bluuebunny/crossref_metadata_2025 huggingface dataset:
Neutron Diffraction Studies of Pd, Ni, FeMn, and Cu(Mn) Single Crystals
Authors: Arrott Anthony
Published: April 2005

The possibility of antiferromagnetism in Pd at 4.2°K was investigated by using neutron diffraction to survey along lines in reciprocal lattice space from the origin through the (002), (111), and (220) positions and along lines from the (111) position to the (002), (001), and (110) positions. The sensitivity (except near nuclear peaks or near the origin) was sufficient to detect a magnetic induction wave of amplitude equal to 200 G (depending on form factor and distance from the origin a 200 G amplitude corresponds to from 0.02 to 0.03 μB). Despite several strange ``peaks'' in the patterns, no evidence of antiferromagnetism was inferred from the data.

The possibility that Ni possesses a helical component to its ferromagnetism (similar to the familiar conical spin arrangement in holmium) was investigated by neutron diffraction with a field applied along the (111) direction of a Ni crystal at 4.2°K. The line from the origin of reciprocal space through the (111) nuclear peak was surveyed with the same sensitivity as the Pd experiment and with the same qualifications one could conclude that any such conical spin arrangement must have a cone angle of less than three degrees.

The same survey as made for Pd was carried out in Cu(5%Mn) and the results were similarly negative as far as demonstrating antiferromagnetism. Cu(15%Mn) shows very broad peaks which could be indexed as (1½0) and (½10) and these vectors added or subtracted with respect to any primitive reciprocal lattice vector. The temperature independence of these reflections from 4.2° to 420°K points to the likelihood that they arise from an atomic ordering rather than from a magnetic ordering. This ordering is just detectable in the Cu(5%Mn) specimen.

The antiferromagnetism of FeMn was investigated as this material appears (from resistivity and susceptibility data) not to possess ``localized moments'' above its Néel temperature. The temperature dependence of the spontaneous magnetization mode (a longitudinally polarized wave with (π00) wave vector) does not show a sharp break at the Néel temperature. This is due to the excitation of sizeable fluctuations in the magnetization modes. The fluctuating modes for a wide range of wave vectors are observed over a wide temperature range above and below the Néel temperature.
Magnetic Structure of Cr2O3
Authors: Corliss L. M. , Hastings J. M. , Nathans R. , Shirane G.
Published: April 2005

Pratt and Bailey have recently explained the optical and anomalous magnetic properties of Cr2O3 by means of a model consisting of the basic Cr2O3 antiferromagnetic structure with moments canted away from the c axis and forming some kind of spiral. Our neutron powder-diffraction data confirm the original Brockhouse moment configuration but indicate that the c-axis component of the Cr moment is 8% lower than the spin-only value. This result can be interpreted as supporting the canted model of Pratt and Bailey. A careful search has been made, using single crystals, to find evidence for an ordered or spiraling perpendicular component. Polarization studies establish that there is no magnetic contribution to the fundamental reflections other than that arising from the c-axis components. A survey of reciprocal space revealed extra spots at forbidden positions, but these could be accounted for semiquantitatively in terms of double-Bragg scattering. We conclude, therefore, that either the Cr moment is intrinsically lower, or, if canting exists, a perpendicular component of the magnitude required by the canted model does not exhibit long-range order.
Exchange Coupling of Uniaxial Magnetic Thin Films
Authors: Siegle William T.
Published: April 2005

The properties of two uniaxial magnetic films in intimate contact have been investigated. It is shown that when the uniaxial easy axes of the two films are orthogonal, and the magnitude of the uniaxial anisotropy the same in each film, uniaxial anisotropy in the composite film vanishes, to be replaced by a field-dependent biaxial anisotropy. The theoretical analysis relates this biaxiality to exchange coupling between the two halves of the composite film. Experimental measurements on several films are compared with the theory and imply for A, the exchange coupling constant, an average value of 0.4×10−6 erg/cm in a 66–34 Ni-Fe alloy film.
Longitudinal Kerr Effect Using a Very Thin Fe Film
Authors: Smith D. O.
Published: April 2005

Using known materials, the optimum magneto-optical light switch utilizing the longitudinal Kerr effect would operate at a wavelength of ∼1 μ and be made from a very thin [D=2π(thickness/wavelength)≤110] Fe film placed on the surface of a mirror (tangential E=0) in an optical standing wave. A multilayer dielectric structure would be used to couple the incident light to the magnetic film and the maximum possible magnitude of the Kerr coefficient k is calculated to be |k|max∼3.4×10−2. This is about 10 times greater than for a thick Permalloy film operating at visible wavelengths.
Wall Motion Reversal in Easy-Axis-Coupled Film Strips
Authors: Daughton J. M. , Chang H.
Published: April 2005

Wall motion reversal of the magnetization in coupled film strips is examined theoretically and experimentally. The structure is a conductor strip sandwiched between two Permalloy strips having their easy directions across the strips. If a train of current pulses of sufficient amplitude passes through the conductor strip, the Permalloy layers may be switched around the conductor in either of two sense depending on the polarity of the current. Criteria are presented for coupling (that is, that the two layers remain essentially oppositely magnetized) as a function of width of the strip, thickness of the Permalloy, coercivities of the films, and thickness of the intermediate conductor. It is found that coupling may break down either if the strip is too narrow or too wide. For strips which are coupled and have relatively thin enclosed conductor layers, the multiple-pulse field necessary to switch the film strip is about the average of the coercivities of the two Permalloy layers. For thicker conductor layers, this field is reduced by a geometric factor accurately predicted by a model using only magnetostatic interactions between the two Permalloy layers. Data are presented for 2000-Å layers of Permalloy in 0.125- to 4-mm strips with separations between the Permalloy strips between 0.6 and 8.6 μ. The coercivities of the films range between 0.6 and 6 Oe.
Magnetic Behavior of Gadolinium Near the Curie Point
Authors: Graham C. D.
Published: April 2005

Magnetization measurements on a single crystal of gadolinium have established that the Curie temperature Tc is 292.5±0.5°K, that the initial susceptibility is given by 1/χ0=A(T−Tc)43 from Tc to 20° above Tc, and that the magnetization is given by σ=CH¼ at Tc. These results are obtained only if measurements are made along the 〈0001〉 easy direction; measurements in other crystallographic directions give significantly different results because the magnetocrystalline anisotropy of Gd is not zero at and above Tc.
Induced Magnetic Anisotropy in Spinel Ferrite Single Crystals at Low Temperatures
Authors: Poplawsky R. P. , Michel R. E. , Chapman F. W.
Published: April 2005

Magnetic resonance measurements have been made at 9.525 Gc/sec on two ferrite single crystals Ni0.782+Fe0.162+Fe2.023+O4 and Mg0.88Fe0.212+Fe1.973+O4 in the temperature range 4° to 20°K. Both samples exhibit induced anisotropy when cooled from above 12°K in a magnetic field. The associated shifts in the field for resonance indicate an induced uniaxial anisotropy energy in both samples of the form K′ Σiαi2βi2, where αi and βi are the direction cosines of the magnetization at the measuring temperature and the annealing temperature, respectively. The shifts in resonance fields due to the anneal decrease smoothly as the measuring temperature is raised and disappear above 12°K. The similarity of the induced anisotropy for both samples irrespective of the difference in compositions suggests that the source is the same and is associated with the Fe2+ ion. The observed symmetry could arise from the proposed directional ordering of the interstitial cations. Since, however, the magnesium ferrous ferrite has, within the limits of chemical analysis, a cation excess while the nickel ferrous ferrite has a cation deficiency, this seems unlikely. Our results thus support the contention that preferentially oriented distortions associated with the Fe2+ ion are responsible for the low-temperature induced anisotropy in nickel ferrous ferrite and also, as reported here, in magnesium ferrous ferrite.
Acoustic Properties of Magnetite as a Function of Temperature and Cation Vacancies
Authors: Suiter W. B. , Blair R.
Published: April 2005

The acoustic loss and resonant frequency of polycrystalline magnetite has been measured from 4.2° to 780°K for various cation vacancy levels between 0.001 and 0.01 vacancies per formula unit. Measurements were made using a magnetic drive technique at a frequency of approximately 1 Mc/sec. The samples show, in general, acoustic loss peaks near 40°, 100°, and 690°K. The 40°K loss peak, which has been previously attributed to electron exchange, is seen to decrease in amplitude with decreasing vacancy concentration and is absent in the sample with 0.001 vacancies. This observation is opposite to that expected from a simple interpretation of the electron exchange model. The 100°K loss peak, which is attributed to ordering of Fe2+ and Fe3+ ions, moves from 100° to 115°K as the number of vacancies changes from 0.01 to 0.001 per formula unit. This observation is consistent with resistivity measurements of Verwey and Haayman. The 690°K loss peak decreases in amplitude and shifts to 660°K as cation vacancies go from 0.01 to 0.001 per formula unit. Using the relation τ=τ0 exp E/kT, τ0=10−14 sec and an activation energy E=1±0.01 eV were determined for the sample with 0.001 vacancies.
Low-Temperature Magnetic Susceptibilities of the Hydrated Nickel Nitrates
Authors: Berger L. , Friedberg S. A.
Published: April 2005

The zero-field magnetic susceptibilities of Ni(NO3)22H2O, Ni(NO3)24H2O, and Ni(NO3)26H2O have been measured in the liquid-hydrogen and liquid-helium ranges. The dihydrate is obtained by evaporation of a solution at 105°C.1 Its powder susceptibility has a large, sharp, peak at 4.20°K, where it reaches 0.74 cgs/mole, then drops down to 0.2 cgs/mole below 2°K. When measured along the a axis, the susceptibility of monoclinic single crystals of the dihydrate shows a similar peak. It reaches 1.5 cgs/mole, but drops to vanishing values at lower temperatures. The susceptibility in the bc plane reaches only 0.3 cgs/mole, and is nearly isotropic. It drops little below 4.20°K. This behavior is similar2-5 to that of FeCl2 or FeCO3, and suggests the existence of two magnetic sublattices, with strong ferromagnetic interactions within each sublattice, and weaker antiferromagnetic interactions between one sublattice and the other (metamagnetism). Direct evidence for such a layer structure is also provided by a recent x-ray structural work.6 A spin Hamiltonian with S=1 and uniaxial one-ion anisotropy gives results in fair agreement with the experimental data if the exchange interactions are described in the molecular field approximation. The best fit corresponds to g=2.25, D/k=−6.50°K, n1=+0.32 mole/cgs, n2=−2.12 mole/cgs, where n1 and n2 are, respectively, the antiferromagnetic and the ferromagnetic molecular field constants. In the case of the tetrahydrate1 and of the hexahydrate, the powder susceptibility approaches a constant value of 0.35 cgs/mole below 2°K; the data can be fitted to the spin Hamiltonian7 for a nickel ion in a rhombic field, without exchange, with E/k=−2.66°K, D/k=−8.67°K, and g=2.25.

A detailed account of this work has been published elsewhere.8
New Mn-Substituted Hexagonal Ferrites
Authors: Kohn J. A. , Eckart D. W.
Published: April 2005

Seven new hexagonal ferrite structures have been identified by single-crystal x-ray diffraction during a study of crystals from Mn-substituted Y phase syntheses. They fall in the M2Yn series and are comprised of a c-axis stacking of 2 five-anion-layer M blocks permuted with 9–13 six-anion-layer Y blocks. The series is thereby extended to larger unit cells and the total number of known hexagonal ferrites raised to 31. Three of the new structures are hexagonal, four are rhombohedral; in polytypic nomenclature they are 192Rc, 70Hb, 228Ra, 76Ha, 76Hb, 228Rd, and 264Re. The latter has a c-axis repeat period of 264 anion layers; a=5.88 Å (common to all hexagonal ferrites), c=636.7 Å. Weissenberg x-ray patterns and 00·l diffractometer traces established symmetry and identity layering. Stacking models were confirmed by 00·l structure-factor computations.
Alpha-Sub-Gamma Phase in Alnico 8 Alloys
Authors: Julien C. A. , Jones F. G.
Published: April 2005

The kinetics of formation at 900°C of the fcc γ phase have been studied metallographically in Alnico 8 alloys with Cu contents from 0.01 to 3.34 at. %. Increasing Cu content is found to increase the gamma-forming tendency. Selected two-phase specimens subjected to electron microprobe analysis showed a systematic depletion of the matrix in Cu, usually accompanied by an enrichment in Co. Ti evidences some partitioning, but scatter prohibits a reliable interpretation. Other elements apparently do not partition during the formation of γ. But in a specimen held for 24 h (i.e., beyond the growth stage), a third phase appears, accompanied by definite shifts in partitioning.

Deterioration of permanent magnet properties (but not 4πIs) as the transformation proceeds is described. The Br decrease is nonlinear, and it appears that interaction between the matrix and second phase is required to account for the observed property effects.
Influence of Static Pressure on the Coercive Force of Barium Ferrite Powder
Authors: Tenzer Rudolf K.
Published: April 2005

In recent studies of ferrite powders, changes of the intrinsic coercive force (Hci) have been ascribed to:(1) lattice defects, and (2) particle size reduction which occurs during milling. In order to test the two interpretations, the Hci of barium ferrite powder (ball milled to particle sizes of about 0.02–0.5 μ) was measured under static pressure. The coercive force increased with increasing pressure, reached a maximum at 8000 psi, and then decreased.

To interpret this result on the basis of dislocations would require that the dislocation density be lowered as the pressure is increased, which is unlikely. On the other hand, this behavior is easily understood on the basis of an increase of the effective particle size due to more contact between the particles at higher pressure. According to the latter interpretation, increasing pressure reduces the effect of thermal fluctuations, thus increasing the coercive force. At pressures above 8000 psi, multidomain behavior becomes a predominant factor in lowering the Hci. This interpretation is supported by the following experimental facts: below 8000 psi the coercive force decreased when the pressure was released. Above 8000 psi, however, the coercive force increased after the pressure was released.

These experiments show that particle size and exchange interactions between the particles are major factors in determining the coercive force of barium ferrite powders.
Resonance Observation of Antiferromagnetic Ordering in RbMnCl3, CsMnCl3, and KMnCl3
Authors: Kedzie R. W. , Shane J. R. , Kestigian M. , Croft W. J.
Published: April 2005

Paramagnetic and antiferromagnetic resonances have been observed as a function of temperature in KMnCl3, CsMnCl3, and RbMnCl3 at 9.5 Gc/sec (X band) and 25 Gc/sec (K band). The linewidth (ΔH) of the nearly cubic KMnCl3 [ΔH (298°K) = 24 G] remains constant in the paramagnetic region. The ordering temperature (TN = 100±3°K) is sharply defined by resonance measurements. At T = TN the K-band PMR abruptly and simultaneously broadens and splits into four anisotropic components. The AFMR lines move rapidly to zero applied magnetic field and then back up to 10.5 kG as the temperature is lowered. In contrast, the PMR linewidth of CsMnCl3 [ΔH (297°K) = 40 G] does not remain constant but rises rapidly from 62 G at 100°K to 240 G at 77°K (TN = 69°±3°K). AFMR is observed below the ordering temperature and, as the temperature decreases, the linewidth decreases to 36 G at 5°K. The origin of an additional resonance in the g = 2 region which is observed down to a temperature of 35°K is discussed. RbMnCl3 has a room-temperature linewidth of 39 G which increases slowly to 60 G at 107°K and then rapidly to more than 155 G at 95°K suggesting an antiferromagnetic transition with TN = 86°±6°K. The resonances observed at X and K band below the ordering temperature are described.
Antiferromagnetic Resonance in CoCl2 and FeCl2
Authors: Jacobs I. S. , Roberts S. , Lawrence P. E.
Published: April 2005

The far-infrared transmission has been measured for anhydrous CoCl2 and FeCl2 which are highly anisotropic hexagonal-layer antiferromagnets at low temperatures. The zero-field, 4.2°K, antiferromagnetic resonance is observed to occur at 19.2±0.4 cm−1 (CoCl2) and 16.3±0.3 cm−1 (FeCl2). The temperature dependence of each has been studied and compared to that of the sublattice magnetization relative to the existing theory and to the presumed origin of the anisotropy. The 0°K position of the CoCl2 resonance is satisfactorily calculated, using newly measured magnetization parameters. The uniaxial anisotropy energy deduced for FeCl2 is approximately equal to that of FeF2. The FeCl2 absorption has been observed in external magnetic fields to 17 kOe along [0001]. The line splits into two branches, but a third absorption (16.7 cm−1) appears at the metamagnetic transition field corresponding to ferromagnetic resonance in the strong anisotropy field. As the transition is completed, the antiferromagnetic absorptions vanish.
Exchange Effects in the Spin-Lattice Relaxation of Impurities in Thulium Garnets
Authors: Bierig R. W. , Rimai L.
Published: April 2005

The presence of rather strong Tm3+ impurity magnetic-exchange interactions in TmGa and TmAl: garnets, as determined from the paramagnetic resonance spectra of the substitutional impurity, has been previously reported by Hutchings and Wolf and the authors. It was also pointed out that these interactions entail dynamic effects which will contribute to spin-lattice relaxation of the paramagnetic impurity. A sufficiently strong exchange contribution can cause a large change, in both the magnitude and temperature dependence of the relaxation rate, from that found in similar diamagnetic hosts. We have previously reported preliminary data on exchange-enhanced relaxation processes for Fe3+; we report herein similar effects observed in the spin-lattice relaxation of Yb3+ in TmAl and TmGa garnets. We find: 1/T = 275T+1.6×107 exp(−41/T) 0.8% Yb3+: TmAl garnet and 1/T1 = 550T+8.9×106 exp(−75/T) 0.01% Yb3+: TmGa garnet while Svare has previously reported 1/T1 = 33T+1.8×10−7T9 for Yb3+ in the isomorphic, diagmagnetic host YGa garnet. A discussion of the matrix elements involved in the observed two-phonon relaxation process is presented. In addition, we also discuss how the dynamic-exchange effects can contribute to the one-phonon relaxation mechanism at low temperatures and to Raman relaxation at high temperatures. We speculate on the connection of the preceding results with the ferrimagnetic relaxation of rare-earth doped YIG.
Multiple Processes of Magnon-Magnon Interactions in YIG
Authors: Le Gall Henri
Published: April 2005

The participation of secondary parametric magnons in the transient growth of the spin-wave population has allowed a study with high accuracy of the three-, four-, and five-magnon relaxation processes. The relative importance of these interactions has been investigated. From the structure of each interaction we have deduced the existence of a maximum scattering angle for the parametric magnons beyond which the probability of magnon-magnon interactions tends to zero.
Standing-Spin-Wave Mode Spectra in Permalloy Films Prepared at Pressures Near 10−7 Torr
Authors: Nisenoff M. , Terhune R. W.
Published: April 2005

The field spacings between the SSWM in Permalloy films prepared in an ion-diffusion-pump vacuum system at pressures near 10−7 Torr obey the predicted quadratic dependence on order number1 for the magnetic field in the plane of the film (H∥) as well as normal to the plane of the film (H⊥). The spacings and intensities of the modes suggest that with H∥ the modes are nearly unpinned, while with H⊥ the modes are pinned with an effective film thickness ∼140 Å greater than for H∥. At some specific intermediate angle, the modes appear to be completely unpinned. This type of pinning can be explained qualitatively by assuming that the film is uniformly magnetized throughout the interior but that there are surface layers five to ten lattice spacings thick which exhibit lower values of M and A/M than the bulk, where M is the saturation magnetization and A is the exchange constant. The data also suggest that the boundary condition imposed on the transverse component of the magnetization at an air-ferromagnetic interface is that the normal derivative vanish. Deviations from this behavior, which looked like the onset of the anomalies reported previously for films prepared in conventional vacuum systems,2,3 were observed in films prepared in this system at pressures near 10−4 Torr.
Domain Orientation in Mo Permalloy and 65 Ni–Fe by Electron Irradiation at 100°C
Authors: Sery R. S. , Gordon D. I.
Published: April 2005

A variety of effects have been observed in flat-ring polycrystalline samples of 5–80 Mo Permalloy and 65 Ni–Fe irradiated by 2-MeV electrons at temperatures within the range of 70° to 170°C. For the Mo Permalloy samples, application of a 0.22-Oe field during irradiation to 1.10×1017 e/cm2 resulted in square hysteresis loops with Br as high as 6700 G (possibly a record high) but with little or no increase in Hc. In zero applied field, Hc increased and Br and μm decreased in all cases, but loop shapes were either rectangular, constricted, tristable, or conventional. The tristable loops, which appeared after a run in which the beam was interrupted several times, resemble those theorized by Kaya for the case of a material having two dominant anisotropy axes. Irradiation of 65 Ni–Fe with a 1-Oe field and a dose of 7×1017 e/cm2 resulted in increases of ∼100% in Br and μm but accompanied by a 50% increase of Hc. The ``directional order theory'' for magnetic annealing (including the case of zero applied field) can be applied to the above results. However, at any given temperature the vacancy concentration increase due to irradiation accelerates the ordering process through enhancement of the diffusion rate. Hence directional ordering can occur at relatively low temperatures in irradiated materials. The thresholds of damage (in zero field) for 5–80 Mo Permalloy and 65 Ni–Fe were >0.17×1017 and >1.0×1017 e/cm2, respectively. Post-irradiation measurements indicate long-term stability of all of the above effects.
Secondary Recrystallization and Its Relation to Magnetic Properties in Thin Grain-Oriented 3% Silicon-Iron
Authors: Littmann M. F.
Published: April 2005

Polycrystalline 3% silicon-iron with (110)[001] texture forms a primary recrystallization texture near the original texture after cold reduction of about 70% followed by primary recrystallization. If rapid heating is used for primary recrystallization, vigorous secondary recrystallization by grain boundary energy takes place after subsequent annealing at 775°C. The secondaries grow to about 5-mm diam with a texture deviating from the primary texture. Annealing twins also form during secondary growth. The activation energy for this growth was found to be much lower than for growth processes dependent on impurities for inhibitors. Such secondary growth must be avoided in commercial applications.

If primary recrystallized material is annealed at 1200°C under conditions favorable for growth of (100) by surface energy, (100)[001] secondaries will grow depending on the amount of prior cold reduction.
Magnetic Aftereffects in Neutron-Irradiated Iron, Nickel, and Cobalt
Authors: Moser P. , Peretto P. , Dautreppe D. , Vigier P.
Published: April 2005

After neutron irradiation of iron at 78°K, we have observed four magnetic aftereffect zones. All these zones annealed out in different temperature ranges corresponding to the well-known stages of recovery in neutron-irradiated iron. If the sample is annealed during 30 min at 500°C after an irradiation at 78°K, a new magnetic aftereffect zone appears. The different characteristics of each zone (activation energy for reorientation, spectrum width, defects symmetry, etc.) have been studied. A model concerning the nature of the defects responsible for these magnetic aftereffects is proposed.

Similar effects have been found in neutron-irradiated nickel and cobalt at 28°K. From the results on nickel a great number of arguments are given in favor of the interstitialcy configuration.
Magnetic Properties under Pressure of Some Transition Metal Alloys
Authors: Bloch D. , Pauthenet R.
Published: April 2005

We have studied the variation of the Curie temperature θf and the spontaneous magnetization σs of several transition metals and some of their solid solutions as a function of the pressure. The measurements were carried out between 77° and 700°K. In the system Ni–Si, dθf/dp varies from 0.32×10−3 °K bar−1 for pure nickel to 0.05×10−3 °K bar−1 for Ni-9 at.% Si. The magnitude of dθf/dp decreases by 0.033×10−3 °K bar−1 per 1% of Si dissolved. In the system Ni–Cu, dθf/dp decreases by 0.01×10−3 °K bar−1 per 1% of Cu dissolved. For polycrystalline cobalt, (σl)−1 (∂σl/∂p), at 293°K, is equal to −10±1.5×10−7 bar−1. The molecular field coefficient, representing the exchange integrals, increases for a decrease in volume in the case of Fe, Ni, Co, and the solid solutions Ni–Si, Ni–Cu, Fe–Si. The relative variation of the spontaneous magnetization with pressure is accounted for by the use of band theory.
Loss Associated with Magnetoelastic Waves in Yttrium Iron Garnet
Authors: Strauss Walter
Published: April 2005

Room-temperature magnetoelastic waves have been observed in yttrium iron garnet from 1.6 to 8.5 Gc/sec. The minimum observed insertion loss, which includes conversion, transmission, and reconversion loss, was 15 dB at 1.6 Gc/sec; at 8.5 Gc/sec the smallest insertion loss was 46 dB. The transmission attenuation increases approximately linearly with frequency from about 6 to 20 dB/μsec over this frequency range. The experimentally observed conversion loss from electromagnetic to magnetoelastic energy ranges from 3 to 13 dB and is compared with theoretical values.
High-Power, SPDT, Fast Ferrite Switch
Authors: Willoughby R. E.
Published: April 2005

A single-pole, double-throw, cutoff-type ferrite switch has been developed for operation at C- and S-band frequencies. The C-band unit is designed for a peak power level of 1 MW with an insertion loss less than 1 dB. Both units display a switching time of 150 μsec. The device consists essentially of a three-port waveguide junction with a section of reduced size ferrite-loaded waveguide at two of the ports. The characteristics of the reduced area sections are such that microwave energy in the frequency range of interest is propagated if no magnetic biasing field is applied. Upon application of the biasing field, the effective permeability of the ferrite is reduced, causing the loaded waveguide to be cut off. The structure is matched so that, if the magnetic field is applied to one section and not the other, a minimum input VSWR is obtained, and there is a maximum transfer of energy to the unbiased port. Switching is accomplished by applying the magnetic biasing field to one ferrite-loaded section, while at the same time removing the magnetic field from the other. The technique of using cutoff waveguide to create the ``off'' condition provides isolation greater than that obtained by other means, e.g., switching circulators. It is believed that this is the first device of this type to be operated at a truly high power level. High-power operation has been achieved by the novel approach of operating above the onset threshold for subsidiary resonance absorption. This technique appears promising for use in the development of various high-power devices in the future.
Paramagnetic Faraday Rotation of EuSe
Authors: Suits J. C. , Argyle B. E.
Published: April 2005

Faraday rotation and absorption measurements were made on a bulk single crystal and on evaporated polycrystalline films of EuSe. Bulk EuSe is ferromagnetic, transparent in the red, and exhibits an unusually large Verdet constant at room temperature: −9.7 min/Oe-cm at 6660 Å where the absorption is 173 cm−1. Measurements at 77°K show that the Verdet constant varies approximately inversely with temperature and thereby correlates with the magnetic susceptibility. These properties are due to the Eu+ + ion and are comparable to those we have observed in other divalent europium compounds such as Eu2SiO4.

The evaporated films of EuSe exhibit a broad but well-defined absorption band at 4600 Å which is essentially duplicated in similarly prepared films of EuS and EuO at 5200 and 5800 Å, respectively. The wavelength dependence of the Faraday rotation of EuSe exhibits a rather complicated structure with two sign reversals in the region of the absorption band. At 6660 Å the Verdet constant measured at room temperature is −6.3 min/Oe-cm agreeing in sign and approximately in magnitude with the bulk value, whereas the maximum value of Verdet constant, +25 min/Oe-cm, occurs at 4330 Å.
Magnetization, Resonance, and Optical Properties of the Ferromagnet CrI3
Authors: Dillon J. F. , Olson C. E.
Published: April 2005

CrI3, noteworthy as one of the few insulating ferromagnets, is one of a series of presumably isomorphous compounds (CrCl3, CrBr3, and CrI3) which show similar or closely related magnetic ordering. CrI3 samples containing some single crystals (plates a few square millimeters in area) were made by reacting chromium metal and iodine in a sealed quartz tube. Magnetization measurements of the powder were made by Williams and Sherwood at several fields up to 15 300 Oe over the range 1.5° to 300°K. In addition, M (H) was plotted at 4.2°K up to 70 000 Oe. The ferromagnetic Curie temperature is 68°K, and the paramagnetic Curie temperature is 70°K. The low-temperature saturation magnetization is 3.10 μB/Cr+ + +, corresponding to 4πM = 2690 G. The field for ferromagnetic resonance was measured at 86, 91, and 99 Gc/sec. The spectroscopic splitting factor g = 2.07, and the anisotropy field 2K/M = 28.6 kOe at 1.5°K.

Optical transmission measurements on CrI3 single crystals showed a very strong absorption band down to a band edge near 10 000 cm−1. The specific magnetic rotations associated with the band edge are almost as large as those observed in the tribromide. Evidence of domain diffraction was seen.
Hall and Faraday Effects in Oriented MnBi Films
Authors: Chen D. , Gondō Y. , Blue M. D.
Published: April 2005

Hall coefficients and resistivity have been measured over the temperature range 77° to 300°K on polycrystalline MnBi films prepared with the c axis of the crystallites normal as well as parallel to the plane of the film. The Hall resistivity follows the well-known relation ρH = R0H+MR1, where R0 and R1 are the ordinary and extraordinary Hall coefficients and M is the magnetization. At room temperature, R0 is 6×10−3 cm3/C for both types of films and R1 is 7×10−2 and 2.5×10−1 cm3/C for the perpendicular and parallel films, respectively.

Measurements of the magneto-optic Faraday rotation of perpendicular films indicate that the Faraday rotation is directly proportional to the magnetization. Over the visible wavelength region, the Faraday rotation was found to increase as temperature decreases from 300° to 87°K, by a factor less than 25%. The specific rotation for a typical magnetically saturated film was 1.4×105 deg/cm at the 6328-Å He–Ne laser line at room temperature.

Our measurements are in agreement with Goodenough's suggestion of metallic conductivity resulting from a d band formed from the transition metal cations with the assistance of large numbers of interstitial cations. An effective hole density of 1021 cm−3 and Hall mobility of approximately 10 cm2/V-sec characterize these films.
Subthreshold Steady-State Absorption under Parallel Pumping
Authors: Hartwig C. P. , Green J. J. , Joseph R. I. , Schlömann E.
Published: April 2005

If the rf and dc magnetic fields are parallel, the absorption coefficient μ″ at low power levels is theoretically expected (for YIG at room temperature, a frequency of 10 Gc/sec, and a dc field of 1 kOe) to be of the order of 2×10−4. We have calculated how the steady-state absorption varies with dc and rf field strength below the instability threshold. Experiments on a high-purity YIG single crystal are in reasonably good agreement with the theoretical expectations.
Microwave Magnetoelastic Resonances in a Nonuniform Magnetic Field
Authors: Kohane T. , Schlömann E. , Joseph R. I.
Published: April 2005

A new magnetoelastic resonance effect is described. A dc magnetic field was applied in the long direction of YIG slabs (1 cm long, 0.5 cm wide, and 0.1 or 0.07 cm high), each end of which was inserted in a stripline cavity. Under appropriate conditions a pulse of microwave power applied to one cavity resulted in a pulse in the second cavity delayed by several microseconds. Small variations were observed in the amplitude of the delayed pulse as the dc field was varied. Similar variations with the same periodicity (∼1 Oe) were also observed in the undelayed reflection from the input cavity. The amplitude variation is attributed to the excitation of magnetoelastic resonances in the nonuniform magnetic field near the endface of the sample. Because of the strong coupling between spin waves and elastic waves, the turning point (at which kspin waves=0) and the endface of the sample define a magnetoelastic quasicavity whose resonances give rise to the effect noted. According to this interpretation the separation of adjacent peaks should be δH = |H′dem|λ/2, where H′dem is the gradient of the demagnetizing field evaluated at the crossover point (kspin wave = kphonon) and λ the wavelength of transverse elastic waves. Measurements have been made showing the dependence on dc field, slab thickness, and frequency. Agreement with theory is satisfactory.
Microwave Modulation of Light in Ferromagnetic Resonance
Authors: Hanlon J. T. , Dillon J. F.
Published: April 2005

Direct spectroscopic evidence has been obtained of microwave sidebands imposed on a monochromatic light beam by transmission through a single crystal of chromium tribromide at ferromagnetic resonance. Microwave frequencies above 13.5 Gc/sec may be used, and the most favorable optical wavelengths for this effect lie between 4750 and 5000 Å. This work has demonstrated modulation of a 4810-Å beam by a 23.5-Gc/sec microwave signal. This paper discusses the conditions under which the modulation may be observed, and how some of these may be optimized.
Electroluminescence and Lasing Action in GaAsxP1−x
Authors: Pilkuhn M. , Rupprecht H.
Published: April 2005

The electroluminescence of Zn diffused diodes was studied in forward and reverse bias. Emission spectra obtained for forward biasing showed a near-edge as well as a low-energy line. In the composition range x>0.55, where the lowest conduction band minimum is at k=0, most photons are emitted in the near-edge line. Lasing action could be observed in this range, and the shortest wavelength where stimulated emission was obtained at 77°K was 6380 Å. For x<0.55, where the lowest conduction band minimum is the (100) minimum, the low-energy emission becomes dominant. The energy separation between near-edge and low-energy line varies between 0.4 and 0.47 eV at 77°K depending on composition. This suggests that the same defect is responsible for the low-energy emission in all these diodes (including GaAs and GaP). In reverse bias, near-edge emission and emission at higher energies than bandgap could be observed for x<0.55. The cutoff energy of the emission on the high-energy side was measured as a function of composition. It was found to vary in a manner similar to the variation of the energy of the (000) conduction band minimum.

The external quantum efficiency of the forward bias emission drops sharply by two orders of magnitude at the composition x=0.55 when x is decreased. The efficiency of the reverse bias emission is independent of composition.
Deactivation of Neon Metastables by Hydrogenic Impurities
Authors: Marshall Thomas
Published: April 2005

Measurements are reported of the total cross section for deactivation of neon 3P2 and 3P0(2p53s) metastables by inelastic collisions with H2, D2, CH4, and NH3. Observations were conducted by applying the methods of resonance radiation absorption and microwave diagnostics to the afterglow plasma following a weak pulsed discharge in a neon-hydrogenic impurity mixture. The cross section for 3P2 deactivation by H2 was found to increase from 0.7×10−15 cm2 at 300°K to 2.5×10−15 cm2 at 650°K. The cross section for ionization of H2 by Ne*3P2 collision was found to represent only a fraction of the above. The reaction which dissociates H2 and partly converts the metastable energy into Hα(6563 Å) light has been observed in H2, D2, CH4, and NH3 and may represent a significant contribution to the total deactivation in each case. No Hα light was produced as a result of the destruction of a helium 3S1 metastable by collision with H2.
Standing Spin Wave Mode Spectra in Thin Permalloy Films Prepared in Vacuum of 10−7 Torr
Authors: Nisenoff M. , Terhune R. W.
Published: April 2005

The spacings between the standing spin wave modes excited in Permalloy films, prepared in a high-vacuum system at pressures near 10−7 Torr, are found to obey a quadratic dependence on order number for the magnetic field normal to the plane of the film (H⊥) as well as in the plane of the film (HII). The spacings and intensities of the modes, as a function of the angle φ which the magnetic field makes with respect to the film normal, indicate that the modes are nearly unpinned for φcrit>φ≥90° (HII), are completely unpinned at φcrit, and partially pinned for φcrit>φ≥0° (H⊥). This type of pinning behavior is explained qualitatively by assuming that the films are nearly uniformly magnetized except for a very thin surface layer, of the order of ten lattice spacings, which exhibits a lower magnetization than the bulk. In addition, the observed pinning for the modes suggests that the boundary condition imposed on the transverse component of the magnetization at an air-ferromagnetic interface is that the normal derivative of the magnetization vanish.

It is concluded that ferromagnetic films prepared in high vacuum should be suitable for the determination of physical parameters, such as A/M, the ratio of exchange constant to the saturation magnetization, as their spectra are relatively free from the anomalous features observed in all of the previously reported SSWM investigations. Experimental evidence is presented that these anomalous features are probably due to contamination of the films by both residual gases in the evaporation chamber and by impurities introduced by the vacuum system itself.
Pure Modes for Elastic Waves in Crystals
Authors: Brugger K.
Published: April 2005

In an anisotropic medium there are only certain directions along which elastic waves can propagate in pure longitudinal and transverse modes. For the determination of third-order elastic coefficients from sound speed measurements in stressed crystals it is desirable to know these modes. Using a method due to Borgnis the pure mode directions are determined for all crystal point groups belonging to the orthorhombic, tetragonal, cubic, rhombohedral, and hexagonal systems. The eigenvalue problem is solved for each of these directions, and the polarization vectors and the wave speeds are tabulated.
Evaluation of Kossel Microdiffraction Procedures: The Cubic Case
Authors: Gielen Paul , Yakowitz Harvey , Ganow DeWayne , Ogilvie Robert E.
Published: April 2005

A complete theory of the lens-shaped intersection of Kossel lines in the transmission pseudo-Kossel method is developed. The general expression gives the lattice parameter with respect to the characteristics of the interaction of two arbitrary conics, i.e., conics corresponding to arbitrary diffracting planes and arbitrary wavelengths. Geometrical considerations involving the conics are developed and from these, the errors involved in lattice parameter measurement are evaluated. Lattice parameter variations of 10−5 can be easily measured with suitably chosen conic intersections. The precision to be expected as a function of measurement errors is expressed as a sensitivity ratio and tabulated for an Fe-3wt.%Si alloy. Several methods of reducing measured lengths to lattice parameter data are evaluated.

The IBM 7090 computer has been used to find suitable intersections for precise lattice parameter measurement. The computer supplies the wavelengths and conics to be used in the transmission pseudo-Kossel method. Consequently, a long and tedious experimental investigation is avoided. Examples using Fe-3wt.% Si are given; the lattice parameter for this alloy is found to be 2.86268±0.00003 Å. Proper radiations for investigation of Ge and diamond are indicated.
Thermal Phase Transitions in Superconducting Nb-Zr Alloys
Authors: Whetstone Clayton N. , Roos Charles E.
Published: April 2005

Experimental data are presented for the thermal propagation of a normal-superconducting boundary along wires of Nb-25%Zr, Nb-37%Zr, and Nb-51%Zr. The thermal propagation velocity was measured as a function of current at 4.2°K in constant longitudinal and transverse magnetic fields up to the upper critical field Hc2 as well as in a zero magnetic field for temperatures between 2.5° and 11°K. Previous models which describe thermal propagation phenomena neglected the temperature dependences of the specific heat, thermal conductivity, and electrical resistivity. A more exact model is proposed here which takes into account the temperature dependences of these quantities, and all the present experimental data are in good agreement with this model. From a measurement at 4.2°K of the dependence of the thermal velocity on magnetic field, the high-field transition temperatures as a function of magnetic field are calculated for temperatures above 4.2°K. In conjunction with the theory, the linear dependence of the thermal velocity on current implies a weak current dependence for both the transition temperature and superconducting-state specific heat in Nb-Zr alloys up to 3×105 A/cm2. A method is discussed for using thermal propagation techniques to determine the superconducting-state specific heat in the presence of known transport currents and magnetic fields.
Electron Paramagnetic Resonance in Irradiated Oxygen-Doped Germanium
Authors: Baldwin John A.
Published: April 2005

Electron paramagnetic resonance studies have been performed in oxygen-doped germanium. Room-temperature irradiation with 2-MeV electrons produces a paramagnetic center of S = ½ whose g tensor has (011), (01̄1), (100) principal axes. The g shifts are consistent with this being the germanium A center, i.e., an oxygen-vacancy complex. Infrared absorption bands at 766, 807, and 847 cm−1 may be associated with this defect.
Photocurrents Through Thin Films of Al2O3
Authors: Shepard Kenneth W.
Published: April 2005

Thin-film sandwiches of Al–Al2O3–Al have been constructed with Al2O3 layers in the range 80–120 Å thick. When illuminated with light in the wavelength range 2600–11 000 Å, the sandwiches exhibit photocurrents which are larger than the dark current. The photocurrent has been measured at room temperature as a function of bias voltage and photon energy, using light pulses of 0.1-sec duration. The results are interpreted to give the shape of the potential barrier in the insulator. Within the accuracy of the data, the potential barrier is trapezoidal, with a relative work function of 1.0 eV at the oxidized electrode, and 2.9 eV at the electrode evaporated over the oxide. There is evidence that collisions of the photoelectrons in the insulator are important.
Photoconductivity Spectral Response and Lattice Parameters of Hexagonal ZnSe
Authors: Park Y. S. , Chan F. L.
Published: April 2005

The hexagonal modification of ZnSe single crystals has been observed. The crystals were grown by the sublimation method. The lattice parameters are found to be a0 = 4.003±0.001 Å and c0 = 6.540±0.003 Å. The photoconductivity peaks observed in the spectral response curves at room temperature reflect the band symmetries of the wurtzite structure and obey the group theoretical selection rules. From the position of the photoconductivity maxima for E ⊥ C, the band gap energy at room temperature is estimated to be 2.795 eV.
Axial Imperfections in Filamentary Crystals of Aluminum Nitride. I
Authors: Drum C. M.
Published: April 2005

Axial dislocations and other imperfections in single-crystal whiskers of aluminum nitride (hexagonal, wurtzite structure) have been studied by transmission electron microscopy. Axial dislocations with c Burgers vectors and faults on the (101̄0) prismatic planes having fault vectors equal to ½ c have been identified. In addition to simple axial dislocations, the variety of axial imperfections included zig-zagged dislocations and wide periodic imperfections attributed to complicated faults, clearly related to the dislocation with a c Burgers vector.

One type of AlN whisker with growth direction 〈c+2a〉 always contained an axial dislocation or the related extended defect, and it is thus concluded that the growth of this type of whisker may have involved an axial dislocation.
Resistive Measurements of Structural Effects in Superconducting Niobium
Authors: Tedmon C. S. , Rose R. M. , Wulff J.
Published: April 2005

Resistive measurements of the critical current density Jc in transverse magnetic fields were made on single crystals of niobium, which had been subjected to systematic thermal, mechanical, and chemical treatments in order to produce a wide range of substructural densities, and variations in the oxygen content. The introduction of plastic deformation into niobium crystals produced a peak in Jc at applied magnetic fields of strength Hc2, the upper critical field. The peaks in Jc were removed by annealing the crystals in the recovery range. The critical current density was increased both below and above Hc2 by producing a dislocation substructure in the crystals. Small additions of oxygen also caused Jc to increase above and below Hc2. The upper critical field, however, was relatively insensitive to structure, varying only through the structure sensitivity of the bulk GLAG parameters.
Internal Friction under Hydrostatic Pressure
Authors: Miles M. H. , DeVries K. L. , Gibbs P.
Published: April 2005

Internal friction measurements of zone-refined Al were obtained up to pressures of 5 kbar. The log of the background damping was found to increase linearly with pressure, with slopes of about 1.5×10−4 kbar−1 and 47.7×10−4 kbar−1 for CS2 and kerosene pressure media, respectively. A reversible, intrinsic, pressure dependence of the amplitude-dependent part of the decrement Δ was found for Al of the approximate form ∂(lnΔ)/∂p = M+N/ε0, where M = −4.5×10−3 kbar−1, N = −4.2×10−8 kbar−1, and ε0 is the strain amplitude. Theoretical expressions for the value of the ``misfit parameter'' ε′ and its pressure derivative are derived from the Granato-Lücke theory in terms of M, N, and elastic constant data. It is suggested that the Granato-Lücke theory does not apply to zone-refined Al at these strain amplitudes.