bluuebunny/crossref_metadata_2025 huggingface dataset:
NMR of 53Cr and 77Se in Ferromagnetic Chalcogenide Spinels
Authors: Berger S. B. , Budnick J. I. , Burch T. J.
Published: January 2006

The NMR of 53Cr nuclei has been observed in ferromagnetic CdCr2Se4, CdCr2S4, and HgCr2Se4 at 4.2°K using spin-echo and cw techniques. The spectra are complex with a principal triplet and have been analyzed considering coaxial anisotropic hyperfine and electric quadrupole fields of comparable magnitude to be acting on the chromium nuclei in randomly oriented domains. An excellent fit has been obtained between the calculated spectrum and spin-echo data. For CdCr2Se4, CdCr2S4, and HgCr2Se4, the separation between the outer components of the triplet is 1.76, 1.90, and 1.96 MHz, the isotropic part of the hyperfine field is −182.6, −191.0, and −178.3 kOe and the anisotropic component of the hyperfine field is +2.33, +2.07, and +2.3 kOe, respectively. The signs of the hyperfine field components indicate their direction with respect to the magnetization and were determined by measuring the frequency shift with applied magnetic field.

The NMR of 77Se nuclei has also been observed in HgCr2Se4 and CdCr2Se4 at 4.2°K. The spectra are consistent with the model of randomly oriented domains and exhibit a strongly anisotropic hyperfine field. The origin of the spectra and the sign of the hyperfine field components were determined by measuring the frequency variation of the spectra with applied magnetic field.
Analysis of Distant-Neighbor Interactions in Cubic Spinels
Authors: Dwight K. , Menyuk N.
Published: January 2006

Ferromagnetic cadmium seleniochromite and antiferromagnetic zinc seleniochromite are examples of normal cubic spinels with nonmagnetic A-site ions. They are both believed to be Heisenberg magnets with strong, ferromagnetic nearest-neighbor exchange interactions and weaker, but significant, more-distant-neighbor ones which play a major role in determining the ground-state spin configuration. This paper presents an analysis of these distant-neighbor interactions in terms of their constituent superexchange linkages. The Goodenough-Kanamori rules of superexchange can be extended to these linkages, which involve additional overlaps of p orbitals from neighboring anions. Summation over all the linkages contributing to each interaction then yields information concerning their signs and relative strengths. These results imply that various simplified sets of interactions which have been used to interpret the properties of such materials are physically unreasonable. In addition, specific modifications arising from covalence of a diamagnetic A-site cation with its surrounding anions can be inferred. Some implications of these findings for the chromium chalcogenide spinels are discussed.
Ferromagnetic Halo-Chalcogenide Spinels (CuCr2X3Y) and Some Properties of the Systems CuCr2Se3Br-CuCr2Se4 and CuCr2Te3I-CuCr2Te4
Authors: Robbins M. , Baltzer P. K. , Lopatin E.
Published: January 2006

A new class of ferromagnetic spinels with the general formula Cu[Cr2]X3Y where X = Se2−, Te2− and Y = Cl−, Br−, I− has been prepared. The compounds CuCr2Se3Br, CuCr2Te3I, and CuCr2Se3Cl all formed with the spinel structure. CuCr2Se3Br and CuCr2Te3I are both ferromagnetic with relatively high Curie temperatures (274° and 294°K, respectively). The compound CuCr2Se3Cl is magnetic at room temperature but is very hydroscopic, making it difficult to obtain reliable magnetic data. Resistivity measurements made on CuCr2Se3Br indicate that this material is a semiconductor. The compositional series CuCr2Se4−xBrx and CuCr2Te4−xIx have been prepared. CuCr2Se4−xBrx unit-cell parameters and Curie temperature in this system were found to vary linearly with composition between x = 0 and x = 1. CuCr2Te4−xIx unit-cell parameters for materials in this system did not vary linearly with composition.
Neutron-Diffraction Study of the Ferromagnetic Mixed-Anion Spinel CuCr2Se3Br
Authors: White J. G. , Robbins M.
Published: January 2006

A new class of mixed-anion spinels has been prepared. These compounds have the general formula Cu[Cr2]X3Y where X = S2−, Se2−, Te2− and Y = Cl−, Br−, I−. The materials are ferromagnetic with TC (Curie temperature) close to room temperature. A neutron-diffraction study was made of CuCr2Se3Br which is a cubic spinel with a0 = 10.416 Å and TC = 274°K. The observed magnetic moment was 5.25 μB at 4°K and a field of 10 kOe.

Neutron-diffraction measurements were made at room temperature and at liquid nitrogen temperature (T/TC = 0.285). From the room-temperature data the material was found to be a normal spinel with u = 0.389±0.002. The low-temperature data showed magnetic scattering which was evaluated in terms of simple models: (a) a spin arrangement corresponding to Cu1+[Cr23+]Se3Br having zero moment on the A sites and a moment of 6 μB on the B sites, (b) a ferrimagnetic arrangement corresponding to Cu2+[Cr3+Cr2+]Se3Br with 1 μB on the A sites and 7 μB on the B sites. The first model gives very good agreement with the experimental data while model (b) is quite incompatible with the data.
Hall Effect of Ferromagnetic CdCr2Se4
Authors: Lehmann H. W.
Published: January 2006

The Hall effect of Ag-doped (p-type) and In-doped (n-type) CdCr2Se4 has been studied in the ferromagnetic temperature range (TC = 130°K). The Hall voltage UH of p-type CdCr2Se4 is proportional to the following expression: Uh ∝ R0H + R1M as has been verified for many other ferromagnetic materials. The normal Hall coefficient R0 has a maximum at 150°K and drops sharply when the material is cooled through the ordering temperature. The anomalous Hall coefficient R1 has the same sign as R0. It is approximately 40 times larger than R0 and decreases steadily with decreasing temperature. In the same temperature range the Seebeck coefficient Q drops sharply with temperature which is consistent with the drop of R0. Both these facts are indicative of the onset of impurity conduction at 150°K. In n-type CdCr2Se4 the Hall voltage is again a strongly nonlinear function of magnetic field H at temperatures around TC. However its field dependence cannot be described by the above mentioned formula. In n-type CdCr2Se4 R1 is much smaller than R0. In this temperature range one observes also the following anomalies: The magnetoresistance is negative (T = 130°K, H = 10 kOe: Δρ/ρ0 = −0.9) and the conductivity rises with decreasing temperature. It can be shown that these effects are not only due to an increasing mobility but also due to an increasing carrier concentration which is caused by the strong red shift of the optical band edge. A complete account of this work will be published elsewhere.
Nuclear Magnetic Resonance and Magnetization Studies of CdCr2Se4
Authors: Stauss G. H. , Rubinstein M. , Feinleib J. , Dwight K. , Menyuk N. , Wold A.
Published: January 2006

We have investigated the NMR lineshapes and temperature dependences of 53Cr and 77Se in the ferromagnetic spinel CdCr2Se4. The internal magnetization directions are determined by shape anisotropy, so that the observed lineshapes are powder patterns extensively broadened by anisotropic dipolar and (for 53Cr) quadrupolar interactions. The 0°K values for the central frequencies are 44.0 and 80 MHz for 53Cr and 77Se, respectively. The temperature dependence of the bulk magnetization was carefully measured and is in close agreement with that of the 53Cr (or 77Se) resonance frequency. The 53Cr resonance signal could not be followed above 120°K because of increasingly rapid relaxation. Up to 100°K the dependence is described by M = M0 (1−3.11×10−4 T3/2). Although the absence of other terms in T is not understood, the T3/2 coefficient is derivable from a simple spin-wave calculation on the basis of the approximate model with two exchange interactions given by Baltzer, Wojtowicz, Robbins, and Lopatin.
New Determinations of the Saturation Magnetization of Nickel and Iron
Authors: Danan H. , Herr A. , Meyer A. J. P.
Published: January 2006

Numerous measurements of saturation magnetization of Fe and Ni are reported. Saturation magnetization is determined by consideration of all contributions in the change of magnetization in high magnetic fields, i.e., internal demagnetizing fields, homogeneous rotations, and paramagnetic terms. The value found for the absolute saturation of iron is σ0,∞ = 221.71±0.08 emu/g, corresponding to M = 2.216 μB, in good agreement with previously accepted values. For Ni, the absolute saturation value obtained is σ0,∞ = 58.57±0.03 emu/g, corresponding to M = 0.616 μB, in good agreement with other previous data but 1.6% larger than the Weiss and Forrer's value of M = 0.606 μB.
Effects of Pressure and a Magnetic Field on Chromium Studied by Neutron Diffraction
Authors: Werner S. A. , Arrott A. , Atoji M.
Published: January 2006

In addition to decreasing the first-order antiferromagnetic-to-paramagnetic phase change near 312°K, pressure also decreases the spin-flip transformation near 122°K, and appears to decrease the amplitudes of the static magnetization waves. By means of neutron diffraction we have determined the initial derivatives of these pressure variations using small pressures up to 100 atm. Magnetic fields applied to samples while cooling through the 312°K transition produce crystals whose magnetic structure can be ascribed to a single fundamental wavevector. This state, however, is not single domain. A model has been proposed previously by two of the authors (S.A.W. and A.A.) for this state in which the crystal spontaneously breaks up into many small domains in each of which the polarization axis is thermally excited. The predictions of this model have been checked by studying the field dependence (to 27 kG) of the mean directions of the polarizations and how this varies with temperature. The agreement between the experiments and the model is good. Small hysteresis effects as a function of magnetic field have also been observed. A magnetic field of 27 kG applied parallel to the wavevector decreases the spin-flip temperature 1°K but does not affect the Néel temperature.
Electrical Resistivity and Antiferromagnetism in Binary Chromium Alloys with Molybdenum and Tungsten
Authors: Arajs Sigurds
Published: January 2006

Electrical resistivity has been studied as a function of temperature between 4° and 325°K on two series of binary chromium alloys containing 0.6, 1.6, 3.2, 5.1, 6.9, or 8.8 at.% molybdenum and 0.3, 0.7, 1.0, or 3.4 at.% tungsten. These studies show that the Néel temperature TN decreases linearly with increasing molybdenum of tungsten concentrations with slopes of about 14°K/at.% Mo and 29°K/at.% W. These decreases of TN are understandable from the viewpoint of the recent theory by Fedders and Martin and the Fermi surface calculations by Lomer and Loucks. The larger lowering of TN by tungsten than by molybdenum can be related to its less pronounced localization of d electron wavefunctions. The contribution to the electrical resistivity due to 1 at.% molybdenum or tungsten in solid solution in chromium is 0.8 and 1.1 μΩ·cm, respectively. The samples containing 3.4 at.% tungsten and 6.9 at.% molybdenum exhibit a minimum in the electrical resistivity-temperature curves at low temperatures. It is suggested that this minimum results from the Kim effect.
Magnetic Properties of Manganese-Gold Alloys and the Effect of Thermal and Mechanical Treatment
Authors: Smith J. H.
Published: January 2006

Anomalies have been found in the variation with temperature of magnetic susceptibility, resistivity, and elasticity for AuMn alloys containing from 40 to 53 at.% Au. These anomalies occur with changes in magnetic order associated with the double martensitic bcc→bct structure transformations previously reported for these alloys. Large values and age dependence of susceptibility previously observed are shown to be due to precipitation at moderate temperatures of metamagnetic Au2Mn from solid solution. On this basis, AuMn 50 at.% behaves as an ordered solid solution. Deformation produces a stress-induced transformation from an ordered bcc structure to a fcc γ-Mn structure. Alloys containing more than 80 at.% Mn are shown by similar measurements, together with neutron diffraction, to have properties resembling those of γ-MnCu alloys. They exhibit long range antiferromagnetic order and a diffuse peak at the (100) position of the neutron-diffraction pattern is also observed. A structure transformation from fcc to fct occurs at the Néel temperature, but for alloys in the composition region around 90 at.% Mn, there is a second transformation to an orthohombic structure with little change in magnetic order. A double transformation in γ-MnNi and γ-MnPd alloys is also reported.
Ferro-, Antiferro-, and Superparamagnetic Behavior of Fe-Al Alloys
Authors: Danan H. , Gengnagel H.
Published: January 2006

In agreement with measurements of Sato and Arrott, and of Kouvel, we also found anomalous magnetic properties of Fe-Al alloys containing more than 28 at.%. Al. In order to investigate the different properties of these alloys in more detail, we have measured the temperature dependence of magnetization, susceptibility, anisotropy, rotational hysteresis, and coercive force of monocrystalline and polycrystalline specimens (containing 28 to 50 at.% Al) between 1.5° and 300°K. The following results have been found: a maximum of rotational hysteresis at about 12°K, high coercive forces and high unidirectional and uniaxial anisotropy in the temperature region below 40°K, magnetization creeping between 4° and 50°K, and superparamagnetic-like behavior at higher temperatures. These results may be interpreted by assuming the existence of two phases one of which is ferromagnetic, the second antiferromagnetic below 40°K. For T∼40°K, the domains of one phase, and for lower temperatures, the domains of both phases interact.
Covalency Correction to the Axial Field of Paramagnetic Ions
Authors: Englman R.
Published: January 2006

Under conditions of covalent bonding the axial-field-spectroscopic-splitting parameter of paramagnetic ions in solids is due not only to the axial field ν acting at the ion but also to the splitting parameter V of the ligand orbitals. A second effect of covalency, smaller in magnitude, cannot be expressed in terms of a unique splitting parameter characteristic of the environment because of its variation with the subshell configuration. The two effects are tabulated for each configuration. The parameter V is estimated.
Acoustic Paramagnetic Resonance of 3d Ions in KMgF3
Authors: Wigmore J. K. , Rosenberg H. M. , Garrod D. K.
Published: January 2006

Using an interference pulse-echo technique at 9 GHz, we have observed acoustic paramagnetic resonance absorption and dispersion from the spin systems KMgF3:Ni2+, KMgF3:Fe2+ and KMgF3:Co2+, and have confirmed that, in the absence of saturation, the functions may be related quantitatively through the Kramers-Kronig expressions. The moduli of the quadrupolar magnetoelastic coefficients | G11 | and | G44 |, for Ni2+ and Fe2+, were inferred to be 58 and 39, and 1340 and 1000 (cm−1 unit strain−1), respectively. For Co2+ we found the dipolar coefficients to be | F11 | = 64 and | F44 | = 35 (unit strain−1). The observed angular dependence of the absorption in Co2+ cannot be accounted for by the simple spin-lattice Hamiltonian. The experimental values of the magnetoelastic coefficients have been compared with point-charge crystal field calculations.
Chromous Ions in Magnesium Oxide
Authors: Stevens K. W. H.
Published: January 2006

Microwave ultrasonic and thermal-conductivity studies have shown that Cr2+ ions in MgO are strongly coupled to the lattice. Their properties cannot be understood in terms of a static crystalline electric field and it is necessary to allow for Jahn-Teller, or dynamic, lattice couplings. An account is given of the theoretical treatment of the dynamical system of ion plus lattice.
Cooperative Jahn-Teller Distortion in Mixed Chromites
Authors: Kanamori Junjiro , Kataoka Mitsuo , Itoh Yoshimasa
Published: January 2006

Calculations of crystal distortions in Cu1−xNixCr2O4 and Fe1−xNixCr2O4 based on effective Hamiltonians in which the orbital states of the Jahn-Teller ions interact with bulk strains are presented. The derivation of the effective Hamiltonian from a microscopic Hamiltonian is discussed in some detail in the case of Cu1−xNixCr2O4. It is discussed that a local distortion accompanying each orbital state quenches the spin-orbit coupling whose role in determining the phase diagram was emphasized previously. The present calculations which neglect the spin-orbit coupling can reproduce almost quantitatively the observed phase diagrams of the mixed crystals. It is pointed out that the jump of | c/a−1 | at the cubic-to-tetragonal transition decreases when x approaches a critical concentration xc from both sides, which is supported by experiment.
Mössbauer Resonance of 57Fe in Oxidic Spinels Containing Copper and Iron
Authors: Evans B. J. , Hafner S. S.
Published: January 2006

The Mössbauer resonance of 57Fe in tetragonal and cubic phases of the spinel copper ferrite (CuFe2O4) has been investigated between 4.2° and 1000°K. Complementary experiments have been performed on the spinel systems Cu1−xZnxFe2O4 and Cu1−xCdxFe2O4, with O≤x≤0.5. At 4.2°K, at least two nonequivalent six-line patterns, I and II, are resolved in the spectra of all phases, exhibiting a combined magnetic and electric hyperfine interaction. The isomer shifts, internal magnetic fields, and nuclear quadrupole splittings have been determined as a function of temperature. At higher temperatures, below the Néel point, the cubic phases show an apparent six-line pattern with lines of non-Lorentzian shape and unusually broad half-widths. Above the Néel temperature, a distinct electric quadruple splitting was observed in the spectra of the tetragonal phases while the cubic phases show an apparent one-line pattern of a complex shape.
NMR Results for the Singlet Ground State of Fe in Cu
Authors: Welsh L. B. , Heeger A. J. , Jensen M. A.
Published: January 2006

Nuclear magnetic resonance studies of the Fe impurity contributions to the 63Cu linewidth indicate the ground state of the magnetic impurity problem is nonmagnetic. The contribution of the Fe impurities to the 63Cu longitudinal nuclear relaxation times is found to depend on the square of the Fe concentration.
Mössbauer Effect in 57Fe in Copper and the Spin-Compensated State
Authors: Schwartz B. B. , Kim D. J. , Frankel R. B. , Blum N. A.
Published: January 2006

The results of Mössbauer experiments on dilute Fe in Cu in high external magnetic fields (42–146 kOe) are presented here as evidence for significant destruction of the spin-compensated state by a magnetic field for which μH0∼kTK, where kTK is on the order of the energy change associated with the formation of the spin-compensated state.
Resistivity of the 4d Transition Series Ru-Rh-Pd-Ag Containing Fe
Authors: Sarachik M. P.
Published: January 2006

The resistivity was measured between 1.5° and 40°K for 1% iron dissolved in various alloys of the 4d transition element series Ru-Rh-Pd-Ag. The scattering was found to decrease in all cases with decreasing temperature, although the magnitude and detailed shape of the anomalous low-temperature resistivity varies with host composition.
Enhanced Effective Exchange Interaction due to Localized Spins in Dilute Alloys and Rare Earth Metals
Authors: Kim D. J.
Published: January 2006

An effective interaction between conduction electrons is obtained by eliminating the exchange interaction between conduction electrons and localized spins in metals both in the paramagnetic and spin-ordered state. In the paramagnetic state the effective electron interaction is mediated by the flipping motion of the localized spin under the action of the local field and the electron interaction derived is of an exchange type and repulsive in the vicinity of the Fermi surface. On this basis we show that the observed ferromagnetism in dilute alloys like Fe in Pd may be understood from the large enhancement of conduction-electron susceptibility.

In the spin-ordered state, such as rare-earth metals below the Curie temperature, the effective electron interaction arises from the exchange of spin waves between electrons. The electron interaction obtained is of a form of repulsion between electrons of opposite spins at the same atomic site in the vicinity of the Fermi surface. The electron self-energy due to this effective electron interaction is calculated for a simplified model and we discuss the possibility of an appreciable enhancement of the electronic specific heat in rare earth metals.
On the Theory of Anomalous Tunneling due to Paramagnetic Impurities
Authors: Solyom J. , Zawadowski A.
Published: January 2006

Recently some anomalies have been observed in the characteristics of tunnel diodes at zero bias. Anderson and Suhl have called attention to the resonance scattering of electrons on paramagnetic impurities in the oxide layer. The effective density of states appearing in the formula of tunnel current is determined and the tunnel current is calculated by summing up the contributions of resonance scatterings.

The actual appearance of the effect varies greatly and is strongly dependent on the parameter values: (1) For ferromagnetic coupling: resistivity minimum at zero bias, relative amplitude: 0–0.2. (2) For antiferromagnetic coupling: (a) giant resistivity maximum at zero bias, relative amplitude 0–100; (b) local resistivity minimum at zero bias superimposed on a background curve with resistivity maximum [type 2 (a)].

The investigation of tunneling characteristics may be a powerful method to check the resonance scattering amplitude for paramagnetic impurities.
Dynamic Susceptibilities of Transition Metal Alloys
Authors: Lederer Pascal , Mills D. L.
Published: January 2006

In this paper, we study dynamical properties of transition metal alloys by examining the form of the frequency and wavevector-dependent magnetic susceptibility within the framework of a simple molecular-field approximation. We describe the metal by a simple one-band model, in which two d electrons in the atomic cell i interact via the intra-atomic Coulomb interaction Ui, which differs from the value in the host if i refers to an impurity site. The impurity also is supposed to produce a local change in crystal potential.

In the general case, an expression for the susceptibility is derived in the form of an N×N matrix, where N is the number of lattice sites. When applied to a pure metal, the result reduces to the expression obtained previously by Izuyama, Kim, and Kubo.

Some applications of the results to the one-impurity problem are considered. In particular, in the case where a magnetic moment has formed in the impurity cell, a description of the electron spin-resonance of the impurity center is obtained.

A discussion of properties of Pd-Ni alloys is presented. The expression obtained for the magnetic susceptibility allows a calculation of the contribution to the electrical resistivity from s-d spin flip scattering. The recent resistivity measurements of Schindler and Rice are interpreted with the results.
Does Logarithmic Accuracy Uniquely Define the Low-Temperature Properties of Dilute Magnetic Alloy Systems?
Authors: Duke C. B. , Silverstein S. D.
Published: January 2006

The various methods used in the calculation of the properties of dilute magnetic alloy systems: truncation of the equation of motion; Suhl's dispersion theory and nonlinear Low equation; Abrikosov's perturbation theory; and a linear theory introduced by the authors, all reproduce solutions for the scattering amplitude and self-energy which are equivalent to logarithmic accuracy in the high-temperature domain, T> Tk, where Tk is the Kondo temperature. In this domain, results obtained using these methods reduce to those of Kondo's third-order perturbation theory calculation plus corrections of order An(ε) ln2+n(ε/kTK); n≥0. Perturbation theory for a contact s-d interaction, permits the evaluation of the An(ε) for the one-electron self-energy or transport lifetime as functions of the complex energy variable ε. The methods listed above give different expressions for the An's and thus define different functions of ε despite their equivalence to logarithmic accuracy. The use of analytic continuation of the various functions into the T < Tk domain evidently leads to different predictions for the low-temperature properties of the system.
A New Explanation for the Magnetic Memory of α-Fe2O3 on the Basis of a Negative Pressure Effect on the Morin Transition Point
Authors: Kawai Naoto , Ono Fumihisa , Hirooka Kimio
Published: January 2006

An α-Fe2O3 crystal was subjected to a negative hydrostatic pressure by mechanically stretching the crystal in several directions. The decrease of the Morin transition point was detected using an astatic magnetometer placed underneath the crystal. A new explanation of the memory effect of the remanent magnetism of the crystal is given.
Effect of Pressure on Magnetic Interactions in Metamagnetic MnP Single Crystals
Authors: Hirahara Eiji , Suzuki Takashi , Matsumura Yoshishige
Published: January 2006

MnP has a Curie point (Tc) at 291.5°K and a screw spin structure below 50°K. The screw axis is parallel to the a axis. The effect of uniaxial compression on the screw-ferromagnetic transition point (Tα) and on Tc is measured by monitoring the resistivity along the a axis of a single crystal. With the compression along the a axis, Tα increases and Tc decreases. The compression along either the b or c axis, on the other hand, decreases Tα and increases Tc. These results imply that the a-axis compression enhances the antiferro-magnetic interaction relative to the ferromagnetic one and that compression along the b or the c axis produces the opposite effect.
First-Order-Paramagnetic-Antiferromagnetic, Metallic-Semiconducting Transition in Nickel Sulfide
Authors: Sparks J. T. , Komoto T.
Published: January 2006

The first-order transition at 263°K occurring in the nickel-arsenide form of NiS has been examined in more detail by neutron diffraction, electrical resistivity, and magnetic-susceptibility measurements on high-purity samples. Neutron powder intensity data at 4.2°K and at room temperature show that the NiAs crystal structure is retained below the transition, no lattice distortion being observed, and confirm the antiferromagnetic ordering reported previously. The intensity data also show that at most only 1% of the nickel atoms migrate from their normal octahedral sites to tetragonal interstitial sites upon being warmed from 4.2°K to room temperature, and no sudden migration is observed at the transition. This is in contrast to the nickel-arsenide form of MnBi, in which 10% of the manganese atoms are reported to migrate suddenly to the tetragonal sites upon being warmed through the first-order transition observed at 633°K. The magnetic moment per Ni2+ ion at 4.2°K as determined from the mixed nuclear and magnetic (101) reflection is 1.66±0.08 μB and at 260°K, just three degrees below the transition, the measured moment is 1.50±0.10 μB. Electrical-resistivity measurements on a compressed-powder sample show an abrupt increase by a factor of about 40 upon cooling through the transition. Above the transition, the resistivity is linear with the temperature, with a positive temperature coefficient indicative of metallic conductivity, and is calculated to be ρ(T)/ρ(0°C) = 0.76+6.8 × 104T(°K). Below the transition, a plot of logρ(T)/ρ(0°C) vs 1/T gives an activation energy for semiconduction of 0.12 eV. The powder magnetic susceptibility at room temperature is 2.24×106 emu/g. Upon cooling, the susceptibility (χ) decreases slightly down to the transition, where it abruptly increases by 16%. Below the transition, χ decreases linearly with temperature. The magnitude of χ below the transition, however, depends on the magnitude of the external applied magnetic field at the time the transition is traversed. Details of this work are to be published elsewhere.
Magnetic Susceptibility of (U1−cThc)O2
Authors: Comly J. B.
Published: January 2006

The magnetic susceptibility χ of UO2 diluted by its diamagnetic isomorph, ThO2, is reported for 1.7° ≤  T ≤ 60°K. In dilute samples, 5%–10% UO2 in ThO2, χ−1 decreases monotonically with decreasing temperature. Blume's singlet ground-state mechanism for the first-order magnetic phase transition in UO2 requires a Γ1 singlet ground state 50°K below a Γ5 triplet. The crystal-field structure of U4+ in ThO2 should be similar and should lead to a rise in χ−1 at low temperature as the triplet depopulates, in striking contrast with observation. Concentrated samples with 0%–40% ThO2 in UO2 show a linear dependence of TN on concentration, with a critical concentration of 42% ThO2. The singlet ground-state mechanism in the molecular field approximation predicts that TN is sharply nonlinear with dilution of the molecular field and falls steeply to zero when diluted by 14%. It is apparent from these two lines of evidence that the static ground state in UO2 is not a singlet. The first-order transition in UO2 is probably related to a dynamic lattice interaction which opposes ordering down to 30°K where a cooperative lattice and magnetic transition takes place.
Ultrasonic Attenuation at the Magnetic-Phase Transition in Gadolinium
Authors: Luthi B. , Pollina R. J.
Published: January 2006

We present ultrasonic attenuation measurements in the vicinity of the Curie temperature. Longitudinal waves along the c axis exhibit a large critical attenuation, whereas transverse waves show only a spurious attenuation peak. Along the a axis the critical attenuation for longitudinal waves is much smaller. In a nonsymmetry direction both longitudinal and transverse waves show large critical attenuation. AH these results can be explained, assuming the spin-phonon coupling is of the volume magnetostrictive type. For longitudinal waves propagating either along the c or a axis we find the following attenuation law for (T − TC)/TC > 1×10−3 α ∝ ω2(T − TC)−1.2.
Linewidth and Off-Resonance Loss in Polycrystalline Ferrites at Microwave Frequencies
Authors: Kohane T. , Schlömann E.
Published: January 2006

The off-resonance loss has been measured in polycrystalline YIG on samples with a controlled (and generally rather large) porosity. The results can conveniently be expressed in terms of an equivalent line-width, which is a function of the dc magnetic field strength. It is defined as the width that an absorption peak with Lorentzian profile would have if the off-resonance absorption of this reference profile at a given dc field matches the actually observed absorption. The equivalent linewidth of polycrystals is in most cases much smaller away from resonance than it is near resonance. For YIG the equivalent linewidth at X-band is approx 10 Oe both at low and high dc fields but rises to 50–600 Oe (depending upon the porosity) in the vicinity of resonance. The experimental results are compared with theoretical predictions. based upon the assumption that the line broadening is primarily caused by inhomogeneity of the local saturation magnetization. It is shown that the linewidth, the magnetic hardness coefficient (which characterizes the approach to magnetic saturation at high field-strengths), and the longitudinal susceptibility are intimately related.
Ferromagnetic Resonance and Nonlinear Effects in Nickel-Zinc Ferrite
Authors: Dixon Samuel , Spencer E. G.
Published: January 2006

Data are given on ferromagnetic resonance properties in annealed (1000°C) single-crystal nickel-zinc ferrite spheres taken at 9300 MHz and between 4.2°K and room temperature. Because of the high saturation magnetization, 4πMs = 5000±100 G, the dc magnetic field for subsidiary ferromagnetic resonance is coincident with the field for uniform precessional resonance for f ≦ 9300 MHz. At 4.2°K, ΔH[111] = 6.9 Oe, rises to 9.1 Oe at 15°K, and is 5.8 Oe at room temperature. At room temperature hc = 3 mOe, from which it is deduced that the intrinsic linewidth ΔHK→0 = 1.3 Oe.
Modified Nickel Ferrites with High Saturation Magnetization and Improved Hysteresis Properties
Authors: Wantuch E. , Degenford J. E. , Whicker L. R.
Published: January 2006

A series of nickel, zinc ferrites with small substitutions of copper were prepared. These materials were tested in toroidal shape under conditions of radial compression. A comparison with a commercially available material, Trans-Tech TT 2-111, was made. The value of remanent flux density was increased by 50% resulting in superior performance of the new materials in latching phase shifter applications. At 35 GHz, a differential phase shift of 200°/in. and a phase shift figure of merit of 370°/dB were measured. At 75 GHz, this performance deteriorated to 110°/in. and 100°/dB, respectively. This may be partially attributed to fabrication difficulties of the optimum geometry. Further improvement of the magnetic properties of nickel, zinc ferrites for microwave applications will require the reduction of their magnetostrictive characteristics.
Magnetic Properties of Ba4Zn2Fe36O60 Single Crystals
Authors: Kerecman A. J. , Tauber A. , AuCoin T. R. , Savage R. O.
Published: January 2006

The dc and microwave magnetic properties of single crystals of Ba4Zn2Fe36O60(ZnU) were investigated. The saturation magnetization ‖ and ⊥ to c, anisotropy constant and anisotropy field were determined as a function of temperature from 4.2 to 600°K. TC = 673±2°K. At room temperature 4πMs = 3700 G, K1 =  1.4×106 ergs/cm3 and HA = 9.6 kOe. At 4.2°K 4πMs = 6190 G, K1 = 2.4×106 and HA = 10 kOe. A magnetic moment nβ = 60 was computed from a collinear spin model, excellent agreement with nβ = 60.5, calculated from σs(H = ∞,  T = 0). This result tends to confirm allignment of spins ‖ to c. Ferrimagnetic resonance linewidths of 210 Oe were measured on unpolished samples in the range 30–40 GHz. An anisotropy in electrical resistivity of 107 Ω·cm ‖ and 4×103 Ω·cm ⊥ to c was noted.
Effective Anisotropy in Polycrystalline Materials. Separation of Components
Authors: Globus Anatol , Duplex Paul
Published: January 2006

A method is proposed to determine the over-all anisotropy K in ferrimagnetic materials from initial susceptibility of single-domain grain samples. Indications on technology of single-domain grain samples are given. The Ni1−xZnxFe2O4 system is studied in detail. The upper limit of the contribution from dipolar energy has been determined by studying Mn0.5Zn0.5Fe2O4 and is found to be negligible. The study of magnetoelastic anisotropy has been carried out on compositions of known K1. This anisotropy (expressed as λsσ) varies very little at low temperatures depending on Zn content, and for a given composition it varies as λs. Thus, σ is temperature independent. σ is shown to be an intrinsic property for a composition and it increases with Zn content. Our investigations show that realization of single-domain grain samples enables us to obtain σ and K1 from measurements of (μ − 1)c, Ms, and λs, which are easily accessible from polycrystalline samples.
Linewidth Reduction through Indium Substitution in Calcium-Vanadium Garnets
Authors: Van Hook H. J. , Green J. J. , Euler F. , Czerlinsky E. R.
Published: January 2006

On the garnets Y3−2xCa2xFe5−x−yVxInyO12, with x ≤ 1.5 and y ≤ 0.5, we have measured the polycrystalline linewidth ΔHpoly at X-band and room temperature and have determined from single crystals the first-order anisotropy constant, K1. Since the single-crystal linewidth of these materials is but a few oersteds and the polycrystalline samples had less than 1% porosity and second phase, the observed ΔHpoly is attributed to anisotropy broadening, according to Schlömann. The introduction of indium reduces both | K1 | and ΔHpoly, for example: x = 0.63y = 0TC = 280°C4πMs = 650 GΔHpoly = 98 Oex = 0.80y = 0.50TC = 155°C4πMs = 750 GΔHpoly = 8 Oe. That last value is the lowest yet reported in the range of T ≈ 23 TC.
Measurements on Lithium Ferrite Crystals having Near-Zero Defect Concentrations
Authors: Spencer E. G. , Lepore D. A. , Nielsen J. W.
Published: January 2006

From a batch of lithium-rich highly ordered single crystals of lithium ferrite, a group of 13 spheres were prepared using regions selected for low defect concentrations. Linewidths measured at 5.1 GHz and ∼300°K ranged from 0.87 to 2.06 Oe with a mean value of 1.35 Oe. The resistivity of the crystals was 3 Ω·cm and 4πMs was 3720±50 G. The narrow linewidths in the presence of such high conductivity suggests a conductivity mechanism other than the usual one involving Fe2+ ions.

The sphere with the lowest ΔH was used to measure the temperature dependence of ΔH, ΔHk→0 and HA[111] between 4.2° and 300°K at 10.4 GHz. The ΔH ranged from 1.45 Oe at 300°K to 0.55 Oe at 4.2°K with a peak of 2 Oe near 30°K. At 250°K, ΔHk→0 was 0.4 Oe. It exhibited a peak near 30°K (whose maximum was not measured) and was only 0.06 Oe at 4.2°K. The anisotropy field HA[111] decreased monotonically from 625 G at 4.2°K to 390 G at 300°K.

The possession of samples having very small linewidths permitted the study of the effect of ordering on the room-temperature linewidth uncomplicated by other effects.
Initial Permeability of Ferrites at Microwave and Natural Gyromagnetic Resonance
Authors: Courtois Louis , Hoffmann Francis
Published: January 2006

At sufficiently high frequencies the initial permeability is attributed to the gyromagnetic motion: Taking into account the effective anisotropy field, the rf field, and the dipolar field we obtain a phenomenon of gyromagnetic resonance called natural resonance (maximum of μ″).

As it was shown by Polder and Smit, the off-diagonal component of the permeability creates magnetic charges on the domain walls. The demagnetizing field and the off diagonal permeability give a component of magnetization which is parallel to the applied field and whose average over the ferrite does not cancel. On a simple model of prolate domains, a derivation of this mechanism is presented. The results do not fully explain the shape of the natural gyromagnetic resonance, but they give however the fundamental aspect of the phenomenon. At lower frequency. Snoek's formula is obtained and at higher frequencies this theoretical value of the permeability is perfectly confirmed by several experiments.
Mechanism of RIS in Thin Magnetic Films
Authors: Fujiwara H. , Sugita Y. , Saito N. , Taniguchi S.
Published: January 2006

Two models, model 1 and model 2, which lead to type 1 and type 2 RIS (rotatable initial susceptibility), respectively, are presented. In model 1, the film is considered to be composed of many crystallites with a uniaxial anisotropy, whose easy axis is randomly oriented within the plane of the film. The magnetization of each crystallite is thought to be coupled with each other through an effective field which is parallel and proportional to the mean magnetization of the film. In model 2, anisotropy centers with the same uniaxial anistropy are distributed in the completely isotropic medium, with their easy axes randomly oriented within the plane of the film. The postulated interaction, in this case, is the one between the anisotropy centers and the isotropic medium only. In this case also, the interaction is thought to be caused through an effective field acting on the anisotropy centers from the isotropic medium, which is parallel and proportional to the magnetization of the isotropic medium whose local magnetizations are always kept parallel with each other. For these two models, critical curves of the external field for irreversible rotation of the mean magnetization, according to which the characteristics of both type 1 and type 2 RIS are derived, have been obtained by numerical calculations.
Influence of Neutron and Argon Ion Bombardment on the Induced Uniaxial Anisotropy in Nonmagnetostrictive Permalloy Films
Authors: Roth M. , Anagnostopoulou-Konsta A. , Paulevé J.
Published: January 2006

Technical magnetic thin films evaporated at 150°, 300°, or annealed at 550°C were bombarded by pile neutrons and 11-keV argon ions in a magnetic field at 200°C. After a sufficiently long bombardment time the uniaxial anisotropy constant attains for all films the same saturation value. The experimental data are well explained by supposing this value to be due to the simultaneous presence of directional pair ordering and partial long-range Ni3Fe type order. Long-range order seems to exist already in films deposited at 300°C whilst in the other cases it is created during bombardment. Films condensed at 150°C show an extra component of magnetic anisotropy, probably due to the ordering of lattice imperfections, which disappears during bombardment or annealing. Comparison of the saturation values of induced anisotropy obtained after neutron and argon-ion bombardment shows that the degree of atom-pair order obtained, decreases with increasing number of displacements per second and per atom of the target.
Stress in Co-Ni-Fe and Ni-Fe Films
Authors: Gorres J. M. , Hanson M. M. , Lo D. S.
Published: January 2006

The stress measured at 25°C in vapor-deposited Co-Ni-Fe and Ni-Fe films was investigated as a function of composition, grain size, substrate temperature, film thickness, and annealing parameters. The stress was determined by measuring the change in curvature of circular substrates with an interferometer. Various compositions were studied. The ranges of each constituent were 0%–50% Co, 50%–90% Ni, and 10%–50% Fe. A dependence of stress on composition existed even when the substrate temperature and grain size remained constant.

The residual stress has a nearly parabolic dependence on substrate deposition temperature with a minimum in the vicinity of 275°C. This is in general agreement with the results for Ni-Fe films using different techniques and previously reported by Weiss and Smith.

The stress is nearly constant for film thicknesses 1000–10 000 Å and can be reduced by annealing, provided the annealing temperature is greater than the temperature of deposition.
Magnetic Anisotropy of Epitaxial Iron, Nickel, and Cobalt Films
Authors: Kirensky L. V. , Pynko G. P. , Pynko V. G.
Published: January 2006

Measurements were made of the first constant of crystal anisotropy K1 and K⊥ = KN−2πJS2−K1 of the films, Fe, Ni, and Co, epitaxially grown on NaCl, LiF, and MgO crystals. Here KN is the constant of anisotropy perpendicular to the plane of a film, and JS is the saturation magnetization.

The conclusion is drawn that the fact that K⊥ ≠ 0 in films cannot be explained only by stress. Stress accounts only for the difference between K1 of single-crystal films and K1 of in massive single crystals.
Kinetics of Annealing of Permalloy Films with Increasing Concentrations of Sulfur
Authors: Luborsky F. E. , Barber W. D.
Published: January 2006

Zero-magnetostrictive films have been annealed isothermally at 60°, 75°, and 90°C in a hard-axis saturating field. The films contained up to 6 wt% of sulfur. The time dependence of the change in anisotropy indicated the presence of simultaneous processes affecting a portion of the total anisotropy. The average relaxation time was independent of sulfur content at a given temperature, but the fraction of the anisotropy involved was directly dependent on the sulfur concentration in the film and independent of temperature. The kinetic equation which described the results was (lnP/lnP∞) = 1−exp[−(t/τ)1/2]. This general form may be derived from the conventional pair reorientational model by making τ = f(t) to take into account the removal, during the annealing in the transverse field, of the effect of the active centers introduced by the sulfur. An activation energy of 0.74 eV was found for the processes affected by the sulfur. Stabilization, i.e., annealing in an easy-axis field at 150°C, made the annealing kinetics in the hard-axis field at the lower temperatures independent of the sulfur content. The changes in anisotropy with time in the hard-axis field after stabilization appeared to follow the same kinetic law as before stabilization, but the fraction of anisotropy involved was greatly reduced and the activation energy was reduced to ∼0.4 eV. It is suggested that the inclusion of sulfur in the film produces vacancies, defects, strain fields, and other structural defects which allow iron-atom pair reorientation to occur at the low temperatures studied. The stabilization treatment anneals out the imperfections.
Excitation of Uniaxial-Anisotropy Relaxation Processes in Magnetic Films by a Rotating Magnetic Anneal
Authors: Harte K. J. , Smith D. O. , Anderson R. M. , Johnston R. C.
Published: January 2006

In hard-axis annealing studies of Permalloy films, which have revealed a number of discrete uniaxial-anisotropy relaxation processes, all processes are annealed simultaneously, making interpretation difficult and ambiguous. In this paper a new method is reported, in which individual processes are excited by a rotating magnetic anneal. Simple physical considerations show that the easy axes of only those processes with relaxation rates comparable to the annealing frequency will lag the annealing field when that field coincides with the easy axis. A theory based on discrete atomic processes predicts Debye peaks for the easy-axis lag angle vs annealing frequency; relaxation rates are determined from the location of these peaks. By varying temperature, activation energies and pre-exponential factors are obtained. The method of detection employs second-harmonic magnetoresistance in a configuration which is insensitive to magnetization dispersion. The measurement is made automatically in ∼0.2 sec twice every cycle; angular sensitivity is ∼10−4 rad. By means of this technique, the anisotropy spectrum in an 83% Ni-17% Fe film is being investigated between 40° and 400°C and over a frequency range 50 μHz to 0.1 Hz.
Implications of Band-Structure Studies on the Understanding of Magnetic Properties of the Ferromagnetic Transition Metals
Authors: Doniach S.
Published: January 2006

Two types of many-body correction to rpa (random-phase approximation) for the ferromagnetic transition metals are discussed in a qualitative way: electron-magnon interaction and electron-electron correlations as formulated by Hubbard. For Ni it is argued that rpa is a reasonable approximation for the ground state. The recent band-structure calculation of Hodges, Ehrenreich, and Lang for the ground-state magnetization density is reviewed briefly. For the excited states (spin waves, spin fluctuations) electron-magnon corrections may be more important. For Fe both types of many-body correction are likely to be considerable. In particular, band-narrowing effects can lead to a model band-structure Hamiltonian in which tight-binding overlap integrals are magnetization dependent. The status of spin waves and spin fluctuations in Fe is briefly reviewed.
Optical Spectra of Transition and Noble Metals
Authors: Phillips J. C.
Published: January 2006

Derivative and photoemission studies of the optical spectra of transition and noble metals are reviewed and interpreted from the viewpoint of energy-band theory.
Energy-Band Theory of Magnetism
Authors: Slater J. C.
Published: January 2006

Recent progress in energy-band theory leads to the hope that we can understand many ferromagnetic and antiferromagnetic substances from an energy-band point of view. One uses a one-electron approach, with different exchange potentials for electrons with spin up or down. The energy bands can be computed using the augmented plane-wave method, which is well adapted to crystals containing transition elements. Calculations along these lines for Ni and Fe have been made by Wakoh and Yamashita in Toyko, and for Ni by Connolly in Gainesville. Cho, formerly in Gainesville, has treated EuS, a ferromagnetic semiconductor. The method is also adapted to antiferromagnetic crystals, and calculations on several such crystals are under way in Gainesville and Toyko. The significance of the energy separation between the bands for spin-up and spin-down electrons is discussed, for both the ferromagnetic and antiferromagnetic cases. These energy separations are connected with intra-atomic exchange effects, and are much too large to have any direct connection with the Curie or Néel temperatures.