bluuebunny/crossref_metadata_2025 huggingface dataset:
Coupled-Film Memory Elements
Authors: Chang Hsu
Published: January 2005

Coupled-film arrays have been fabricated on insulated Cu ground plane with 0.004-in.-wide bit lines on 0.006-in. centers and 0.007-in.-wide word lines on 0.014-in. centers, resulting in an unusually high packing density of 12 000 bits/in.2 A sense signal of 2 mV under worst-case testing conditions has been measured at 200-mA word current (6 nsec risetime) and 15-mA bit current. The low word and bit currents have been achieved by miniaturizing the devices while providing flux closures. The etched Permalloy-Cu-Permalloy bit/sense lines are plated with Permalloy at the edges. The word lines are embedded in ferrite. Permalloy backing on word line and Permalloy embedded in ground further improve flux closure. Available Permalloy materials have intrinsic limitations on the obtainable Hk, Hc, α and the ratio Hc/α Hk (a measure of disturb immunity). The device operating margin can be extended by using doublet word and/or bit currents. The doublet bit current increases the bit disturb threshold, while the doublet word current decreases the bit write threshold. With both doublet bit and word currents, both beneficial effects are achieved.
Simultaneous Nanosecond Kerr Magneto-Optic and Inductive Measurements of Coupled Films
Authors: Chang H. , Genovese E. R.
Published: January 2005

A technique for magneto-optic sensing of film switching in 5 nsec over an area 20-μ in diameter has been reported by Thompson and Change (Ref. 1). The technique, when used in conjunction with inductive sensing, enables the analysis of the switching behavior of each layer in a coupled film structure. An experimental structure consists of an insulated ground plane on top of which two Permalloy layers (125-μ wide, 900 Å/layer) sandwiching a word conductor (125-μ wide, 2-μ thick, 6 μ above ground) are deposited with each axis along the strips. Two strands of lines (100-μ wide on 200-μ centers) on glass are connected in parallel to form a bit/sense line. The sense line is 40 μ above the coupled film lines. The openings between strands provide optic access for Kerr magneto-optic sensing of the top film.

The word current and its ground image create fields of the same polarity at the bottom film, but of different polarities at the top film. It has been surmised that only the bottom film is switched by the drive current and its image, while the top film is switched by the stray field from the switched bottom film. Experimental results, indeed, confirm the above. Furthermore, the switching speed of the bottom film is found to be limited by flux trapping in the ground plane. During read, the switching speed of the top film is limited by its own demagnetizing field cancelling the stray field. During write, the switching speeds of both films are limited by the subtraction of shape-anisotropy field from induced-anisotropy field due to hard direction-flux closure. The device signal is found to be only slightly altered by a hard-direction bias field in the range of ±10 Oe.
Magnetic Recording Materials
Authors: Speliotis D. E.
Published: January 2005

The increasing demand for higher storage capacity in magnetic recording media has led to an intensive examination of magnetically hard particles and films in a search for better magnetic properties and improved storage capabilities than those offered by the traditional particulate dispersions of γ-Fe2O3 micropowders.

In this paper, we discuss the effect of the magnetic properties and of the thickness of recording surfaces in high-resolution recording applications, and specify design criteria for their optimization.

The properties and the origin of magnetic hardness in oxide and metallic particles and in metallic films are discussed, and their high-resolution recording behavior is compared. It is concluded that the greatest potential in particulate coatings is offered by single-domain ferromagnetic metallic particles, while ultimate recording optimization can be achieved in thin metallic surfaces.
Thermal Expansion and Magnetostriction of Single-Crystal Europium Oxide
Authors: Argyle B. E. , Miyata N.
Published: January 2005

Thermal expansivity and magnetostriction of an EuO single crystal were determined by using the strain gauge method in the temperature ranges 20° to 250°K and 4.2° to 150°K, respectively, and in magnetic fields up to 20 kOe. The magnetoelastic component of expansivity αme is observed to be proportional to the magnetic specific heat Cm.1 As a result we obtain a temperature independent ``magnetic'' Grüneisen constant ∂ ln Um/∂ ln V=[minus]5.3 given by −3αmeCm−1BT using BT (isothermal bulk modulus) =1.07×1012 dyn/cm2. For Um, the internal magnetic energy, we derive also the variation with temperature and magnetic field Um(T, H)/Um(0), the variation with pressure ∂ ln Um/∂ P=4.9×10−12 dyn−1cm2, and the value Um(0) = −4.9×108 erg·cm−3 at 0°K. These results are obtained from treating various combinations of measurables including magnetization, isotropic forced magnetostriction, and zero-temperature volume anomaly as well as αme and Cm. The manner of suppression of the λ-transition by a magnetic field is also revealed by the data. Linear magnetostriction coefficients extrapolated to 0°K are λ100=−22×10−6 and λ111=55×10−6. Their decrease with increasing temperature is explained by a 1:1 admixture of single-ion and two-ion magnetoelastic coupling as described by λ(T)=̇λ(0){Î5/2[L−1(m)]} and λ(T)=̇λ(0)m2, respectively.2
Propagation of Magnetostatic Surface Waves in YIG Rods
Authors: Olson F. A. , Kirchner E. K. , Mehta K. B. , Peternell F. J. , Morley B. C.
Published: January 2005

Analysis of the mode spectrum of a long unshielded ferrimagnetic cylinder yields solutions in the magnetostatic approximation, which can be categorized as surface and volume modes. Observation of the volume modes has been reported previously. Experimental observation of the propagation of magnetostatic surface modes in single-crystal YIG rods is reported here. Surface modes are characterized by energy density concentration near the rod surface and are identified as occurring at frequencies above the low wavenumber limit of the spinwave manifold. Propagation involving asymmetric coupling to multiple-order surface modes results in 7–11-dB total insertion loss over a relatively smooth, broad passband whereas selective coupling to the lowest-order mode produces length-cavity responses. Extension of the previous surface mode theory of Joseph and Schlömann for axially magnetized, unshielded rods to the case with metal boundaries yields similar mode patterns but a broadened frequency passband and no cutoff wave number. A theory has also been formulated for transversely magnetized rectangular rods with metal boundaries. Experimental results with finite length rods agree qualitatively with theory.
EPR Pressure Experiments on Rare Earths in Diamagnetic Garnets and the Single-Ion Magnetostriction of Rare-Earth Iron Garnets
Authors: Phillips T. G. , White R. L.
Published: January 2005

The EPR spectra of Gd3+, Yb3+, and Er3+ in diamagnetic garnet hosts have been measured as uniaxial pressures were applied to the crystal, and the parameters ∂gkl/∂εij and ∂Dkl/∂εij evaluated. A theory connecting these parameters with the magnetoelastic energy of the rare-earth iron garnets has been developed, and the single-ion contribution to the magnetostriction constants λ100 and λ111 of GdIG, YbIG, and ErIG calculated. In most cases the predicted single-ion magnetostriction constants are of the same sign and within a factor of 2 of the observed magnetostriction constants at low temperatures. We conclude that single-ion effects play a dominant role in the magnetoelastic behavior of the rare-earth iron garnets.
Magnetoacoustic Effects in Rare-Earth Iron Garnets
Authors: Franz Judy R. , Luethi Bruno
Published: January 2005

We have used the techniques of linear magnetoacoustic birefringence and transverse ferroacoustic resonance to measure the real and imaginary parts of the index of refraction of soundwaves in the rare-earth iron garnets. The sound waves act as a probe to study the magnetoelastic coupling and the large rare-earth ion relaxation effects in concentrated samples. We investigated YbIG, DyIG and TbIG in the temperature range from 77° to 300°K. The transverse ferroacoustic resonance geometry, RπM, (R=acoustic shearwave polarization vector, M=magnetization) was used to study the linewidth broadening. In YbIG, even at 77°K, the linewidth is only slightly broader than in YIG and GdIG; in DyIG the broadening is pronounced, especially towards lower temperatures; and in TbIG it is so big that no ultrasonic echoes are observable below the magnetization compensation point. The linear birefringence geometry, R and M at 45°, was used to measure the difference in phase velocity between coupled and uncoupled shearwave components.

We have attempted to calculate linewidths and effective magnetoelastic coupling constants, by applying the so-called ``slow relaxation theory'' to the phonon-coupled spin system. A comparison of this theory with our experimental results will be given.
Magnetoelastic Interaction in EuIG
Authors: Bertram N. , Jones R. V.
Published: January 2005

The magnetoelastic behavior of Eu3+ ion has been studied in the magnetic garnets by means of the stress-induced shift in the FMR. At low temperatures the energy of the Eu3+ ion is determined by the exchange interaction which mixes excited J multiplets into the J=0 ground state. The anomalously large strength of the magnetoelastic interaction of Eu3+ may be understood in terms of a relatively simple model which involves strain-induced variations in the anisotropic Eu3+−Fe3+ exchange coupling. The stress-induced shifts in the FMR of EuIG may be attributed, mainly, to a change of order χHex2(∂/∂ε)(lnHex) in the magnetic energy. The model successfully accounts for the variations in the magnetoelastic behavior for the mixed crystal system Eu3−x YxFe5−yGay012.
Magnon-Magnon Interactions as Deduced from Harmonic Generation in YIG
Authors: Bierlein J. D. , Hinderks L. W. , Richards P. M.
Published: January 2005

Second-harmonic generation has been measured in a single-crystal YIG sphere of ΔH=0.38 Oe at an incident frequency of 8.42 GHz. Both transient and steady-state effects are reported. The following anomalies exist above the Suhl threshold: (1) there is a sizable variation in the initial part of the harmonic pulse with no corresponding variation seen on the transverse magnetization; (2) after the driving field is turned off, the harmonic power initially increases, and this reradiation effect is again absent in the transverse magnetization; (3) steady-state harmonic power decreases with increasing incident power over part of the region. Effects (2) and (3) can be explained reasonably well by considering parametric coupling between the spinwaves k initially excited by the Suhl mechanism and other spinwaves k′. In this model, the spinwaves k′ then contribute to the harmonic magnetization π out of phase with that of the uniform mode, accounting for both (2) and (3). These effects cannot be explained simply by lumping all magnon-magnon interactions into effective relaxation rates. Explicit computer solutions of spinwave buildup have been attempted in an effort to account for (1), but with no success.
Rapid Amplitude Fluctuation of Magnetoelastic Waves in Axially Magnetized [110] Oriented YIG Rods
Authors: Kirchner E. K.
Published: January 2005

Rapid amplitude fluctuations of magnetoelastic waves have been observed in axially magnetized, [110]-oriented YIG rods as the magnetic field, and hence delay time, are varied. The fluctuations are characterized by an 8 to 14 dB amplitude fluctuation of the entire delayed pulse with a period varying from 0.025 to 0.08 μsec. Analysis based on the interference of two pure shear elastic modes of the YIG sample coupled to the magnetic-spin system predicts an amplitude fluctuation of 11.8 dB with a period of 0.04 μsec, which compares well with the observed results. A description of the observed amplitude fluctuation, and its analysis, is presented. Factors necessary for the observation of this amplitude fluctuation and means by which it can be eliminated are discussed.
Interactions of Parametric Magnons in Ferromagnets
Authors: Le Gall Henri , Lemaire Bernard
Published: January 2005

Conditions for the appearance of the three, four, and five magnon fusions have been derived by Gottlieb and Suhl by making use of the dispersion relation of the spin wave, restricted to the Zeeman and exchange terms. In this paper we have determined these conditions of existence from the correct relations of dispersion containing the dipolar term neglected in the previous calculations. Experimental studies of the transient growth of parallel-pumped spin waves are in good agreement with these theoretical results, thus verifying that the parametric magnons are propagating perpendiculary to the dc magnetic field as predicted by the theory of Sparks and Kittel.
Stable Spin-Wave Trajectories
Authors: Schlömann Ernst , Joseph Richard I.
Published: January 2005

The propagation of spin waves in nonuniform magnetic fields has been theoretically investigated using a ``geometrical optics'' approximation and a simplified dispersion relation. In this approximation, the beam trajectory is identical with the path of a particle whose potential energy is proportional to the local magnetic field. The latter satisfies Laplace's equation and hence does not assume a minimum inside the sample. A general criterion has been derived for the existence of stable trajectories (a beam which starts out close to the axis of symmetry of the sample will never depart very far from it, even after arbitrarily many reflections). The stability criterion has been evaluated in detail for a number of special cases. Stable trajectories occur only when the potential V(x) along the axis of symmetry has a region in which it is ``concave down'' [(∂2V/∂x2)<0], and when the total energy of the particle lies within one of several bands of stability. The relevance of the theory to magnetoelastic delay lines is discussed.
Similarity of the Magnetization Distribution around Transition and Nontransition Element Impurities in Nickel
Authors: Comly J. B. , Holden T. M. , Low G. G.
Published: January 2005

The magnetization distribution around a wide variety of impurities in nickel (Al, Ga, Si, Ge, Sn, Sb nontransition metals; Nb, Mo, Ru, Rh 4d; W, Re, Os 5d) has been measured. This work is an extension of the study initiated by Low and Collins1 of the 3d transition elements V, Cr, Mn, Fe dissolved in nickel. Two distinct kinds of magnetization distribution have been observed. In one category (Mn, Fe, Rh), the magnetic disturbance is confined to the impurity site. In the other category the magnetic disturbance is widespread, extending some 6 Å into the nickel lattice. With the exception of V, Ru, and Os, the individual scattering curves of the second class, when normalized at a single point, superpose. This leads to the conclusion that the spatial form of the moment disturbance in the nickel matrix is similar for Al, Ga, Si, Ge, Sn, Sb, Nb, Cr, Mo, W, and Re. This suggests that this wide variety of impurities affects the nickel matrix through the same mechanism. Differences between the impurities show up only in the strength of the disturbance. The normalization factor, which causes superposition of the scattering lengths, for a particular impurity appears to be proportional to the number of electrons outside closed shells in that impurity.
Optical Densities of States of Magnetic and Nonmagnetic Transition Metals
Authors: Yu A. Y-C. , Spicer W. E.
Published: January 2005

A systematic photoemission study of the electronic structure of transition and noble metals has been undertaken to enhance the understanding of ferromagnetism.1,2 Previous work on Ni1 and Fe3 and our current results on Co indicate the presence of a large maximum in the optical densities of states about 5 eV below the Fermi level. This peak is in strong disagreement with the predictions of conventional energy-band theory. In order to determine whether this peak is associated with ferromagnetism, a study of Pd and Pt was undertaken. Band theory suggests that their electronic structure will be similar to that of Ni. In the present Pd and Pt studies, no density of states peak is found near −5 eV. Rather in the energy range −5≤E−Ef≤0, the Pd and Pt optical densities of states are found to be closely related to that of Ag4 via the rigid-band model. Available optical reflectivity data confirm the photoemission results. From these experiments, it is concluded that an optical-density-of-states peak appears at about −5 eV in the ferromagnetic materials, but not in the paramagnetic materials studied. These results suggest that this peak is probably associated with ferromagnetism.
Correlation of Electronic Specific Heats and Curie Temperatures in Dilute Alloys of Iron
Authors: Shinozaki Samuel S. , Arrott Anthony
Published: January 2005

If itinerant electrons play an important role in ferromagnetism, one might expect some correlation between the magnetic parameters, e.g., the strength of the exchange interactions and the density of electronic states as revealed by low-temperature specific heat measurements. Such a correlation is looked for in Fe alloys with small amounts of Ti, V, Cr, Mn, Co, Ni, Al, Si, Mo, and W. The quantity (1/γ)dγ/dc, where γ is the coefficient of the term in the specific heat which is linear in temperature and c is the solute concentration, is determined for these alloy systems. This quantity is compared with the similar derivatives for such quantities as spontaneous magnetization, Curie temperature, lattice parameter, and electrical resistivity. The correlation with Curie temperature is significant. Ti, V, Cr. W, and Co all raise the Curie temperature and depress the electronic specific heat, while Mn, Ni, Al, and Si lower the Curie temperature and increase the electronic specific heat. Mo is the exception producing a slight decrease in both the quantities. The measurements of specific heat are carried out using simultaneous calorimetry on three samples, one of pure iron, one with one percent solute, and one with two percent solute. The cancellation of errors achieved in this manner permits the measurement of a Δγ/γ of one percent to a precision of about ten percent. Brailsford's formulation of the dilute alloy specific heat problem is applied to a ferromagnetic solvent. It appears that the ``rigid band'' terms are not sufficient to account for the experimental results.
Spin Correlations in Paramagnetic Nickel
Authors: Cable J. W. , Lowde R. D. , Windsor C. G. , Woods A. D. B.
Published: January 2005

The spin-correlation function 〈Sα(−K,0)Sα(K,ω)〉=(ℏ/πg2μ2)[1−exp(−ℏωβ)]−1 Imχαα(K,ω) (away from ω=0) has been determined experimentally for paramagnetic nickel at ∼1.6 Tc by measurements of the inelastic scattering of neutrons. The range of energy transfer ℏω studied extends from 25 to 120 meV. Features of the correlation are compared with predictions for the Hartree—Fock electron gas and for a Heisenberg paramagnet.
Spin Value and Moment Determination for the Localized Magnetic States of Very Dilute Fe Impurities in Pt and Pd
Authors: Maley M. P. , Taylor R. D. , Thompson J. L.
Published: January 2005

The paramagnetic behavior of very dilute (<0.1% total magnetic impurities) Fe impurities has been investigated in Pt and Pd hosts, utilizing the Mössbauer effect in 57Fe. The magnetic behavior of the localized magnetic state is inferred from the measurement of the hyperfine field at the 57Fe nucleus. The measurements have been carried out in applied magnetic fields up to 62 kOe and over the temperature range of 0.4° to 300°K. The data were computer-fit to a Brillouin function to give values for Hsat, the saturation internal hyperfine field, μ, the magnitude of the moment associated with the localized state, and J, the effective-spin value. The assumption of a localized magnetic state exhibiting free-spin behavior appears to be valid for Fe in both hosts at 4°K and above. The least-square parameters obtained for the moment localized on the Fe impurity are: for Pd, Hsat=300.8±1.0 kOe, J=3.76±0.4, μ=11.1±0.3 μB; and for Pt, Hsat=316.2±0.2 kOe, J=2.98±0.18, μ=6.46±0.13 μB. The value of J for Fe in Pd is significantly lower than that previously reported. Below 4°K both systems exhibit very definite departures from free-spin behavior. The lowest temperature data have been analyzed with the addition of a parameter, which describes a random coupling between the localized moment and its host environment.
Paramagnetic Relaxation of Manganese in Copper Metal
Authors: Gossard A. C. , Heeger A. J. , Wernick J. H.
Published: January 2005

The temperature-dependence of the electron-spin resonance of dilute Mn (0.3% and 1.5%) in Cu has been studied in a series of samples containing small concentrations (0.01% to 0.5%) of other transition-metal impurities (Ti, Fe, Co, Ni). In Cu–Mn the measured linewidth above 20°K showed the characteristic linear temperature-dependence expected for a Korringa-type relaxation process from Mn d spins to the conduction electrons via the s-d exchange interaction. The magnitude of the measured width is, however, smaller than expected from estimates based on known values of Jsd; and increasing the Mn concentration reduces the temperature-proportional linewidth still further. These results demonstrate the role of the Cu-conduction electrons in the relaxation process and indicate the existence of a ``bottleneck'' in the energy transfer between the conduction electrons and the lattice. When nonmagnetic impurities, Ni and Ti, are introduced, an increase in the coefficient of the linear term is observed. This increase is interpreted as an opening of the ``bottleneck'' by conduction-electron relaxation from spin-flip scattering at the impurity sites. The inferred conduction electron rates are 24×1010 sec−1/at. % Ti and 94×1010 sec−1/at. % Ni. Magnetic impurities, Fe and Co, are an order of magnitude more effective in enlarging the linear term in the Mn linewidth, by virtue of an additional relaxation mechanism involving transfer of spin energy from the Mn spin to the Fe and Co spins.
Magnetic Properties of the Iron-Group Metal Phosphides
Authors: Gambino R. J. , McGuire T. R. , Nakamura Y.
Published: January 2005

We have investigated the temperature-dependence of the magnetic moment of Cr3P, Mn3P, Fe3P and Ni3P including solid solutions of these compounds with each other. These measurements indicate Ni3P and Cr3P have a temperature-independent Pauli-type paramagnetism. Mn3P is antiferromagnetic (TN≈115°K) with a moment of 1.68 μB for Mn based on the high-temperature susceptibility. Solid solutions of Fe3−xCoxP up to x=0.6 show that Co contributes a moment of 1.6 μB ferromagnetically aligned with the iron. In the Fe3−xNixP system, nickel acts as a diluent for all values of x. Solid solutions of Fe3−xMnxP up to x=1.5 could also be formed; in this case, antiferromagnetic ordering lowers the magnetic moment significantly. The variation of the magnetic moments with composition for the M3P series closely resembles the Slater-Pauling curve.
Relationship between the Spin Susceptibility Enhancement and the Superconducting Transition Temperature
Authors: Jensen M. Anthony , Andres K.
Published: January 2005

The observed relationship between the magnetic spin susceptibility and the superconducting transition temperature for the fcc transition metals is analyzed in terms of the recent theory of Berk and Schrieffer for the effect of spin fluctuations on the pairing interaction. The results indicate that the decrease in the transition temperature and the increase in the susceptibility are intimately connected and are both basically caused by an increasing Coulomb repulsion. The band density of states is found to decrease on going from iridium to rhodium, platinum, and palladium in qualitative agreement with recent x-ray emission spectroscopy results of Claus and Ulmer. The theory allows one to estimate the size of the spin susceptibility in the superconducting alloys to within about 5%, from which one concludes that the decrease in the transition temperature past iridium should be even more rapid that is actually observed.
Effect of Phosphorus on the Magnetization of Nickel
Authors: Albert P. A. , Kovac Z. , Lilienthal H. R. , McGuire T. R. , Nakamura Y.
Published: January 2005

The effects of phosphorus on the magnetization of nickel have been examined for thin films made by electroless deposition, electrodeposition, and by vacuum evaporation. While P has a very low solubility in bulk nickel, the results indicate that all three processes result in a metastable solid solution of P in Ni, which is transformed into the stable (paramagnetic Ni3P plus Ni) configuration by annealing at 850°K. The concentrations of P in the deposited films were varied and quantitatively established through the use of NaH232PO2 in the deposition process, coupled with radio-analysis techniques.

The magnetic data obtained are in qualitative agreement with z=5 in the expression, μB=n0−cz, where n0 is the number of holes in the 3d band of nickel, c is the concentration of phosphorus, and z its valence. Data on the behavior of magnetic moment and Curie temperature with P content are presented and a tentative explanation put forth for some anomalous behavior of these parameters.
Effect of Aluminum on the Saturation Moments of Fe-Ni Alloys
Authors: Bardos D. I. , Aldred A. T. , Beck P. A.
Published: January 2005

The saturation magnetizations of Ni-Fe-Al terminal solid solution alloys have been measured by a force method. Field intensities up to 12.5 kOe were applied and the temperature of the specimens varied from room temperature to 8°K. Average atomic magnetic moments were calculated from values of σ∞,0 which were obtained by customary extrapolation procedures.

In the fcc alloy series with constant Ni-to-Fe ratios of 4:1, 3:2, and 2:3, the average-magnetic-moment-per-atom vs Al-content curves were found to have initial slopes of −2.6, −3.1, and −3.8 μB per atom, respectively. The decrease of the saturation moment in the disordered fcc alloys can be satisfactorily accounted for if the average Ni spin moment in any ternary alloy is assumed to be the same as that of the binary Ni-Al alloy with the same Al content, and if the average Fe moment is taken to be the same as in a binary Ni-Fe alloy with the same number of Ni nearest neighbors adjacent to each Fe atom.
Effects of Mechanical and Thermal Treatment on the Structure and Magnetic Transitions in FeRh
Authors: Lommel J. M. , Kouvel J. S.
Published: January 2005

Well-annealed bulk samples of the intermetallic compound FeRh exhibit a first-order transition from antiferromagnetic to ferromagnetic order on heating near 330°K. Plastic deformation has been found to convert the normal CsCl-type ordered structure of FeRh to a disordered fcc structure, which is only weakly magnetic and does not exhibit the first-order transition. On annealing the disordered material at Ta=510°K, three stages of effects have been observed. In the first, the fcc phase converts to a highly ordered CsCl-type structure, the magnetization at Ta increasing with a time constant of ∼10 min; the material is strongly ferromagnetic down to low temperatures. In the second stage, there is a much slower (τ≈400 min) increase in magnetization at Ta with a gradual return of the first-order transition at lower temperatures. In the third stage, there is no further increase in magnetization at Ta, but the first-order transition continues to increase in completeness and sharpness. The slow return of the first-order transition is attributed to the gradual attainment of perfect long-range order or, alternatively, to the annealing out of defects produced by plastic deformation.
Investigation of the First-Order Magnetic Transformation in Mn3Pt
Authors: Krén E. , Kádár G. , Pál L. , Szabó P.
Published: January 2005

The effect of composition on the first-order transformation from triangular into collinear antiferromagnetic structure (AF-AF transformation) occurring in ordered Mn3Pt has been investigated on ternary Mn3Pt1−xRhx and binary Mn3+yPt1−y alloys using x-ray and neutron-diffraction methods.

On increasing the concentrations x and y an increase in both the Néel and the transition temperatures with a simultaneous decrease in the lattice parameter were observed. The magnetic moment of Mn remained the same irrespective of the concentration and the AF-AF transformation. The results suggest the existence of a critical lattice-parameter value at which the transformation occurs, like that observed for the Mn2−xCrxSb system.
Low-Temperature Susceptibilities of Rh and Ir with Fe Impurities
Authors: Knapp Gordon S.
Published: January 2005

The magnetic susceptibilities of dilute (<1%) solid solutions of Fe in Ir and Rh have been measured from 293° to 0.37°K in magnetic fields up to 11 000 G. Neither system shows the properties of a normal local moment in that they do not obey a Curie law when μβH/kT≪1 and the moment does not saturate at μβH/kT≫1; the magnetic moment is practically linear with field at all temperatures and fields measured. The temperature and field dependence cannot be explained on the basis of Fe–Fe ordering because (a) neither system has a field-dependent susceptibility below 1°K, (b) both systems show a heat capacity increase over that of the pure material that is too small to be explained on the basis of Fe–Fe order,1,2 (c) the increase of the susceptibility over that of pure Rh or Ir is linear in concentration of Fe and (d) a Curie-Weiss law can be made to fit the data only over a small temperature range. It is concluded, therefore, that these systems cannot be explained on the simple model of localized magnetic impurities in a weakly paramagnetic host.
Spin-Density Distribution and Electronic Structure in Fluorides with the Perovskite Structure (ABF3, where A=Na, Rb; B=Mn, Ni, Co)
Authors: Smolenskii G. A. , Petrov M. P. , Pisarev R. V.
Published: January 2005

The local magnetic fields and spin density on 19F and on A nuclei have been studied by NMR method; in RbCoF3 the measurements being also made on 59Co. The spin density on A nuclei differed from zero only in those crystals where unpaired electrons were on t2g orbitals of paramagnetic ions. The results were analyzed by MO–LCAO.

The optical absorptions of NaNiF3, RbNiF3, NaCoF3, and RbCoF3 were studied from 0.24 to 15 μ. The results were analyzed on the basis of the ligand field theory. The energy of the exchange interaction in the ground and excited states was estimated in some cases from the shift of absorption lines near Néel temperature. The intensity of some lines increased when cooling the crystals. A great increase of intensity of some Mn2+ lines was observed in NaNi0.96Mn0.04F3. The increase took place in those parts of the spectrum where Mn2+ and Ni2+ ions had near-lying electronic states.
Dipolar Induced Nuclear Spin-Lattice Relaxation in Ferromagnetic Insulators
Authors: Beeman D.
Published: January 2005

We consider the nuclear spin-lattice relaxation rate (T1−1) in a cubic ferromagnetic insulator with an isotropichyperfine interaction. In the absence of dipolar fields, angular momentum conservation forbids the two-magnon process. The electronic dipole-dipole interaction breaks down this symmetry requirement, thus inducing a Raman process. The mechanism we have calculated is as follows: (1) a nuclear spin flips and creates a virtual spin wave via the hyperfine interaction; (2) this virtual magnon is absorbed, via the dipolar field, by a thermal magnon, creating a third final-state spin wave. The relaxation rate is found to be given by T1−1=(A2/ℏ2ωex) (gβM/ℏωex)2F(kBT/gβH), for H≫M and ℏωex≫kBT. Here H is the sum of the applied dc magnetic field and the anisotropy field, Mis the saturation magnetization, ℏωex is the exchange energy, and A is the strength of the isotropic hyperfine interaction. The function F(kBT/gβH), which is evaluated numerically is nearly proportional to (T/H)2 for kBT≫gβH. Using parameters typical of 57Fe in YIG, with H = 5×103 Oe, this process is faster than the three-magnon process, up to about 30°K. At this temperature, T1∼50 sec. At higher temperatures, the three-magnon process, which is proportional to T7/2, dominates.
High-Magnetic-Field Studies of Orthorhombic and Rhombohedral Al2−xFexO3 Compounds
Authors: Schieber M. , Frankel R. B. , Blum N. A. , Foner S.
Published: January 2005

Mössbauer and magnetic susceptibility experiments at temperatures down to 4.2°K and in external fields up to 140 kOe show orthorhombic Al2−xFexO3 (0.6<x<1.0) to be a collinear highly anisotropic ferrimagnet; the material is also piezoelectric and has magnetic properties similar to those of the isomorphous compound GaFeO3. Rhombohedral Al1.6Fe0.4O3 is paramagnetic above 80°K, and at 4.2°K exhibits a Mössbauer spectrum characteristic of a nonunique hyperfine field; the application of an external magnetic field produces a spectrum with an enhanced Δm=0 line which suggests a canted spin structure similar to that in the high-temperature phase (T>260°K) of αFe2O3.
Relaxation of Gallium Nuclei in Ga3+-Doped YIG
Authors: Tancrell R. H. , Jones R. V.
Published: January 2005

We report a study of the NMR of gallium impurities in YIG. In this magnetic system a nonmagnetic impurity is added to a ferrimagnetic host where the observed nucleus is located at the magnetic defect site. This nucleus is coupled to the surrounding magnetic ions by a transferred hyperfine interaction, similar in form to the Heisenberg interaction, giving rise to local impurity states. These local states have been of much theoretical interest in recent years. Spin echo techniques were used to measure the relaxation behavior of 71Ga and 69Ga in single-domain samples of Y3Fe5−xGaxO12 for x between 0.05 and 1.0. The observed linewidth at x=0.25 shows a strong inhomogeneous broadening due mainly to the interaction between impurity sites. T1 is very sensitive to concentration, ranging from 1 sec for x=0.25 to about 10 msec for x=1.0 and varies as 1/T for T between 1.9° and 4.2°K. In contrast T2−1 varies almost linearly with concentration and is temperature independent.
Investigation of Magnetic Relaxation Effects in Fe(NO3)3·9H2O and NH4Fe(SO4)2·12H2O by Mössbauer-Effect Spectroscopy
Authors: Housley R. M.
Published: January 2005

Mössbauer spectra of ferric ammonium alum and hydrated ferric nitrate taken at room temperature in various applied fields up to 50 kOe are presented. A distinctive feature of these spectra is a division into a broad and a sharp component at higher fields. A qualitative interpretation of this and other features of the spectra in terms of atomic-spin relaxation is given. It will be shown that Mössbauer spectroscopy can be expected to yield information not obtainable from other types of measurements.
Mössbauer-Effect Measurements in FeTi Spinels with Local Disorder
Authors: Banerjee S. K. , O'Reilly W. , Johnson C. E.
Published: January 2005

Local variations in hyperfine fields produce very broad lines in the Mössbauer spectra of FeTi spinels. These may result from two effects: (A) random variations of local symmetry at the iron sites which are characteristic of the local disorder and independent of temperature and (B) temperature-dependent electron hopping on the octahedral sites. We have studied these two processes in the 57Fe Mössbauer-Effect spectra of polycrystalline Fe3O4, Fe2.4Ti0.6O4 and Fe2TiO4 measured at temperatures between 1.3° and 300°K. In Fe3O4, hopping occurs. In Fe2.4Ti0.6O4, both hopping and local disorder influence the spectrum. In Fe2TiO4, hopping cannot occur and the broadening arises from local disorder. At low temperatures, the quadrupole splitting of the Fe+ + ions in octahedral sites in Fe3O4 was found to be −1.0 mm/sec.
Accurate Measurement of Small and/or Inhomogeneous Magnetic Fields using a Set of Transistorized Marginal Oscillators and a Narrow-Linewidth Free Radical
Authors: Rubin S.
Published: January 2005

Magnetic flux density measurements have been made at a field intensity of 30mT (300 G) using a single-knob tunable transistorized marginal oscillator, with a narrow linewidth (0.04mT) free radical. The free radical (picryl-n-amino carbazyl) is commercially available. A commercial sample purchased at the end of 1965 was compared with a sample synthesized prior to 1958, and the resonance frequencies of the two samples differed by less than 5×10−4 at 1.2mT (12 G). A complete set of transistorized marginal oscillators has been built to cover the range of field intensities from below 0.5mT to above 30mT. At 30mT, free radical samples can be checked against a commercial proton NMR magnetic flux density meter. This brings accurate calibration of small and/or inhomogeneous magnetic fields within the range of most university and industrial laboratories. A free radical sample116 in. in diameter and116 in. long was used to check the calibration of a solenoid at a magnetic flux density of 1mT (10 G). The repeatability of the measurement was better than 1×10−3. It was possible to obtain a clear resonance signal at 1.3mT (13 G) with a sample measuring 0.011 in. in diameter and 0.150 in. long, without the use of enhancement techniques.
Diffraction Effects in Lorentz Microscopy
Authors: Wohlleben D.
Published: January 2005

Studies of microscopic magnetic field inhomogeneities with electron optical arrangements (Lorentz microscopy) have become common in recent years. The field distributions are derived from electron intensity distributions in various image planes of the microscope. The quantitative evaluation of the electron distribution is usually achieved via a geometric optical approach.1 High-resolution arrangements, however, reveal electron diffraction patterns. Quantitative information about field inhomogeneities from such patterns must be derived from a wave optical calculation.2 A criterion for the limit between the two treatments is presented.3 This resolution criterion is independent of the electron wave-length or the particular optical arrangement. According to this criterion, the magnetization distributions in the transition region between ferromagnetic domains and of ripples within such domains as well as structure in flux quanta in superconductors can be obtained from a wave optical treatment only. High-resolution images of ferromagnetic layers in several electron optical arrangements are discussed. The diffraction pattern behind a convergent wall in the defocussed mode has been treated earlier.2 For the case of ripples the diffraction integral has now been expanded to give a solution in closed form for the ripple contrast. It is found that this contrast can vanish for certain ripple wave-lengths. Calculations are presented for a single fluxon in a type II superconductor. At very small London penetration depths the diffraction pattern is symmetric with an intensity zero at the center. However, this intensity zero vanishes and the contrast becomes asymmetric and weak if a penetration depth of 1000 Å is assumed. The diffraction integral has also been applied to the Foucault method for the case of 180° zero-width walls between ferromagnetic domains and explains qualitatively the features observed in an experimental case.
The Rotating-Sample Magnetometer
Authors: Flanders P. J.
Published: January 2005

To illustrate applications and adaptability of the rotating sample magnetometer a series of experiments was designed and performed to measure magnetization, anisotropy, switching and field-induced transitions on samples in the 10−2 emu range. This instrument is inexpensive and simple to construct and requires only a pair of sense coils, a synchronous motor and an oscilliscope for operation.
A Shielded Facility for Low-Level Magnetic Measurements
Authors: Cohen David
Published: January 2005

A facility has been constructed for the detection and measurement of time-varying magnetic fields of ∼10−9 G amplitude, in a bandwidth of 0.5 to 100 000 cps. The facility includes a shielded room and magnetic detector, which now consists of a copper coil, eventually to be cooled in liquid helium, feeding a parametric amplifier; it will initially be used to investigate bioelectric current flow in human heart muscles by mapping the time-varying fields outside the body. The shielded room now has two layers of 0.060 in. Moly-Permalloy, and a third inner layer of 0.19 in. aluminum enclosing a 86 in.×88 in.×88 in. volume will soon be installed. Measured shielding factors are given; at present magnetic ``shaking'' is used to produce a shielding factor of ∼400 in the 0–5 cps range, which rises rapidly with increasing frequency.
Electron Microscope Observations of Ferromagnetic Domains in Chromium Tribromide
Authors: Matricardi V. R. , Lehmann W. G. , Kitamura N. , Silcox J.
Published: January 2005

A liquid-helium object stage for the electron microscope has been used to observe directly magnetic domains in CrBr3, an ionic ferromagnet with a Curie point of 36°K. Some of the contrast effects observed are typical of the magnetic-domain wall observations made by Lorentz microscopy on materials such as Co which are similar magnetically to CrBr3. The more common contrast effects are contiguous black and white lines which correspond to the domains directly and look similar to observations with the optical Faraday effect. These effects occur with the objective lens far off focus. Evidence that the effects are due to magnetic domains includes disappearance of the structure in in-focus micrographs and disappearance on warming the specimen through the Curie point. The scale of the domain structure is ∼200–2000 Å, consistent with specimen thicknesses ∼1000 Å and a foil orientation with the c axis normal to the plane of the foil. The observations corroborate the domain structure deduced by Dillon et al. from magneto-optical studies for thicker specimens of this material.
Automated Induction Magnetometer
Authors: McGuire T. R.
Published: January 2005

An automated, high sensitivity, digital magnetometer operating on the induction principle and utilizing a 50-kOe superconducting coil has been constructed. The sample is moved between two 16 000-turn coils and the time integral of the induced voltage pulse (proportional to the magnetic moment) is integrated by an electronic voltage-to-frequency converter and counting system. At the same time, the magnetic field and the temperature are obtained as the output from digital voltmeters. The resolution of the instrument is 10−4 emu, and is independent of the applied field, temperature, and sample moment. Evaluation of the magnetometer was made with measurements on a 0.218-g EuO single-crystal sphere oriented with H along a [111] easy axis of magnetization. From several sets of data at 4.2°K the fluctuations of the moment-field curve had a mean deviation of one part in 8000. At 1.4°K and 15 kOe the specimen is about 99.8% saturated and from 15 to 50 kOe the moment is given by the relation, σH=σ0[1−a/H]+bH, where H is the applied field, σ0=225.0±1.0 emu/g, a≈24 Oe, and b≈1.0×10−6cm3/g. The 1/H term represents a 0.1% volume of the sample which is difficult to saturate probably because of imperfections and strains in the sample.
Contrast in the Electron Microscope due to Stray Magnetic Fields near Single-Domain Iron Whiskers
Authors: Rodgers J. M.
Published: January 2005

Single-domain iron whiskers having diameters of 0.5 to 5 μ have been investigated under in-focus Lorentz (Foucault) conditions in normal specimen stages of A.E.I. EM6 and R.C.A. EMU-3 electron microscopes. Contrast is observed in the region of object space surrounding whisker tips which is consistent with that predicted by considering the effect of stray magnetic fields on the electron beam. Such contrast is readily distinguished from that due to electrostatic fields.

A slight modification of the Lorentz technique enables quantitative measurements of the field to be made for certain configurations of the whisker surface. In particular, micrographs of tapered whiskers show the presence of stray fields due to free poles along the prism faces. The measured magnitude of the effect of these fields is in fair agreement with calculated results assuming the magnetization to be uniform and parallel to the whisker axis.

Iron whiskers 300 Å in diameter show no evidence of any magnetic contrast; a suggested detection limit is ∼1000 Å. Reversal of magnetization direction is easily detectable; it is suggested that precise measurements of coercivities of individual whiskers could be made using this technique.
Resonance Method for Measurement of Small Uniaxial Anisotropy in Fine Ferromagnetic Wires
Authors: Rossol F. C.
Published: January 2005

A small uniaxial anisotropy is induced in Permalloy wires cold drawn to diameters of 1 mil and less. Knowledge of this induced anisotropy is important in the study of domain-wall behavior in such wires. The anisotropy field, HA, is typically less than 50 Oe with easy direction parallel to the wire axis. Static methods of measuring HA, as well as resonance methods under usual conditions, are hampered by the fact that the large shape anisotropy arising from the wire geometry tends to mask out the effects of HA. These short comings are overcome in the method discussed here by exciting ferromagnetic resonance with curl hrf obtained by driving rf current parallel to the wire axis. This method permits observation of resonance in the range from 2 to 3 Gc/sec at fields comparable with HA. The greater than 100-Oe linewidths observed are found to be dominated by a mechanism other than pure eddy-current exchange damping which would give rise to considerably smaller linewidths. The large variation in HA along the wire suggests that the linewidth is largely due to inhomogeneity in HA. The influence of eddy-current exchange effects on the determination of HA is evaluated.
Direct Observation of Domain-Wall Movements in MnBi Films
Authors: Chen Di
Published: January 2005

MnBi films epitaxially grown on mica substrates possess an easy axis perpendicular to the film plane. The easy-direction magnetic hysteresis exhibits a sharp magnetization change near Hc but requires a much higher field for saturation. This behavior was studied by direct observation of the dynamic domain-wall formation and wall movement on a microscopic scale using the magneto-optic Faraday effect. The results were recorded on photographic films, using a polarized light source, an analyzer, a lens system of 1.3-μ resolution, and a high-speed movie camera. In the demagnetized state, a mosaic domain pattern consisting of closely packed hexagonal-like units was formed with the magnetization inside a ring within each unit remaining unswitched. After the entire film was covered with this mosaic pattern, further switching was accomplished mainly by the wall motion within each unit. A domain theory calculation based on the above observation gives detailed explanation of the idealized magnetization process.
Pressure Dependence of Curie Temperature in Ni
Authors: Lang N. D. , Ehrenreich H.
Published: January 2005

A band-theoretical estimate for dT/dCP in Ni in good agreement with experiment is obtained by considering the shift of the pole in the uniform, static susceptibility. The principal mechanisms determining dTC/dP have opposite sign: The positive effect of the increased electron-electron interaction outweighs the negative one associated with the decreased density of states due to band widening in the vicinity of the Fermi level, leading to dTC/dP>0. The electron-electron interaction is here considered to be purely intra-atomic and is described in terms of a model proposed by Kanamori.
Change of Magnetic Properties of Dilute Gold-Chromium Alloys by Substitutions of Tin, Aluminum, and Copper for Gold
Authors: Yasukōchi K. , Kuwasawa Y. , Sekizawa K.
Published: January 2005

The change of antiferromagnetic behaviors of gold-chromium alloys, Au0.98Cr0.02 and Au0.94Cr0.06, by substitutions of nonmagnetic metals, tin (up to 6 at.%), aluminum (up to 14 at.%), and copper (up to 30 at.%), for gold was investigated. The temperature Tm at which magnetic susceptibility shows a maximum decreases rapidly with the increase of tin and aluminum concentrations. Tm is almost unchanged by the copper substitution and slightly decreases with the increase of the copper concentration. It is shown that the spin coupling in dilute alloys of chromium is much affected by the change of the number of conduction electrons and almost independent of the lattice constant of the alloys.