Showing papers on "Ferrimagnetism published in 1985"
TL;DR: In this paper, the ternary tetragonal structure R2Fe14B has been used for growing permanent magnet materials, where R is one of the rare earth elements.
Abstract: A whole new class of high‐performance permanent magnet materials is based on the ternary tetragonal structure R2Fe14B, where R is one of the rare‐earth elements. We have successfully grown single crystals of this structure with R=Y, Nd, and Tb. Y is a nonmagnetic rare‐earth substitute, while Nd and Tb couple ferro‐ and ferrimagnetically, respectively, relative to the iron moment. All three of the compounds have [001] easy axes at room temperature, although the Nd compound exhibits a spin reorientation away from the [001] below about 150 K. Nd2Fe14B has a saturation induction at room temperature of 16.2 kG, which places an upper limit of approximately 65.6 MGOe on the energy product obtainable by magnets based on that material. While Tb2Fe14B exhibits a smaller magnetization because of ferrimagnetic coupling of the rare earths and the iron, it also has an extremely large magnetic anisotropy which is nearly temperature independent between 4.2 and 300 K.
116 citations
TL;DR: In this article, Mossbauer et al. showed that on increasing dilution t, the collinear ferrimagnetic phase breaks down before reaching the percolation limit as a result of the presence of competing exchange interactions.
Abstract: Mossbauer and DC susceptibility studies are reported on the mixed spinel Mg1+tFe2-2tTitO4 at various temperatures and in an external magnetic field. Results are obtained indicating that on increasing dilution t, the collinear ferrimagnetic phase breaks down before reaching the ferrimagnetic percolation limit as a result of the presence of competing exchange interactions. In this dilution region there is a second transition, at Tf, to a spin-glass-like (SGL) state, well below the ferrimagnetic ordering temperature TN. The lower limit of re-entrant ferrimagnetism is determined by observing the spontaneous spin canting which occurs in the presence of the external magnetic field on going into the SGL state. At higher dilution a transition to a pure spin-glass state occurs. The results are discussed in terms of the model proposed by Villain (1979) based on the competition between dilution and frustration in the spinel lattice. The re-entrant ferrimagnetism found in this insulating system with near-neighbour interactions is similar to the re-entrant ferromagnetism found in some metallic alloys, and the authors propose a canting order parameter for the low-temperature state as in the metallic case.
81 citations
TL;DR: Rietveld analyses of neutron powder diffraction data on Pr2Fe14B and Dy2Fe 14B are reported in this paper, showing that all magnetic moments in each compound are collinear with the c axis.
Abstract: Rietveld analyses of neutron powder diffraction data on Pr2Fe14B and Dy2Fe14B are reported. Both phases form the Nd2Fe14B tetragonal crystal structure (P42/mnm). At 77 and 293 K our analyses indicate that all magnetic moments in each compound are collinear with the c axis. The rare‐earth moments in Pr2Fe14B are parallel to the Fe moments (ferromagnetic) and are antiparallel in Dy2Fe14B (ferrimagnetic).
74 citations
TL;DR: In this article, self-consistent spin-polarized energy band calculations for the two Laves phases show that a ferrimagnetic state is more stable than the paramagnetic one, but at a slightly larger volume.
Abstract: Self-consistent spin-polarized energy band calculations for the two Laves phases show that a ferrimagnetic state is more stable than the paramagnetic one, but at a slightly larger volume. For ZrFe2 the interaction between the low lying Zr and the exchange-split Fe states leads to covalent magnetism which is discussed using site- and spin-projected densities of states. The different interaction between Fe and Zr for majority and minority spin is responsible for the ferrimagnetic ordering which is analyzed in terms of spin densities. The resulting magnetic moment of about 1.9 μB for Fe is spatially localized near the Fe site, while around Zr a small but extended negative spin density causes (through the large volume) a moment of about -0.56 μB a prediction which should be verified experimentally. YFe2 is qualitatively similar, but contrasts YCo2 which is near a possible metamagnetic transition.
56 citations
01 Jan 1985
TL;DR: In this paper, the application of magnetic domain theory to the particle-size-dependent properties of magnetite and the various kinds of intrinsic remanent magnetization contributed to by magnetite is discussed.
Abstract: Magnetite (Fe3O4, ferrous–ferric oxide) is ubiquitous as the source of the magnetism of most biological magnetic systems. Although a cation-deficient form of it, maghemite (γ- Fe2O3), and impurity-substituted magnetite (titanomagnetite) have on occasion been identified in biomagnetic systems, magnetite continues to be the primary magnetic source in biology. It is of interest, therefore, to inquire into the origin of its magnetism, or more properly, the ferrimagnetism of magnetite. In this chapter we deal with the ferrimagnetism of magnetite single crystals first. We then occupy ourselves with the application of magnetic domain theory to the particle-size-dependent properties of magnetite and the various kinds of intrinsic remanent magnetization contributed to by magnetite. The only type of natural remanent magnetization which we have not discussed here is depositional remanent magnetization (DRM), as it is still rare to find examples where biogenic magnetite has been convincingly shown to be responsible for the DRM in a sediment. Future research may prove otherwise. Finally, we deal with some practical magnetic techniques for determining the magnetic domain state, hence the effective particle size, of magnetite.
53 citations
TL;DR: In this article, the singularity in the magnetization curve is transformed in the case of a polycrystalline specimen, and it is demonstrated that the singular point detection theory can be extended to first-order magnetization processes (FOMP), thus allowing extremely clear and accurate measurements of critical fields.
Abstract: Ferromagnetic crystals can show discontinuous jumps in the magnetization curve for certain combinations of the anisotropy constants. These are called first‐order magnetization processes (FOMP) and have been recently observed in a large variety of compounds. We analyze the problem of how this singularity in the magnetization curve is transformed in the case of a polycrystalline specimen. The problem is the same as that of the singular point detection theory (SPD) that was originally concerned with the singularities of the anisotropy fields and with the way of enhancing them. SPD is now a widely used method for measuring anisotropy fields. In the present work it is demonstrated that SPD can be extended to FOMP, thus allowing extremely clear and accurate measurements of critical fields using polycrystalline specimens. This provides in principle a powerful method for deep investigations in the anisotropy properties of ferromagnetic and ferrimagnetic materials. In Sec. II we examine how the critical parameters...
53 citations
TL;DR: In this article, the authors measured the heat capacity of three manganese minerals, namely, pyrolusite, hausmanite, and bixbyite, using a fully automatic adiabatically-shielded calorimeter.
50 citations
TL;DR: In this paper, it was shown that amorphous alloys of non S-state rare earth elements with Fe are not ferrimagnetic as inferred from magnetization data, but rather exhibit a spin-glass type of order.
Abstract: Recent neutron small angle scattering studies have shown that amorphous alloys of non S-state rare earth elements with Fe are not ferrimagnetic as inferred from magnetization data, but rather exhibit a spin-glass type of order. The data show no divergence in the spin correlation length below T c , and the gradual evolution of the scattering lineshape from Lorentzian to a Lorentzian plus Lorentzian squared form appropriate for a system in which random fields destroy the long range order. SANS data taken in applied fields indicate the formation of an infinite cluster in low fields which is responsible for the ferrimagnetic magnetization response and which co-exists with increasingly smaller residual clusters.
43 citations
TL;DR: In this article, the exact solutions of the so-called ferrimagnetic Ising chain made up of two sublattices (S0,S1) are derived from a transfer matrix method.
Abstract: The exact solutions of the so‐called ferrimagnetic Ising chain made up of two sublattices (S0,S1) are derived from a transfer matrix method. The short‐range ferrimagnetic order occurs when considering different spins and/or different Lande factors on both sublattices. Most of the physical features of interest are shown to be involved in the S0=S1=1 system including an alternation of Lande factors (g0,g1) and local anisotropies (K0,K1). Thus, in the limit K0→∞ stabilizing a Kramers doublet, Sz=±1, on even sites, the system behaves like the ferrimagnetic chain (S0=1/2, S1=1). The susceptibility and magnetization curves are discussed in various situations as a function of the significant parameters.
29 citations
TL;DR: The high field magnetization of RMn 2, where R stands for a rare earth element, has been measured at 4.2 K by using pulsed magnetic fields up to about 300 kOe as discussed by the authors.
Abstract: The high field magnetization of RMn 2 , where R stands for a rare-earth element, has been measured at 4.2 K by using pulsed magnetic fields up to about 300 kOe.The magnetizations of YMn 2 , PrMn 2 , NdMn 2 and SmMn 2 increase almost linearly with increasing magnetic field. The magnetization curves of GdMn 2 , TbMn 2 , DyMn 2 , HoMn 2 and BrMn 2 show a trend of saturation at high fields. The saturation magnetic moments per formula unit were estimated as 6.2 µ B , 9.5 µ B , 10.0 µ B , 10.3 µ B , 10.1 µ B , and 8.9 µ B for GdMn 2 , TbMn 2 , DyMn 2 , HoMn 2 (C15), HoMn 2 (C14) and ErMn 2 , respectively. These values are in agreement with the R 3+ moments except for GdMn 2 . The analysis on GdMn 2 excludes particularly a simple ferrimagnetic coupling between Gd and Mn moments.
28 citations
TL;DR: In this article, the lattice parameter shows a minimum at x=0.5, indicating a redistribution of the cations in the A and B sites on introduction of Zn2+.
Abstract: The AC susceptibility and the low-field magnetisation measurements on the disordered spinel system ZnxCo1-xFeCrO4 (x=0.0, 0.2, 0.4, 0.5, 0.8) are reported. The X-ray analysis shows that the lattice parameter shows a minimum at x=0.5, indicating a redistribution of the cations in the A and B sites on introduction of Zn2+. The low-field AC susceptibility and DC magnesidation indicate two transitions for x=0.0 and 0.2 while only one for x>or=0.4. The high-temperature peak in chi corresponds to a ferrimagnetic transition at TN. The magnetic phase below the lower-temperature peak at Tf could be considered as that of clusters of spins randomly frozen. This state is characterised by strong irreversibility in low DC fields, rapid decay of remanence on increasing the temperature and saturation in rather low applied magnetic fields. For Tf >Tf. For Tf
TL;DR: In this article, the limitations imposed on powder neutron diffraction methods by particle-size effects are discussed, and the limitations of particle size effects on powder-neutron diffraction are discussed.
TL;DR: In this article, the results of low-field magnetisation measurements on a representative system show for the first time that the system undergoes a ferrimagnetic transition at TN and then, on cooling, enters into a cluster spin-glass state below Tf with the magnetisation of different clusters randomly frozen.
Abstract: Disordered spinel ferrites exhibit relaxation behaviour in their Mossbauer spectra. The results of the low-field magnetisation measurements on a representative system show for the first time that the system undergoes a ferrimagnetic transition at TN and then, on cooling, enters into a cluster spin-glass state below Tf with the magnetisation of different clusters randomly frozen. The observed relaxation features in the Mossbauer spectra could be related to the instability in the ferrimagnetic state at higher temperatures.
TL;DR: In this article, the results of a.c. susceptibility, d.c., magnetization and Mossbauer measurements on the insulating spinel system Ga 0.8 Fe 0.2 NiCrO 4 are reported.
TL;DR: The lowest transition field in the series of the easy-plane R2T17 compounds (where R=rare-earth metal and T=Fe, Co) occurs for Ho2Co17 and amounts to 21 T as discussed by the authors.
Abstract: The basal-plane anisotropy in a hexagonal easy-plane ferrimagnetic system yields discontinuities in the magnetisation curve for external fields applied in the easy plane. At the discontinuities first-order moment reorientation (FOMR) transitions occur. The lowest transition field depends strongly on the difference between the values of the sublattice magnetisations and is very sensitive to the intersublattice coupling. The transition field provides a direct method for evaluating the exchange coupling between the 3d and 4f spins. The lowest transition field in the series of the easy-plane R2T17 compounds (where R=rare-earth metal and T=Fe, Co) occurs for Ho2Co17 and amounts to 21 T.
TL;DR: In this article, a correlation between lattice parameters and magnetic character is pointed out for 7':'8 isomorphs of transition element selenides, showing that the magnetic states up to at least x=0.3 are those attained by a simple replacement of magnetic moments of Fe ions by those of Co ions.
Abstract: (Fe1−xCox)7Se8 samples have NiAs‐type structures with or without ordered arrangements (3c or 4c) of cation vacancies. With increasing x, the lattice parameter a remains unchanged but c exhibits a fairly large reduction (∼10% by variation of x from 0 to 1). The Curie temperature decreases with increasing x and the ferrimagnetism disappears at x≊0.6. The effective magnetic moments (∼5.5 μB for x≤0.3) evaluated from the high‐temperature portion (range of vacancy disorder) of the 1/χ versus temperature curves are close to the value expected on the ionic model. Results show that the magnetic states up to at least x=0.3 are those attained by a simple replacement of magnetic moments of Fe ions by those of Co ions. Samples with x>0.6 are weakly magnetic. Nearly temperature‐independent ac susceptibility at x≊0.7 indicates the absence of localized moments. In this connection, a correlation between lattice parameters and magnetic character is pointed out for 7 : 8 isomorphs of transition element selenides. The easy‐...
TL;DR: In this article, the disordered spinel system, Zn 0.5 Co 0.4 FeCrO 4, was investigated using low field magnetization and ac susceptibility measurements, and it appears that this system orders into a cluster spin glass state with the magnetic moments of the ferrimagnetic clusters randomly frozen.
TL;DR: In this paper, the authors measured magnetic properties and electrical conductivity of polycrystalline Lu 2 Fe 3 O 7 from 4.2 K to 650 K and compared with those of LuFe 2 O 4.
Abstract: Magnetic properties and electrical conductivity were measured on polycrystalline Lu 2 Fe 3 O 7 from 4.2 K to 650 K and were compared with those of LuFe 2 O 4 . The electrical conductivity, the magnetic susceptibility per Fe at low temperatures and the induced moment per formula unit are nearly the same for both materials. It is concluded that Lu 2 Fe 3 O 7 is constructed by an alternate stacking of Lu 3+ Fe 2 2.5+ O 4 and Lu 3+ Fe 3+ O 3 and that the magnetic moment is induced by the field cooling mainly in the former part. The origin of the moment induction (parasitic ferrimagnetism) is discussed briefly.
TL;DR: For the mixed crystal system Rb 2 Mn x Cr 1− x Cl 4, the authors have calculated the magnetic phase diagram at low temperatures by means of an average model and the results are in agreement with the available experimental data.
TL;DR: In this article, the authors investigated the electrical conductivity and thermoelectric power of polycrystalline nickel-zinc ferrites of different compositions as a function of composition and temperature.
Abstract: Electrical conductivity (σ) and thermoelectric power (Q) of polycrystalline nickel-zinc ferrites of different compositions was investigated as a function of composition and temperature. The electrical conductivity in these ferrites is explained on the basis of the hopping mechanism. Plots of log (σT) versus 103/T are almost linear and show a transition near the curie temperature. The activation energy in the ferrimagnetic region is in general less than that in the paramagnetic region. The carrier concentration and mobility of charge carriers has been discussed as a function of composition and temperature.
TL;DR: In this paper, conditions for the coexistence of ferro- and antiferromagnetism are obtained in the itinerant electron model by taking into account the effect of spin fluctuations.
TL;DR: In this article, the perovskite-like compounds Ca(Cu1−xMnx)3Mn4O12 (0.09 ≦ x ≦ 1) within the temperature range 4.2 to 400 K were determined.
Abstract: Neutron diffraction and magnetic methods are used to investigate the perovskite-like compounds Ca(Cu1−xMnx)3Mn4O12 (0.09 ≦ x ≦ 1) within the temperature range 4.2 to 400 K. Magnetic structure and temperature dependence of magnetization are determined. It is shown that with substituting the Cu2+ ions by the Mn3+ ones the ferrimagnetic collinear structure transforms into a non-collinear ferromagnetic one. For x > 0.69 a short-range order transition occurs. According to the data of paramagnetic susceptibility the CaMn3Mn4012 compound is antiferromagnetic. A model for exchange interactions is proposed.
[Russian Text Ignored].
TL;DR: In this article, an analysis of previous magnetic susceptibility, specific heat and magnetization data as well as of new magnetization results reported on Mn3.2Ga0.8N is performed.
TL;DR: In this paper, the authors investigated the magnetic properties of Dy(Fe 1− x Al x ) 3 pseudobinary compounds and found that they are ferrimagnetic among which only DyFe 2 exhibits the compensation point.
TL;DR: In this paper, a new intermediate ferrimagnetic phase has been found at the metamagnetic transition from the antiferromagnetic to the paramagnetic state below 1.27 K. Although this new phase extends only over a field range of about 1 mT, it is clearly seen in specific heat experiments since for crystals with finite demagnetising factor it produces additional mixed phases at the first order phase boundaries.
TL;DR: In this article, the preparation of a thick-film ferrimagnetic paste using lithium ferrite powders and its physical, electrical, and magnetic properties are described, and a resonance technique for the measurement of the dielectric constant, saturation magnetization, loss tangents, and resonance linewidth of the ferrite films at microwave frequencies is presented.
Abstract: The preparation of a thick-film ferrimagnetic paste using lithium ferrite powders and its physical, electrical, and magnetic properties are described. A resonance technique for the measurement of the dielectric constant, saturation magnetization, loss tangents, and resonance linewidth of the ferrite films at microwave frequencies is presented. Applicability of the ferrite pastes developed for the fabrication of nonreciprocal microwave components such as isolators and circulators is described.
TL;DR: In this paper, the phenomenological theory broadly applicable to magnetic transitions in ferrimagnetic garnets is discussed briefly and the experimental techniques, particularly nuclear magnetic resonance and Mossbauer effect spectroscopy, are reviewed.
Patent•
03 Jun 1985TL;DR: In this paper, a signal converter consisting of a filter formed of a first ferromagnetic resonator which supplied with an input signal that is to be converted and produces a filtered signal having a first frequency, a local oscillator formed of an active element and a second ferromantic resonator connected to the active element, produces an oscillating signal with a second frequency.
Abstract: A signal converter comprises a filter formed of a first ferromagnetic resonator which supplied with an input signal that is to be converted and produces a filtered signal having a first frequency, a local oscillator formed of an active element and a second ferromagnetic resonator connected to the active element, produces an oscillating signal having a second frequency, a mixer receives and mixes the filtered signal and oscillating signal and produces a converted signal, the first ferromagnetic resonator is formed of a first ferrimagnetic crystal, a microstrip line magnetically coupled to the ferrimagnetic crystal and a first D.C. bias magnetic field means which applies a first D.C. bias magnetic field to the first ferrimagnetic crystal, the second ferromagnetic resonator is formed of a second ferrimagnetic crystal, a second microstrip line is magnetically coupled to the second ferrimagnetic crystal, and a second D.C. bias magnetic field means which applies a second D.C. bias magnetic field to the second ferrimagnetic crystal. The first and second ferrimagnetic crystals are composed of ferrimagnetic thin films such as YIG film formed by a thin film forming technique, such as liquid phase epitaxial growth.
TL;DR: In this article, the electrical conductivity and Seebeck coefficient for nickel ferrite with 5% silica was studied as a function of temperature and the lattice constant and the existence of a single phase were established from X-ray studies.
Abstract: The electrical conductivity and Seebeck coefficient for nickel ferrite and nickel ferrite with 5% silica has been studied as a function of temperature. The lattice constant and the existence of a single phase are established from X-ray studies. Both the ferrites exhibit a transition near the Curie temperature with a change in slope of the conductivity (log σT) versus temperature (103/T) curves. It is found that the activation energy in the paramagnetic region is higher than that in the ferrimagnetic region for both the ferrites.