoichiometry
Authors: Srinivasan G. , Seehra Mohindar S.
Published: February 2003

First studies of the magnetic susceptibility χ in nonstoichiometric FezO samples, free from any ferromagnetic-type impurities, are reported. These polycrystalline samples for z=0.929, 0.938, and 0.950 were prepared by rapid quenching to 77 from 1100 K and characterized for ferromagnetic impurities by χ studies at room temperature. The χ data on the impurity-free three compositions were taken from 4.2–320 K for both fc (field cooled in 8 kOe) and zfc (zero field cooled) conditions. For zfc samples, χ measured at 200 Oe showed antiferromagnetic ordering with TN =199.2, 195.7, and 192.4 K for z=0.929, 0.938, and 0.950, respectively. The change of TN with z is attributed to a change in lattice constant a and it is found that (∂J2/J2)/(∂a/a)≂−22 (J2= nnn exchange constant). For fc samples, an excess susceptibility χf which increases with decreasing z, is observed and this is attributed to defect clusters.
Magnetic properties of lithium ferrite doped with aluminum and gallium
Authors: Neto J. Maria , Domingues P. H. , Barthem V. M. T. S. , de Souza Barros F. , Guillot M.
Published: February 2003

Measurements are reported on high-field magnetization of powder samples of ordered lithium ferrite doped with Ga and Al [LiFe4.5(Ga,Al)0.5O8]. We found a linear behavior of the spontaneous magnetization with the difference in Ga-Al concentrations. The data were interpreted with the Néel model to give the cation distribution and with the method of Rado–Folen to estimate the molecular field parameters (n, α, β) and the bilinear exchange integrals ( Jij).
Unusual ferrimagnetism in Mn2Mo3O8 and Sm2In
Authors: McAlister S. P.
Published: February 2003

The hexagonal compound Mn2Mo3O8 orders as a ferrimagnet but the spontaneous magnetization below TC is shown to reduce to zero as T → 0. This is possible according to the Néel collinear mean field model for ferrimagnets but has not been observed in single phase unmixed materials before. Magnetization results on single crystals show that the c axis is the easy axis. Magnetization measurements on polycrystalline Sm2In, which is also hexagonal, show similar ferrimagnetic properties.
Effect of electron-phonon interaction on itinerant electron magnetism (invited)
Authors: Kim D. J.
Published: February 2003

Starting from a consideration on how the phonon frequency and, therefore, the phonon free energy change with the spin splitting of the electron bands, we show how important a role the electron-phonon interaction (EPI) plays in the magnetism of a metal. In the paramagnetic state we find EPI to be the dominant mechanism of the temperature dependence of the spin susceptibility of a metal. Among others, the Curie-Weiss behavior is quite naturally obtained for an itinerant electron ferromagnet, without requiring the presence of localized moments. In the ferromagnetic state of a metal we find that EPI can affect the spontaneous magnetization as much as ∼ 1μB per atom.
Transition between fundamental magnetic behaviors revealed by generalized Slater–Pauling construction
Authors: Williams A. R. , Malozemoff A. P. , Moruzzi V. L. , Matsui M.
Published: February 2003

Recently, we introduced the ‘‘generalized Slater–Pauling’’ construction, in which the magnetization of most transition-metal alloys fall near a universal and easily interpreted straight line. The construction is based on the idea that, in transition-metal alloys, the solute d states lies either close (in energy) to the host d states, and join them in forming a ‘‘common band,’’ or they lie well above the host d states, forming a ‘‘split-band’’ configuration. While most alloys are either split- or common-band in character, we focus here on the exceptions, those that exhibit the transition from split- to common-band behavior. These include the alloy series Ru-Rh-Pd and Os-Ir-Pt as solutes in ferromagnetic Co and Ni.
Magnetic polarization clouds, percolation, and the critical concentration for ferromagnetism
Authors: Garland J. W. , Kioussis N.
Published: February 2003

The magnetic properties of many alloys are described in terms of magnetic polarization clouds. This is true in particular of dilute alloys of magnetic atoms in strongly exchange-enhanced hosts and of concentrated but magnetically dilute alloys of Ni in nonmagnetic hosts. In such alloys the locally averaged magnetization density is observed by diffuse neutron scattering to fall off as a Yukawa function away from the center of a polarization cloud. We present numerical calculations which confirm this Yukawa form and present an approximate theoretical derivation which gives a formula for the inverse range κ of a polarization cloud in an alloy in terms of the uniform exchange-enhancement factor α and the band susceptibility Γ(q) for the alloy. Assuming ferromagnetism in such alloys to arise from percolation amongst the polarization clouds, we also derive a relationship between the critical concentration c*cr, of polarization clouds for the onset of ferromagnetism and the average magnetization μ*cr and inverse range κcr of those clouds. This relationship is found to be in good agreement with experiment. Approximate calculated values of c*cr, μ*, and κ are presented for two cases. The effects of chemical ordering and clustering are considered briefly.
Curie temperature of PdFe films
Authors: Long J. R. , Mattozzi R. W.
Published: February 2003

Ferromagnetic ordering of giant moments formed by dilute Fe in Pd host bulk alloys has been the subject of many investigations, but thin films have had little attention. Thin films exhibit evidence of a spin glass phase not observed in the bulk and a crossover from three-dimensional to two- dimensional ferromagnetic ordering. The range of ferromagnetic ordering for PdFe is long compared to that of pure Fe, so that the crossover to two-dimensional behavior should occur in relatively thick films. A study of the effect in pure Fe would require uniform films of a few tens of angstroms. The crossover is manifested by a depression of the Curie temperature, which is expected to vary as a critical exponent of the thickness. Using a mutual inductance technique with SQUID detection, the temperature dependences of the spontaneous magnetization and the ac susceptibility were measured for some sputtered films with approximately 8% Fe. As expected, the Curie temperature decreased as the film thickness decreased. Unlike Fe, the Curie temperature of PdFe is dependent upon microstructure, and the microstructure of a film may have a systematic thickness variation that could result in a false crossover effect. The extent to which a model sensitive shift exponent can be extracted from the results is discussed.
Magnetism and disorder in palladium-iron alloys
Authors: Sapir G. N. , Levy A. , Walker J. C.
Published: February 2003

The magnetic and structural properties of palladium-iron (6.5 at. %) films have been studied using Mössbauer spectroscopy. The films were prepared by the method of dc diode sputtering. It is found that the magnetic and structural properties are interrelated, and depend strongly on the sputtering rate. The degree of disorder in the film increases and the Curie temperature, TC, decreases as the sputtering rate is lowered. The films sputtered at the lowest rate are magnetic only near 4.2 K while those sputtered at the highest rates are magnetic above 80 K. Annealing the films decreases the disorder and results in a higher ferromagnetic transition temperature. The films prepared at the lowest rate show an increase of over 70 K in TC when annealed at 200 C.
Magnetic properties of cubic La(FexAl1−x)13 intermetallic compounds
Authors: Palstra T. T. M. , Nieuwenhuys G. J. , Mydosh J. A. , Buschow K. H. J.
Published: February 2003

We report susceptibility and magnetization measurements for La(FexAl1−x)13 which can be stabilized over the x range 0.46–0.92. At low x values a mictomagnetic regime occurs with distinct cusps in the ac susceptibility. Upon increasing the Fe concentration a soft ferromagnetic phase is found which at lower temperatures shows anisotropy effects related to mictomagnetic behavior. Finally for x>0.86 antiferromagnetic order appears along with a very sharp metamagnetic transition in external fields of a few Teslas. The saturation moment increases linearly with x from 1.3μB to 2.3μB throughout the ferro- and metamagnetic regimes. These unusual properties are discussed in terms of local moment magnetism and the particular crystal structure which permits a large Fe-Fe coordination number at small distances.
Ferromagnetism of Pd-Fe (abstract)
Authors: Griffith G. , Carnegie D. W. , Claus H.
Published: February 2003

We present new low field ac susceptibility measurements on Pd1−xFex alloys (0.002≤X<0.01). The Curie temperature TC, determined from these measurements, are significantly lower than those previously obtained in higher magnetic fields [G. J. Nieuwenhuys, Adv. Phys. 24, 515 (1975)]. We also found that for a given sample, TC depends very sensitively on its heat treatment. As an example, for an alloy with 0.4 at. % Fe, TC can be varied between 4 and 10 K. In other alloys, like PdNi or RhNi similar changes in TC are due to changes in the degree of atomic short-range order [S. Crane, D. W. Carnegie, Jr., and H. Claus, J. Appl. Phys. 53, 2179 (1982)]. However, for PdFe we show evidence that the changes in TC are due to absorption of small amounts of oxygen, the samples with the highest amount of oxygen having the highest TC. It thus seems that oxygen has the opposite effect from hydrogen on the exchange enhanced susceptibility of Pd [J. A. Mydosh, Phys. Rev. Lett. 33, 1562 (1974)].
On the lower critical dimension of the random field Ising model (invited)
Authors: Grinstein G.
Published: February 2003

The debate over the lower critical dimension of the Ising model in a random magnetic field is briefly reviewed. Simple energy accounting estimates of the surface tension of the model at zero temperature are summarized. These arguments predict that the lower critical dimension is two. Existing theoretical, numerical, and experimental support for this conclusion is assessed.
Random-field effects in two and three dimensions (invited)
Authors: Belanger D. P. , King A. R. , Jaccarino V.
Published: February 2003

Random fields Hrf, which are generated in diluted antiferromagnets by uniform fields H, have been studied using optical birefringence. Their effects on the critical behavior of the magnetic specific heat Cm of d=3 and d=2 Ising systems differ dramatically. For d=3 (Fe0.6Zn0.4F2), the phase transition appears sharper and more divergent for H≠0 than it does at H=0. For d=2 (Rb2Co0.85Mg0.15Fe4), the sharp peak in Cm at H=0 immediately rounds in small fields, indicating the phase transition is destroyed in Hrf. From these studies we conclude that 2≤dl<3, where dl is the lower critical dimensionality of the random field Ising model (RFIM). Moreover, all of the observed crossover and scaling behavior (e.g., shift of TC and decrease of Cm peak height with H at d=2, crossover exponents), are exactly as predicted. The new critical behavior in Hrf for d=3 (logarithmic divergence of Cm with reduced temperature) shows that d̄≂2, where d̄ is the new effective space dimensionality of the RFIM; hence d̄≂d−1, in disagreement with early perturbation theory and supersymmetry predictions of d̄=d−2. Recent neutron scattering results support all of the above conclusions. The above, and magnetization and computer simulation studies, strongly suggest the early interpretation given to the domains seen in field-cooled experiments on d=3 systems, as evidence that dl≥3, is in error. Rather, it appears that the ground state has long-range antiferromagnetic order, corresponding to that obtained by zero-field cooling.
Finite-size scaling and integer-spin Heisenberg chains
Authors: Bonner Jill C. , Müller Gerhard
Published: February 2003

Finite-size scaling (phenomenological renormalization) techniques are trusted and widely applied in low-dimensional magnetism and, particularly, in lattice gauge field theory. Recently, investigations have begun which subject the theoretical basis to systematic and intensive scrutiny to determine the validity of finite-size scaling in a variety of situations. The 2D ANNNI model is an example of a situation where finite-size scaling methods encounter difficulty, related to the occurrence of a disorder line (one-dimensional line). A second example concerns the behavior of the spin-1/2 antiferromagnetic XXZ model where the T=0 critical behavior is exactly known and features an essential singularity at the isotropic Heisenberg point. Standard finite-size scaling techniques do not convincingly reproduce the exact phase behavior and this is attributable to the essential singularity. The point is relevant in connection with a finite-size scaling analysis of a spin-one antiferromagnetic XXZ model, which claims to support a conjecture by Haldane that the T=0 phase behavior of integer-spin Heisenberg chains is significantly different from that of half-integer-spin Heisenberg chains.
Quasi-one-dimensional antiferromagnetism in (CH3NH3)MnCl3⋅2H2O
Authors: Simizu Satoru , Chen Jiing-Yann , Friedberg S. A.
Published: February 2003

(CH3NH3)MnCl3⋅2H2O, MMC, contains chains of cis-[MnCl4(H2O)2] octahedra corner-linked via single Cl atoms. These chains are very similar to those in CsMnCl3⋅2H2O, CMC, but more widely separated by the larger cations. We have measured the magnetic susceptibilities of MMC between ∼1 and 100 K at 80 Hz and its heat capacity between ∼1 and 20 K. Susceptibilities above ∼10 K are well described by models of the antiferromagnetic linear Heisenberg chain with S=5/2, g=2.00, and J1/k=−3.01 K, very nearly the same intrachain coupling as in CMC. Below TN =4.12 K weak interchain interactions (∼6×10−3‖J1‖) produce long-range AF order in three dimensions with preferred spin alignment along or near the a axis. The linear chains in MMC are more nearly independent than those in CMC.
Critical properties of x
y spin-one chains with uniaxial single-ion anisotropy
Authors: Schneider T. , Glaus U. , Stoll E. P.
Published: February 2003

We use finite-size methods to estimate the critical properties of s=1 xy chains with uniaxial single-ion anisotropy of strength D. Strong evidence is presented for a phase transition, belonging to the universality class of the 1D quantum 0(2) model, with the weak coupling phase gapless, an essential zero in the gap at the critical coupling D*, and critical exponents z(D*)≊1, η(D*)≊1/4. Like the quantum 0(2) system, one of the models turns out to be a 1D quantum analog of the classical and isotropic 2D xy model.
(n-methyl-2-aminopyridinium) copper (II) trichloride: A new series of spin-1/2 linear chain antiferromagnets
Authors: Geiser Urs , Willett Roger D.
Published: February 2003

The structural and high-temperature magnetic properties are reported for a new series of one-dimensional spin-1/2 antiferromagnets. These salts, of stoichiometry (C6N2H9) CuCl3, where C6N2H9+ is the cation n-methyl-2-aminopyridinium (n=3, 4, or 6), contain bibridged copper (II) chloride chains well separated by the organic cations. They are compared to the structurally similar ferromagnet cyclohexylammonium copper (II) trichloride. The difference of the sign of the magnetic interaction is explained in terms of the Cu-Cl-Cu bridging angles. From susceptibility measurements the values of J/k=−53, −43, and −55 K, respectively for the three members of the series are calculated. Single crystal EPR data suggest a very small (J′/J<0.001) interchain coupling for the 6-methyl derivative.
Temperature dependence of domain growth
Authors: Grest Gary S. , Safran S. A. , Sahni Paramdeep S.
Published: February 2003

Monte Carlo simulations have been carried out to study the effect of temperature on the growth kinetics of a circular grain in two dimensions (2D) and a spherical grain in three dimensions (3D) for the Ising model. The domain radius shrinks as R2(t)=R20−αt , where R0 and R(t) are the initial and instantaneous radii, respectively. The slope α is strongly temperature dependent for T>0.6Tc in 2D and for T>0.2Tc in 3D, in contrast to earlier theories which neglect fluctuations. An analytical theory for d=2 which considers the thermal fluctuations which give rise to roughening of the domain walls agrees with the T dependence of the Monte Carlo data in this regime.
Linked cluster series expansion and phase transitions in complex models
Authors: Wang Yung-li , Lee Felix
Published: February 2003

We show that the use of the linked-cluster series expansion aided by the extrapolation techniques is an effective method in the study of complex models which display first-order phase transitions as well as second-order phase transitions. The Blume–Capel model is used for the demonstration.
Computer-controlled measurements of ferrimagnetic resonance losses in polycrystalline ferrites
Authors: Warin D. , Mage J. C. , Simonet W.
Published: February 2003

To facilitate the recent developments of computer-aided microwave device designs and to improve polycrystalline materials, the knowledge of ferrite loss parameters (ΔH, ΔHeff, ΔHk) is required over a large range of frequencies and temperatures. As a first step, a fully automatic resonance linewidth spectrometer has been designed and set up. The ferromagnetic resonance linewidth ΔH is measured versus frequency (0.5–18 GHz), temperature (100–600 K), and power level (≤10 mW). With numeric and automatic instrumentation, our technique using a nonresonant coupling circuit has sufficient sensitivity to measure linewidths from 2 Oe up to 250 Oe with an accuracy of ±5%. The technique is based on the fact that a superimposed dc field modulation allows the differentiated uniform precession (UPR) mode peak to be extracted with a lock-in amplifier. Results on narrow linewidth garnets (Y-Ca-V-In) agree reasonably well with the predicted anisotropy and porosity contributions model. A peculiar, very low power nonlinear effect, which has been observed at levels of the order of 100 mW/cm3 as the UPR passes through the top of the magnon manifold, is discussed.
Effects of critical fluctuations on Gilbert damping in iron near T
C
Authors: Heinrich B. , Arrott A. S.
Published: February 2003

Low field ferromagnetic resonance (FMR) is measured near TC. The whisker is magnetized along its long axis (001), but not uniformly so because of demagnetizing effects and the nonlinear response of the magnetization to the internal field. A current at fm frequencies is passed along the axis creating a fm magnetic field which is transverse to and circulating about the axis in a skin depth of 0.01 mm. The condition of FMR is reflected in the measured impedance. The frequency and temperature dependence of the Gilbert damping is extracted using a five parameter parametric equation of state taking into account the FMR equation of motion and the magnetostatics. The Gilbert damping is greater than that measured in high field microwave FMR and it peaks near TC. The results are consistent with extrapolation of neutron measurements to extract the wave vector zero loss.
Photothermal detection of magnetic polaritons in FeF2
Authors: Toussaint R. M. , Jaccarino V.
Published: February 2003

The technique of photothermal detection has been extended to the FIR and used, in conjunction with a high-resolution FIR-laser spectrometer, to directly measure the absorption spectra of antiferromagnetic FeF2. Samples of various thicknesses were studied and the results successfully compared to computer generated spectra of magnetic polaritons—the propagating coupled photon-magnon modes. Spectra for the downgoing branch were taken at a fixed frequency of ν=1.3623 THz with H0∥ĉ. In addition to the expected peak associated with the FeF2 AFMR, a second, smaller peak appears at a slightly higher magnetic field. This double peak structure is shown to be characteristic of magnetic polaritons, with the second peak corresponding to the upper boundary of the polariton ‘‘forbidden band.’’ Both the intensity and width of this second peak are particularly sensitive indicators of the intrinsic AFMR linewidth.
Green function ansatz for the Ising model
Authors: Frank B.
Published: February 2003

Previous work on difference equations for the Ising model in d dimensions suggests that a useful ansatz for the k-space pair correlation function is G(k)∼1/[1−AJ(k)/J(0)]1−η/2, where A is the quantity that appears in the criticality equation A=1 at T=Tc, the transition temperature. This ansatz is in accord with the usual definition of η. The scaling relation γ=ν(2−η) follows automatically. Using the i−δ equations, the criticality equation and the U equations together with the above ansatz, the theory predicts, for the two-dimensional Ising model on the square lattice, η=0.2249, Tc/TMF=0.5854 and U2 (critical)=0.1731. The known values are, respectively, 0.2500, 0.5673 and 0.1768.
Experimental temperature dependence of the magnetization of surface layers of Fe at interfaces with nonmagnetic materials
Authors: Walker J. C. , Droste R. , Stern G. , Tyson J.
Published: February 2003

Theoretical studies have investigated the temperature dependence of the magnetization at the surface of ferromagnets. It has become clear that surface anisotropy can significantly influence this temperature dependence. For isotropic exchange uniform throughout the sample the temperature dependence of the magnetization varies as M(T)/M(0)≊(1−BT3/2) with a B factor at least twice as great as the bulk value. For cases in which the exchange interaction is weaker in the surface layer, or in which there is a significant surface exchange anisotropy a linear temperature dependence may result. These theoretical results have seen little experimental test. We report here measurements made on epitaxial (110) Fe films in which different temperature dependences are found depending upon the interfacial material chosen as a covering layer. The ferromagnetic films were made of 56Fe, permitting Mössbauer spectroscopic measurements of the magnetic hyperfine field of the surface alone by growing a surface layer of 57Fe. These hyperfine measurements were made at a number of temperatures from 4.2 to 300 K. For Ag as the interfacial covering material a T3/2 dependence was seen. For MnF2 a linear T dependence was noted. Covering materials such as MgO have also been used. Results will be discussed in terms of expected surface anisotropy.
Diminished magnetization in ultrathin MBE-grown iron films (abstract)
Authors: McGuire T. R. , Krebs J. J. , Prinz G. A.
Published: February 2003

We have performed direct SQUID measurements of the average magnetization M̄ of a series of ultrathin (18–130 Å) Fe single crystal films grown by molecular beam epitaxy (MBE) on GaAs substrates and overcoated with Al. These measurements were motivated by earlier FMR measurements [G. A. Prinz, G. T. Rado, and J. J. Krebs, J. Appl. Phys. 53, 2087 (1982); J. J. Krebs, F. J. Rachford, P. Lubitz, and G. A. Prinz., J. Appl. Phys. 53, 8058 (1982)] on the identical films which showed a monotonic increase in average resonance field with decreasing thickness. In-plane M̄ data were taken over the ranges 0.5≤H≤30 kOe and 5≤T≤295 K and corrected for the (significant) substrate diamagnetism. The data clearly indicate that M̄ is diminished for the thinnest films and, for a film of thickness L, the behavior of M̄ is given by M̄=M0[(η+1/2(1−η)L/L0)] to a good approximation, where M0 is the bulk magnetization of Fe, L0 is a characteristic decay depth, and ηM0 is the magnetization at the interface where the Fe film is compressed by 1.4% due to lattice mismatch. At 295 K we find η=0.49 and L0=91 Å with only modest changes at 5 K. The absolute M̄ values are known to ±10% due largely to the uncertainty in L as determined by x-ray fluorescence and Dektak measurements. We conclude that this effect is not due to a nonuniform film thickness (voids or islands) nor to interdiffusion at the interface. Rather it is thought to be due to the depth dependent lattice compression arising from mismatch although the mechanism is not yet clear.
Slowly dispersive, short time delay line based on very thick liquid phase epitaxially grown yttrium iron garnet
Authors: De Gasperis P. , Miccoli G. , Di Gregorio C. , Roveda R.
Published: February 2003

Preliminary results on a magnetostatic volume wave delay line based on very thick yttrium iron garnet films (=110 μm) and operating in the 2–12 GHz frequency range, are presented. As expected from the theoretical dependence on the film-thickness, dispersion characteristics appear to be particularly interesting whenever short and slowly varying (slope of 0.05 ns/MHz) delay times are needed. Typically, for forward modes in the 9.5-10.5 interval, the average insertion loss is 12 dB with a −3 dB bandwidth of 550 MHz (reaching almost 900 MHz in the −10 dB limit). The precautions taken to eliminate (within a ±1.5 dB tolerance) band ripples, and relative consequences on the bandwidth and delay time linearity, are also discussed.
Electronically variable time delays using cascaded magnetostatic delay lines
Authors: Adkins L. R. , Glass H. L. , Stearns F. S. , Carter R. L. , Chang Kok Wai , Owens J. M.
Published: February 2003

A magnetostatic wave (MSW) variable time delay device with a phase deviation from linearity of less than 20 deg over a bandwidth of 300 MHz centered at 3 GHz has been demonstrated. The device consists of two cascaded delay lines. One delay line is biased to operate in the surface wave (MSSW) mode to provide a positive slope delay versus frequency characteristics, while the other operates in the backward volume wave (MSBVW) mode to provide a dispersive characteristic with negative slope. Both dispersions have been linearized by modifying the spacing between the propagation medium (YIG film) and the ground plane. The net device dispersion is the sum of the dispersive characteristics of the individual delay lines, and delay variability is achieved by varying the bias field of one of these components. A bias field change of 100 G will change the total delay by more than 40 ns.
Spin wave damping in the ferromagnetic semiconductor CdCr2Se4
Authors: Fontana E. , Coutinho-Filho M. D. , Rezende S. M.
Published: February 2003

The relaxation rate of magnons has been measured in nominally pure CdCr2Se4 with the parallel pumping technique at 9.4 GHz, as a function of temperature T and wave vector k, for 4.2<T<40 K and 0<k<106 cm−1. Three relaxation mechanisms have been identified as responsible for the measured rates. Impurity ions provide relaxation processes which are a strong function of the direction of the applied magnetic field with respect to the crystallographic axes. The damping rate due to this process is maximum along the 〈111〉 axis and minimum along 〈100〉. The measured rates at all temperatures show two distinct k dependences: at higher k values a linear dependence with k and at smaller values a nearly constant behavior. The linear dependence is due to a three-magnon relaxation process, as shown by detailed numerical calculations. The constant behavior at lower k results from the decay of the pumped π/2 mode into degenerate magnons and their subsequent relaxation to the thermal bath via three-magnon processes. A simple two coupled mode calculation explains qualitatively both the T and the k dependence of the data.
Relaxation in polycrystalline YIG
Authors: Bhatia S. N. , Joshi P. B. , Srivastava C. M.
Published: February 2003

The wave vector and temperature dependence of the spin wave linewidth in YIG has been studied for polycrystalline samples of average grain diameter 12.8, 8.4, and 3.5 μm and has been compared with the calculated relaxation times of basic three magnon confluence and four magnon scattering processes.
A wave-vector selective light scattering magnon spectrometer
Authors: Wilber W. D. , Wettling W. , Kabos P. , Patton C. E. , Jantz W.
Published: February 2003

A new type of magnon spectrometer has been developed, based on inelastic light scattering from magnetic excitations. This spectrometer enables one to study magnetic excitations of a specific frequency and wave vector as a function of static field, microwave power, temperature, or any other external experimental parameter. The sample is excited by an applied microwave field and simultaneously probed by laser light. The inelastically scattered light corresponding to a particular magnon wave vector k is selected and its intensity at a specific frequency ωk is recorded. The intensity of this light is a direct measure of the strength of that particular magnetic excitation at k and ωk. Spectra taken in this way present a direct and localized measurement of specific, selectable magnons, in contrast with standard microwave measurements which give only a measure of the total response of all excited modes over the entire sample.
Ferromagnetic resonance of bubble garnet films with a new planar microstructure
Authors: Herman Dean A. , Seagle David J. , Mundie Robert E. , Terrenzio Ennio
Published: February 2003

We report ferromagnetic resonance (FMR) of magnetic bubble films using a single loop-double loop (SLDL) planar structure with the static magnetic field applied both parallel and perpendicular to sample surfaces. Spectra were taken by direct transmission without modulation. Depending upon the positioning of the sample on the SLDL structure, two types of spectra were observed. With the sample positioned away from the coupling region (between the SL and DL conductors), transmission was decreased somewhat asymmetrically about resonance; in some cases, a weak transmission maximum occurred on the low field shoulder of an absorption line. We briefly discuss the correlation of these line shapes with a model based on a transmission line whose parameters are perturbed by the sample film’s susceptibility near resonance. The fields at transmission minima are in excellent agreement with resonance fields calculated from the Kittel equations for both the perpendicular and parallel field cases. With a film positioned to cover the SL-DL coupling region, transmission was reduced by more than one half at all fields. Resonance line shapes were sharply anomalous, evidencing strong maxima and minima similar to the derivative spectra seen in modulated FMR. In this case, transmission spectra appear to reflect a different combination of the perturbed transmission line phenomena. We conclude that resonance is not completely localized to the input-output coupling region. This sheds light on the line shapes seen by researchers with different microstructures.
Characteristics of coupled-mode optical filters
Authors: Laurenti J. P.
Published: February 2003

We provide a quantitative picture of the characteristics of a CdS coupled-mode band-pass optical filter. The operating principle of these coupled mode filters (CMF) is the energy exchange between the ordinary and extraordinary modes when the sample, inserted between two crossed polarizers ∥ and ⊥C, is strained by uniaxial stress at 45° from the C axis. The filter operates at the isotropic wavelength λi where ne=n0 ensures phase matching. The transmission rate and the selectivity are investigated as functions of the stress magnitude T and the sample thickness e. The best results are obtained by adjusting T so that the coherence length Lc=2e. For a 1-mm-thick crystal, the half-height passband is ∼4 Å, while the transmission rate is ∼70% at 77 °K and 20% at 300 °K. The large field of view, in practice ∼45°, constitutes a significant advantage over interference filters. We compare the CMF with zero crossing birefringent filters (ZCBF). Around λi, the characteristics of both filter types are rather similar, but the single transmission window of CMF gives the latter a distinct advantage over ZCBF. Transmission control by variation of applied stress is an added advantage of CMF.
A ferroelectric domain layer surface wave
Authors: Xing-jiao Li
Published: February 2003

A theoretical analysis is made of the effect of the 180° ferroelectric domain structure on the dispersion of the surface wave at an oscillatory domain boundary. From the general dispersion equation, the equation of Meerfeld–Tournois (or Privorotskii) mode, the equation of Bleustein–Gulyeav mode, and the dispersion expression of the ferroelectric domain layer mode are derived with the oscillatory boundary.
Characterization of a multipole ion source for ion implantation
Authors: Cope D. , Keller J. H.
Published: February 2003

A design for a single-slit multipole source for ion implantation was investigated. Some of the general physical processes involved are reviewed. Argon plasma characteristics are described for four multipole configurations. Langmuir probe data was found to agree in form with continuity theory. In addition, we present scaling relations for secondary electron temperature and density. Superior performance was observed for gas and arc efficiencies compared to a similar Bernas-type source.
The use of in-material stress gauges for estimating the dynamic yield strength of shock-loaded solids
Authors: Rosenberg Z. , Partom Y. , Yaziv D.
Published: February 2003

We present stress-time history measurements, with in-material manganin gauges, from which we obtain the dynamic yield strength of shock-loaded 2024 Al and Ti-6 Al-4 V specimens. This yield strength is inferred from the cusp in the release curve which results from the elastoplastic nature of the release process. We show that while the strength of the aluminum alloy increases with shock amplitude, in the 0–100 kb range, that of the titanium alloy does not.
Thermodynamic considerations in refractory metal-silicon-oxygen systems
Authors: Beyers Robert
Published: February 2003

Thermodynamic considerations in thin-film reactions involving refractory metals, refractory metal silicides, silicon, and silicon dioxide are described using ternary phase diagrams. Calculated metal-silicon-oxygen phase diagrams for Mo, W, Ta, and Ti are used to explain the reactivity of the metal with silicon dioxide, the effectiveness of native oxide in preventing metal-silicon interdiffusion, and the formation of silicon dioxide in preference to metal oxides during silicide oxidation. Distinctions are drawn between experimental results which can be explained solely on thermodynamic grounds and those requiring consideration of both thermodynamic and kinetic factors.
Calorimetric studies of light absorption by diamond turned Ag and Cu surfaces and analyses including surface roughness contributions
Authors: Bass M. , Liou L.
Published: February 2003

The total absorption of diamond turned Ag and Cu was measured directly by laser calorimetry. These measurements were carried out at wavelengths from 0.468 to 10.6 μm. The data were analyzed with a model which includes the contribution to the absorption due to surface roughness. As a result, an effective electron relaxation time was found as a function of frequency.
Pulsed photothermal evaluation of layered materials
Authors: Cielo P.
Published: February 2003

A pulsed photothermal technique is described for the nondestructive evaluation of stratified materials. The time history of the surface temperature after the absorption of a short laser pulse is used to obtain information about the subsurface structure and the thermophysical properties of the material. Applications to the inspection of plasma-sprayed coatings and graphite-epoxy laminates are presented.
Nonlinear resonance interaction of ultrasonic waves under applied stress
Authors: Hirao M. , Tomizawa A. , Fukuoka H.
Published: February 2003

The stress effect on the nonlinear resonance interaction T+T→L is experimentally investigated using an Al 5083 specimen. Compressive stress applied at the localized region where two noncollinear transverse waves intersect each other is shown to vary, up to ±8.5%, of the amplitude of the longitudinal wave generated through the resonance interaction. The amplitude variation with stress is explained by relating the stress induced change of elastic wave velocities (acoustoelastic effect) to the change in the resonance angle, and then to the directional characteristics of the two incoming transverse beams. The weak anisotropy of the material is taken into account.
A quantum model of the orotron free-electron laser
Authors: Šoln Josip , Leavitt Richard P.
Published: February 2003

A quantum model of the orotron (Smith–Purcell) free-electron laser is formulated in which the classical electron current density derived from a linearization of the equation of motion exhibits hybrid properties between the current densities of the Čerenkov and the wiggler free-electron lasers. Here, consistent with the (four-dimensional) current-density conservation law, the current density is proportional to the average change of the electron velocity Δv in the interaction region. From the interaction of the electron current with the quantized radiation field in an interaction volume of finite extent, we arrive at the multiphoton distribution function, which in turn yields the full ‘‘quantum-mechanical’’ gain after quantum recoil is taken into account. In an example where the radiation wavelength is 0.4 cm and the electron beam velocity is 0.1 c [corresponding to the Harry Diamond Laboratories (HDL) orotron experiment], we estimate that the maximum gain can easily be 8% or larger although the interaction length is chosen to be only 4 cm.
Photoluminescent properties of films of CdTe on glass grown by a hot-wall-close space vapor transport method
Authors: Cárdenas M. , Mendoza-Alvarez J. G. , Sánchez-Sinencio F. , Zelaya O. , Menezes C.
Published: February 2003

Cadmium telluride films on glass substrates were grown using a new hot-wall-close space vapor transport deposition system denominated gradient recrystallization and growth. Control of crystalline quality has been obtained through the temperature gradient in the system. Photoluminescence measurements in polycrystalline films show a crystal-like spectrum including exciton recombination and phonon emission, evidencing that good quality films can be obtained with this system. Ag diffusion in these films was used to get p-doped material. The Ag doped CdTe film shows an improved stability that does not show evidence of aging behavior.
Effects of heating-temperature gradient and scanning direction on crystallographic properties of zone-melting recrystallized silicon on square-shaped fused quartz
Authors: Fujita Shizuo , Okamoto Masaya , Yamamoto Hideki , Sasaki Akio
Published: February 2003

A new system in which a sample is heated by three different lower strip heaters was used for zone-melting recrystallization of Si on square-shaped fused-quartz substrates. By heating the two side heaters to a temperature higher than that of the center, and/or by recrystallizing the sample from the corner, the crystallographic properties (i.e., alignment of crystallographic axes and grain size) can be improved. Grain size as large as 1.15×10 mm was successfully obtained by simultaneously applying the two techniques described above.
Effect of Au addition on the magnetic properties of Co-Zr amorphous films
Authors: Shimada Yutaka
Published: February 2003

The effect of Au addition on the magnetic properties and thermal stability of amorphous CoyZr1−y alloys produced by sputtering is described. Change of the saturation magnetization, the saturation magnetostriction, and the crystallization temperatures were measured for Au additions up to 2.0 at. %. For y=87.2 little appreciable effect was observed, but for y=93.2 and 94.2 rapid decrease of the magnetostriction was observed for small amounts of Au additions. Thermal stability of magnetic softness is also improved appreciably.
Room temperature elastic constants and Debye temperature of PdPb2
Authors: Basu B. K. , Samudravijaya K. , Nigam A. K.
Published: February 2003

We have measured the room temperature elastic constants of tetragonal PdPb2 and derived from it the Debye temperature of the material. The Debye temperature evaluated from elastic constants is compared with that obtained from low-temperature resistivity measurements.
Interpretation of 1/f noise in phosphorus-doped polycrystalline silicon films: Hooge’s model of lattice scattering
Authors: Loh Eugene
Published: February 2003

The empirical relation by Asbrock and Brand between the 1/f noise power, i2n[A2/Hz], and relevant parameters in phosphorus-doped polycrystalline silicon films at cryogenic temperatures is shown to follow Hooge’s 1/f noise model of lattice scattering, i2n/Idc∼2 =α(μ/μ1)2/(Nf), where α≂2×10−3 is a dimensionless universal constant, N is the number of carriers in the sample, and Idc is the dc current. It is assumed here that the temperature dependence of lattice mobility is μ1∼T−1.5 and that of electronic mobility is μ∼T, in polycrystalline Si:P+ films. The former relation is because of acoustic phonon interaction in covalent silicon and the latter is attributable to the decreasing barrier resistance at grain boundaries as the sample warms up.
Optical properties and damage analysis of GaAs single crystals partly amorphized by ion implantation
Authors: Erman M. , Theeten J. B. , Chambon P. , Kelso S. M. , Aspnes D. E.
Published: February 2003

Dielectric functions of partly amorphized GaAs layers produced by deep ion implantation of different doses of 270-keV As+ ions in crystalline (c-) GaAs have been measured from 1.5 to 6.0 eV by spectroscopic ellipsometry. We show that these dielectric functions cannot be described as physical mixtures of amorphous (a-) and c-GaAs, as such models exhibit strong deviations with respect to the data near 3 eV. We determine representations of these dielectric functions as finite sums of harmonic oscillators, which allows us to describe these spectra as analytic functions of a single parameter related to the amount of damage. In this harmonic oscillator approximation (HOA), we show that damage profiles of ion-implanted material can be nondestructively determined from ellipsometric spectra in terms of multilayer models. In a representative case, good agreement is found between damage profiles determined nondestructively in the HOA and destructively by chemical etching.
Picosecond photoconductivity studies of light-ion-bombarded InP
Authors: Downey P. M. , Tell B.
Published: February 2003

An investigation of the dependence of the photoconductive lifetime and dark resistivity on ion mass, bombarding dose, and substrate temperature is presented for ion-implanted Fe-doped InP. Be and He ion bombardments at low doses cause a decrease in the dark resistivity of the semi-insulating InP and introduce defects which act as efficient carrier recombination sites without impairing the free-carrier mobility; above a threshold dose a second phase of damage is evidenced by a sharp decrease in carrier mobility and dark resistivity. Proton-induced damage is shown to result in an anomalous decrease in the dark resistivity of the Fe-doped InP, while being less effective at introducing carrier recombination sites.
Determination of inhomogeneities of elastic modulus and density for one-dimensional structures using acoustic dimensional resonances
Authors: Testardi L. R. , Norton S. J. , Hsieh T.
Published: February 2003

We derive a simple relation which allows the reconstruction of the inhomogeneity of the elastic modulus and density along a rod based only on the measured fundamental and overtone frequencies. The technique, analogous to one-dimensional tomography in the frequency domain, permits the quantitative detection of both continuous and localized defects. Experimental tests using impressed temperature profiles and drilled holes are reported. Observed sensitivities are found to be better than 1 °C for the former and 1×10−4 (of the rod volume) for the latter.
Amplification of acoustic lattice vibrations by electrons in semiconductors under intense laser radiation
Authors: Nunes O. A. C.
Published: February 2003

The rate of change in the acoustic phonon population due to scattering by conduction electrons in the presence of an intense laser is obtained from which the phonon generation rate is calculated. It is found that under certain conditions the generation rate may exceed the phonon relaxation rate and the acoustic phonon system may reach instability. An application is made for the case of an InSb sample.
Reference materials for piston-displacement pressure-volume measurements: Indium, lead, and NaCl
Authors: Anderson M. S. , Swenson C. A.
Published: February 2003

Measurements of the room temperature compressions of NaCl, lead, indium, and indium-jacketed iron together with published results for these materials have been used to evaluate the piston-displacement technique for obtaining pressure-volume relations. The internal consistency of these measurements appears to be better than ±5×10−4 in V/V0 at 20 kbar, which suggests a comparable accuracy. Indium, for which published data show appreciable discrepancies, is a very useful material since it is relatively incompressible and retains its plasticity to very low temperatures. The resulting pressure-volume relation for indium can be represented by a Murnaghan relation with B0=397 kbar and B′0 =5.45, and an estimated accuracy in the 20-kbar room temperature compression of 1%. The temperature dependences of these equations of state also are discussed.
Measurements of adherence of residually stressed thin films by indentation. II. Experiments with ZnO/Si
Authors: Rossington C. , Evans A. G. , Marshall D. B. , Khuri-Yakub B. T.
Published: February 2003

Indentation-induced delamination between thin films of ZnO and Si substrates is examined. Delamination occurs by the growth of lateral cracks, either along the interface or within the film adjacent to the interface. The crack path is determined by the indenter load and the film thickness, as well as by residual stresses formed during deposition. A change in crack path from the interface to the film, accompanied by an increase in crack radius, is observed and is interpreted as a buckling-induced stress intensification. The interface fracture toughness is estimated from the relative crack lengths in the buckled and unbuckled films.