Showing papers on "Ferromagnetism published in 1971"
TL;DR: In this paper, the spin-dependent tunneling density of superconducting aluminum and ferromagnetic nickel is determined by a polarization of the magnetic moments of the Ni current carriers parallel to the applied field.
Abstract: Tunneling measurements on junctions between very thin superconducting aluminum films and ferromagnetic nickel films in a high magnetic field show that the tunneling current is spin dependent. The effective tunneling density of states in Ni determined by this means implies a polarization of the magnetic moments of the Ni current carriers parallel to the applied field. The technique offers a new method for investigating spin-dependent states in magnetic materials.
399 citations
TL;DR: In this paper, the crystallographic and magnetic structures of the distorted perovskites La 1−x Ba x Mn 1− x Me x O 3 (Me = Mn or Ti) have been determined by neutron powder diffraction.
254 citations
143 citations
TL;DR: In this paper, the magnetic specific heat of CoCl 2 ·2NC 5 H 5 was determined experimentally for the first time and the results showed that the magnetic susceptibility of this salt showed the rapid increase which is also the characteristic of the ferromagnetic Ising linear chain.
Abstract: The magnetic specific heat of CoCl 2 ·2NC 5 H 5 agreed with the exact solution of the ferromagnetic Ising linear chain with J / k =9.5±0.2 K above 6 K. The broad maximum expected theoretically to appear at 3.9±0.15 K was observed at 4.3±0.2 K. The magnetic susceptibility of this salt showed the rapid increase which is also the characteristic of the ferromagnetic Ising linear chain. About 85% of the total magnetic entropy Rln 2 was left above the Neel point 3.17±0.02 K. The characteristic features of the antiferromagnetic linear chain of the isotropic Heisenberg spins were obtained in the case of CuCl 2 ·2NC 5 H 5 : The magnetic susceptibility quite agreed with the one calculated theoretically for | J |/ k =13.6±0.8 K and g =2.06±0.06. The linear dependence of the specific heat on temperature in the lowest temperature region, which is expected theoretically, was ascertained experimentally for the first time. The absolute experimental values of the magnetic specific heat agreed with the theoretical ones for...
120 citations
01 Jan 1971-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the effect of local atomic environment on the atomic moment of Fe in Fe−Al alloys and of V in Au−V alloys is reevaluated, using improved methods of analysis and new magnetic data.
Abstract: The effect of local atomic environment on the atomic moment of Fe in Fe−Al alloys and of V in Au−V alloys is reevaluated, using improved methods of analysis and new magnetic data. Magnetic clusters with giant moments occur in many alloys in which one of the components has no magnetic moment. This is true for FeAl in spite of the presence of well-developed atomic long range order, although the concentration of magnetic clusters does decrease with increasing long range order. The phenomena of mictomagnetism are reviewed. Mictomagnetism occurs in many alloys having no long range atomic order, and it is characterized by the freezing of the spin orientations at low temperatures but, in contrast to ferromagnetism and to antiferromagnetism, without long range magnetic order.
108 citations
TL;DR: In this article, the authors presented heat capacity data for the five LnAl 2 compounds, where Ln=La, Ce, Pr, Nd and Gd, in approximate agreement with R In (2 J + 1) except for GdAl 2 in which the discrepancy was about 25 percent.
99 citations
TL;DR: The single crystal elastic moluli of an Fe + 5.86 at.% Si alloy have been measured from 77 to 1300°K as discussed by the authors, showing that the shear modulus c' = (c11 − c12)2 to ferromagnetism and to the gamma loop in the Fe-Si phase diagram is identical to that of pure iron at 1 ≤ TTc < 1.03, where the short-range magnetic-order effect is evident.
92 citations
88 citations
TL;DR: In this article, the electronic spin-spin relaxation time, T2, was calculated for Heisenberg ferromagnets in the region immediately above the Curie point, which pertains to zero field, predicts that 1/T2 diverges as χT3/4 where χ T is the isothermal susceptibility.
83 citations
TL;DR: In this paper, a detailed analysis of the magnetization curve mx(Hx) provides an unambiguous determination of the quartic and uniaxial type anisotropy in the x −z plane of YFeO3 (spin= 52).
Abstract: Application of a sufficiently strong magnetic field Hx along the antiferromagnetic easy axis (x) of the isomorphic, distorted perovskites YFeO3 and YCrO3, results in the smooth rotation of the antiferromagnetic vector in the x‐z plane, reaching the z axis at the critical fields Hcr=74±1 kOe and Hcr=40±1 kOe at 4.2°K, for YFeO3 and YCrO3, respectively. A detailed analysis of the magnetization curve mx(Hx) provides an unambiguous determination of the quartic and uniaxial‐type anisotropy in the x‐z plane of YFeO3 (spin= 52). In agreement with theory, quartic anisotropy terms are not found in YCrO3 (spin= 32). Only in the latter case are the uniaxial anisotropy and the reorientation field calculable from the initial susceptibilities. Comparison of mx(Hx) with mz(Hz) for H>Hcr provides a quantitative separation between the antisymmetric exchange (HD) and single‐ion anisotropy (Hxz) contributions to the weak ferromagnetic canting. We find |Hxz/HD| <0.02 for YFeO3 and |Hxz/HD| <0.05 for YCrO3, at 4.2°K.
80 citations
TL;DR: The spin structure and energy of ferromagnetic domain walls in Dy and Tb have been calculated, using an iterative method which takes into account exchange interactions, magnetocrystalline anisotropy, and magnetoelastic anisotropic.
Abstract: The spin structure and energy of ferromagnetic domain walls in Dy and Tb have been calculated, using an iterative method which takes into account exchange interactions, magnetocrystalline anisotropy, and magnetoelastic anisotropy. The domain walls are found to be very thin (less than 20 atom layers) and to have relatively high energy (∼10 erg/cm2), as compared to the ferromagnetic transition metals. An intrinsic coercive force for wall motion is predicted for these very thin walls; it is analogous to the Peierls‐Nabarro force on a dislocation, and is estimated to be of the order of 1 kOe for Dy and 30 Oe for Tb at absolute zero.
TL;DR: In this article, it was shown that a magnetic field of 2 kilogauss in the basal plane of hematite can significantly increase the attenuation and velocities of ultrasonic wave propagation.
Abstract: Domain wall-stress interaction causes pronounced increases in attenuation and decreases in the velocities of ultrasonic (30 MHz) waves in hematite at 298°K relative to the values in a saturating magnetic field. For compressional modes, these effects are about 10 db/cm in attenuation and less than 1% in velocity and may be eliminated by the application of a magnetic field of 2 kilogauss in the basal (c) plane. At zero applied field, it was not possible to propagate shear waves in the single crystal; as the field is varied from 2 to 4 kG, the attenuation decreases by about 30 db/cm, and the velocities increase by as much as 10%. These data are consistent with the fact that hematite exhibits weak ferromagnetism at room temperature, with the spins largely contained in the c plane. The large fields needed to saturate the crystal indicate the presence of a hard component of magnetization. These magnetoelastic interactions can also be eliminated by cooling through the Morin temperature (TM=261°K), below which point the spins are aligned parallel to the trigonal c axis and the weak ferromagnetism vanishes. At low pressures, TM increases by 3.6°K/kb and occurs at 298°K near 30 kb. The results of this study have important consequences for ultrasonic studies of the elastic properties of third-transition metal oxides, for static compression experiments on these materials, and for studies of phase transitions in solids.
TL;DR: In this article, a model is proposed to account for the metallurgical and physical properties of f.c. Fe−Ni alloys, including the Invar anomalies around 34 at.% Ni.
TL;DR: In this article, the average magnetic moment was evaluated to be 0.25 µ B assuming the antiferromagnetic stacking of ferromagnetic (001) sheets, which is the same as in this paper.
Abstract: Antiferromagnetism in hcp Fe-Mn alloys (17.8, 25.9 and 28.6 at %Mn) was investigated by means of Mossbauer effect and neutron diffraction measurements. Neel temperatures and internal magnetic fields at 0°K were determined to be 230°K and 16 kG, respectively, over the composition range of the measured alloys. Consequently, hcp alloys have weaker internal magnetic fields and lower Neel temperatures than the fcc modifications. In the neutron diffractions on powder and sheets with preferred orientation of hcp Fe 0.714 Mn 0.289 , only (001) magnetic reflection was found. The averaged magnetic moment was evaluated to be 0.25 µ B assuming the antiferromagnetic stacking of ferromagnetic (001) sheets. Isomer shifts relative to bcc Fe and quadrupole splittings of hcp alloys are extrapolated to the zero Mn concentration to be -0.20 mm/sec and 0.14 mm/sec, respectively. The results are discussed in connection with magnetism in hcp Fe.
TL;DR: In this paper, a band-structure calculation for the ferromagnetic state of iron is given particularly careful treatment, where the roles of intra-atomic exchange and itinerancy in the origin of iron's ferromagnetism are discussed.
Abstract: A new band-structure calculation is reported for the ferromagnetic state of iron, in which the exchange interaction is given particularly careful treatment. A variational procedure was used with the wave functions expanded in terms of tight-binding functions and orthogonalized plane waves. Hybridization and spin polarization of the wave functions were allowed. Correlation corrections were incorporated. The energy bands are somewhat wider than those previously published; comparison is made with photoemission and optical reflection and x-ray emission data. The calculation leads self-consistently to the observed magnetic moment. The roles of intra-atomic exchange and itinerancy in the origin of iron's ferromagnetism are discussed.
TL;DR: In this paper, the magnetic properties of five intermetallic compounds were investigated at temperatures between 42 and 1200 K with magnetic field strengths up to 30 kOe in the Th-Co and Th-Fe systems.
Abstract: The Th–Co and Th–Fe systems were studied by x‐ray diffraction methods Five intermetallic compounds were observed in each system For each of these compounds the lattice parameters were determined The magnetic properties of the various compounds were investigated at temperatures between 42 and 1200 K with magnetic field strengths up to 30 kOe In the Th–Co system the compounds Th2Co17 and ThCo5 are ferromagnetic; the Curie temperature and the cobalt moment decrease rapidly with Th‐content The compounds Th2Co7, ThCo, and Th7Co3 are paramagnetic In the Th–Fe system the compounds Th2Fe17, ThFe5, Th2Fe7, and ThFe3 are ferromagnetic; with increasing Th content the Curie temperatures and iron moments first rise, then decrease The compound Th7Fe3 is paramagnetic A comparison is made with the magnetic properties of rare‐earth‐iron and ‐cobalt compounds Magnetic data are reported for La3Co, Y3Co, and YCo2 which are paramagnetic Curie temperatures are also given for YCo3 and YCo5
TL;DR: In this paper, the spontaneous volume magnetostriction of Fe 65 (Ni 1- x Mn x ) 35 alloys at temperatures down to 4.2°K was evaluated from their thermal expansion curves.
Abstract: Thermal expansion measurements were made on f.c.c. Fe 65 (Ni 1- x Mn x ) 35 alloys at temperatures down to 4.2°K and the spontaneous volume magnetostriction of these alloys was evaluated from their thermal expansion curves. The results indicate that the spontaneous volume magnetostriction at 0°K is positive and decreases with increasing x in the ferromagnetic alloys ( x <0.3), and is positive and increases with increasing x in the antiferromagnetic alloys (0.3< x ). The spontaneous volume magnetostriction varies with temperature as T 2 in the temperature range below about half of the magnetic transition temperature. If a simple and reasonable density of states curve is assumed, these experimental results can be understood on the basis of the weak itinerant electron ferromagnetism or of the weak itinerant electron antiferromagnetism.
TL;DR: In this article, thin iron films were grown on (110) copper single crystal substrates and examined by reflection electron diffraction and found to be f.c. in parallel orientation with the copper substrate.
Abstract: Thin iron films, ∼ 30 A thick, have been grown on (110) copper single crystal substrates. The structure of the films was examined by reflection electron diffraction and found to be f.c.c. in parallel orientation with the copper substrate. The specimens were examined by electron spin resonance and found to be ferromagnetic.
TL;DR: In this paper, single-phase alloys with the compositions T2MnX and TMnX have been described, where T represents the platinum group or palladium group metal and X is an element of groups III, IV, or V. Their crystal structures are ordered forms of the bcc structure.
Abstract: New single‐phase alloys have been prepared having the compositions T2MnX and TMnX, where T represents the platinum‐group or palladium‐group metal, and X is an element of groups III, IV, or V. Their crystal structures are ordered forms of the bcc structure. Some are apparently ferromagnetic with Curie temperatures of several hundred degrees Kelvin and magnetic moments between 3 and 4 Bohr magnetons per formula unit.
TL;DR: In this paper, the degree of polarization of electrons emitted from the neighborhood of the Fermi level was found to be + 54, + 21, and + 15% for Fe, Co, and Ni, respectively.
Abstract: This experiment shows that photoelectrons from $3d$ ferromagnets exhibit a large spin polarization, which is in contrast to earlier investigations. The degree of polarization of electrons emitted from the neighborhood of the Fermi level was found to be + 54%, + 21%, and + 15% for Fe, Co, and Ni, respectively. The preferential direction of the magnetic moment is parallel to the magnetization, and this provides strong evidence against the applicability of the Stoner-Wohlfarth-Slater band theory for the interpretation of photoemission data. On introducing disorder in the lattice by depositing thin films onto cold substrates, the spin polarization decreases; for Fe and Ni the decrease scales with the number of Bohr magnetons per atom.
TL;DR: By the controlled thermal degradation of ferricinium nitrate, a material composed of iron oxide particles embedded in an inert carbonaceous matrix was obtained as discussed by the authors, which exhibited exchange anisotropy in the form of a shifted hysteresis loop.
Abstract: By the controlled thermal degradation of ferricinium nitrate a material composed of iron oxide particles embedded in an inert carbonaceous matrix was obtained. The iron oxide particles were found to be mostly magnetite, and their average diameter about 35 A. This value was obtained from both x‐ray diffraction line broadening and from static magnetic measurements. The small particle size caused the material to be superparamagnetic down to and below liquid‐nitrogen temperature. At liquid‐helium temperature the material was ferromagnetic and exhibited exchange anisotropy in the form of a shifted hysteresis loop. A coupling energy of 2.28×105 erg/cm3 was calculated from the shifted hysteresis loop. EPR and Mossbauer‐effect spectra showed electron hopping at room temperature within the Fe3O4. In the ferromagnetic state, local disorder around the magnetic ions manifests itself as broadening of the Mossbauer spectra and displacement of the hysteresis loop.
TL;DR: The magnetic properties of ZrZn2 and related alloys and compounds are discussed in this paper, where the results of specific heat, magnetic susceptibility, and nmr measurements are presented to show that the Fermi level of the ZrCu1.1Al 0.9 lies at the top of a sharp narrow d-band peak that is about 0.1 eV in halfwidth and has a maximum value of 2.5.
Abstract: The magnetic properties of ZrZn2 and related alloys and compounds are discussed. In particular, we present a study of the pseudo‐ZrZn2 alloy system ZrCu2−xAlx, where 0.76≤x≤1.5. The results of specific heat, magnetic susceptibility, and nmr measurements are presented to show that the Fermi level of ZrCu1.1Al0.9 lies at the top of a sharp narrow d‐band peak that is about 0.1 eV in half‐width and has a maximum value of 2.7 states (eV‐Zr atom spin)−1. We also show that ZrZn2 has a sharp narrow peak in the d‐band density of states at the Fermi level. This peak has a half‐width of about 0.05 eV and has a maximum value of 5.4 states (eV‐Zr atom spin)−1. The ferromagnetism of ZrZn2 is understandable in terms of this feature of the band structure. The occurrence of a high narrow peak at the Fermi level is the most favorable condition for the existence of itinerant ferromagnetism.
TL;DR: In this article, the magnetic properties of the single crystals of Cr 2-δ Te 3, prepared by the chemical transport method, were investigated, and it was shown that the Bohr magneton numbers per Cr-ion are 2.0 2 and 1.9 6 µ B for Cr 1.96 Te 3 and Cr 0.98 Te 3 respectively, in contradiction to those expected from the magnetic susceptibility.
Abstract: The magnetic transitions of the Cr-Te system has not been explained by a suitable model. Therefore, the magnetic properties of the single crystals of Cr 2-δ Te 3 , prepared by the chemical transport method, were investigated. From the measurement of the magnetic susceptibility above room temperature S =3.0 8 /2 per Cr-ion is obtained, which is coincident with the spin only value of Cr 3+ ion and a ferromagnetic transition is found to be expected. While, from the extrapolated magnetization value to 0 K, the Bohr magneton numbers per Cr-ion are 2.0 2 and 1.9 6 µ B for Cr 1.96 Te 3 and Cr 1.98 Te 3 , respectively, and these values are in contradiction to those expected from the magnetic susceptibility. Qualitative considerations about these anomalous magnetic transition are given.
TL;DR: Ferromagnetic electron spin resonance spectra of Apollo 11 lunar samples, using model for polycrystalline spectra simulation as discussed by the authors, were used for the simulation of the Apollo 11 moon landing.
TL;DR: In this article, the authors studied polycrystalline thin films of MnAlGe formed on various substrates by getter sputtering, and the optimum substrate temperature to obtain films with uniform magnetic properties was 500°C.
Abstract: MnAlGe is a uniaxial ferromagnetic compound with a saturation 4πMs of 3600 G, and Curie temperature of 245°C. We have studied polycrystalline thin films of this compound formed on various substrates by getter sputtering. The optimum substrate temperature to obtain films with uniform magnetic properties was 500°C. Films prepared at this temperature have a substantial component of magnetization normal to the plane of the substrate, and a coercive force of approximately 2000 Oe. Information was written into films approximately 700‐A thick by Curie point writing or with a fine permanent magnet wire, and read with good optical contrast by means of the polar Faraday effect. The relatively low Curie temperature is advantageous in reducing the power required for Curie point writing for magneto‐optic memory or holographic applications.
TL;DR: In this article, experiments in the Van Vleck paramagnets PrPt5 and PrTl3 are described in which end temperatures of 3.5 and 1.5 mK are obtained starting from about 60 mK and 20 kOe.
Abstract: In strongly Van Vleck paramagnetic rare‐earth alloys or compounds, large hyperfine fields can be induced at the rare‐earth nucleus with moderate external fields. These fields are useful to generate low temperatures by the method of nuclear adiabatic demagnetization. Experiments in the Van Vleck paramagnets PrPt5 and PrTl3 are described in which end temperatures of 3.5 and 1.5 mK are obtained starting from about 60 mK and 20 kOe. The possibility of nuclear ferromagnetism in PrTl3 is discussed and compared with observations.
TL;DR: In this article, the electrical resistivity associated with spin scattering near magnetic critical points is calculated in the model where conduction electrons interact with another electron system such as d electrons through the spin exchange interaction using the temperature Green's functions and diagram technique.
Abstract: The electrical resistivity associated with spin scattering near magnetic critical points is calculated in the model where conduction electrons interact with another electron system such as d electrons through the spin exchange interaction using the temperature Green's functions and diagram technique. It is shown that the origin of the resistive anomaly near the ferromagnetic critical point is different from that near other critical points such as the antiferromagnetic transition point. In the ferromagnetic case the resistive anomaly arises from scattering associated with the short-range spin fluctuations and consequently the tem perature derivative of the resistivity dp/ dT should vary like the magnetic specific heat, as was suggested by Fisher and Langer. On the other hand, in other magnetic cases with periodic magnetic structures such as rare earth metals, resistive anomalies originate from critical scattering due to long-range spin fluctuations around the magnetic lattice vector. In such cases dpjdT shows the anomaly proportional to -sign(t) ltl-
TL;DR: In this paper, annealing at 1000 K is performed on the trivalent ligands of C14 ErFeAl and C15 ErFe2 to ErAl2 and the results show that the ligands become nonmagnetic toward the Al-rich phase boundary.
Abstract: Specimens annealed at 1000 K are of C15 type from ErFe2 to Er0.333Fe0.425Al0.242, of C14 type from Er0.333Fe0.412Al0.255 to Er0.333Fe0.237Al0.430, and of C15 type from Er0.333Fe0.222Al0.445 to ErAl2. Magnetic investigations in the paramagnetic and ordered region show evidence for electron transfer to Fe from the trivalent ligands to the extent that Fe becomes nonmagnetic toward the Al‐rich phase boundary of C14 ErFeAl. The materials order ferromagnetically on rare‐earth sites, while Fe aligns antiparallel to the lanthanide. The saturation mechanism, however, is complex. Domain‐wall effects, anisotropy, and the development of disordered magnetic components may be responsible for depressions in the saturation values of certain concentrations, stepwise increases of magnetization with field, and almost linear increases in magnetic moment in higher fields (10–47 kOe).