bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Properties of Dilute Alloys of Scandium
Authors: Isaacs L. L. , Lam D. J. , Fradin F. Y.
Published: February 2004

Previous experiments have shown that small quantities of cerium will induce a spin-compensated state in the d1 elements yttrium and lanthanum. The magnetic susceptibility of scandium alloys with 0.02–2-at.% cerium has been measured over the temperature range of 4°–300°K. No evidence for a spin-compensated state is found. Addition of gadolinium has been shown to polarize the scandium matrix. To study the influence of a heavy rare earth with nonzero orbital angular momentum on the polarization of the scandium matrix a series of dilute dysprosium alloys have been studied. The effect of dysprosium is found to be similar to that of gadolinium. Also the influence of the nonmagnetic alloying elements titanium and thorium on scandium has been investigated in order to separate the various factors affecting the magnetic properties of dilute scandium alloys.
Diagrammatic Approach to the Anderson Model for Dilute Alloys
Authors: Keiter H. , Kimball J. C.
Published: February 2004

Applications of a new diagrammatic technique for the grand partition function Z and the susceptibility of the Anderson Hamiltonian are presented, where the hopping is treated as a perturbation. Z is expressed quite generally in terms of statistical quasiparticles. For -εd>W (bandwidth) and for U→∞ for simplicity, this formulation allows one to show that the thermodynamics of the Anderson model and of an s-d model with an effective J (essentially in agreement, but slightly renormalized compared to the one obtained from the Schrieffer-Wolff transformation) are equivalent. Indication is given that this equivalence is more complicated for the dynamical properties of the model, as reflected, e.g., by the scattering matrix.
Electrical and Magnetic Properties of Single-Crystal Hexagonal Nickel Sulfide
Authors: Horwood J. L. , Ripley L. G. , Townsend M. G. , Tremblay R. J.
Published: February 2004

Hexagonal nickel sulfide shows a metal-to-semiconductor first-order phase transition at a temperature TN which depends on sulfur content. Electrical and magnetic susceptibility measurements have been made on five single crystals of compositions ranging from NiS to NiS1.02 in the temperature region 78°–300°K. For T<Tn the Ni 3d states are essentially localized or form a very narrow band. The predominant mechanism of conduction below TN is by holes in a wide band. The discontinuity in conductivity at TN is most likely due to a discontinuity in carrier mobility.
Magnetic Behavior of a Layer-Type Antiferromagnet RbFeF4
Authors: Eibschütz M. , Guggenheim H. J. , Holmes L.
Published: February 2004

The orthorhombic compound RbFe3+F4 has been studied by magnetic susceptibility and Mössbauer-effect (ME) measurements. The magnetic susceptibilities for H∥b and H⊥b are characterized by a broad maximum in χ∥ and χ⊥ at Tmax=(215±10)°K, followed by a rapid decrease in χ∥ and a shallow minimum in χ⊥ below 135°K. The susceptibility behavior is similar to that observed in a number of antiferromagnetic layer-type structures. In the antiferromagnetic state, ME yields well-resolved hyperfine spectra, revealing a unique magnetic field and EFG at all iron nuclei. The temperature dependence of the sublattice magnetization in powder samples has been determined by measuring the internal fields at the iron sites, over the range 4.2°–300°K. At low temperatures the results are found to agree with the simple two-dimensional spin-wave theory for T≤TN/2. From about 0.40<T/TN<0.99 the hf fields follow a (TN−T)β law with β=0.245±0.005 and TN=133.4°K.
Crystal Preparation, Structures, and Magnetic Properties of Layer-Type Cs4B3F10 Compounds (B = Fe, Co, Ni)
Authors: Shafer M. W. , McGuire T. R. , Weidenborner J. E.
Published: February 2004

Cs4B3F10-type compounds are found in systems where B=Fe, Co, Ni, Mg, and Zn. Structurally, they can be considered as consisting of units of three face-shared BF6 octahedra (B3F12 groups) which are connected to each other by corner sharing to form layers consisting of linked B3F12 groups. The layers are separated by the large Cs+ ions and exhibit mica-like cleavage along this plane. Structures of this type usually have intraplane magnetic interactions which are markedly stronger than those between planes. Our magnetic results show Cs4Fe3F10 to be an antiferromagnet with TN∼22°K, while the Co and Ni compounds have a more complicated magnetic order with TN's of 33° and 15°K, respectively. Their magnetizations at 4.2°K are 16 and 1.0 emu/g and the easy directions are parallel to the cleavage plane. The structure does not allow a simple superexchange between B ions of neighboring planes. A more involved interaction involving the Cs+ ions and enhanced by the intraplane ordering is likely. Large anisotropy of the paramagnetic susceptibilities of the cobalt and nickel compounds was observed.
Crystal-Field Splitting and Spin Waves in Antiferromagnetic CeSb
Authors: Busch G. , Stutius W. , Vogt O.
Published: February 2004

The specific heat of crystalline samples of CexY1−xSb (x=1, 0.2, 0.1, and 0) and LaSb was measured for temperatures between 1.5° and 70°K. The Néel temperature of CeSb is found to be 16.0 (±0.2)°K. The magnetic specific heat between 1.5° and 3.8°K is proportional to T2. This temperature dependence is correlated with spin waves in the anisotropic magnetic structure of CeSb. The crystal-field splitting of the 2F5/2 ground state of the Ce3+ ion in CeSb is 24 (±2)°K.
Magnetic Ordering and Mn3+ Ion Surroundings in (Mn1−xFex)2O3
Authors: Geller S.
Published: February 2004

The crystal structures of α-Mn2O3 and (Mn1−xFex)2O3, x=0.017 and 0.63, have been refined from single crystal x-ray data. Interatomic distances and angles in (cubic) (Mn0.983Fe0.017)2O3 are equal to the analogous average distances and angles in α-Mn2O3. There is significantly less distortion of the oxygen polyhedra about 24(d) sites in (Mn0.37Fe0.63)2O3 than in (Mn0.983Fe0.017)2O3. Evidence based on these results and on magnetic studies of systems (Mn1−xMx)2O3, M≡Fe3+, Sc3+, Ga3+, Cr3+ supports the suggestion that the antiferromagnetic ordering temperatures depend on the allowed distortion of the Mn3+ ion surroundings. The paper entitled ``Structures of α-Mn2O3, (Mn0.983Fe0.017)2O3 and (Mn0.37Fe0.63)2O3 and Relation to Magnetic Ordering'' from which this has been taken will be published in Acta Crystallographica (probably in the first half of 1971). Two other especially pertinent references are: R. W. Grant, S. Geller, J. A. Cape, and G. P. Espinosa, Phys. Rev. 175, 686 (1968); S. Geller and G. P. Espinosa, Phys. Rev. 131, 3763 (1970).
Metallurgical Control of Magnetic Properties in Co–Fe and Ni–Fe Alloys for Memory Applications
Authors: Chin G. Y. , Tisone T. C. , Grupen W. B.
Published: February 2004

Magnetic memories such as the Twistor require materials which exhibit a square hysteresis loop, controlled value of coercive force, and low stress sensitivity of the magnetic properties. Recent work on optimizing these properties in Co–Fe and Ni–Fe alloys as storage and sensing elements, respectively, will be reviewed. Co–Fe alloys in the face-centered cubic phase (∼90% Co) exhibit low values of magnetostriction and high values of magnetocrystalline anisotropy with 〈111〉 easy axes. Square hysteresis loops are obtained in cold-drawn wires and tapes roll flattened from such wires, as a sharp 〈111〉 axial texture is developed by the cold working. With alloying additions such as Au and Ti, values of coercive force up to 42 Oe can be attained via precipitation aging. For Ni–Fe alloys near the 4% Mo–79% Ni composition, a predominant 〈111〉 axial texture is developed in wire drawing and is converted to 〈100〉 via recrystallization anneal. Since the magnetostriction and magnetocrystalline anisotropy constants are near zero in this vicinity and are sensitive to crystal orientation, optimization of high squareness and low stress sensitivity requires close composition control depending on the particular texture. In cold-worked material, the squareness behavior is also complicated by the dominance of slip-induced anisotropy. Finally, additions such as Be and Zr have been made for precision control of coercive force through precipitation.
Nuclear Spin Waves
Authors: Hinderks Larry W. , Richards Peter M.
Published: February 2004

Nuclear spin waves belong to the nuclear branch of the coupled electronic-nuclear modes in an ordered magnetic system. They appear to be well defined even though the nuclear polarization is 1% or less. Their existence was originally postulated to explain ``pulling'' of the NMR (k=0) frequency in canted antiferromagnets. We have shown that nuclear spin waves of nonzero k can be excited by parallel pumping in flopped antiferromagnets because of the high ellipticity of electron spin precession and strong electronic-nuclear coupling. Results of parallel pumping experiments have given relaxation rates vs wave vector and temperature in CsMnF3 and RbMnF3. They are at least an order of magnitude less than observed NMR widths. Agreement with theory is relatively good for temperature dependence in CsMnF3. For both substances the rates are nearly independent of k, whereas theory predicts a linear dependence. In RbMnF3 rates are much higher than theoretical values, while in CsMnF3 they are less than theoretical at the higher k's. Linear coupling of the parallel pump to the field-independent mode has drastic consequences, as shown by Platzker and Morgenthaler. Results in RbMnF3 confirm their predictions.
Hyperfine Enhanced Nuclear Magnetic Cooling in Van Vleck Paramagnetic Intermetallic Compounds
Authors: Andres K. , Bucher E.
Published: February 2004

In strongly Van Vleck paramagnetic rare-earth alloys or compounds, large hyperfine fields can be induced at the rare-earth nucleus with moderate external fields. These fields are useful to generate low temperatures by the method of nuclear adiabatic demagnetization. Experiments in the Van Vleck paramagnets PrPt5 and PrTl3 are described in which end temperatures of 3.5 and 1.5 mK are obtained starting from about 60 mK and 20 kOe. The possibility of nuclear ferromagnetism in PrTl3 is discussed and compared with observations.
Magnetization Discontinuities in Cobalt-Rare-Earth Particles
Authors: Becker J. J.
Published: February 2004

Hysteresis loops of single particles of Co5Sm have previously shown that magnetization discontinuities (jumps) occur at fields Hn that are quite discrete and whose values depend on the previous magnetizing field Hm. Some effects of chemical polishing and air aging on the values of Hn and their Hm dependence in Co5Sm particles are described. Jumps have now been observed in Co5Y. A particle of Co5Y showed a rectangular hysteresis loop with Hn=3800 Oe for Hm of only 4100 Oe, the loop remaining unchanged for Hm up to 30 kOe, and a maximum energy product of 27.6×106 G Oe.
Evaluation of the Utility of a (Pr,Nd)Co5 Alloy for Permanent Magnets
Authors: Tsui J. B. Y. , Strnat K. J. , Harmer R. S.
Published: February 2004

Neodymium substitution for Pr in PrCo5 increases Curie point and saturation and lowers the coercive force of powders. Attritor-milled powders of Pr0.87Nd0.13Co5 have up to MHc = 4100 Oe. They can be improved only insignificantly by treating the particles with citric or dilute nitric acid. Magnets having (BH) max = 4.5 and 5.5 MG Oe were pressed from such powders. A magnet of 13 MG Oe was produced by liquid-phase sintering.
Localized Spin Fluctuations in Exchanged Enhanced Alloys: the Thermal Resistivity as an Experimental Probe
Authors: Rice M. J.
Published: February 2004

It is pointed out that the electronic thermal resistivity contributed by the effects of local spin fluctuations in a paramagnetic transition metal containing nearly magnetic transitional impurities, reflects two salient features of the theoretical model conventionally employed in the description of the local spin fluctuations in such systems. The desirability of thermal conductivity studies is thus argued for.
139La NMR Studies in LaIn3
Authors: Welsh L. B. , Gambino R. J. , Toxen A. M.
Published: February 2004

Normal-state nuclear magnetic resonance studies of the superconductor LaIn3 have been made in order to investigate the origin of the large temperature-dependent normal-state susceptibility χ attributed to exchange enhancement of the La d-electron spin susceptibility. The 139La Knight shifts, linewidth, and nuclear-spin relaxation times (T1 and T2) have been measured with cw and pulsed techniques from 1.6°K to 300°K. The Knight shifts (+0.402%±0.002% at 1.6°K−+0.371%±0.002% at 300°K) vary linearly with χ. The relaxation times vary from T1T = 1.1±0.05 sec °K at 4.2°K to T1T = 1.6±0.1 sec °K at 300°K. The small magnitude and temperature dependence of the La T1 and Knight shift as well as the value of the Korringa product K2T1T/S of 1.28 at 4.2°K appears in the independent band approximation to be inconsistent with the expected large La d-band hyperfine contribution. This suggests a breakdown of the independent band approximation in LaIn3 due to interference effects between the various hyperfine interactions.
Single Crystal Growth of Yttrium Orthoferrite by a Seeded Bridgman Technique
Authors: Blank S. L. , Shick L. K. , Nielsen J. W.
Published: February 2004

Single crystals of yttrium orthoferrite (YFeO3) 15 mm in diameter and 28-mm long have been grown from pure Y2O3–Fe2O3 melts contained in platinum crucibles. At the melting point of YFeO3, 1680±5°C, the equilibrium oxygen pressure over the Y2O3–Fe2O3 system is approximately one atmosphere, hence a modified Bridgman technique was used. A Pt-40% Rh resistance furnace capable of continuous operation at 1750°C under one atmosphere of oxygen was provided with baffles to obtain the desired temperature profile. Supercooling of pure Y2O3–Fe2O3 melts was found to be excessive, ∼100°C, so the Bridgman-type crucibles were modified to permit seeding. When growth rates were kept below 1.5 mm/h, crystals exhibiting coercivities as low as 0.009–0.012 Oe were obtained. Crystals grown at high rates or from off-stoichiometry melts contained several types of defects. Precipitate-bubble pairs, isolated bubbles, a-b type twins, cracks and optical density variations have been observed. The origin of these defects and steps taken to eliminate them, as well as their effect on cylindrical domain propagation, are discussed.
High-Pressure RbFeCl3-A Transparent Ferrimagnet
Authors: Longo J. M. , Kafalas J. A. , Menyuk N. , Dwight K.
Published: February 2004

The structure of RbFeCl3 at atmospheric pressure contains hexagonal close-packed RbCl3 layers with Fe filling all the chlorine octahedra, which form continuous face-shared chains. RbFeCl3 transforms at 700°C and 20–35 kbar to the RbNiF3 structure, which has two cubic-stacked for every hexagonal-stacked RbCl3 layer to give face-shared pairs of octahedra joined by octahedra sharing only corners. The high-pressure phase is retained under ambient conditions and is ferrimagnetic with Tc = 109°K. Above 225°K, the susceptibility obeys the Curie-Weiss law with CM = 3.89 emu°K/mole (μeff = 5.58 μB) and θp = −134°K. The powder samples do not saturate at 4.2°K in fields up to 17.2 kOe. The saturation magnetization calculated from a 1/H vs M plot is 1.1 μB (25.4 emu/g), which approaches the theoretical value of 1.3 μB predicted for ferromagnetic pairs of iron-filled octahedra coupled antiferromagnetically to a third octahedra, as is found in RbNiF3 and CsFeF3. Optical transmission data on the tan powdered samples pressed in KBr show transparency from 0.3 to 24 μ with some absorption bands between 0.3 and 0.6 μ. The change in Tc with hydrostatic pressure is linear to 8 kbar (dTc/dP = 2.13±0.05°K/kbar). This is about four times larger than that found for the isostructural ferrimagnetic fluorides, reflecting the higher compressibility of the chloride anion.
Enhancement of Mode Locking of Spin Waves at Low Temperatures
Authors: Hsu Ta-Lin , Wang S.
Published: February 2004

Investigations of mode locking of spin waves in YIG by nonlinear magnetoelastic coupling have been extended to low temperatures. Due to an increase of the spin-wave linewidth of YIG at low temperature, more spin-wave modes can be excited and, consequently, stronger mode-locking effects are observed. In our experiment more than 10 modes of spin waves have been mode locked. The variation of number of modes as a function of temperature is presented. In addition, a pickup coil is placed near the sample to measure any changes in mz. Since, for small perturbations, mz = 1 − ½ (mx1+my2), beating among different spin-wave modes will cause time variations of mz at the various beat frequencies. An enchancement of the harmonic content is observed upon the application of a mode-locking acoustic wave.
Importance of the Cubic Field for Axial Zero-Field Splitting of a Magnetic Ion
Authors: Sharma R. R.
Published: February 2004

The variation of the excited energy levels of a 6S ion as a function of the strength of the cubic field has been investigated and its effect on the zero-field splitting of the ground level of the ion in an axial field has been determined. The usual belief that the splitting always diminishes as the strength of the cubic field decreases, has been found to be incorrect. In fact, in some cases, the splitting decreases as the strength of the cubic field is increased. A striking and new result has been pointed out which shows that the splitting can be zero even in the presence of an axial field. These results are useful to understand why in a certain crystal evniroment the splitting is very small while in the other it is vary large. Furthermore, the splitting is found to be sensitive to the strength of the cubic field and may even change sign by varying the strength. Application to various crystals containing Mn2+ impurity has been discussed.
Solid Hydrogen: The Ideal Analog of an Antiferromagnet
Authors: Harris A. Brooks
Published: February 2004

A physically meaningful analogy is drawn between the ordering and dynamical behavior of molecular rotations in solid hydrogen and the ordering and dynamical behavior of magnetic spin systems. In solid hydrogen the magnitude J of the rotational angular momentum is a good quantum number. Molecules having J = 1 resemble spin one magnetic moments, whereas those with J = 0 are ``non-magnetic.'' Solid solutions of these two species are analogs of magnetic alloys. The thermodynamic properties, in particular the order parameter, the specific heat, and the nuclear magnetic resonance properties are similar to those of magnetic systems. As for the dynamics, the small librations about the ground state are analogs of spin waves, and the interactions between the librational excitations are similar to, but larger than, the usual spin-wave interactions. This circumstance enables the direct observation of the two-libron spectrum and also leads to large anharmonic shifts in the single-libron spectrum.
Observation of Antiferromagnetic Phase Transitions by Ultrasonic Techniques
Authors: Shapira Y.
Published: February 2004

The usefulness of ultrasonic techniques in determining the phase boundaries of antiferromagnets (in the H-T plane) is discussed. The various magnetic phase transitions which occur in antiferromagnets are described with particular emphasis on transitions in uniaxial antiferromagnets of the easy-axis type. The phase boundaries between the antiferromagnetic, spin-flop, and paramagnetic phases are discussed in the molecular field approximation. Some results of more sophisticated treatments are also included. The main ultrasonic phenomena which occur near the various phase transitions of uniaxial antiferromagnets are described. They are (a) λ anomalies in the attenuation and velocity near the second-order transitions, (b) an attenuation spike (velocity dip) at the spin-flop transition, and (c) an abrupt attenuation increase (velocity decrease) at the spin-flop transition. Examples of phase boundaries determined ultrasonically in MnF2, FeF2, CoF2, Cr2O3, α-Fe2O3, Cr, and EuTe are summarized.
Sublattice Magnetization of Quadratic-Layer Antiferromagnets
Authors: De Wijn H. W. , Walstedt R. E. , Walker L. R. , Guggenheim H. J.
Published: February 2004

Both the temperature dependence and zero-temperature value of the sublattice magnetization have been investigated for the quadratic-layer antiferromagnets K2NiF4, K2MnF4, and Rb2MnF4 using magnetic resonance techniques. The temperature dependence has been determined by measuring the NMR frequency of out-of-layer 19F nuclei in these compounds. The results are found to agree with a simple two-dimensional spin-wave theory for T⪝TN/2, with TN = Néel temperature. For K2NiF4, the zero-point spin reduction Δ0 has been estimated by combining these results with the exchange constant obtained from neutron experiments, giving Δ0 = 0.20±0.03. For the Mn2+ compounds Δ0 has been determined by measuring the 55Mn NMR at helium temperatures with an ENDOR technique, giving Δ0 = 0.17±0.03. The zero-point spin reduction values are in excellent agreement with spin-wave theory. These as well as related results from the literature on other compounds will be discussed.
Clustering and Giant Moments in Cu–Ni Alloys
Authors: Jach J. , Borg R. J. , Lai D. Y. F.
Published: February 2004

There are several studies of paramagnetic susceptibility and neutron diffraction revealing the presence of giant moments associated with chemical clustering. However, in contrast to the paramagnetic state, there are but few analogous studies extending below Tc. We prepared Cu–Ni alloys of about 50–50 composition as Mössbauer sources containing 57Co. Internal fields, Tc, and isomer shifts were determined as functions of composition and heat treatment. The temperature dependence of the hyperfine spectrum changes very little as a result of annealing at low temperature. Nevertheless, the value of Tc itself dramatically increases in response to clustering, and the isomer shift and internal field at ∼0°K are singificantly altered in response to the change in chemical short-range order.
Magnetic Structures of Ferrimagnetic RbNiF3 and CsFeF3
Authors: Pickart S. J. , Alperin H. A.
Published: February 2004

Powder neutron diffraction measurements have been taken on the hexagonal fluorides RbNiF3 and CsFeF3. The results are consistent with a ferrimagnetic model having antiparallel 2a and 4f site spins, the spin axis being perpendicular to and 75° from the c axis, respectively. Possible origins of the discrepancy of this latter value from magnetization data are discussed.
Magnetic Structure of FeOCl
Authors: Grant R. W.
Published: February 2004

Mössbauer spectroscopy has been used to study the magnetic properties of ferric oxychloride FeOCl. A paramagnetic to antiferromagnetic transition occurs at 92°±3°K. Near liquid-helium temperature the antiferromagnetic structure is noncolinear; at least two sets of nonequivalent Fe3+ sites and a doubling of the unit cell are required. All Fe3+ spins are confined to the bc plane (c<a<b). The most probable magnetic space group is P2cm′2m′ which has two antiferromagnetic sublattices with spins ‖ b and ‖ c, respectively.
Magnetic Structures of Tb2C3 and Ho2C3
Authors: Atoji Masao
Published: February 2004

Tb2C3 and Ho2C3 are isostructural (the cubic body-centered Pu2O3-type structure), but neutron diffraction revealed markedly different ordered spin configurations. In Tb2C3 below 33°K, two out of four body-diagonal linear Tb arrays become individually a one-dimensional antiferromagnetic chain, but the remaining two arrays show no ordered spins at all. The nearest Tb atoms between the different ordered arrays are ferromagnetically coupled. The moment direction lies most likely along a face diagonal and the saturation moment is essentially equal to the free ion value of 9 Bohr magnetons. In Ho2C3, below 19°K, two out of four linear Ho arrays become ferromagnetic and the remaining two undergo antiferromagnetic ordering. Among three closest Ho–Ho approaches linking the different linear arrays, two pairs are antiferromagnetically related and the remaining pairs are ferromagnetally coupled. The moments are directed along one of the ferromagnetic arrays and the saturation moment is 7.3 Bohr magnetons which is considerably smaller than the free ion value of 10 Bohr magnetons. The energy levels due to a highly asymmetric crystal field should at least partly be responsible for the differences between the Tb2C3 and Ho2C3 spin structures. Both the magnetically long-range ordered Tb2C3 and Ho2C3 exhibit a sizeable, magnetic diffuse scattering having the characteristics of ferromagnetic short-range order.
Crystal Axis Switching Effects in the Thermal Expansion and Magnetostriction of Magnetite
Authors: Vittoratos E. , Baranov I. , Meincke P. P. M.
Published: February 2004

The twinned state of natural magnetic below the Verwey transition was studied by measurements of the thermal expansion and longitudinal magnetostriction with a three-terminal capacitance technique. The thermal expansion was negative near the transition with a peak at 115 K. Between 30 and 115 K a relaxation was observed in the magnetostriction. Above a temperature-dependent critical field a step increase in field results in an immediate step increase in length but then the length begins to decrease approximately logarithmically with time. The length relaxes noticeably for at least 1 h and the final length is often shorter than the equilibrium length before the field change. No relaxation was observed above the transition. These effects can be explained by the intimate coupling between magnetic and crystal symmetries which give rise to a crystalline axis switching mechanism.
Anisotropy and Magnetostriction of Cr3+ Ions in NiFe2O4 Crystals
Authors: Krishnan R. , Cagan V.
Published: February 2004

Magnetocrystalline anisotropy constants K1 and K2 and magnetostriction constants λ100 and λ111 were determined by ferrimagnetic resonance techniques for NiFe2−xCrxO4 crystals with x=0, 0.04, and 0.07. K1 from Cr3+ ions is negative and at 0°K corresponds to −0.04 cm−1. A theoretical estimate from a spin Hamiltonian considering a trigonal field yields K1=+0.006 cm−1, which disagrees both in sign and magnitude with our experimental results. K2 at 4.2°K is of the order of 104 erg/cm3. The magnetoelastic constants b1 and b2 are decreased by the addition of Cr3+ ions.
Radio-Frequency Determination of New Growth-Induced Anisotropy in Garnets for Bubble Devices
Authors: LeCraw R. C. , Wolfe R. , Bobeck A. H. , Pierce R. D. , Van Uitert L. G.
Published: February 2004

A new type of magnetocrystalline anisotropy has been observed under {110} faces in several fluxgrown mixed rare-earth iron garnets. This anisotropy is different in direction and magnitude from that previously reported in similar garnets under {211} faces. In Eu2ErGa0.6Fe4.4O12 with 4πM near 350 G at 300°K, microwave resonance measurements have shown that {110} face material has a large effective uniaxial anisotropy. The [100] in the growth plane is the easy axis, [011] normal to this plane is medium, and [011̄] parallel to this plane is hard. Using a resonance equation appropriate to the orthorhombic magnetic symmetry and neglecting the relatively small cubic terms, the effective uniaxial anisotropy field is ∼1300 Oe. This anisotropy leads to a new cutting procedure (type 3 cut) for bubble devices: {100} platelets are cut normal to the natural {110} faces. Using 15-μ-thick platelets of this type, bubbles ∼8μ in diameter were propagated. The domain wall mobility is ∼170 cm/sec/Oe. These properties are comparable to those of {111} platelets cut under {211} surfaces of the same crystals.
Magnetic Field Dependence of Magnon Frequencies in the Canted-Spin Antiferromagnet NiF2
Authors: Fleury P. A. , Loudon R. , Walker L. R.
Published: February 2004

Below TN=73°K, NiF2 is a canted-spin antiferromagnet with the spins lying in the x-y plane. The magnetic excitations (magnons) of the structure form two branches whose Brillouin zone-center frequencies in zero field are 3.3 and 31 cm−1. We have measured the dependence of these frequencies in [100]-directed magnetic fields of up to 100 kOe using inelastic light scattering. The upper branch exhibits negligible field dependence, while the lower branch frequency increases monotonically to 14.4 cm−1 at 95 kOe. Our results join smoothly with previous ir measurements taken at lower magnetic fields. A spin-wave spectrum appropriate to NiF2 for the above field orientation has been derived within a theory which considers the excitations between the lowest pair of single-ion states in the combined crystal, Zeeman, and molecular fields. The excitations on different ions are coupled by the transverse part of the exchange. The calculated zone-center frequencies are in good agreement with the experimental observations over the entire magnetic field range for both branches.
Hyperfine Splitting in a Metal of a Localized Moment
Authors: Barnes S. E. , Dupraz J. , Orbach R.
Published: February 2004

Phenomenological equations describing the hyperfine splitting of a localized electron resonance in a metal are studied. The transverse susceptibility χ+(ω) is obtained for the case of nuclear spin I=½, and its poles and residues are displayed. The corresponding eigenvectors are determined, enabling a physical generalization to arbitrary nuclear spin. The validity of the generalization procedure is verified by an examination of the generalized susceptibility. The conditions for the observation of the hyperfine splitting in a dilute magnetic alloy are detailed. Three distinct regions are found to be important, depending on the strength of the exchange coupling. Region (1), corresponding to a very weak exchange coupling, exhibits hyperfine splittings of the same character as in an insulator. The linewidth of each hyperfine component equals Δse+ΔsL, where Δse is the second-order localized-conduction electron exchange relaxation rate, and ΔsL the localized spin lattice relaxation rate. Region (2) corresponds to sufficiently larger values of the exchange coupling for a magnetic resonance bottle-neck to obtain, but for which ωhf/Δse≫1, where ωhf is the electronic hyperfine splitting frequency. In region (2) the hyperfine splitting is the same as in region (1), but the width of each component equals [2I/(2I+1)]· [Δse+ΔsL]. Region (3) corresponds to yet larger values of the exchange coupling, such that ωhf/Δse≪1. In this more strongly bottlenecked region the hyperfine split resonance is narrowed into a single line, and the resonance properties are those one would derive in the complete absence of a hyperfine interaction. Recent successful observations of the hyperfine splitting of a localized moment resonance for rare-earth alloys belong to category (1). Unsuccessful measurements in transition metal alloys indicate their character is appropriate to region (3). It is suggested that lower temperature measurements may shift some of these materials into region (2) (because Δse ∝T), allowing for a direct determination of the magnitude of the exchange coupling constant, even though the resonance system is still in the bottlenecked regime.
Spin-Wave and Critical Neutron Scattering from Chromium
Authors: Als-Nielsen J. , Axe J. D. , Shirane G.
Published: February 2004

Chromium and its dilute alloys are unique examples of magnetism caused by itinerant electrons. The magnetic excitations have been studied by inelastic neutron scattering using a high-resolution triple-axis spectrometer. Spin-wave peaks in q scans at constant energy transfer ℏω could, in general, not be clearly resolved at any temperature below TN but it is still possible to deduce the slope ω/q of the dispersion curve and also to estimate the spin-wave lifetimes. The scattering displays a divergence as q→0, ω→0, T→TN characteristic of critical fluctuations. The critical scattering is confined to small values of q, but the ω range is very wide compared to critical scattering from systems with localized magnetic moments. The experimental results agree generally with the theoretical predictions of Liu [Phys. Rev. Lett. 23, 311 (1969); Phys. Rev. (to be published)].
Uniaxial Stress Experiments and Magnetoelastic Interactions in Rare Earths
Authors: Bartholin H. , Beille J. , Bloch D. , Boutron P. , Féron J. L.
Published: February 2004

We have determined the effect of uniaxial stress on the magnetic transition temperatures of gadolinium, terbium, and dysprosium. The problem of stress homogeneity has received particular attention. From the variation with stress of the Curie (Gd) or Néel (Tb, Dy) temperatures, spontaneous magnetostriction in Gd, Tb, and Dy is quantitatively interpreted.
Study of Magnetic Interactions in (SnTe–MnTe) and (SnTe–EuTe) Systems
Authors: Mathur M. P. , Deis D. W. , Jones C. K. , Patterson A. , Carr W. J.
Published: February 2004

As reported earlier the alloy system Sn0.97−xMnxTe orders ferromagnetically with Curie temperatures varying linearly with x. The present work has extended this and includes: (i) More superconductivity results which indicate that for low carrier densities (∼1021 cm−3), the paramagnetic impurity influences Tc very drastically, e.g., 100-ppm Mn destroys the superconductivity completely. However, if the carrier density is increased to 4×1021 cm−3, the transition temperature decreases gradually with increasing Mn content and superconductivity persists even for x=0.001. In both cases, however, the transition is broadened probably due the presence of the internal fields. (ii) Electrical resistivity measurements made on these samples (0.00001<x<0.10) between 4° and 100°K, show a characteristic metallic behavior but with no maxima or minima appearing in the residual part. (iii) A study of s-f interactions by means of Eu doping for comparison with s-d interaction results (Mn doped). Eu-doped samples are single phase, determined from x-ray measurements, for x<0.10. Magnetic measurements on the Eu-doped system have been carried out between 4° and 100°K at a carrier density of ∼1021 cm−3. Superconductivity (down to 0.02°K) measurements have been made in order to complete the comparison between the two systems.
Mictomagnetism in Pd–Cr and V–Mn Alloys
Authors: Chakravorty S. , Panigrahy P. , Beck Paul A.
Published: February 2004

Face-centered cubic Pd–Cr alloys with 25%–35% Cr, quenched from 1200°C, have an average paramagnetic moment μ̄Cr of 0.5–1.2 μB. Below Tf=36°–76°K the moments are largely frozen, without long-range magnetic order, but ferromagnetic clusters of up to about 24 μB account for the thermomagnetic or isothermal remanence. These giant moments can be aligned in successive small thermally activated steps by cooling in a magnetic field. Once aligned, the giant moments can be turned collectively by much smaller fields. The bcc V–Mn alloys with 50%–76% Mn have similar magnetic properties, but with supergiant moments of more than 1000 μB, as quenched from 1200°C. For the Pd alloys with more than 25% Cr the minimum fields and temperatures necessary to align the moments are decreased considerably by annealing at 400°C, when the ferromagnetic clusters acquire dipole moments of up to 3600 μB, as measured in the superparamagnetic state, above Tf. The total moment of all supergiant clusters in the annealed 33% Cr alloy is equal to the thermomagnetic remanence of this alloy at 4.2°K. In the quenched as well as in the annealed condition the alloys with 29% and 33% Cr show the largest thermomagnetic remanence, presumably because the tendency for atomic ordering is largest at these compositions.
Occurrence of Invar Anomalies in Binary Alloys of Fe with Ni, Pd, Pt, and Mn
Authors: Schlosser W. F.
Published: February 2004

The Invar anomalies in the Fe–Ni, –Pd, –Pt, and –Mn binary alloy systems are explained by a model based on concepts which have recently been successful in the interpretation of transition metal alloy properties. The various near-neighbor atomic configurations about an Fe atom are assumed to have a considerable effect on the electronic structure at this Fe atom. The atomic distribution is not random; the alloys are assumed to be inhomogeneous, and to contain small regions of ordered compound (FeNi3, FePd, FePt) or Mn rich clusters. These assumptions are sufficient to allow a common explanation of the relative intensity and composition dependence of the Invar anomalies, in particular the magnetoelastic coupling, in all four systems. Many physical and metallurgical properties of these systems, the temperature and composition dependence of the magnetization, the alloy instability, and the large effect of cold work are related through this model. For the Fe–Ni system, the model prediction of exchange coupling between small, coexisting ferromagnetic and antiferromagnetic regions at low temperatures explains the composition independent drop in the magnetoelastic coupling below 20 K as well as the existence of a time-dependent volume anomaly observed below 10 K.
Dependence of the s-f Exchange Coupling Parameter on Rare-Earth Atomic Number
Authors: Levy Peter M.
Published: February 2004

The s-f exchange coupling parameter Γsf has been independently determined for the rare-earth dialuminides from a variety of phenomena. All the results show a similar variation of the parameter across the rare-earth series. We discuss the origins of this variation.
Magneto-Optical Properties of Sputtered Mn5Ge3 Films
Authors: Sawatzky E.
Published: February 2004

The Faraday rotation and optical absorption of ferromagnetic Mn5Ge3 thin films have been measured in the visible and near infrared. Apart from a gradual rise in optical density in the near uv, the absorption is featureless to 2.5 μ. The Faraday rotation behaves similarly. At 500 mμ the room-temperature absorption coefficient α and the 5°K saturation rotation F are 3.5×105 cm−1 and 2.1×105 deg/cm, respectively. The rotation decreases with rising temperature and vanishes at 40°C which agrees well with the bulk Curie temperature of 37°C. The in-plane coercive field Hc decreases monotonically with temperature as Tc is approached. For a 900-Å-thick film Hc is 260 Oe at 0°C. The dependence of magnetic and magneto-optical properties on film structure is discussed.
Investigation of the Magnetic Behavior of Some Conducting Am Systems
Authors: Dunlap B. D. , Lam D. J. , Kalvius G. M. , Shenoy G. K.
Published: February 2004

A number of Am compounds have been investigated by bulk magnetic and nuclear gamma resonance (NGR) measurements. For the latter type of investigations, the compounds were used as a source for the 59.6-keV resonance in 237Np. AmSb, Am3Se4, and Am3Te4 show no magnetic ordering down to 4.2 K, and the NGR isomer shifts show that the Am ions are present in the trivalent state. The susceptibility of AmSb is temperature independent. Similarly, no ordered magnetism is seen in Am2C3, although Np2C3 has a ferromagnetic transition at 109 K. These results show the tendency of conducting Am compounds to form a trivalent, nonmagnetic state. The results are discussed in terms of a crystal-field calculation which includes J mixing caused by the large crystal-field interaction present in actinide compounds.
Calculation of Standing Spin-Wave Resonance Modes in Ferromagnetic Metal Films
Authors: Vittoria C. , Barker R. C. , Yelon A.
Published: February 2004

We have combined Maxwell's equations with the Landau-Lifshitz equation for finite thickness metal plates of nickel and Permalloy with infinite plane symmetry, and have imposed the boundary conditions corresponding to a constant rf driving field and complete pinning of m at the surfaces. The objective is to evaluate the effect of including conductivity and other refinements of the calculated spin-wave spectra of ferromagnetic films. In order to compare results with simplified calculations and experiment, we have taken the case of perpendicular resonance and calculated the frequency derivative of the power absorption spectrum. We find that for plate thicknesses such that the modes do not overlap, the mode spacing is quadratic, as found by the simpler theories, but that the mode intensities and linewidths are significantly increased. Overlap of the modes does not simply linearize the spacing of the lower modes, as is often found experimentally.
Inhomogeneously Broadened Resonance Lines in Bulk Ferromagnetic Metals
Authors: Randles M. H. , Henry R. D. , Brown S. D. , Wigen P. E.
Published: February 2004

The angular and temperature dependences of the ferromagnetic linewidth in thick samples of 81Ni–19Fe Permalloy are analyzed in terms of a volume inhomogeneity in the internal field. The samples were prepared by flattening the material to a thickness of approximately 3 mils and it is assumed that the fabrication process produces ``rough'' surfaces which introduce significant inhomogeneities in the internal field. The observed linewidths on the order of 1000 G in the perpendicular resonance configuration suggests that the lines are inhomogeneously broadened. The line shape and the intrinsic linewidth, Δω/γ, observed at 10, 24, and 34 GHz, are analyzed in terms of this inhomogeneity model.
Direct Observation of Spin Polarization of Conduction Electrons and Location of Magnetic States in Eu1−xGdxS
Authors: Busch G. , Campagna M. , Siegmann H. C.
Published: February 2004

The dependence of photoelectron spin polarization on photon energy was measured for films of Eu1−xGdxS at 4.2 K. The conduction electrons were found to be only 10% polarized for x of the order of 0.07. This indicates, for these states, either a lower 4f-6s exchange interaction or a more important spin-orbit coupling effect than previously assumed. It indicates also that these alloys are not promising for the production of polarized electrons. The states with high polarization (magnetic states) lie in the bandgap between valence and conduction states. A few of these magnetic states are shifted, relative to those for pure EuS, nearer to the bottom of the conduction band.
Temperature Dependence of the Initial Susceptibility of Fe–3.25% Si Alloy
Authors: Qureshi A. H. , Chaudhary L. N.
Published: February 2004

Temperature dependence of the initial susceptibility of Fe–3.25% Si has been investigated between −196° and 700°C for undeformed and deformed specimens. In the undeformed specimens the χi-vs-T behavior exhibits a minimum around room temperature and a second minimum around 450°C. The first maximum occurs between these two temperatures around 350°C, where χi is almost three times its room-temperature value. The χi rises again to extremely high values at temperatures slightly below the Curie point. With increasing deformation the first maximum is gradually flattened and disappears almost completely in specimens with 7% deformation.
Effect of Carbon Content on the Magnetic Properties of Iron-30% Cobalt-15% Chromium Alloys
Authors: Olsen K. M. , Stoffers R. C.
Published: February 2004

Past studies have indicated that an alloy containing 55% iron-30% cobalt and 15% chromium could be substituted for the more costly Remendur alloy (48% Fe-48% Co-4% V) now being used in ferreed cross point switching devices. However, commercial utilization of this alloy has not been realized mainly because of difficulties in obtaining reproducible magnetic properties in cold worked rod or strip given a final hardening heat treatment. Data presented in this paper show that small amounts of carbon, in the range of 0.01%–0.1% by weight, have a pronounced effect on the magnetic characteristics of the alloy. With proper control over carbon content, degree of cold working, and final heat-treating conditions, it is possible to produce material having a remanence of over 16 500 G, coercive forces ranging from 30 to 55 Oe and a hysteresis loop squareness ratio greater than 0.90. Commercial trials are now underway to determine whether control over this additional parameter, carbon content, will yield material having the close tolerance magnetic properties needed for switching applications.
Application of Cube-Oriented 3% Si–Fe Steel in Cores for Rotating Machines
Authors: Frost R. M. , Larson R. A. , Myers L. S. , Pavlovic D. M. , Purdy G. L.
Published: February 2004

As compared to AISI Grade M-15 electrical steel, the use of cube textured 3% Si–Fe steel, 0.012-in. thick, as limination material in cores of 400-Hz generators covering ratings between 15 and 90 kVA, brought about improvements in generator weight, stack length, efficiency, and voltage transients. Conventional core fastening and stress-relief annealing practices were applicable, but stress concentrations during lamination punching had to be minimized in order to prevent cleavage cracks in the highly cube-textured material.
Reorientation and Curie Point Writing in Orthoferrites
Authors: Kurtzig A. J. , Townsend R. L. , Wolfe R. , Sosniak J.
Published: February 2004

The spin reorientation phenomenon in materials such as the orthoferrites can be used for thermomagnetic writing. This mechanism has been used to write into platelets of Sm0.7Er0.3FeO3 which has its spin reorientation just above room temperature. Curie point writing can be done in those orthoferrites in which there is no spin reorientation in the working temperature range. Spots 5 μ in diameter were written into 2-μ-thick sputtered epitaxial TbFeO3 films by the Curie technique to demonstrate the feasibility of high storage densities.
Comparison of Bitter Patterns and X-Ray Images of Domains in Fe–Si Crystals
Authors: Wu Carl Cm. , Roessler Barton
Published: February 2004

Ferromagnetic domains as well as imperfections in the interior of Fe–Si single crystals are observed by the x-ray topographic technique employing the anomalous transmission of x-rays (Borrmann effect). X-ray topographic images of domains are compared with the Bitter patterns obtained in the same region of a single crystal of Fe–3% Si. It is shown that when a suitable reflecting plane is used and the domain arrangement remains unchanged during the experiment, an exact correlation exists between the Bitter pattern and the x-ray topograph.
Magneto-Optic Signal Processing
Authors: Fuller Harrison W.
Published: February 2004

A modification of the well-known methods for optical processing recorded signals using coherent light and the Fourier-transform properties of lens systems is described, in which the signals are magnetically recorded in a conventional fashion on high-coercivity metallic magnetic films and in which the longitudinal Kerr effect is used to spatially modulate the light beam. The recorded signals act as a 180° phase object when using the Kerr magneto-optic effect which allows the polarizer and analyzer to be accurately crossed for extinction of the zero-order diffraction spot that would otherwise be troublesomely intense. The principal advantages offered by magnetic film signal recording compared with recording on photographic film are the elimination of developmental processing and the ability to erase and rerecord. High writing speed and relatively high recording density are possible. Experimental results indicate an achievable optical efficiency in the general range of 10−6, an integration time-bandwidth product approaching 106, and practical operating frequencies from the very lowest to the multimegahertz range.
Long Delay Lines Employing Surface Acoustic Wave Guidance
Authors: Adkins L. R. , Hughes A. J.
Published: February 2004

Folded-path guided surface wave delay lines offer a significant potential advantage over single-propagation path delay lines for obtaining very long delay times. Measurements are reported here for a spiral folded-path delay line employing a gold strip on fused quartz as the guidance structure. A 260 μsec delay was obtained at 20 MHz. The spurious signal was ≥35 dB down and the differential propagation loss was 0.03 dB/μsec. These favorable results indicate that practical long delay lines based on surface acoustic wave guidance techniques are quite feasible and that delay times into the millisecond range are attainable at higher frequencies.
Crystallographic Polarity of Gel-Grown β-AgI Crystals
Authors: Bhalla A. S. , Suri S. K. , White E. W.
Published: February 2004

A double crystal x-ray spectrometer was used to determine the crystallographic polarity of the structure of gel-grown β-AgI single crystals showing that the Ag+ plane is the (00.1) and the I− plane is the (00.1̄). This result is consistent with chemical etching studies, polarizability, and electronegativity of the ions.