bluuebunny/crossref_metadata_2025 huggingface dataset:
Anisotropic Magnetic Resonance and Relaxation in Silicon-Substituted YIG
Authors: Judy J. H.
Published: April 2005

The magnetic resonance behavior of silicon-substituted yttrium iron garnet (YIG) crystals having the average ionic composition {Y33+} [Fe1.953+Fe0.052+] (Fe2.953+Si0.054+)O12 has been investigated as a function of temperature and orientation at 9 Gc/sec. Unexpectedly, four extrema were observed in the resonance field Hres at low temperatures. For example, the values of Hres(100)=1575 Oe, Hres(111)=1985 Oe, and Hres (110)=2175 Oe were measured at 77°K. Further measurements at 24 Gc/sec indicated that g=2±0.02 from 300° to 77°K. This inverted anisotropy can be described phenomenologically by an isotropic downward shift of 1260 Oe and the cubic anisotropy fields K1/M0=200 Oe and K2/M0=−540 Oe. These K1>0 and K2<0 values are attributed to the Si4+-induced Fe2+ ions. The enormous isotropic depression of Hres is shown to be predicted by an extended formulation of the ``slow'' relaxation theory. A peak was observed in the resonance linewidth ΔH(100) of 60 Oe at about 350°K corresponding to ωτ(100)=1. Because of the appearance of multiple absorption modes due possibly to nonuniform Si substitution, the second predicted peak in ΔH could not be observed. Since the activation energy of both the resistivity and relaxation time constant τ(100) was 0.30 eV, it is suggested that the quasi-free valence electrons of the induced Fe2+ ions constitute the slow-relaxing system in YIG (Si0.05).
High-Field Susceptibilities of Iron and Nickel
Authors: Herring C. , Bozorth R. M. , Clark A. E. , McGuire T. R.
Published: April 2005

The dependence of magnetization M on field H has been measured in high fields (15–150 kOe) for single crystals of Ni and Fe+4% Si in their directions of easy magnetization. The specimen, at liquid-nitrogen or liquid-helium temperature, was pulled from one to the other of two balanced coils connected in a series opposition to an integrating digital voltmeter. Over the range 15 to 50 kOe, where the most accurate data were obtained, the mean volume susceptibility κ=∂M/∂H is a little over 0.5×10−4 emu/cm3 for Ni, 1.1×10−4 for Fe, with an error probably <0.1×10−4. Although there is a small contribution to each of these figures from orbital paramagnetism and, at the higher temperature, from the dependence of spin-wave amplitudes on field, the major contribution is almost certainly from the exchange-enhanced Pauli paramagnetism of itinerant d-band electrons. For this contribution to be as large as is observed for Ni, it seems necessary that the commonly accepted band structure of Ni be replaced by one with holes of both spins in the d-like bands.
Magnetization of Iron-Gallium and Iron-Arsenic Alloys
Authors: Aldred A. T.
Published: April 2005

The magnetizations of bcc α-phase iron-gallium and iron-arsenic alloys have been measured by a force technique between room temperature and 8°K. Customary extrapolation procedures were used to obtain mean atomic magnetic moments from these data. The linear rate of decrease of mean moment with solute concentration was found to be 1.428±0.095μB per atom for the iron-gallium system and 1.403±0.143μB per atom for the iron-arsenic system. This is in contrast with the usual behavior of nontransition metal solutes which are generally considered to dilute a constant iron moment.
Paramagnetic Scattering of Neutrons by an Iron-Nickel Alloy
Authors: Collins M. F.
Published: April 2005

Paramagnetic neutron scattering has been observed from an alloy of 65% Fe-35% Ni at temperatures up to about twice the Curie temperature (Tc=490°K). A cold-neutron technique was employed with energy analysis of the scattered beam so that all scattering processes with energy transfers below about 0.1 eV could be observed. The phonon scattering, which is of comparable intensity to the paramagnetic scattering, has been subtracted by two independent techniques that give results substantially in agreement with one another. The paramagnetic scattering integrated over energy transfer can be associated with a mean value of S(S+1) for the scattering atoms giving an apparent iron atom moment of 1.4±0.3 μB. The scattering has a half-height of 0.050±0.015 eV for wave vectors which are not near the center of a zone. This figure is an order of magnitude greater than has been predicted for a simple band model which ignores correlation effects and intra-atomic exchange. The existence of so much paramagnetic scattering at such small energy transfers indicates that atomic moments in the paramagnetic phase are defined for a relatively long period of time.
Some Properties of an Anisotropic Thin-Film-Waffle-Iron Memory Cell
Authors: Bobeck A. H. , Perneski A. J. , Reekstin J. P.
Published: April 2005

A new mode of operation of the cubic waffle-iron memory cell in which an anisotropic, rather than isotropic, storage film is used has been investigated. When a conventional 1000-Å NiFe film is combined with a high-permeability ferrite baseplate a high-speed, low-current device is obtained. Typical operating parameters using a waffle baseplate containing 0.005-in. slots on 0.015-in. centers are:Iword=90 mA, Idigit=10 mA, Vsignal=1 mV, and a creep threshold of 5 mA.

A number of 1000-Å NiFe films have been evaluated in both a continuous and a discrete shape configuration. It was found that the allowable skew for a particular film may be increased if bipolar rather than unipolar word currents are used.

Because of the complex nature of the field patterns in the waffle-iron structure it was necessary to supplement the standard operational pulse tests with direct domain observations using the Kerr magneto-optic effect.

The observed domain patterns were completely unexpected. Study of these patterns disclosed large range flux spreading along the easy-direction axis of the film. This spreading of flux, called the ``domino effect'' has been exploited in a remotely sensed memory cell. Output signals completely free from the usual digit current couplings have been obtained.
Saturable Shielding-A Technique for Nonlinear Coupling in Magnetic Circuits
Authors: Berger R. , Crowther T. S. , Raffel J. I.
Published: April 2005

If a magnetic film (the shield) with transverse saturation demagnetizing field Hd and anisotropy field Hk is placed in a transverse field below saturation strength (Hd+Hk), it experiences a net field less than Hk. A second film (the storage film), when placed on top of the first, will experience the same net field. If the anisotropy field of the storage film is much greater than that of the shield, the magnetization of the storage film undergoes a negligible rotation for all applied fields below Hd+Hk. Once the shield has saturated, any further increase in field is applied directly to storage film. The resulting plot of the net field at the storage film versus applied field shows a symmetrical offset threshold of approximate magnitude Hd. Control of the shield geometry provides a means for adjusting this threshold.

To investigate the shielding effect, two experiments were performed. The first used a 0.5-in.-wide Supermalloy tape to approximate an ideal shield and measured net field at its center line as a function of field applied with Helmholtz coils at very low frequencies. The second sought to demonstrate the practicality of shielding in a film memory. Both shield and storage medium were thin films of 0.004-in. width driven by pulsed word and digit fields using a technique which eliminated the readout from the shield. The results of both experiments show agreement with the theoretical models proposed in the paper.

Possible applications of the shielding technique are to all-magnetic selection in film memories and to creep reduction in conventional word-organized film memories.
Design of a 1.5-Million-Bit Plated-Wire Memory
Authors: Fedde G. A.
Published: April 2005

A complete feasibility model is now being utilized to demonstrate the design of this miniature space-borne memory. A continuous layer 10 000 Å thick of nonmagnetostrictive Ni-Fe alloy, plated on 5-mil-diam Be-Cu wire, is the memory element. No significant changes were measured in operating current margins of two 768-bit memory systems. Each was continuously operated for 1000 h at 75°–80°C. The magnetic properties are stable for the transverse drive duty factors tested which were less than 100%. More than 1000 h in a 95°C and 85% relative humidity atmosphere show that a clean, uncoated surface is nearly free of corrosion. The few tiny points that form seem to be self-limiting after 100 h. A temperature coefficient of −0.06%/°C on the transverse drive current results in a constant output signal from −55°C to +80°C. The transverse field drive line is a composite Cu-plated Ni-Fe alloy structure. This makes possible lower drive current and higher bit packing density. The 1.5×106 bit momory stack, with 2300 diodes, is designed to fit in 6×2.4×13 in. (187 in.3) including the case. The entire memory system consisting of two independent 1.4×106 bit memories consumes 1.5 W operating at a 500-kc/sec bit rate.
Nondestructive-Readout Coupled Film Memory Device
Authors: Sie C. H.
Published: April 2005

By magnetostatically coupling a soft film and a hard film with their easy axes orthogonal to each other, an NDRO (nondestructive readout) memory device with fast read cycle speed has been achieved. This device differes from the previously investigated NDRO devices as follows: (1) The partially magnetized state of the hard film is utilized for information storage. (2) Since the device is read and sensed along the transverse axis of the soft film, low read current can be used. The calculated results of possible combination of the soft and hard film characteristics that will result in a device with this mode of operation are presented. A 10-kÅ NiFe (80–20) film and a 10-kÅ CoFe film (50–50) each evaporated on a DuPont polymer substrate are used, respectively, as the soft and hard films of the device. The insensitivity of this device to bit disturb pulses is established by measuring the pulse hysteresis of the CoFe film's partially magnetized state. It is interesting to note that as long as the CoFe film is switched into these partially magnetized states not by time-limited process, these are stable states. Finally, the feasibility of this device for memory operation is evaluated experimentally in terms of driver current tolerances and signal to noise ratio.
High-Field Destruction of the Nonmagnetic Ground State in TmN
Authors: Cooper B. R. , Jacobs I. S. , Fedder R. C. , Kouvel J. S. , Schumacher D. P.
Published: April 2005

The octahedral cubic symmetry at a Tm site in TmN gives a singlet (nonmagnetic) level as the ground state of the Tm3+ ion in the crystal field. We have used pulsed magnetic fields up to 265 kOe to counteract the crystal-field effects and induce large ionic moments. Magnetizations measured at 4.2°, 20.4°, and 77°K show an approach to saturation at the highest fields used. For 4.2°K, the moment at 265 kOe is 4.5 μB per molecule as compared to the saturation value of 7 μB. The experimental results for the magnetization and susceptibility are compared to the theoretical results for crystal-field calculations. This comparison enables us to discuss the way in which exchange forces enter the magnetization process at high magnetic fields as the ground state becomes polarized. The fourth- and sixth-order crystal-field parameters have been evaluated by observing paramagnetic resonance at 9.35 Gc/sec for the Γ5(2) excited triplet.
Ferromagnetism in CdCr2Se4 and CdCr2S4
Authors: Menyuk N. , Dwight K. , Arnott R. J. , Wold A.
Published: April 2005

A study has been made of the magnetic properties of the spinels ACr2X4, where A is diamagnetic zinc or cadmium, and X is oxygen, sulfur, or selenium. CdCr2Se4 and CdCr2S4 are apparently ferromagnetic with moments somewhat below the predicted value of 6.0 μB/molecule. By contrast, ZnCr2Se4 and ZnCr2S4 are antiferromagnetic at low temperature despite having positive asymptotic Curie points (TA). We found very little thermal variation of cell size in these materials, which further corroborates Lotgering's conclusion that the antiferromagnetism is due to next-nearest-neighbor interactions.

Disagreement between experimental values of TA/TC and the theoretical value calculated assuming nearest-neighbor interactions indicate that next-nearest-neighbor interactions are playing a role in the ferromagnetic materials as well.

Comparisons of TA and TN in these materials indicate that the magnetic interactions are strongly dependent upon the diamagnetic A-site ion. However, the data cannot uniquely attribute this effect to an exchange coupling directly involving the A-site cation.
Linear Magnetoelectric Effects in Gallium Iron Oxide at Low Temperatures and in High Magnetic Fields
Authors: Rado George T.
Published: April 2005

The magnetoelectric (ME) experiments1 on monocrystals of the piezoelectric ferromagnet Ga2−xFexO3 (x≈1) are extended to low temperatures (T≳4.2°K) and high magnetic fields (H≲150 kOe). It is found that: (1) The linear ME susceptibility α, which has a maximum1 at some T=Tmax, exhibits a minimum at some T=Tmin satisfying 4.2°K<Tmin<Tmax; moreover, the value of α is almost as large at 4.2°K as at Tmax. (2) If H is sufficiently large so that the direction u=Ms/Ms of the spontaneous magnetization Ms is parallel to H, then the electric polarization Pb induced at constant T along the polar crystal axis (b axis) is given by Pb=ηu+αuH+βu H2, where βuH≪α for H≲150 kOe. The ``spontaneous ME polarization'' ηu is strongly u-dependent. However, αu is approximately u-independent, its u-dependent part being only about 2% at 145.2°K and 77.4°K and about 10% at 4.2°K. Since the (approximate) u-independence of αu indicates that the details of the spin canting assumed in the previous theoretical model1 are inapplicable to Ga2−xFexO3, a new thermodynamic description of ME effects is presented which does apply to ferromagnets having u ∥ H and satisfactorily describes (2). Finally, a thermodynamic calculation is given of a new mechanism of linear ME effects, namely the combined action of forced magnetostriction (i.e., a kind of piezomagnetism) and piezoelectricity. This mechanism, which ultimately arises from the strain dependence of exchange (and other) interactions, must exist in all unclamped piezoelectric ferromagnets having u ∥ H, and is probably significant in Ga2−xFexO3 near the Curie point.
Magnetic Structure of Ga2−xFexO3
Authors: Frankel R. B. , Blum N. A. , Foner S. , Freeman A. J. , Schieber M.
Published: April 2005

High-magnetic-field-Mössbauer and magnetic-moment experiments have been performed with Ga2−xFexO3. This magnetic system is of considerable interest because it is piezoelectric, weakly magnetic,1 and magnetoelectric.2 The crystal structure has been determined3 and a magnetic ordering inferred.3 The magnetic-moment measurements were made using a vibrating sample magnetometer in fields up to 75 kOe. The samples used for the Mössbauer absorption experiments consisted of 57Fe enriched powders, grown from a flux, embedded in lucite, and having x=0.8 and 1.2. A mosaic absorber made of small x-ray oriented single crystals was also studied. Measurements were made over the temperature range 4.2° to 320°K and in external magnetic fields up to 130 kOe. At low temperatures the zero-external field-absorption spectra indicate that there are at least two magnetically nonequivalent sites. In a large external field the hyperfine spectrum lines corresponding to Δm=0 vanish, while each of the outer lines (corresponding to Δm=±1) splits into two well-resolved components of unequal intensity. Detailed analysis of the experimental results for both the single crystal and polycrystalline absorbers indicates that at zero external field all spins lie in the a−c plane (c<a<b), that the observed moment is due to ferrimagnetism4 rather than to a canted spin structure, and that the spins are unequally divided between the two sublattices.

A detailed account of these measurements will be published elsewhere.
Some Properties of Ferromagnetoelectric Nickel-Iodine Boracite, Ni3B7O13I
Authors: Ascher E. , Rieder H. , Schmid H. , Stössel H.
Published: April 2005

Ferroelectricity and weak ferromagnetism have been found to set on simultaneously in Ni3B7O13I at about 64°K. This is evidenced by dielectric hysteresis, spontaneous Faraday effect, quadratic magnetoelectric hysteresis, etc. The strong coupling between the mutually perpendicular spontaneous polarization—[001]—and spontaneous magnetization—[110]—is such that, when the former is reversed, the latter turns by 90°. The magnetic point group is most probably m′m2′. Dielectric constant, magnetic, and magnetoelectric susceptibilities and magnetic coercive field are shown as a function of temperature.
Magnetic Behavior of Substituted Ferrimagnetic Garnets
Authors: Geller S.
Published: April 2005

The results of magnetic measurements on a large number of substituted yttrium iron garnets may be interpreted in terms of solid solutions between the ideal ferrimagnet and antiferromagnet. It is proposed that when substitution of diamagnetic ions is made exclusively in one Fe3+ ion sublattice, the moments of the Fe3+ ions in that sublattice remain parallel, while the weakened average a—d interactions and the intrasublattice interactions lead to random canting of the Fe3+ ion moments of the other. This tendency occurs as soon as substitution begins. On continued substitution a point is reached beyond which canting increases more rapidly with increasing substitution; in this region the intrasublattice interactions dominate the a—d interactions, but it is probable that the canting continues to be random. The model accounts for the results of simultaneous substitution of diamagnetic for Fe3+ ions in both sublattices. It has been found that different diamagnetic ion substituents may produce different magnetic behavior. Usually this is especially noticeable when the interactions are weak. However, in the case of V5+ ion substitution, dramatic effects are observed even for small substitution. It is suggested that these effects result from chemical bonding subtleties. The 0°K magnetic behavior of substituted gadolinium iron garnets may also be explained in terms of the model derived for the substituted YIG's. In particular, the behavior of the Gd3+ ion moments is linked directly with that of the tetrahedral Fe3+ ion moments. The model also leads to an explanation of the behavior of paramagnetic ion substituted YIG's.
Growth of Crystals and Magnetic Properties of β-Mn2O3 Solid Solutions
Authors: Banks E. , Kostiner E.
Published: April 2005

Crystals having the β-Mn2O3 structure have been grown electrolytically from a sodium polytungstate melt. The electrolysis was carried out at approximately 750°C in the eutectic mixture 80 mole % Na2WO4−20 mole % WO3 with the oxide crystals developing at the anode. From a melt containing manganese and aluminum oxides, crystals of the composition Mn1.8Al0.2O3 were obtained. Upon substitution of iron for aluminum, crystals of various compositions were obtained, as determined by chemical analysis. Magnetic susceptibility measurements showed θ values in the range of −140° to −180°K. A sample with manganese and aluminum was antiferromagnetic with a Néel temperature of about 70°K. The magnetic moment in the paramagnetic region was 4.80 μB, suggesting that Mn3+ was present. A sample containing iron and manganese showed spontaneous magnetization of the order of 4 emu/g below 66°K.
Magnetic and Semiconducting Properties of Perovskites Containing Manganese and Cobalt
Authors: Jonker G. H.
Published: April 2005

In this paper it is shown that a combined investigation of the magnetic and the semiconducting properties of the solid solutions of LaMnO3 and LaCoO3 is necessary for a complete understanding of this rather complicated system. The conductivity gives information on the valency states of the ions and with this knowledge the magnetic properties become understandable. Mixtures of Mn3+ and Co3+ ions tend to the formation of Mn4+–Co2+ pairs having a positive magnetic superexchange interaction.
Single-Crystal Growth and Properties of the Perovskites LaVO3 and YVO3
Authors: Rogers D. B. , Ferretti A. , Ridgley D. H. , Arnott R. J. , Goodenough J. B.
Published: April 2005

LaVO3 and YVO3 are intermediate between LaTiO3 (metallic and Pauli paramagnetic) and LaCrO3 (an insulator and antiferromagnetic below TN=320°K). Single crystals of these vanadites were grown from the melt by a modified Bridgman technique. The temperature dependences of electrical resistivity indicate that both materials are semiconductors in the temperature range 120°–670°K. However, the activation energies for semiconduction are considerably lower than those reported in the literature for powder specimens. Magnetic susceptibilities reveal antiferromagnetic ordering at 137° and 110°K for LaVO3 and YVO3, respectively. LaVO3 undergoes a structural transition at the Néel point that is suggestive of spin-orbit-coupling electron ordering. These results clearly support a localized-electron model at low temperatures. However, the low activation energies for semiconduction at temperatures above TN probably reflect a covalent-mixing parameter λ near the critical value λc for localized vs collective electron behavior.
Exchange Constants and Effective Masses in the Ferromagnetic Rare-Earth Metals
Authors: Darby M. I. , Taylor K. N. R.
Published: April 2005

The value of the term kf4ΣF(2kfRn) occurring in the RKY theory of indirect interaction has been calculated by summing over 1.5×105 lattice sites for the six heavy rare-earth metals which exhibit ferromagnetism. The sum ΣF(2kfRn) has previously been assumed to be constant; however, these calculations show that it varies from −6.62×10−3 to −6.91×10−3 using free-electron kf values, or from −2.97×10−3 to −7.07×10−3 using the kf values obtained by Yosida. Using these values and experimental results of θp and ρspin the variation of Γ and mx through the six elements has been found. In some instances these new values differ appreciably from those currently accepted. The variation of Γ and mx with volume has been investigated using the results of high-pressure studies, and the values of ∂logΓ/∂logV and ∂ logmx/∂ logV have been found. The change in the g values resulting from these Γ and mx values is compared with the experimental values.
Interband Mixing and Induced Local-Moment—Conduction-Band Spin Distributions
Authors: Watson R. E. , Freeman A. J.
Published: April 2005

The spin distribution induced in free-electron-like conduction bands by local (rare-earth) electronic magnetic moments has been investigated quantitatively. Both interband mixing effects and the more familiar Ruderman—Kittel—Kasuya—Yosida exchange-polarization terms have been accounted for. The former include (1) effective exchange1,2 terms, arising from the interband mixing, which contribute to both the average induced spin density and its spatial distribution; and (2) direct interband admixture terms1 which affect only the spatial distribution (and affect neither the average density nor the density at the origin of the impurity moment). The results are found to be sensitive to the conduction electron Fermi wave vector kF: in some cases, the admixture terms have little effect on the spin distribution outside of the impurity site; in others, they produce spin-density oscillations which are large in amplitude compared with the RKKY result.
Perturbation Expansion for the Magnetization of the Spin ½ Antiferromagnet
Authors: Kenan R. P.
Published: April 2005

A perturbation expansion of the sublattice magnetization of a spin ½ antiferromagnet is developed. The theory proceeds from a Fermion representation of the spin operators for spin ½, in which an auxiliary (drone) set of Fermi operators is introduced to account for the boson character of spin operators attached to different lattice sites. The development of the present theory is parallel to that derived earlier by Mills, Kenan, and Korringa, with the role of the ``contracted lines'' of the earlier theory being played by the drone lines of the present theory. Integral equations are derived for the single-particle spin propagator. A resummation over a class of graphs contributing to the kernel, which gives the spin-wave result at low temperatures, is outlined.
Space Group Theory for Spin Waves
Authors: Brinkman W. , Elliott R. J.
Published: April 2005

The symmetry properties of spin waves in ferro-, antiferro-, and ferrimagnetic crystals can be conveniently discussed in terms of an appropriate space group as are electron energy states in band theory and normal modes in the theory of lattice vibrations. Dimmock and Wheeler have pointed out that the magnetic space group, because of the directional properties of the moments, has fewer elements than the lattice space group, and have discussed the spin-wave properties in terms of this group. While this is strictly correct, the main part of the Hamiltonian usually used in such systems often has much more symmetry than this. For Heisenberg interactions the spins can be rotated independently so that the total group is a product of a lattice space group and a set of spin—space rotations which leave the spin pattern unchanged. This lattice space group is obtained by considering atoms with different spin orientations as inequivalent. The single ion anisotropy restricts the spin rotations. This leads to considerably more degeneracy in the spin-wave spectrum than is predicted by the magnetic space group, the degeneracy being removed in real crystals by small interactions like dipole—dipole. Such groups have been constructed for common systems for use in evaluating the form of spin-wave spectra, selection rules, etc.
Unidirectional Anisotropy in Multilayer Films of Cr and NiFe
Authors: Sharp R. W. , Archibald P. C.
Published: April 2005

Layered films of Cr and NiFe alloy have been made which exhibit biased hysteresis loops in the easy direction and asymmetric hysteresis loops in the hard direction. The asymmetry in the hard direction is reversed by rotating the film a few degrees in the loop tester. The magnitude of the bias is 0.5 Oe for films consisting of a 500-Å layer of 76% NiFe on top of a 500-Å layer of Cr on a soft glass substrate.

No loop bias was observed for films of 82% NiFe, for films on hard glass substrates, or for films with layer thicknesses departing from 500 Å by a factor of two.

The films exhibit high sensitivity to externally applied stress. Loop bias can be eliminated by raising the temperature above the Néel point of Cr. The unidirectional axis is a function of the direction of a magnetic field applied during cooling of a film through the Néel point.

The observed phenomena are believed due to exchange anisotropy between antiferromagnetic (strain sensitive) Cr and ferromagnetic NiFe. Crystal anisotropy, shape anisotropy, magnetostriction, etc. are not unidirectional. The only unidirectional effects reported in the literature have resulted from exchange anisotropy.
Measured Relaxation Times for the Uniaxial-Anisotropy Spectrum in Nonmagnetostrictive Permalloy Films
Authors: Smith D. O. , Weiss G. P. , Harte K. J.
Published: April 2005

The relaxation time τ for realignment of an atomic anisotropy by 90° has been measured for a number of fast processes (τ<103 sec) occurring in nonmagnetostrictive Permalloy films. The method of measurement utilizes the magnetoresistance effect and is described in detail elsewhere. For films deposited between 23° and 200°C at 10−6 to 10−5 Torr and measured at the same temperature and pressure, three distinct processes plus two probable ones have been found, which together account for about one-quarter of the total anisotropy. The activation energy Q and period factor τ0 which determine the relaxation time τ=τ0 exp (Q/kT) have been determined for each of these processes.
Sensitive Pulsed Magnetoresistive Measurement of Magnetic Film Hk
Authors: Johnston R. C.
Published: April 2005

For a magnetic annealing experiment with Permalloy films it was necessary to measure the uniaxial anisotropy field Hk without breaking vacuum after deposition, while maintaining a transverse field H⊥≳Hk. The annealing mechanism could then be studied as a function of temperature by a plot of Hk vs time. In the presence of the field H⊥, longitudinal ac (500 cps) field H∥«Hk, and longitudinal dc film current, a second harmonic magnetoresistance signal is generated. The measurement is based on the phase reversal of this signal when H⊥ = Hk. Rather than sample only one cycle of the 2nd harmonic output, 30 cycles are used and averaged in an integrator. The transverse field consists of a dc bias and a 1-cps triangular or sinusoidal waveform. The minimum resultant field is maintained at Hk by means of negative feedback to the dc bias. Typical system performance is as follows: For an Hk of 5 Oe, ΔHk is readable to 0.01 Oe or 0.2%. Absolute value of Hk is measured to about 5% accuracy. The system will follow changes at a maximum rate of 0.2 Oe/sec.

A second-generation system will also be described which uses simpler electronics and is more flexible with regard to the annealing and sensing directions of the film.
Magnetoelastic Sensitivity and Composition of Permalloy Films
Authors: Long T. R.
Published: April 2005

The compositional dependence of the magnetoelastic sensitivity of Permalloy films has been studied by a number of investigators, but their results are in disagreement regarding the compositions required for zero magnetostriction, the agreement with bulk values, and the anisotropy of the magnetoelastic coefficients. This paper reports measurements on cylindrical films of torsional strain sensitivity (H l/γ) and absolute compositional analyses by refined x-ray fluorescence techniques to a precision not attained before. Although the average zero magnetostriction point (ZMP) is found at 80.3% Ni, the data suggest that there are probably structural variations from film to film which cause real variations of ±0.5% in the ZMP. Torsional strain sensitivity is correlated with measurements of tensile strain sensitivity (η). The shear coefficient Bγ is found to be 1.21 times the tensile coefficient Bβ. The slope of η versus composition for these electroplated films is in reasonable agreement with the other data on evaporated films. The inferred slope of magnetostriction λ versus composition is significantly below that for bulk Permalloy.
Uniaxial Anisotropy in Permalloy Films at Temperatures Below 4.2°K
Authors: Mitchell E. N. , Briscoe C. V.
Published: April 2005

Permalloy films (80%-84% Ni; 20%-16% Fe) of the order of 1000 Å thickness were prepared by vacuum deposition from a tungsten filament onto heated glass substrates at a temperature of 600°K in the presence of a 200-Oe magnetic field. The anisotropy field (Hk) of these films was measured at temperatures ranging from 295° to 1.46°K. It was possible to measure induced voltages proportional to M with at least 4% precision at drive levels of 0.01 Oe at all temperatures. In general, the shapes of the difficult-direction magnetization curves changed with temperature between 295° and 4.2°K especially at drive levels of about 1.0 Oe, but shape changes were not observed below 4.2°K and changes below 77°K were reversible. These changes were presumably due to strain effects. The changes in the loops with temperature at 0.1 Oe drive levels were small enough to allow meaningful measurement of Hk throughout the temperature range. While Hk (77)/Hk (295) was found to be about 1.5, Hk(1.46)/Hk(4.2) was found to be about 1.9, implying that a new source of anisotropy is observed at temperatures below 4.2°K. This added anisotropy can be represented analytically as Hk(T) = A exp (−T/T0), with A about 50 Oe and T0 about 2.6°K. It is perhaps significant that kT0 corresponds to the energy of about four Bohr magnetons in the internal field of the film.
Study of the Lattice of Vortex Lines in Superconducting Niobium by Neutron Diffraction
Authors: Cribier D. , Jacrot B. , Farnoux B. , Rao L. Madhav
Published: April 2005

The magnetic behavior of type II superconductors in the mixed state is well explained by the model of vortex lines. Following A.A. Abrikosov, the superconductor in an applied field H (Hc1 < H < Hc2) is divided in regions where superconductivity is strongly perturbated, the magnetic field penetrates inside a hard core surrounded by rings of supercurrents which screen the field (vortex lines). Moreover, there should exist a regular two-dimensional lattice of these lines: the field is periodical. Each line carries a flux quantum φ0 = ch/2e; the total magnetic induction B = αφ0/d2; α is a geometrical coefficient depending on the lattice type and d the lattice parameter. In a preliminary report1 a periodicity of the field was detected and the flux quantization was proved. Actually the experiments yielded √3/2>α> 1. A new set of experiments with better angular and wavelength definition of the neutron beam has given more accurate results. The main points are: (1) The Bragg peak is very sharp so that there exists a long-range order. (2) The second-order Bragg peak is unobservable, i.e., that the periodical variation of the field is well represented by the first Fourier component. (3) The value of α is given by 2α = √3 for a set of magnitude of B when applied field H is far from Hc1 and Hc2. The lattice is thus triangular.
Antiferromagnetism of the Spinel MnGa2O4
Authors: Boucher B. , Herpin A. G. , Oles A.
Published: April 2005

The cubic spinel MnGa2O4 is partially inverse with 87% of the Mn atoms on tetrahedral A sites. Neutron diffraction with a powder has shown that, at low temperatures, the spin moments on A sites are antiferromagnetically coupled (TN=33°K). The variation of the (200) magnetic reflection as a function of the magnetic field allows the determination of both the direction of the magnetic moments along [111] and the value (K1=−4.104 erg/cm3) of the anisotropy constant. The 1/χ(T) curve does not show the typical minimum at the Néel point but instead decreases rapidly at low temperatures. We explain that phenomenon by taking into account the paramagnetism of the spins on octahedral sites.
Magnetic Ordering in VF2
Authors: Stout J. W. , Boo W. O. J.
Published: April 2005

The compound VF2 has been prepared by treatment of vanadium metal with HF gas at 1250°C to form VF3, and subsequent reduction to VF2 at 1150°C with a controlled mixture of HF and H2. Debye—Scherrer photographs show VF2 to have the rutile structure, isomorphic with MnF2, FeF2, CoF2, NiF2, and ZnF2. Heat-capacity measurements from room temperature to 5°K, using a platinum resistance thermometer, show a peak in heat capacity at 7.0°K, presumably associated with long-range magnetic ordering, and a large magnetic contribution to the heat capacity at higher temperatures. The major fraction of the magnetic entropy of Rln4 is acquired in the short-range-order region. The behavior of the magnetic entropy is similar to that found in CuCl2 and CrCl2 where there is extensive short-range magnetic ordering in one-dimensional chains of metal atoms coupled by relatively strong exchange forces. This suggests that in VF2, unlike the other iron group fluorides, the strong exchange interactions are between neighboring vanadium atoms which form one-dimensional chains parallel to the tetragonal axis and that the exchange forces between a vanadium atom and its eight nearest neighbors in 〈111〉 directions are relatively weak.
Magnetic Ordering in Eu3O4 and EuGd2O4
Authors: Holmes L. , Schieber M.
Published: April 2005

The magnetic susceptibilities of single crystalline and polycrystalline Eu3O4 and of polycrystalline EuGd2O4 in the range between 2° and 300°K are reported. The compounds are antiferromagnetic with TN=5.0° and 4.5°K, respectively. Above TN the susceptibilities follow Curie—Weiss laws, with θP=−5° and +2°K, respectively. Eu3O4 is metamagnetic below TN with Hc=2.4 kOe at 2°K. Possible magnetic structures for Eu3O4 are discussed.
Antiferromagnetic—Ferromagnetic Transition in the Compound Mn3GaC
Authors: Bouchaud Jean-Pierre , Fruchart Robert , Pauthenet René , Guillot Maurice , Bartholin Henri , Chaissé Francis
Published: April 2005

The compound Mn3GaC has been found to have a crystal structure of the perovskite type and a ferromagnetic Curie point of 246°±2K°. At a lower temperature, about 150°K, it exhibits a rather abrupt transition to an antiferromagnetic state. At this transition, there is a rapid decrease of lattice parameter and of resistivity with increasing temperature. The transition has been studied as a function of magnetic field up to 200 kOe while both transitions have been examined in hydrostatic pressures up to 4000 bar. From these data, the latent heat of the abrupt transition is calculated to be about 1 cal/g.
Magnetic Structures in CrTe—CrSb Solid Solutions
Authors: Takei W. J. , Cox D. E. , Shirane G.
Published: April 2005

Neutron diffraction studies have been made of solid solutions of ferromagnetic CrTe and antiferromagnetic CrSb which crystallize in the hexagonal NiAs structure. Similarities are found with the isostructural system MnSb-CrSb, in which good agreement is obtained with de Gennes predictions for the effects of double exchange on an antiferromagnetic system. The most striking feature is the formation of a canted spin structure with cosine of the cant angle varying as a linear function of composition. The variation of angles and transition points when analyzed in terms of double exchange theory gives about the same value of b/|J| S2 in the two systems. At very high CrTe contents, a different type of canted spin structure occurs.

The possibility of deviations from the ideal structure as can occur in CrTe is examined. A least-squares structure analysis was made which indicated the absence of distortions in most of the solid solutions.
Magnetic Properties of RbFeF3
Authors: Wang Franklin F. Y. , Kestigian Michael
Published: April 2005

The magnetic susceptibility of a powder sample of RbFeF3 has been measured from 12° to 300°K in magnetic fields up to 11 kOe. Its Curie constant agrees with S=2 and g=2.17 for an Fe2+ ion. Its Néel point is 75°K. The data yield the exchange interactions for a two-sublattice model: W12=−43.9°K, W11=+4.5°K, and W22=−7.5°K. The ratios of θ to TN (1.17) and of W11 to W12 (0.10) are consistent with a magnetic ordering of the first kind. Weak ferromagnetism occurs around 74°K. The weak ferromagnetic moment extrapolates to about 0.27 μB (Bohr magnetons) at 0°K and corresponds to a canting angle of 1°56′.
Effect of Electron Concentration on Magnetic Properties of EuTe—GdTe
Authors: Holtzberg F. , McGuire T. R. , Methfessel S.
Published: April 2005

The systems EuSe—GdSe and EuS—GdS show a strong increase in the positive value of the paramagnetic Curie temperature (θ) as a function of the Gd3+ concentration. The pure europium chalcogenides in both systems have positive θ values. This paper discusses the effect of the increase of electron concentration on magnetic interactions in EuTe, which is antiferromagnetic in its pure state. We find that θ increases from −10°K for EuTe to a maximum of +28°K for Eu0.8Gd0.2Te and then decreases monotonically with increasing Gd content to θ=−90°K for GdTe. The variation of θ is interpreted as a result of a Ruderman-Kittel-Yosida type interaction via the conduction electron donated by Gd3+. In contrast to the selenide and sulfide systems, no true ferromagnetic order occurs in EuTe-GdTe at 4.2°K for any composition. As an example, the magnetization of Eu0.8Gd0.2Te (θ=+28°K) saturates at 4.2°K for magnetic fields only above 45 000 Oe, which may be due to either spin canting or a more complex magnetic structure involving ferromagnetic clusters.
Linear and Circular Acoustical Birefringence in Ferroacoustic Resonance
Authors: Lüethi B.
Published: April 2005

Experimental results of the linear and circular magnetoacoustical birefringence effects are presented for gadolinium iron garnet and yttrium gallium iron garnet. Some special features of these effects, such as directional dependence on the magnetic field and internal field variation are discussed. Magnetoelastic coupling constants and anisotropy constants deduced from these experiments are presented.
Parallel Pumping of Magnetoelastic Waves
Authors: Cole P. H.
Published: April 2005

A general analysis of the longitudinal pumping of magnetoelastic waves near the magnon—transverse-phonon crossover region has been performed. Variation of the directions of propagation and the applied field within the crystal lattice are taken into account and the effects of magnetic, elastic, and magnetoelastic anisotropy are included. When the applied field H0 is in a [100] direction, the theory gives a magnetoelastic dispersion relation in agreement with previous treatments. When H0 is in a [111] direction, the usual assumption that the body displacement vector is polarized along H0 is found to be incorrect and a new dispersion relation is obtained. This correction modifies the calculation of magnetoelastic constants from experimental data. Variation in the direction of propagation of the unstable magnetoelastic wave, not considered in previous treatments, is found to be important in determining the asymmetry and size of the phonon pip. High-resolution spin-wave instability measurements near the transverse phonon interaction region have been performed at a pump frequency of 34 Gc/sec on yttrium iron garnet. The lineshape is in agreement with the present theory. Calculations of the elastic mode Q factors, taking into account the variation in propagation direction, give values an order of magnitude lower than would otherwise be obtained. Data showing the variation of effective exchange constant with magnetization in YGaIG are included.
Precipitation Effects in Diffused Transistor Structures
Authors: Fairfield J. M. , Schwuttke G. H.
Published: April 2005

Transmission x-ray diffraction microscopy was used to detect precipitation effects in phosphorus-diffused silicon—especially after subsequent gold diffusion. The precipitate (after gold diffusion) appears to be a complex—formed by gold combining with excess phosphorus in the silicon lattice. This complex formation is responsible for the apparent high solubility of gold in phosphorus-diffused areas, and it has a potentially detrimental effect upon diode reverse characteristics. Furthermore, this phenomenon provides a sink for gold atoms that would otherwise fill silicon lattice sites. This effect has important consequences on the fabrication of fast switching devices, since it tends to rob the crystal lattice of gold recombination centers.
Ultrasonic Attenuation in Insulators at Room Temperature
Authors: Oliver D. W. , Slack G. A.
Published: April 2005

In many insulating crystals, the attenuation of sound waves of microwave frequencies is a result of energy transfer from the sound wave to thermal phonons. A simple correlation exists between sound attenuation in such crystals near room temperature and their thermal properties. This correlation is exhibited at 300°K for a number of crystals for which both sound attenuation and thermal measurements have been made. Crystals which have low sound attenuation at microwave frequencies and room temperature appear to be those with light mass atoms, high Debye temperatures, and complex crystal structures. Estimates are made of the sound attenuation to be expected at 300°K in two materials for which thermal data alone are available.
The Tl2Te3-Bi2Te3 System
Authors: Spitzer Donald P. , Sykes James A.
Published: April 2005

The pseudobinary system Tl2Te3-Bi2Te3 was studied by means of microscopy, differential thermal analysis, and x-ray diffraction. No ternary compounds are found within the system. In particular, we do not find the compound TlBiTe3 previously reported by Borisova, Efremova, and Vlasov. Thermoelectric properties near the composition TlBiTe3 are determined primarily by TlBiTe2, which is the major phase to form.
Hardening of Silver-Doped Potassium Chloride by Low-Temperature X-Ray Irradiation
Authors: Nadeau John S.
Published: April 2005

Silver-doped KCl was much more susceptible than pure KCl to radiation hardening at low temperature. Pulse-annealing experiments showed that a large fraction of the hardening was caused by self-trapped holes, Cl2−. The silver ion which substitutes for the potassium ion in the structure performs the function of electron trap, thus stabilizing large numbers of isolated holes. The silver is relatively ineffective as a hardening agent in any of its several ionization states. This indicates that electrical interactions between dislocations and point defects are not an important source of hardening in ionic crystals. Just as with metals, the strongest hardening effects are caused by elastic interactions.
Skin Effect in Anisotropic Plasmas and Resonance Excitation of Electron-Cyclotron Waves. I. Theory
Authors: Pfeiffer B.
Published: April 2005

The complete electromagnetic field has been calculated within a homogeneous infinite two-dimensional plasma sheath with a perpendicularly applied static magnetic field. The plasma is produced by a high-frequency electromagnetic field at the surface. When the electron-cyclotron frequency is greater than the frequency of the applied high-frequency electromagnetic field at the surface, the refractive index of the medium becomes real for the right-hand polarized wave and one has an increased penetration of high-frequency energy into the interior of the plasma.

It is also possible for the refractive index to reach a value such that the thickness of the plasma sheath is half a wavelength. In this case, resonance effects should be expected for the electron-cyclotron wave which propagates in the plasma.
Impurity Photovoltaic Effect in Cadmium Sulfide
Authors: Cuong N. Duc , Blair J.
Published: April 2005

Photovoltaic cells were fabricated by evaporating a thin copper layer on low-resistivity single-crystal n-type cadmium sulfide. It was found that the spectral response of the cells in the infrared was enhanced by as much as two hundred fold when the cell was illuminated by radiation with energy corresponding to the energy gap (green light). The enhancement of the infrared photovoltaic response is attributed to creation of additional minority carriers by transitions of electrons from the valence band to impurity levels. These impurity levels were emptied by the green excitation making infrared transitions to the impurity states more favorable. The net effect is the broadening of the spectral response of the cell. Transient measurements of the emptying and filling of the impurity states were made by illuminating the sample from two monochromatic light sources. The recombination statistics of holes was analyzed. A single recombination level model was adequate to explain the results. Recombination center concentration and hole and electron capture cross sections were calculated with the results: Nr=1.3×1017/cm3, Sn=1.2×10−23 cm2, and Sp=2.08=10−20 cm2.
Kinetics of Coarsening of Spherical Particles in a Liquid Matrix
Authors: Sarian S. , Weart H. W.
Published: April 2005

The theory of particle coarsening kinetics under control by diffusion through the matrix and by phase-boundary reaction is reviewed, and extended to the case of diffusion control when the particles are closely spaced and for impurity control at the interface. For the first case, d̄=f(T,φ)t⅓, Nv=f(T,φ)t−1, where d̄ is the mean particle diameter, φ is the volume fraction solid, T is temperature, and Nv is the number of particles per unit volume. For the latter two cases, d̄=f(T)t12,Nv=f(T)t−32, the temperature-dependent functions being different for the two cases.

The models are used to discuss existing kinetic data on the iron-liquid copper and oxide-liquid silicate systems. New data on the NbC-liquid iron system reveal the absence of the expected diffusion-field interaction effect when particles are close together. The role of surface-active impurities, particularly boron, on the mechanism of growth is discussed and it is shown that, while growth may be diffusion-controlled in the absence of impurities, it may become phase-boundary reaction controlled when appreciable quantities of impurities are present. The apparent coefficient of diffusion of iron in copper is calculated to be about 6.06×10−4 cm2/sec at 1120°C.