Showing papers on "Ferrimagnetism published in 1972"
TL;DR: In this article, the development of microwave S - and C -band lithium ferrites with substantially improved properties, comparable to those of the more expensive ferrimagnetic garnets currently in use, were reported.
Abstract: Lithium ferrites are low-cost materials which are attractive for microwave device applications. For a number of years these materials have been prominent in the computer core industry because of excellent temperature performance and the squareness of their hysteresis loops. Previous attempts at exploiting lithium ferrites for microwave applications have met with limited success. Properties which required further improvements were the dielectric and magnetic loss tangents, anisotropy, coercive force, and density. This paper reports primarily the development of microwave S - and C -band lithium ferrites with substantially improved properties, comparable to those of the more expensive ferrimagnetic garnets currently in use. Extensive applications are also expected for higher frequencies up to and including K u band. Because a number of factors can affect the performance of microwave devices, the lithium ferrites reported herein are heavily doped to optimize the numerous properties of interest. The following additives were employed: 1) Ti-to tailor saturation magnetization for various frequencies; 2) Zn-for its beneficial effects on coercive force, magnetic loss, and densification; 3) Mn-to decrease the dielectric loss, improve the remanence, and reduce the stress sensitivity of the remanence; 4) Co-to provide a range of spinwave linewidths ; 5) Ni-for increased remanence ; and 6) Bi (the most important additive)-to increase the densification at low firing temperatures and thereby provide low dielectric loss and low coercive force. The microwave lithium ferrites offer a high degree of latitude for tailoring various parameters for special device requirements. However, the optimization of selected properties is sometimes accomplished at the expense of other properties. Although this investigation was directed mainly toward applications for latching devices, lithium ferrites have been altered for use in a variety of devices such as limiters and circulators. The requirements for ferrite materials in latching phasers are reviewed, the compositional factors which result in useful properties are discussed, and performance in circulators and latching phasers is reported.
200 citations
TL;DR: In this article, it was shown that in these compounds the π-type interactions dominate and the ferrimagnetism is rationalized by showing that π type interactions dominate.
176 citations
TL;DR: In this article, the magnetic properties of synthetic Fe3S4 have been studied using both static magnetization measurements and Mossbauer effect spectrometry and two alternative band schemes are proposed to account for this feature and explain the magnetic moment.
Abstract: The magnetic properties of a number of samples of synthetic Fe3S4 have been studied using both static magnetization measurements and Mossbauer effect spectrometry. The distinction is made between the intrinsic properties of bulk Fe3S4 and observations resulting from superparamagnetic behavior and nonstoichiometry. Mossbauer spectra in applied fields show that the bulk material has a simple Neel ferrimagnetic spin arrangement. The magnetic moment at 4.2 °K is 2.2 ± 0.3 μB per formula unit and the ordering temperature is 606 ± 2 °K. Conductivity measurements indicate semimetallic behavior and two alternative band schemes are proposed to account for this feature and explain the magnetic moment.
104 citations
TL;DR: The magnetism of pure iron and gadolinium films, and of Fex Gdy alloy thin films with 15 to 94 at.% iron prepared by codeposition on a cold (77 °K) substrate were measured at 77 °K and at room temperature.
Abstract: The magnetism of pure iron and gadolinium films, and of Fex Gdy alloy thin films with 15 to 94 at.% iron prepared by codeposition on a cold (77 °K) substrate were measured at 77 °K and at room temperature. All the alloys had an amorphous structure that was stable to room temperature. The amorphous alloys were found to be ferrimagnetic. The magnitude of the magnetization in rare‐earth transition‐metal alloys does not appear to be structure sensitive since the magnetization of the amorphous alloys follows a linear concentration dependence calculated from an antiparallel coupling of the magnetic moments of crystalline iron and gadolinium.
56 citations
TL;DR: In this paper, the magnetic properties of cobalt-doped γ-Fe2O3 were investigated using the Mossbauer technique and x-ray diffraction, and an increase in lattice parameter with cobalt concentration was observed.
Abstract: The magnetic properties of cobalt‐doped γ‐Fe2O3 were investigated, and the crystallographic properties were examined using the Mossbauer technique and x‐ray diffraction. An increase in lattice parameter with cobalt concentration was observed. A large increase in coercive force, especially pronounced at low temperatures, was proportional to cobalt concentration, and may be accounted for by single‐ion anisotropy. The magnetic moment changed very little. Measurements on partially aligned particles indicated that the particles were single domain. The Mossbauer spectra provided no evidence for the presence of Fe2+ or Fe4+ ions. Also, at helium temperature the anisotropy was such that the samples were not saturated at 50 kOe. The experimental data are consistent with the hypothesis that the cobalt ions replace iron on B sites and also fill B‐site vacancies. Conversion to α‐Fe2O3 on heating was never attained completely, and it is proposed that cobalt ferrite is present in the heated samples.
41 citations
TL;DR: Transparent CoCr2S4 has been vacuum hot pressed at 850°C and 50,000 psi and has a Curie temperature of 221°K as discussed by the authors, with a refractive index of 3.56 and residual absorption coefficient of about 7 cm−1.
18 citations
TL;DR: In this article, the hardness of the alloy Ag5MnAl has been investigated after heat treatment at various temperatures in the range 250°c-895°c and the coercivities ranging from 3800 oe to 7800 oe were obtained.
Abstract: The hard magnetic properties of the alloy Ag5MnAl have been investigated after heat treatment at various temperatures in the range 250°c–895°c. A new ‘ferromagnetic’ (probably ferrimagnetic) phase has been observed which is produced by rapid cooling to room temperature from the range 880°c–895°c. Although the remanent magnetization of the new phase is relatively low, ∼0.66 e.m.u./g, the coercivity is ∼5000 oe. Heat treatment at other temperatures resulted in a very wide range of properties, e.g. coercivities ranging from 3800 oe to 7800 oe were obtained while the remanent magnetization varied from 0.65 to 5.0 e.m.u./g. The maximum magnetic hardness was obtained by heat treatment at 280°c for 130 hr. One of the most striking properties of all the ferromagnetic specimens is that they can be magnetized with equal facility in any direction regardless of the specimen geometry. The effects of temperature and of the application of a field of 164 koe have also been investigated. The coercivities H c and ...
17 citations
TL;DR: In this article, a comparison 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 was made.
16 citations
TL;DR: In this article, the Weberit structure with orthorhombic symmetry (Imm2−C2V20) was found to be ferrimagnetic below a magnetic transition at Tc=88K.
10 citations
TL;DR: In this paper, the spectral sensitivity of the photoconductivity exhibits maxima near the absorption edges and a pointed minimum is observed at the magnetic ordering temperature, indicating that at 4.2 K the spontaneous magnetic order is not ferromagnetic or metamagnetic.
8 citations
TL;DR: In this paper, the crystal and magnetic structure of the Mn3Pd5 phase, occurring after long annealing below 500°C, was determined by neutron diffraction method, and the crystal structure is of orthorhombic Ga3Pt5 type with the space group Cmmm.
TL;DR: The strong field magnetization as a function of temperature has been determined for over 50 marine and fresh water ferromanganese nodules with the aim of defining the forms in which iron is present.
Abstract: The strong field magnetization as a function of temperature has been determined for over 50 marine and fresh water ferromanganese nodules with the aim of defining the forms in which iron is present. Both marine and fresh water nodules have 0.1–0.5 emu/g at 20°C in a 7.2-koe field, corresponding to upper limits of 0.1–0.6% of magnetite or maghemite in particles larger than superparamagnetic. Hysteresis loops at 20°C show the presence of small and varying amounts of ferrimagnetic components in the predominately paramagnetic nodules. When the deep sea nodules are heated to 700°C, the dominant changes are characteristic either of paramagnetic phases alone or of paramagnetic phases plus a material with a 580°C Curie point. When they are cooled from 700° back to 20°C, the deep sea nodules show a large increase in magnetization, the Curie point being 100°–200°C. This behavior is due to the partial conversion of the initial Fe/Mn oxides and oxyhydroxides to jacobsites (Fe, Mn)3 O4. Six of the seven fresh water nodules behaved quite differently on heating in air, showing a large bump in the heating curve and 580°C Curie points on cooling. This latter type of behavior cannot now be adequately explained.
TL;DR: In this paper, the stability of rare earth-iron garnets is investigated under high temperature-pressure conditions by means of a girdle type and a piston-cylinder type high pressure apparatus.
Abstract: The stability of some rare earth-iron garnets is investigated under high temperature-pressure conditions by means of a girdle type and a piston-cylinder type high pressure apparatus High pressure transformation of R3Fe5O12 (R=Y3+, Gd3+ and Tb3+) from the garnet structure to the distorted perovskite structure is found to occur These results make it possible to draw the boundaries of these transformations in equilibrium as P(Kb)=0038T(^°C)-261(±28) for Y3Fe5O12, P(Kb)=0035T(^°C)-194(±30) for Gd3Fe5O12 and P(Kb)=0048T(^°C)-372(±41) for Tb3Fe5O12 Ferrimagnetism is observed in these high pressure phases and this property can be explained by the number of superexchange coupling between iron atoms on the octahedral and dodecahedral sites
TL;DR: In this paper, the magnetic phases of pyrrhotites were studied by the method of powder patterns, the chemism of the magnetic phase by means of the electron microprobe method, and the crystal phases by etching the polished sections.
Abstract: The magnetic phases of natural pyrrhotites were studied by the method of powder patterns, the chemism of the magnetic phases by means of the electron microprobe method, and the crystal phases by etching the polished sections. The method of powder patterns distinguished the ferrimagnetic and antiferromagnetic phases in the transition-type pyrrhotites. The method of absorbed electrons lead to the discovery that both phases have a different chemical composition and that the ferrimagnetic phase has a lower denisty and an average atomic number. The linear and point-by-point analysis disclosed that the ferrimagnetic phase has a lower weight content of Fe and a higher weight content of S than the antiferromagnetic phase. Both the magnetic phases displayed different properties when etched, and therefore they not only have a different chemical composition, but also a different crystal structure. The necessity of studying the image of the absorbed electrons and the image of the etched surface of the polycrystalline samples of pyrrhotites of the transition type separately on individual grains was pointed out.
Patent•
12 Apr 1972
TL;DR: A ferrimagnetic garnet material containing either gadolinium or indium has a formula corresponding to Y 3-2x Ca 2x Fe 5-x V x O 12 where V = rare earth metal ion as discussed by the authors.
Abstract: 1,270,663. Magnetic garnets. MARCONI CO. Ltd. 12 June, 1969 [15 Aug., 1968], No. 39016/68. Heading H1H. A ferrimagnetic garnet material containing either gadolinium or indium has a formula corresponding to Y 3-2x Ca 2x Fe 5-x V x O 12 or Bi 3-2x Ca 2x Fe 5-x V x O 12 (0 3+ ) 3-2x-a-b Gd a R b Ca 2x Fe 5-x-y-z V x (M B 3+ )y x In z O 12 where R = rare earth metal ion provided that if: the materials are used in microwave devices operating at cryogenic temperatures.
TL;DR: In this article, the authors observed from microwave measurements made on crystal spheres at temperatures between 80°K and 300°K a large reduction both in the resonance field and in the ferrimagnetic anisotropy energy.
Abstract: The introduction of small amounts of iodine in ferrimagnetic single crystals causes an extensive modification of the magnetic properties. We observe from microwave measurements made on crystal spheres at temperatures between 80°K and 300°K a large reduction both in the resonance field and in the ferrimagnetic anisotropy energy. Thus for NiFe2O4 and for YIG, −K1/Ms at 80°K decreases from 340 to 12 Oe and from 45 to 15 Oe, respectively. The large reduction of anisotropy can be explained on the basis of a single ion anisotropy model. The new properties (very weak magnetic anisotropy and low resonance field) are very favourable for microwave ferrite devices.
TL;DR: In this paper, the authors studied the abrupt changes of the magnetization which occur in the H −T region where the net Yb and Fe moments are not collinear, and found that these jumps in the magnetic moment are at variance with the temperatureindependent magnetization in the canted phase predicted by models of isotropic ferrimagnets, and arise from the large aniso-tropy in the Yb g−factor and Yb •Fe exchange.
Abstract: Ytterbium iron garnet (YbIG) is a cubic ferrimagnet having a compensation point Tcomp ≃ 6°K. We have undertaken precision magnetization measurements along [111] and [100] of a YbIG crystal in the temperature range 2°K < T < 30°K, with applied fields H up to 23 kG, in order to study the abrupt changes of the magnetization which occur in the H‐T region where the net Yb and Fe moments are not collinear. These jumps in the magnetic moment are at variance with the temperature‐independent magnetization in the canted phase predicted by models of isotropic ferrimagnets, and arise from the large aniso‐tropy in the Yb g‐factor and Yb‐Fe exchange. A recently derived phase diagram for anisotropic YbIG predicts first order phase transitions, corresponding to abrupt sub‐lattice reorientations while in the canted state, which accord well with the observed moment variations.
TL;DR: By examining the Heisenberg Hamiltonian for a spinel ferrimagnet containing two types of magnetic ions in both of its sublattices, it was seen that the Weiss molecular field coefficients chosen by Stephenson to explain the compositional dependence of the Curie temperatures are incorrect for some ferrimagnetic compounds.