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Small angle neutron scattering measurements were made on amorphous HoFe2 and GdFe2. For HoFe2 the intensity for T≳Tc (195 K) is Lorentzian in form and can be analyzed for an inverse correlation length κ1 which remains finite at Tc. Below Tc a giant anomalous magnetic component appears, which follows a q−2.4 dependence and can be analyzed in terms of magnetic inhomogeneities of dimension comparable to κ1−1 at Tc. Limited measurements at fixed q indicate the absence of this component in GdFe2, suggesting an origin based on local crystalline field effects.Small angle neutron scattering measurements were made on amorphous HoFe2 and GdFe2. For HoFe2 the intensity for T≳Tc (195 K) is Lorentzian in form and can be analyzed for an inverse correlation length κ1 which remains finite at Tc. Below Tc a giant anomalous magnetic component appears, which follows a q−2.4 dependence and can be analyzed in terms of magnetic inhomogeneities of dimension comparable to κ1−1 at Tc. Limited measurements at fixed q indicate the absence of this component in GdFe2, suggesting an origin based on local crystalline field effects.

Inelastic neutron scattering measurements have been made on sputter‐deposited amorphous Tb.33Fe.67 using time‐of‐flight spectrometers at Argonne and at Oak Ridge. At 433K (above Tc) the magnetic scattering function S(Q,ω) exhibited an approximate Gaussian dependence on energy transfer characteristic of a paramagnet. Below Tc, at 299K, a broad distribution of magnetic inelastic scattering is present centered approximately at ΔE=11 meV. As expected this distribution was significantly broadened and was shifted to a lower energy than the equivalent polycrystalline compound TbFe2 which showed a single inelastic peak near 18 meV. Polarized beam time‐of‐flight data taken at Oak Ridge showed evidence for discrete spin wave excitations for Q≲1.0 A−1 in the amorphous sample.

Curie temperatures of the series of amorphous rare earth‐iron alloys RFe2 (where R=Gd, Tb, Dy, Ho, Er, and Y) have been determined from Belov‐Goryaga plots of the magnetization isotherms. The Curie temperature of GdFe2 is 500 K, and drops sharply (e.g., ErFe2 Tc=105 K2) as one proceeds to the right in the above series (decreasing R spin). The observed Curie temperatures exhibit a smooth variation with the DeGennes factor of the rare earth ion, with the zero spin limit YFe2 exhibiting no long‐range order. This is in marked contrast to the analogous crystalline Laves phase compounds for which YFe2 has a 535 K Curie temperature and which show a much weaker dependence on the rare earth spin. These results imply a more significant effect of the structural disorder on the direct Fe‐Fe exchange versus the RKKY Fe‐R and R‐R couplings. A molecular field model decsribing these interactions has been used to calculate the expected Curie temperature for both the amorphous and crystalline series. Overall agreement with the observed Tc’s was less satisfactory for the amorphous than for the crystalline materials.

TbxSc1−x and CdxSc1−x alloys have been shown to exhibit no long‐range magnetic order for x

The excitation of single, k=0 magnons in the antiferromagnetic, ferrimagnetic, and ferromagnetic phases of CoBr2·2H2O at ∼2°K are described and fit to a five parameter spin wave theory. In addition, 2‐magnon and 3‐magnon bound states are observed in the ferromagnetic phase. At higher energies, another series of single spin excitations is observed and identified as due to the simultaneous excitation of a magnon plus a phonon. It is shown that these magnons are excited near the Brillouin zone boundary in the b‐direction.

The equations of motion of a 180° domain wall in an infinite, uniaxially anisotropic medium exposed to an instantaneously applied uniform dc magnetic field, Ho, have been integrated numerically. Media resembling YIG and an orthoferrite have been studied with Gilbert α's from .001 to .03. Fields above and below the critical value, Hc = 2πOMo (Mo, the saturation magnetization), below which a steady state solution is known to exist have been considered.

Results of neutron diffraction, magnetic susceptibility and specific heat measurements on single crystal samples of the hexagonal linear chain compound CsMnBr3 are reported. Three‐dimensional magnetic ordering occurs at TN=8.3°K. Above TN neutron scattering maxima are observed at reciprocal lattice planes, indicative of one‐dimensional correlations along the chain. Below TN the Mn2+ magnetic moments are coupled antiferromagnetically along the chains but lie in the basal plane, where they form a triangular array. The magnitude of the Mn2+ moment extrapolated to 0°K is indicative of a substantial zero‐point spin deviation. From about 90°K to 300 °K the susceptibility data could be fit with Fisher's exact solution for the susceptibility of a classical, nearest‐neighbor, one‐dimensional Heisenberg antiferromagnet. We found J=9.6°K and χmax at 90°K. Evidence of anisotropy was observed in the susceptibility data. The specific heat data below 13°K is dominated by a term linear in T. The coefficient of the linear...

A method of producing extraordinary bubbles (EB's) in epitaxial garnet films is presented together with their static and dynamic properties. EB's can be produced by applying a number of pulse fields to strip domains through a loop conductor. The collapse fields of bubbles cut from these strip domains are distributed between the collapse field of ordinary bubbles (Ho) and a higher value of up to 1.4Ho for samples of composition (EuEr)3(GaFe)5O12. Also presented is an analysis of a domain wall structure model for EB's, in which a cylindrical domain wall is assumed to consist of N pairs of right‐ and left‐handed Bloch‐type sections connected with Neel‐type sections. By choosing suitable values for N, the model reproduces the static properties of EB's quite well.

We extend micromagnetic nucleation theory by removing the customary constraint of rigidity. The magnetoelastic interaction is added to the magnetic free energy as a perturbation and it is evaluated for various competing nucleation patterns or their linear combinations to determine the pattern yielding the lowest energy. We apply this technique to the initiation of magnetization reversal in long cylindrical particles and we compute the reduction of the nucleation field for curling and buckling as a function of particle radius. We find that the radial ranges over which curling and buckling are favored are nearly unaffected by magnetostriction if the particles are free, but that buckling is dominant over a slightly extended range of radii for particles imbedded in a matrix, as in a permanent magnet. We determine the nucleating domain pattern of a platelet with easy axis perpendicular to the faces, initially saturated by a large in‐plane field. The domain nucleation threshold depends on the thickness, anisotropy, and magnetoelastic coupling of the plate. The nucleation mode has incipient stripe domains parallel to the field (the mode always predicted in the absence of magnetostriction) in thin plates, perpendicular to the field in thick plates, and inclined with respect to the field in the intermediate thickness range.

A study was undertaken to examine various processing parameters in the manufacture of (PrxSm1−x)Co5 magnets. Parameters studied included the samarium to praseodymium ratio, sintering temperature and time, and aligning and compacting conditions. All of the alloys studied were nominally 63 wt% cobalt, with the total rare earth content being on the order of 37 wt%. Compositional variations which were investigated included: 20.7 wt% Pr ‐ 16.3 wt% Sm, 20.7 wt% Pr ‐ 15.8 wt% Sm, 20.35 wt% Pr ‐ 16.30 wt% Sm, 24.67 wt% Pr ‐ 12.33 wt% Sm and 27.75 wt% Pr ‐ 9.25 wt% Sm. Sintering temperatures were varied over the range of 1085°C to 1140°C, while the sintering times were either 30 or 60 minutes. Alignment fields of 10 kOe and 36 kOe were used and compacting was performed by either uniaxially pressing in a die or by isostatic pressing. Although the best magnet produced in the course of this investigation had an energy product of 22.6 MGOe, a possibly more significant result was that a magnet with an energy product of...

The magnetic hyperfine fields for Fe in alloys of chromium with manganese additions have been obtained as functions of temperature and manganese concentration using the Mossbauer Effect. With increasing manganese concentration the mean hyperfine field at 4.2K decreases to a minimum for ∼10% manganese and increases slightly for 40% manganese. Near neighbour effects on the Fe57 resonance are small, suggesting the rigid band model is appropriate for these alloys. All samples gave unusual temperature dependences of the magnetic hyperfine field, there being a temperature region where the field is very small, with large fields above and below this temperature. The behaviour of the hyperfine fields as functions of temperature and concentration can be interpreted in terms of a weak exchange coupling between the iron magnetic moments and neighbouring chromium moments (giving a Brillouin function dependence on the host magnetization and the temperature) plus a contribution of the opposite sign proportional to the host magnetization and which is attributable to a conduction s electron polarization.

Computer simulations of domains propagating in lateral displacement coded circuits of the conductor‐groove type are presented. The simulations show that single wide LDC groove circuits propagate bubbles around turns with difficulty while there exists no such difficulty with a pair of smaller grooves, or dual grooves. Simulations of dual groove circuits indicate an operating margin of 600 A/m (7.5 Oe) at a propagation frequency of 500 kHz and an assumed mobility of 0.15 M2/A‐sec (1200 cm/Oe‐s). The simulated circuit results were consistent with the behavior of single domains in actual circuits.

Electron‐spin‐resonance (ESR) measurements at 24 GHz have been made on single crystals of K2ZnF4 doped with Mn. The spectra obtained in these measurements correspond to Mn2+; in the Zn2+ sites (point group 4/mmm) in this material. The measured values of the spin‐Hamiltonian parameters corresponding to the fine and hyperfine structure are g∥ = 2.0030, g⊥ = 2.0028, A = − 88.7 × 10−4cm−1, B = − 89.3 × 10−4cm−1, D = 36.0 × 10−4cm−1, a = 5.6 × 10−4cm−1, and F = 1.9 × 10−4cm−1. In addition, the transferred hyperfine interaction (TEI) parameters were obtained from the ESR measurements. The measured values of these parameters [which result from interactions between the Mn2+ 3d electrons and the F− and which refer to the four equivalent nearest‐neighbor F− ions in the (001) plane (type I) and the two equivalent nearest‐neighbor F− ions along the fourfold axis (type II)] are AsI = 18.1, AsII = 14.9, AσI = 0.4, AσII − 1/2 AπII = 0.3, and AπI ≈ 0, where the subscripts s, σ, and π refer to s, Pσ and Pπ electronic bond...

Mossbauer spectroscopy has been used to study single iron atoms (monomers) and groups of iron atoms trapped in a frozen rare‐gas matrix. Matrix isolated Fe(3d6 4s2) and Fe+(3d7) give two new calibration points for the ψ2 (0) vs isomer shift relationship. These data yield ΔR/R = − (8.7±0.3) × 10−4 for the 14.4 KeV transition in Fe‐57. The observed l/T temperature dependence of the monomer line‐width shows that the direct phonon process is dominant in the spin‐lattice relaxation time. Spin‐lattice relaxation times of the order of 2.5 × 10−10 sec at 4.2K are obtained by assuming a hyperfine field of 1.1 × 106 Oe at the Fe‐57 nucleus due to an iron atom with unquenched orbital momentum. We observe the quadrupole splitting of the I = 3/2 excited state of Fe‐57 in the axial field produced by an iron nearest neighbor. At iron atom concentrations above about 5 percent, the magnetic hyperfine field at the Fe‐57 nucleus is very close to the field observed in iron metal.

Detailed magnetization‐field‐temperature data were taken on a weakly ferromagnetic Ni‐Rh alloy of ∼35 at.% Rh near its Curie point (Tc≃44°K). The critical exponents determined for the temperature dependences of the spontaneous magnetization (σsp) and the initial paramagnetic susceptibility (χo) and for the critical magnetic isotherm are respectively as follows: β = 0.476 (±0.015), γ = 1.50 (±0.05), and δ = 4.15 (±0.08). These exponent values, though anomalous in comparison to various model predictions (unlike those for pure nickel, which are remarkably Heisenberg‐like), nevertheless obey the scaling relation, δ = 1 + γ/β. Moreover, all the data in the critical region are found to conform to a homogeneous equation of state. From the values of the coefficients A and B in the expressions, σsp = A(Tc − T)β and χo = B(T − Tc)−γ, it is deduced that the elementary moments involved in the ferromagnetic‐paramagnetic transition of this alloy have an average magnitude of ∼20 μB. This is consistent with the size of t...

Using an argon ion laser, optical Raman scattering associated with an electronic crystal field state of FeF2 has been studied, A broad spectrum has been observed, dominated at low temperatures by an intense line 28 cm−1 broad, located at 1082 cm−1. The exact nature of this Raman excitation is not well understood at present. The Raman line intensity is strongly dependent on magnetic ordering, and its spectrum is unaffected by magnetic fields up to 80 kOe, with H ∥ c. The 1082 cm−1 feature is also observed as a magnetic dipole infrared absorption close to the stronger magnetic dipole transition at 1115 cm−1 reported previously. Because of its Raman polarization rules and its energy, the excitation seems to be associated with the low‐lying B1g (paramagnetic group) manifold arising from the orthorhombic splitting of the 5T2g cubic field ground state of Fe2+.

It is shown experimentally that the antiferromagnet TbPO4 exhibits a linear magnetoelectric (ME) effect and that its ME susceptibility tensor α↔ has a component αaa whose largest absolute value is considerably larger than any component of α↔ previously reported for any material. Here a denotes one of the axes (a, a′, c) of the tetragonal crystal structure existing above the Neel temperature. The electrically as well as the magnetically induced ME effect was used to measure the temperature (T) dependence of ∣αaa∣ on a single crystal which had been annealed magnetoelectrically (with an appropriate electric field and a necessarily “small” magnetic field) so as to maximize ∣αaamid;. The largest value of ∣αaa∣ is ∣αaa∣max = 11 × 10−3 Gaussian units and occursat T = 1.92 ± 0.01°K. Using the previously proposed atomic mechanism 1 of the ME effect in rare earth crystals and the fragmentary spectroscopic data presently available, we compare this value of ∣αaa∣max with the value ∣αaa∣max = 1.2 × 10−3 Gaussian units...

The Curie temperatures of the ferromagnetic spinel CuCr2Se4−xBrx have been reported to decrease sharply with bromine concentrations x in the range 0.98

The possible spectroscopic consequences of unequal distribution of the RE3+ ions on the six nominally equivalent Y3+ sites of garnet are described. The crystal material is in the general case biaxial rather than cubic, and we derive expressions for the absorption coefficient as a function of polarization and growth direction. For non‐Kramers RE3+ ions the transitions are x, y or z polarized and the dichroism of the ion can be used to quantitatively determine the distribution on the sites, and to partially determine the symmetry of the crystal field states. The effect of site selectivity on the electronic Raman spectrum is also discussed. Components of the Raman tensor not readily accessible by other means can be measured.

The temperature dependence of the Hall and transverse magnetoresistance effects has been measured in a polycrystalline sample of Yb (RRR = 17) showing the fcc‐hcp transformation. The data cover the temperature range 1.8–420°K and field range up to 26 kOe, and they indicate that the behaviour of the Hall effect through the transition arises primarily from the structural change and not from the associated magnetic transition. However, the entire interpretation is handicapped by the present lack of detailed knowledge of the Fermi surface of hcp Yb.The temperature dependence of the Hall and transverse magnetoresistance effects has been measured in a polycrystalline sample of Yb (RRR = 17) showing the fcc‐hcp transformation. The data cover the temperature range 1.8–420°K and field range up to 26 kOe, and they indicate that the behaviour of the Hall effect through the transition arises primarily from the structural change and not from the associated magnetic transition. However, the entire interpretation is handicapped by the present lack of detailed knowledge of the Fermi surface of hcp Yb.

Additional adiabatic heat capacity calorimetry has confirmed the bifurcated nature of the Verwey transition in pure and doped Fe3O4 samples. Two sharp peaks occur at 113.3 and 118.8 K for a 99.99% pure ceramic sample. Data on a hydrothermal sample confirmed the presence of both peaks. However, the presence of 0.2 weight per cent of Mn(II) raised them by 3.7 and 4.1 K, respectively. Large single‐crystals of naturally occurring magnetite revealed only a broad transition with a high temperature shoulder. The total transitional enthalpy for the pure ceramic sample was 155 cal mol−1 or a value about 10 ± 1% higher than that for the two doped samples. Observation of the positive shift of transition temperatures for the Mn(II)‐doped (hydrothermal) sample appears contradictory not only to the trend reported in a recent study (in which magnetic sensing was used) but in particular to that observed for a Zn(II)‐doped sample. Calorimetric sensing of the transition temperature appears to be more reproducible than eith...

The mutual interaction between cylindrical domains of reversed magnetization in two separate sheets of uniaxial materials placed parallel one above the other has been studied. There are different reasons for doing this study. On the one hand the interaction between the domains(commonly called bubbles), which is quite strong in certain circumstances, can be used in magnetic bubble devices, for example to perform logical functions (section III.1). On the other hand, this study gives an impression of the cross‐talk one can expect between the domains in different sheets in a device (section III.2).

Single crystals of the 1:1 complexes tetrathiafulvalinium tetracyanoquinodimethane (TTF‐TCNQ) and tetrathianaphthacinium tetracyanoquinodimethane (TTN‐TCNQ) have been synthesized and the electron transport properties and magnetic susceptibility have been measured from 2°K to room temperature. For TTN‐TCNQ, σ at room temperature is 1Ω−1 cm−1. For TTF‐TCNQ, σ at room temperature along the long axis (σ∥) is in the range 192–652Ω−1 cm−1 depending on sample whereas perpendicular to the long axis σ⊥ is 1Ω−1 cm−1. The conductivity remains metallic down to 66°K in both directions whereupon a continuous metal to insulator transition occurs. The activation energy in the insulating state is 0.0062 ev. The transition is associated with a small hysteresis between the heating and cooling curves suggesting a possible structural change. In the metallic region, ρ∥ follows a T2 dependence whereas ρ⊥ follows a T+1 behavior. The magnetic susceptibility is diamagnetic below 20°K becoming increasingly more paramagnetic with increasing T even in the metallic region. It is suggested that spin disorder scattering may account for the anomalous temperature dependence of ρ⊥.

Electron spin resonance measurements on Gd in LaAl2 exhibit appreciable changes in the g value and linewidth upon 1) changing the Gd concentration, 2) introducing Kondo‐like impurities in place of La (e.g. Ce), 3) introducing non‐magnetic impurities in place of La (e.g. Th), and 4) introducing “fluctuation moments” in place of La (e.g. U). These changes are interpreted in terms of the magnetic resonance bottleneck, allowing for the extraction of the spin flip lattice scattering rate δeL of the conduction electrons in all four categories. We find (in units of 107 sec−1 per ppm) ∂δeL/∂c = 1±0.6 (Gd), 7±3 (Ce), 5±2 (Th), and 20±8(U). We attribute the very much larger cross section for Ce and U, as compared to Gd and Th, respectively, to the proximity of the 4f and 5f resonance levels to the Fermi level. This allows for large admixtures, leading to rapid spin‐orbit relaxation of the conduction electron spin.

In this paper we present a self‐consistent treatment of the effect of the exchange interaction on the dielectric response of each spin band of an itinerant electron system. Our equation gives a simple physical picture for the role of exchange interaction, as well as that of the direct Coulomb interaction, in the dielectric responses both for the paramagnetic and ferromagnetic state. In the ferromagnetic state, the self‐consistent inclusion of the exchange interaction effect leads to a rather drastic result in which the electrons of one spin band can be repelled by a positive point charge while the electrons of the opposite spin band can be attracted.

According to the increasing demands for magnetic tape printing especially for video tape, the magnetic tape duplication using a contact process is one of the most attractive solutions. There are two major methods, i. e. anhysteretic transfer and thermal transfer. The coercivity of the master tape should be 2.5 times higher than the slave by computer simulation for anhysteretic transfer, but is not important for thermal transfer. The highest coercivity of the slave tape will be decided by the master tape which, in turn, is limited by the recording head saturation for anhysteretic transfer, however, the thermal characteristics of coercivity and magnetic induction under Tc are more dominant for thermal transfer. The tape surface roughness as well as the coercivity is very important for short wavelength printing. In this paper, the properties of the master and slave tapes for anhysteretic and thermal transfer are discussed with theoretical and experimental results.

Thin films in the Mn‐Ga‐Ge system have been prepared by thermal vaporization and their magnetic and magneto‐optical properties have been studied as a function of chemical composition. It has been found that the tetragonal MnGaGe structure exists over a wide range of compositions with corresponding large variations in properties. The Curie temperature of films with the tetragonal structure ranges from 120° to 250°C, and was found to increase with increasing Ga content and decrease with increasing Ge content. Films of Mn‐Ge and Mn‐Ga were ferromagnetic and did not show the tetragonal structure.

The initial susceptibilities of powder (CH3)2NH2CuCl3 and (CH3)4N NiCl3 have been measured from 1.3 − 90 degrees K. The results deviate from Curie‐Weiss behavior below 10 degrees K for the Cu salt, and below 20 degrees K for the Ni salt. The structures of both salts are such that a reasonable interpretation of such deviations is to consider both systems as ensembles of linearly interacting chains. The Cu salt exhibited antiferromagnetic deviations, and the Ni salt ferromagnetic deviations from Curie‐Weiss behavior. The following models were used to fit the experimental results: 1) the Ising Model, 2) the Bonner‐Fisher Model (for the Cu salt), 3) a model in which each system has available a ground singlet and a thermally accessible triplet, and the ensemble is Avagadro's number of such weakly interacting systems (for the Cu salt), 4) the Duffy‐Barr Model for an infinite chain with alternating exchange parameters. The fits to theory are discussed.

Measurements of linewidth versus angle between the static field and the film plane have been made at 9 GHz for high quality Ni3Fe films 300–2700 A thick. Both the parallel and perpendicular frequency linewidths increase with thickness, and the increase is more rapid for parallel FMR. The data for 300 A films can be fitted with a constant Landau‐Lifshitz damping. The difference between the parallel and perpendicular linewidths [Δ(ω/γ)∥ −Δ(ω/γ)⊥] shows a striking thickness dependence indicative of two‐magnon relaxation.

The physical properties of most metallic elements can be deduced from band calculations based on a knowledge of the potential field of the isolated ions and the observed crystal structure. These detailed computations can be approximated by pseudo‐potential calculations which suppress detail of the atomic core structure and within that simplified framework the relative energy of different simple crystal structures can be accounted for. Furthermore the phonon frequencies can be calculated and any instabilities of the lattice structure detected as imaginary frequencies. Magnetic superstructures may be explained by analogous calculations of the spatially varying static susceptibility. Alloys can be treated by assigning a different pseudo potential to each kind of atom, and despite some difficulties about self‐consistent electron transfer between species, band structures can be evaluated. In some situations where strong compound formation is found, the band structure of the d electrons splits into parts, some of which are completely occupied in a way reminiscent of valence bonded crystals like diamond. Perturbation of simple elemental structures may be a satisfactory approach to the stability of some compounds, but the intercomparison of the energy of formation of unrelated complex structures is still beyond theoretical treatment.

A technique for improving the rate of convergence of the solution of field problems by the method of finite differences called SER (successive extrapolated relaxation) has been developed. Sufficient saving in computing time is obtained by the method so that it is feasible to solve three‐dimensional field problems. This method uses conventional overrelaxation for every three iterations and then extrapolates simultaneously to the solution using a modification of Aitken's formula. In this paper, this method is applied to obtain the field in three dimensions from “T bar” circuits used for propagating magnetic bubbles. Symmetry considerations have been used so that the analysis is required over only one half of the propagating period. The permalloy circuit is idealized for these calculations.

The magnetic scattering intensity is investigated for Ising lattices with antiferromagnetic next‐nearest‐neighbor (nnn) coupling. At sufficiently high temperatures, anomalous features can appear, but for cubic lattices in two and three dimensions the scattering has only normal Ornstein‐Zernike form. The latter result stems from a curious numerical correspondence between (a) the physical condition that the nearest‐neighbor (nn) interaction determines the ground state, as expressed in terms of the nnn to nn interaction ratio and (b) the geometrical ratio of nnn to nn lattice spacings. A mean‐field approximation, valid at high temperatures, is employed to estimate the disorder‐point for a variety of two and three dimensional lattices.

A special type of 180° wall has been observed in (111) wafers of Y3Fe5−tGatO12 [1] with M⇒ normal to the wafer plane where the Ga content varied laterally by Δt/Δx = 0.02 mm−1. This Ga gradient gave rise to a line of magnetic compensation extending across the platelet where t ≈ 1.3. Applying a magnetic field this new wall which we further call ‘compensation wall’ generates along the compensation line [2]. The wall is characterized by essentially three properties: (1) It is fixed by an applied field to a compensation line; (2) its wall energy and wall thickness depend on the applied field; (3) it moves with changing temperature. The compensation wall separates domains of different sublattice orientations, but equal direction of the total magnetization M⇒(r⇒), since M⇒(r⇒) aligns parallel to the applied field. With increasing field strength the wall expands, while its center line stays fixed. A small temperature variation results in a considerable displacement of the compensation line and, consequently, the...

A theory employing finite strains and angular momentum invariants is applied to the rare earth metals of hcp structure. A Hamiltonian is written down which is invariant under combined rotations of the magnetic and elastic systems. When the usual small strain approximations are subsequently made there appear new terms linear in the antisymmetric strains. The coupling of transverse acoustic waves to the magnetic system has been studied and expressions obtained for the dependence of the elastic constants c44 and c66 on an applied magnetic field in the ferromagnetic phase. Estimates of the effects to be expected for Gd, Tb, Dy, Ho and Er indicate that it should be possible to obtain in a direct manner the values of certain magnetoelastic constants and anisotropy constants. Calculations have also been performed for the field‐dependent changes in c11 and c33 for longitudinal waves in the paramagnetic region. These changes result from the fact that the finite strains Eμμ include terms of the form eμμ2.

An attempt was made to use an InSb Hall‐effect transducer to detect magnetic bubble domains. An InSb film of 1.4μ thickness was evaporated on a glass substrate and then photoetched to cross shape. The width of each branch was 50μ. The product sensitivity of the detector in a uniform field was 220V/AT for a low input current (< 1 mA) and 110V/AT for a high current (7mA). By using this detector a maximum signal voltage of 8mV was obtained at an input current of 7mA for 100μ bubble domains of TmFe03. At 2Hz operation, S/N was quite large (26dB). Noise voltage becomes higher with increasing frequency. This is induction noise in the lead wires by the rotating field. The value of S/N was 10dB at a 38kHz operation.

Garnets of the type {Nd3−y Ry}[RxGa2−x](Ga3012, in which R is Yb, Tm, Er, Ho, or Dy, and x is as high as 2, have been subjected to magnetic measurements. All preparations have been studied over the temperature range 78°‐300°K. and some also at 4.2°K. and/or over the range 1.6°–300°K. The materials are paramagnetic with Curie‐Weiss behavior but in some the slopes of 1/XM vs. T plots change at very low temperature. Comparisons are made between experimental Curie constants and those calculated from theoretical values and from values obtained with garnets containing the same rare earth ions on only one or the other of the two crystallographic sites. Over the temperature ranges in which the various materials were studied, no evidence has been found for long‐range ordering which results in ferrimagnetism, ferromagnetism, or antiferromagnetism.Garnets of the type {Nd3−y Ry}[RxGa2−x](Ga3012, in which R is Yb, Tm, Er, Ho, or Dy, and x is as high as 2, have been subjected to magnetic measurements. All preparations have been studied over the temperature range 78°‐300°K. and some also at 4.2°K. and/or over the range 1.6°–300°K. The materials are paramagnetic with Curie‐Weiss behavior but in some the slopes of 1/XM vs. T plots change at very low temperature. Comparisons are made between experimental Curie constants and those calculated from theoretical values and from values obtained with garnets containing the same rare earth ions on only one or the other of the two crystallographic sites. Over the temperature ranges in which the various materials were studied, no evidence has been found for long‐range ordering which results in ferrimagnetism, ferromagnetism, or antiferromagnetism.

The evolution of magnetic “bubble” technology has continued at a rapid pace. Many garnet compositions, prepared as epitaxial films, are now available for both materials and device characterization. Films of the nominal composition Er2Eu1Ga.7Fe4.3012, grown by LEE with growth induced anisotropy, have been most extensively studied. Although films with defect counts less than 5 defects/cm2 are readily produced, this particular garnet is hampered by the rather modest mobility of 80 cm/sec/0e and 100 kbits/sec device data rates. Although most garnets easily provide storage densities of 106 bits/in2, the higher device data rates achievable with increased mobility have prompted a widespread materials search. However, improvements in bubble propagation circuits can also increase the device data rate. Improved high speed performance has been achieved with a “chevron” bubble circuit which consists of columns of permalloy ∧'s arranged as “(see PDF for diagram)”. Domains will be driven to the right by the fields of moving lines of magnetic poles generated by an in‐plane field rotated clockwise. Within the range of device operation either bubbles or island strip domains propagate. The number of ∧'s in a column can be adjusted to suit individual circuit requirements. For example, a two element 20 μm period chevron circuit has operated at 300 kHz with an epitaxial garnet film Er1.99Gd1.01Ga.22Fe4.78012 with a mobility 89 cm/sec/0e. Simultaneous propagation of as many as three domains with movement lateral to the direction of propagation in a 13 element circuit has made possible the design of a full adder. Details of a chevron bubble mass memory will be described.

The positions of the metamagnetic transitions of FeCl2·2H2O have been measured as a function of temperature from 1.5 K up to the Neel temperature TN = 23 K using strain gage techniques. We find that the transitions meet at a triple point at T3=11.5±.5K and H3 = 41±1 kOe.

Conduction electron spin densities and their contribution to the diffuse part of the neutron magnetic form factor of Gd metal, measured by Moon et al., have been determined by means of spin polarized APW calculations. Although our spin density is similar to that of Moon et al., we are unable to reproduce their large region of negative spin density. Thus, our theoretical form factor is considerably lower than experiment at the first (hkl) reflection. Possible reasons for this difference are discussed here.

An improved formalism is proposed for calculating the dynamic susceptibility of itinerant ferromagnets. This procedure is based on a simple extension of the random phase approximation and an interpolation method for treating wave functions and matrix elements throughout the Brillouin zone. In contrast to previous work, this formalism incorporates momentum‐dependent spin‐splitting of the electronic energy bands as well as multi‐band effects. It is found that all parameters which appear in the theory can be determined directly from a self‐consistent treatment of the ferromagnetic band structure. We have used this formalism to numerically calculate the dynamic susceptibility of ferromagnetic nickel for several “realistic” band structures which incorporate these momentum‐dependent exchange effects. The spin‐wave dispersion curve obtained from such calculations is found to be in excellent agreement with experiment. A comparison of our results with those obtained from the simple enhanced susceptibility theory w...

Measurements of the magnetocaloric effect in a single crystal nickel sphere have been carried out for applied fields from 90 to 900 oersteds for temperatures close to Tc. The field dependence is consistent with a parametric equation of state fitted to magnetization data. For this equation the adiabatic exponent π=(γ+2β−1)/β=2.78. The data are normalized to and compared with the specific heat data of Connelly, Loomis and Mapother [Phys. Rev. B 3, 924 (1971)].

Detailed NMR spectra are presented for host and impurity nuclei in dilute alloys of Fe and Ni containing Ru. All shifts in the spectra of the Ni¯Ru alloys are toward lower hyperfine fields while Fe¯Ru exhibits both positive and negative shifts. Interpretation of the host spectra requires consideration of impurities out to at least the third neighbor shell. The field distribution about the impurity has the same spatial behavior as the moment disturbance deduced from neutron scattering results. Each Ru spectrum is directly compared with its host spectrum and the relationship is discussed.

The results of neutron diffraction in α ‐RbFeF4 and Mossbauer effect measurements in KFeF4 are characteristic of a two‐dimensional antiferromagnet. Powder neutron data for α ‐RbFeF4 reveal that there is antiferromagnctic coupling between nearest neighbors within the layers and between those in adjacent layers. Single crystal neutron data show that above TN the magnetic scattering is in the form of reciprocal lattice “rods” characteristic of long‐range two‐dimensional correlations. Mossbauer Effect (ME) measurements in the antiferromagnetic state of KFeF4 yield well‐resolved hyperfine spectra, revealing a unique magnetic field and EFG tensor at all iron nuclei. The temperature variation of the sublattice magnetization in KFeF4 has been determined by measuring the internal field at the iron site. At low temperature (T ≲ TN/2) the results are found to agree with simple two‐dimensional spin wave theory. For 0.72 < T/TN < 0.99 the internal field follows a(TN−T)pbeta; law with β = 0.185±0.005 and TN = 137.2±0.1°K.

High‐ and low‐temperature series analysis of the Blume‐Emery‐Griffiths model of the He3‐He4 tricritical point confirms the qualitative features of mean field behavior but reveals some significant inaccuracies.

Studies are reported of the fields surrounding the T‐bar pattern commonly used in magnetic bubble propagation devices. Large, appropriately scaled, T‐bar circuits were used to experimentally determine the normal field patterns in the vicinity of the T‐bar elements. These patterns were determined with external drive fields having various in‐plane orientations. From these data the approximate stable position of the bubble was determined for each external field orientation. The magnitudes of the perpendicular (driving) field gradients were estimated from the changing field patterns and bubble velocities were calculated. The discussion of these results includes comparisons with available data on bubble velocity along the propagation path. Bubble oscillations normal to the propagation direction are noted.

Metal‐insulator phase transitions have been found in all the Magneli phases VnO2n−1 (n=3 – 9) but V3O5 and V7O13. The V7O13 phase remains metallic down to 4.2°K. In addition, phases with n = 3, 4, 5, 6, 7, 8 order magnetically at a lower temperature. These electrical and magnetic properties are collated and reviewed in summarized form.

The materials used in magnetic recording surfaces and their associated writing and reading transducers include both hard and soft magnetic materials, conductors, insulators, adhesives, fillers, housing materials and wear‐resistant coatings. Only the magnetic materials will be considered here. Writing and erasure heads must generate enough field to reverse permanently the remanent magnetization of the recording surface while having near‐zero remanence themselves. This calls for a high saturation magnetization and a low coercivity (to reduce the required input power). These properties together suggest that a high value of maximum permeability is desirable. In the reading transducer, the magnetic material must be switched by the weak fields existing over the surface of the tape or disk. High initial permeability of the highest signal frequency is the principal requirement and again, we ask that the material have no memory of its previous magnetic states. In contrast, the particles of which recording surfaces are composed should display permanent magnet‐like properties. The energy product (coercivity x remanence) must be high to ensure a detectable field outside the magnetic coating. However, resolution of high‐density signals requires at the same time that the ratio of coercivity to remanence be high.

Recently it has been proposed by Tucciarone that the relative magnitude of photoinduced dichroism in YIG(Si) can be calculated by imposing axial symmetry on the electric‐dipole photodetachment cross section. By means of this method, the polarization dependence of the dichroism induced by linearly and circularly polarized light was calculated, and, while the former case was found to be uniquely determined by symmetry alone in the framework of the model, the latter effect was found to be particularly sensitive, by means of a “shape parameter” r, to the details of the excitation process. In this paper we apply the same method to the calculation of the temperature dependence of the dichroism induced by both linearly and circularly polarized light. We find that the temperature variation of the magnitude of the dichroism depends on the strength of the trigonal field, while the temperature dependence of the shape parameter r is strongly coupled to the spin‐orbit constant. In case the trigonal field is assigned the values recently proposed by Alben et al., the calculated magnitude of the dichroism is practically constant between 0°K and nitrogen temperature, if the relaxation time of the effect is neglected.