Showing papers in "Physica B-condensed Matter in 1975"
TL;DR: In this paper, it was shown that at low temperatures the spin dynamics of an antiferromagnetic linear chain can be governed by propagation of boundaries between one-dimensional superlattice points.
Abstract: It is shown that at low temperatures the spin dynamics of an antiferromagnetic linear chain can be governed by propagation of boundaries between antiferromagnetic one-dimensional domains. A double maximum results in the neutron-scattering function S(q, ω) if the one-dimensional momentum transfer q is not too close to a one-dimensional superlattice point. In contrast with ordinary magnons of an anisotropic system, the dispersion law corresponding to the maximum exhibits no gap. If q = π, S(q, ω) is centered at ω = 0 but has a nonlorentzian shape. At moderately low temperatures the neutron linewidth at q = π amd the spin-lattice relaxation time are both proportional to the inverse correlation length K , whereas at very low temperature T, they are proportional to K T 1 2 . Much smaller values of T1 and of the neutron linewidth are expected if the spin dynamics is governed by thermally activated processes, as occurs if boundaries are trapped by lattice imperfection and cannot propagate. In the ferromagnetic Ising-like chain, spin dynamics is always governed by thermally activated processes.
92 citations
TL;DR: In this paper, the magnetocrystalline anisotropy constants of Y-, Ce-, Pr-, Nd-, Sm- and CeMMCo5 were determined from magnetization and torque curve measurements on single crystals in the temperature range between 77 K and the ferromagnetic Curie point and in fields up to 16 kOe.
Abstract: The magnetocrystalline anisotropy constants of Y-, Ce-, Pr-, Nd-, Sm- and CeMMCo5 were determined from magnetization and torque curve measurements on single crystals in the temperature range between 77 K and the ferromagnetic Curie point and in fields up to 16 kOe. The anisotropy of Y-, Ce-, Sm- and CeMMCo5 can be described by the constant K1 alone, whereas K2 and K4 are necessary for NdCo5 and PrCo5, for temperatures below 300 K. A comparison of the temperature dependence of K1 with the classical temperature dependence of magnetocrystalline anisotropy shows that the intrinsic anisotropy itself is a function of temperature. The change in type of anisotropy from NdCo5 and PrCo5 is consistent with crystal field calculations.
69 citations
TL;DR: In this paper, the influence of axially symmetric anisotropies in the exchange interaction was studied for S = 1 2 and 1. This influence proved to be qualitatively the same in both cases.
Abstract: Energy spectra and thermodynamical quantities of finite linear chains and polygons of axially symmetrically interacting spins have been numerically calculated. Extrapolation of the molar heat capacities versus the number of spins yielded estimates for infinite systems. Ground-state energies were also obtained. Data are presented for both ferromagnetic and antiferromagnetic chains. The influence of axially symmetric anisotropies in the exchange interaction was studied for S = 1 2 and 1. This influence proved to be qualitatively the same in both cases. For S = 1 to 5 2 , data are included for isotropic exchange in combination with several crystal field anisotropy parameter (D) values, both positive and negative. Further, the effect of the simultaneous presence of a D term and exchange anisotropy is studied for several cases. Agreement of the extrapolated data is found with some existing experimental and theoretical results.
68 citations
TL;DR: In this article, the relationship between the exchange constants and the bond lengths in the series of insulating antiferromagnetic compounds XMF3 and X2MF4 is investigated.
Abstract: In the series of insulating antiferromagnetic compounds XMF3 and X2MF4 (X=K, Rb, Tl; M=Mn, Co, Ni) the superexchange paths connecting nearest magnetic neighbours are identical collinear (180°) M-F-M bonds. The available experimental data on the exchange constants, J/k, and the bond lengths, R, are reviewed. They enable one to give an estimate of the dependence of J/k on R, as well as the ratio of the J/k values of Mn2+, Co2+, and Ni2+ for a fixed bond length. Assuming a power-law dependence, |J/k|∼R−n, our analysis yields n≃12 for Mn2+, Co2+ as well as Ni2+, in the R range covered experimentally. The ratio of the J/k values of Mn2+, Co2+, and Ni2+ at fixed R=4.074 A is found to be 1:3.6:7.7. The experimental findings are compared with theoretical calculations based upon a recently proposed exchange-perturbation treatment for the cation-anion-cation unit in a three-centre four-electron model. The unpaired electrons on either cation are replaced by one effective electron and the closed-shell electrons of the anion by two spin-paired electrons. Qualitatively, the agreement with the experiment is good in that the model reproduces correctly the observed R dependences as well as the ratio of the J/k's of the three different cations. Also in quantitative respect a close agreement with the experimental J/k values can be obtained within the uncertainties inherent to the effective-electron model.
65 citations
TL;DR: In this paper, the magnetic phase transformation from a triangular to a long-period anti-ferromagnetic structure in Mn3Sn has been studied in polycrystalline samples in the 21-25 at% Sn concentration range using magnetic, X-ray, and neutron diffraction methods.
Abstract: The magnetic phase transformation from a triangular to a long-period anti-ferromagnetic structure that takes place in Mn3Sn has been studied in polycrystalline samples in the 21–25 at% Sn concentration range using magnetic, X-ray, and neutron diffraction methods. The crystallographic and magnetic phase diagram has been constructed from the results. A sharp decrease in the transition temperature Tt can be observed below 23.3 at% Sn. The reported dependence of Tt on annealing can be interpreted as a consequences of the change in the composition due to the special shape of the stability range of the Mn3Sn phase at high temperatures.
52 citations
TL;DR: The magnetic properties of the pseudo-binary alloy series Y2(Co1-xFex)17 have been investigated between 77 K and 1100 K using vibration and torque magnetometry techniques as mentioned in this paper.
Abstract: The magnetic properties of the pseudo-binary alloy series Y2(Co1-xFex)17 for 0 ⩽ x ⩽ 1 have been investigated between 77 K and 1100 K using vibration and torque magnetometry techniques. In particular the temperature and composition dependences of the magnetocrystalline anisotropy constants K1 and K2 have been determined, and comparisons made to the known behaviour of metallic cobalt and iron. Changes in the type of anisotropy, with both composition and temperature, are established, and comments made as to the relevance of certain structural features of the compounds in explaining these observations.
39 citations
TL;DR: In this paper, the resistivities of liquid lithium-sodium alloys have been determined as a function of temperature for alloy compositions covering the entire concentration range and the immiscibility loop of the phase diagram has been determined.
Abstract: The resistivities of liquid lithium-sodium alloys have been determined as a function of temperature for alloy compositions covering the entire concentration range. When the resistivity is plotted as a function of concentration, the nonlinear terms corresponding to the Nordheim rule appear to be remarkably small. A shallow minimum was found at the lithium-rich end of the composition range. As the measurements were carried out from 500°C down to temperatures below the phase separation temperature, the temperature coefficient of the resistivity could be calculated. Additionally, the immiscibility loop of the phase diagram has been determined. Calculations along the lines of the diffraction model provide satisfactory agreement with experiment but appear to be rather sensitive to one of the input parameters.
27 citations
TL;DR: In this paper, strain dependence of the interconduction-band adsorption is used in evaluating the ∈ 2 spectra of Cu, Ag, and Au, and the proposed criteria facilitate the analysis of experimental spectra, amongst others with regard to their relationship to calculated spectra.
Abstract: The strain dependence of the interconduction-band adsorption is used in evaluating the ∈ 2 spectra of Cu, Ag and Au. In Cu and Au the height of the second absorption maximum (between 3.5 and 5 eV) relative to that of the first maximum (between 2 and 3.5 eV) provides a criterion for judging the quality of the sample. In Ag similar information is derived from the width and height of the absorption edge around 4 eV. The proposed criteria facilitate the analysis of experimental spectra, amongst others with regard to their relationship to calculated spectra, the tailing of the absorption edge in Ag, and the interpretation of alloy spectra. Some as yet unexplained absorption structure in Ag (around 3.9 eV) and Au (around 3.6 eV) is speculatively attributed to the onset of interconduction-band absorption ( E F →≈ L 1 ) in partially deformed specimens.
25 citations
TL;DR: In this paper, the results of Monte-Carlo computations are used to show that an interionic potential to which corresponding-state theory can be rigorously applied is insufficiently flexible to account for details of the thermodynamic properties of molten alkali-metal salts.
Abstract: Aspects of the corresponding-states correlation of certain properties of ionic liquids and liquid mixtures are examined. The results of Monte-Carlo computations are used to show that an interionic potential to which corresponding-states theory can be rigorously applied is insufficiently flexible to account for details of the thermodynamic properties of molten alkali-metal salts. The specific model studied is one frequently referred to in discussions of the application of dimensional methods in the statistical mechanics of ionic salts. Use of the same idealized potential model in the case of mixtures leads to values of the excess thermodynamic properties which are consistent with the predictions of conformal solution theory but differ qualitatively from those observed experimentally. The possibility of using results obtained by computer simulation to extend the range of validity of existing corresponding-states relations is discussed and the example of ionic diffusivity is treated as an illustration.
25 citations
TL;DR: In this paper, the optical absorption spectrum of Ho3+ in HoPO4 and HoAsO4 and the specific heat of HoAO4 has been studied to obtain information on magnetic and hyperfine interactions in these substances.
Abstract: The optical absorption spectrum of Ho3+ in HoPO4 and HoAsO4 and the specific heat of HoAsO4 has been studied to obtain information on magnetic and hyperfine interactions in these substances. Both substances are Ising systems which order antiferromagnetically in a simple two-sublattice structure with magnetic moment direction parallel to the optical axis at TN = 1.39K and 0.557 K, respectively. The interactions to nearest (nn), next nearest (nnn), and third nearest neighbours (tnn) were estimated. The most striking result is that the exchange interaction to the nearest neighbours was found to be ferromagnetic however cancelled by the third nearest neighbour's exchange interaction in HoAsO4 and even overcompensated in HoPO4.
12 citations
TL;DR: In this article, specific-heat data in the temperature range of 1.3 K to 80 K are presented on polymeric M(II)(N2H5)2(SO4)2 compounds where m(II) = Cu, Ni, Co, Fe and Mn.
Abstract: Specific-heat data in the temperature range of 1.3 K to 80 K are presented on polymeric M(II)(N2H5)2(SO4)2 compounds where M(II) = Cu, Ni, Co, Fe and Mn. Broad maxima in the magnetic specific heat, pointing to magnetic linear chain exchange interactions, are observed. For the Co, Fe and Mn compounds, λ-like anomalies have also been observed which are indicative of the onset of three-dimensional long-range spin ordering. From the specific-heat measurements information is obtained about the anisotropy of the intrachain exchange interaction, single-ion anisotropy and the magnitudes of the intrachain and interchain interaction parameters of these compounds. The results on the Cu and Mn compounds were fitted to the antiferromagnetic Heisenberg linear chain model with spin 1 2 and 5 2 , respectively. Although this model yields reasonable fits, deviations were observed near the maxima of the curves. For the Cu compound this is ascribed to anisotropy in the exchange interactions and for the Mn compound to interchain coupling effects. In order to fit the data on the Ni and Fe compounds it was found necessary to introduce single-ion anisotropy. The results for the Ni compound were fitted to the Ising spin 1 2 linear chain model with in addition a Schottky curve, and to recent calculations for the spin 1 antiferromagnetic Heisenberg linear chain model with in addition uniaxial single-ion anisotropy. The exchange parameter J/k is found to be much smaller than the zero-field splitting parameter D/k, thus giving rise to Ising properties of the spins at low temperatures. The Co compound was found to exhibit anisotropic exchange interactions which are, in contrast to what is generally found for Co2+, of the planar type. The results were fitted to the spin 1 2 antiferromagnetic XY linear chain model, as calculated by Katsura, with an exchange parameter J/k = −7.05 K.
TL;DR: In this article, the intensity and polarization of diffraction phenomena are calculated and experimentally demonstrated, and the meaning of these diffraction phenomenon for the correct interpretation of magneto-optic images and for technical applications is discussed.
Abstract: Magnetic domain structures give rise to diffraction phenomena since they influence the light by magneto-optic effects. The intensity and polarization of these diffraction phenomena are calculated and experimentally demonstrated. The special properties of diffraction phenomena caused by thick samples of CrBr 3 are explained by multiple diffraction. The meaning of these diffraction phenomena for the correct interpretation of magneto-optic images and for technical applications is discussed.
TL;DR: In this paper, the influence of an increasing field normal to the specimen on these structures was studied and the measured field dependences of domain sizes were in good agreement with theoretical calculations given in the literature.
Abstract: Ferromagnetic domains in CrBr 3 were made visible by means of the magneto-optic Faraday effect at 15 K. Meander, strip, and honeycomb domains could be produced at will by applying suitable fields during the cooling of the specimen. The influence of an increasing field normal to the specimen on these structures was studied. A honeycomb structure is transformed into a high-density state of bubbles. In a structure of wavy strip domains new cone-shaped domains detach from the wavy peaks, thereby straightening the strips which finally contract to a low-density state of bubbles. The measured field dependences of domain sizes are in good agreement with theoretical calculations given in the literature.
TL;DR: In this article, the fourth-order spin-hamiltonian terms required for 3rd4 and 3d6 ions are studied theoretically with regard to their role in magnetocrystalline single-ion anisotropy.
Abstract: The fourth-order spin-hamiltonian terms required for 3rd4 and 3d6 ions are studied theoretically with regard to their role in magnetocrystalline single-ion anisotropy. Contributions of these ions to the cubic anisotropy constants K1 and K2 are calculated for several spinels and garnets and are found to be modified considerably by the fourth-order terms. The detection, from magnetic anisotropy measurements, of the fourth-order parameters B(4)0, B(4)4, (B(4)3), is shown to be feasible. Qualitative explanations for the complicated temperature variation of K1(Fe2+B) in some spinels and for the as yet theoretically unexplained sign of K2(Fe2+B) in garnets, are proposed.
TL;DR: The compound EuCu5 (CaCu5 structure; a=5138 A, c=4114 A ) is found to order ferromagnetically at Tc=57 K as mentioned in this paper.
Abstract: The compound EuCu5 (CaCu5 structure; a=5138 A , c=4114 A ) is found to order ferromagnetically at Tc=57 K The saturation moment and the effective magnetic moment are close to the values expected for Eu2+ The 151Eu Mossbauer effect has been studied at various temperatures below and above Tc Also the isomer shift and the effective hyperfine field in the magnetically ordered state are indicative of the divalent state of Eu in EuCu5 The easy direction of magnetization is found to be parallel to the crystallographic c axis
TL;DR: In this paper, the diffusion coefficient of 20Na atoms in a cylindrical cell filled with 3.5 × 1024 atoms/m3 neon has been measured at 300 K. The diffusion has been simulated by a numerical model.
Abstract: The diffusion coefficient of sodium in neon has been measured at 300 K. In a cylindrical cell filled with 3.5 × 1024 atoms/m3 neon, the radioactive 20Na isotope is produced by means of a short irradiation of 20 MeV protons. Starting 40 ms after the irradiation, the decrease in the 20Na atom density at several positions in the cell was measured using the resonance fluorescence technique, The decrease is determined both by radioactive decay and by diffusion of the atoms to the wall. The diffusion has been simulated by a numerical model. From comparison of the experimental with the numerical results the diffusion coefficient D of 20Na atoms in neon is obtained. The value of D found is (35 ± 8) × 10-6 m2/s at 1 atm and 300 K.
TL;DR: The Cr-Co-Fe-Legierungen basieren auf einer Gefugestruktur, die durch spinodale Entmischung der kubisch-raumzentrierten Hochtemperaturphase bei 640° C gebildet wird and aus formanisotropen Teilchen einer ferromagnetischen eisenreichen phase and einer schwach magnetischen chromreichen Phase besteht as discussed by the authors.
Abstract: Zusammenfassung Die Dauermagneteigenschaften der Cr-Co-Fe-Legierungen basieren auf einer Gefugestruktur, die durch spinodale Entmischung der kubisch raumzentrierten Hochtemperaturphase bei 640° C gebildet wird und aus formanisotropen Teilchen einer ferromagnetischen eisenreichen Phase und einer schwach magnetischen chromreichen Phase besteht. Molybdanzusatz bewirkt eine 〈100〉-Ausrichtung und eine verbesserte Formanisotropie der stabformigen. Einbereichsteilchen, woraus eine Hc-Erhohung resultiert. In Analogie zu den Alnico-Legierungen werden die optimalen Hc-Werte nicht bereits nach der 640° C-Anlassbehandlung gemessen, sondern erst durch eine 3stufige Temperung bei 600, 580 und 550° C erreicht. Da Formanisotropie und Grosse der Teilchen durch das Tempern nicht verandert werden, lassen sich die Hc-Erhohungen nur mit einem Diffusionsaustausch von Eisen und Chrom zwischen den beiden Phasen und der dadurch bedingten Erhohung der Differenz der Sattigungsmagnetisierung erklaren. Der Nachweis fur einen derartigen Vorgang ergibt sich aus den Messungen der Temperaturabhangigkeit von Hc, Br und Is nach den verschiedenen Warmebehandlungen. Bei 400–500° C beobachtete irreversible Anderungen von Hc in Richtung geringerer Werte sowie von Br und Is in Richtung hoherer Werte deuten auf eine weitere Entmischung in der bei 640° C gebildeten schwach magnetischen Phase hin. Dieser Effekt tritt bei zusatzlich ein- oder mehrstufig getemperten Proben, in denen also ein Diffusionsaustausch erfolgen konnte, nicht mehr auf.
TL;DR: In this paper, a renormalized version of the Weinstock weak-coupling model was used to obtain an exact Fourier model with an asymptotic turbulent collision operator and a modified source term.
Abstract: A general stochastic treatment is performed from the fluctuating Vlasov equation describing an ensemble of collisionless turbulent plasmas. The method used takes advantage of exact properties of the noncommuting propagators, and avoids the usual particle-trajectory calculations. The general result consists in an apparently markovian form of the Weinstock equation (master equation for the average function). This equation clearly exhibits the role of turbulent collisions and ballistic term associated with the propagation of the initial fluctuation. As a particular case, one recovers of course the quasilinear (QL) description. By using a renormalized expansion for the Weinstock propagator, one recovers as a first term the Dupree—Weinstock weak-coupling description which appears here as a renormalized quasilinear approximation (RQL). Such a description is fully analogous to Kraichnan's model equation for fluid turbulence. Explicit results are derived in this RQL approximation by using a useful interaction representation for the propagators. The resonance broadening and frequency shift in the RQL dispersion relation appear to be more involved than those previously known from particle-trajectory calculations. The wellknown “Dupree damping” appears to be modified, and the diffusion tensor of the evolution equation appears to be an operator in velocity space. Another approach is used in order to study the validity of the asymptotic approximation which is usually applied. This method is based on the existence of two subdynamics, i.e., of two independent equations describing the evolution of two complementary projections of the distribution function. As a result, we have obtained an exact equation with an asymptotic turbulent collision operator and a modified source term. The advantage is that this new source term is shown to vanish identically when the initial fluctuations belong to the class of the so-called “natural fluctuations”.
TL;DR: In this article, the paramagnetic Curie temperature θ of Cu 1- x In x Cr 2 S 4 spinels with 0.49 ≲ × ≲ 0.6 is a function of their room temperature resistivity ϱ.
Abstract: The paramagnetic Curie temperature θ of Cu 1- x In x Cr 2 S 4 spinels with 0.49 ≲ × ≲ 0.6 is a function of their room temperature resistivity ϱ. It is θ = -100 K and ϱ = 3.6 X 10 5 Ω cm for compensated semiconducting spinels with x = 0.5, and θ = -5 K for ϱ = 10 3 Ω cm for both p-type and n-type spinels with x x 0.5, respectively. The molar Curie constant C M (rational system) is 49 cm 3 K/mol for x = 0.5. This C M value is close to 47.2 cm 3 K/mol, the value calculated from the spin-only magnetic moment of the Cr 3+ ions. C M decreases both for x x 0.5. These results indicate that in Cu 1- x In x Cr 2 S 4 spinels ferromagnetic exchange via mobile holes for x via mobile electrons for x 0.5 is superimposed to antiferromagnetic superexchange.
TL;DR: In this paper, specific heat measurements were performed on four nickel compounds of formula Ni(II)X2L2 with X=Cl or Br and L=pyrazole or pyridine.
Abstract: Specific-heat measurements are presented on four nickel compounds of formula Ni(II)X2L2 with X=Cl or Br and L=pyrazole or pyridine. From the low-temperature data it can be concluded that the exchange interactions strongly predominate along chains. Analysis of the short-range order heat capacities with one-dimensional theories shows that the ferromagnetic intrachain interactions in these compounds interplay with the crystal-field splitting of of the Ni(II) ions. The intrachain exchange parameters are found to lie between 1.9 K (NiBr22NC5H5) and 7.3 K (NiCl2.2N2C3H4). The very large crystal-field anisotropy results in a doublet-singlet splitting of the Ni(II) ground state of about 30 K with the doublet lower. The λ-like anomalies observed in the specific heats can be associated with a phase transition which is, according to susceptability experiments, an antiferromagnetic-ferromagnetic transition in these materials. The specific heat of NiBr2.2pz measured in a constant external magnetic field supports this conclusion, which suggests that these Ni(II) compounds can be classified as metamagnets.
TL;DR: In this paper, the expression proposed by Jhanwar et al. for the energy-loss cross sections and the available excitation cross sections were used to calculate the stopping power of He, N 2 O 2 and atomic oxygen for 30 eV - 10 keV electrons.
Abstract: The expression proposed by Jhanwar et al. 7 ) for the energy-loss cross sections and the available excitation cross sections are utilised to calculate the stopping power of He, N 2 O 2 and atomic oxygen for 30 eV - 10 keV electrons. The results for He, N 2 and O 2 are in satisfactory agreement with other theoretical values while for atomic oxygen the present values are lower than most of the previous results.
TL;DR: In this paper, the stabilization field due to the reorientation of interstitials was measured for one (001) 180° wall in a (010) [100] frame-type crystal of 4.5% silicon-iron containing solute carbon.
Abstract: The stabilization field due to the reorientation of interstitials was measured for one (001) 180° wall in a (010) [100] frame-type crystal of 4.5% silicon-iron containing solute carbon. The sample was connected to a control circuit, which impressed the time rate of the wall displacement instead of applying a magnetic field. Therefore, it was possible to record relaxed initial magnetization curves, which directly show the decrease of the stabilization field beyond its maximum, as is calculated for 180° walls in α-iron. Moreover it was possible to observe the stabilization field, when the wall fell back into its stabilized position. Wall displacements of less than 0.1 μm were resolved, and the experimental results compared with the theoretical shape of the stabilization field as a function of the wall displacement. The experiments also give information about the radius of action of other restoring forces of the wall.
TL;DR: In this article, an analysis of the dependence of the reduced critical temperature kTc/J on the ratio R ≡ H′E/HE of the interlayer (H′E) and intralayer (HE) exchange coupling, as observed for a number of layer type copper compounds, is presented.
Abstract: In this paper an analysis is presented of the dependence of the reduced critical temperature kTc/J on the ratio R ≡ H′E/HE of the interlayer (H′E) and intralayer (HE) exchange coupling, as observed for a number of layer-type copper compounds. The analysis aims at a determination of the critical parameters of the susceptibility of the ideal (R = 0), quadratic, S = 12, Heisenberg ferromagnet. For the ideal system, the experimental data—when compared with the available theoretical calculations—seem to point to a critical behaviour, characterized by an exponential divergence of the susceptibility rather than to a power-law divergence. From the analysis an upper bound kTc(0)/J⩽ 0.25 is inferred for the reduced critical temperature kTc(0)/J of the ideal, quadratic, S = 12, Heisenberg ferromagnet. However, kTc(0)/J = 0 has to be taken into consideration, since the data are not inconsistent with the results of the S = 12, Green's-function approach of Yamaji and Kondo, in which the susceptibility is predicted to diverge exponentially at kTc(0)/J = 0, according to χ ≡ X J/(kC)= A(kT/J)−1 exp [C(kT/J)−1], with C = π. Under the assumption kTc(0)/J = 0, our analysis points to C=3.0. On the other hand, on basis of the presently available experimental data it is not possible to exclude a χ divergence of the form χ=Aexp{C[k(T−Tc(0))/J]0−v}, with kTc(0)/J > 0,0.5$ν < 1. The latter expression, with ν⋍0.8, has been suggested by Camp and Van Dyke for the S=∝, triangular Heisenberg ferromagnet from an analysis of high-temperature series expansions.
TL;DR: In this paper, the ac susceptibility of HoAsO 4 (Ising model) and GdVO 4 (Heisenberg model) was studied to localize the phase transitions in dependence upon temperature and magnetic field.
Abstract: Using a simple but nevertheless sensitive experimental arrangement, the ac susceptibility of HoAsO 4 (Ising model) and GdVO 4 (Heisenberg model) was studied to localize the phase transitions in dependence upon temperature and magnetic field. The purpose of this work was the verification of Fisher's theory connecting the specific heat and the reduced susceptibility of an antiferromagnet, the determination of the exchange and anisotropy constants, and a quantitative proof of the renormalization of the spin-wave frequencies.
TL;DR: The angular variation of the EPR linewidths in the crystallographic ac and ab planes of CaCu(OAc) 4 ·6H 2 O is studied in this paper.
Abstract: The angular variation of the EPR linewidths in the crystallographic ac and ab planes of CaCu(OAc) 4 ·6H 2 O is studied In discussing the results it is demonstrated that the magnetic properties of this compound need not be described with a linear-chain model as suggested earlier
TL;DR: In this paper, the vibration spectra and lattice heat capacities of copper, silver and gold have been calculated on the basis of a model developed by combining the ion-ion interaction from an axially symmetric model to the electron ion interaction from the Krebs model.
Abstract: The vibration spectra and lattice heat capacities of copper, silver and gold have been calculated on the basis of a model developed by us combining the ion-ion interaction from an axially symmetric model to the electron-ion interaction from the Krebs model. The theoretical results are found to be in close agreement with the experimental ones. It is demonstrated that electron screening in all noble metals is governed by thev Bohm and Pines theory.
TL;DR: In this article, the magnetic properties of the antiferromagnetic compounds CoCl 2.6H 2 O (T c = 2.29 K) and CoBr 2.6H2 O ( T c = 3.15 K) were analyzed in terms of the 2-dimensional (quadratic) XY model.
Abstract: The magnetic properties of the antiferromagnetic compounds CoCl 2 .6H 2 O ( T c = 2.29 K) and CoBr 2 .6H 2 O ( T c = 3.15 K) are analysed in terms of the 2-dimensional (quadratic) XY model. The experimental information includes measurements of the differential susceptibility as a function of field and temperature, the antiferromagnetic phase diagrams, and specific-heat measurements. The theoretical results on the XY model used are the high-temperature series expansions for the specific heat and the initial susceptibility, and the spin-wave prediction for the limiting low-temperature specific-heat behaviour. Good agreement between theory and experiment is obtained, yielding the values J / k = -2.05 ± 0.05 K and -2.45 ± 0.05 K for the intralayer exchange in the Cl and the Br compound, respectively. Furthermore the experiments, in particular the field-dependent susceptibility measurements, indicate the presence of substantial zero-point spin deviations in these compounds. Estimates of the spin reduction and the ground-state-energy shift, resulting from these zero-point motions, are deduced.
TL;DR: In this article, an elektrostatischen Analogmodellen the magnetischen Feldverteilungen um hochpermeable Zylinder with kreis-and rechteckformigen Querschnitten ermittelt.
Abstract: Zusammenfassung Mit Hilfe von Kohleschicht-Potentialpapieren wurden an elektrostatischen Analogmodellen die magnetischen Feldverteilungen um hochpermeable Zylinder mit kreis- und rechteckformigen Querschnitten ermittelt. Die Auswertung der Feldlinienbilder liefert den ballistischen Entmagnetisierungsfaktor und die relative Flussbelastung entsorechend geformter dunnwandiger Abschirmzylinder. Aus diesen beiden Grossen lasst sich der magnetische Abschirmfaktor bei vorgegebener Permeabilitat mit relativ hoher Genauigkeit bestimmen.
TL;DR: In this article, the experimental magnetization curves were compared with calculations for the observed domain structures, and it was shown that the maximum magnetization lies always approximately in the direction in which the crystal had been premagnetized in higher magnetic fields.
Abstract: At TD = 27.7 K TbAsO4 undergoes a crystallographic phase transition from tetragonal to orthorhombic symmetry. The magnetization perpendicular to the tetragonal axis exhibits a 180°-periodicity at T < TD and in small magnetic fields (≲ 800 Oe). The maximum magnetization lies always approximately in the direction in which the crystal had been premagnetized in higher fields (5 kOe). This striking behavior is explained by the appearance of crystallographic domains. The experimental magnetization curves are compared with calculations for the observed domain structures.
TL;DR: In this article, the effect of surface distortions on Tamm surface states has been studied and the dependence of surface states on δ-barrier strength, interatomic spacing near the surface, and other crystal-potential properties is considered.
Abstract: The Kronig—Penney model has been used to study the effect of surface distortions on Tamm surface states. The dependence of surface states on δ-barrier strength, interatomic spacing near the surface, and other crystal-potential properties is considered.