Showing papers on "Single domain published in 1983"
TL;DR: In this paper, a low-temperature approximation for the reduction in the magnetic hyperfine splitting of the Mossbauer spectrum of a microcrystal was derived for arbitrary magnetic energy, and explicit expressions for particles with special types of magnetic anisotropy and for particles exposed to external magnetic fields.
296 citations
TL;DR: In this article, it was shown that nucleation can explain several important aspects of PSD behavior, such as the formation of fully developed domain walls by intervening energy barriers, and the creation and expansion of walls into the particle volume.
Abstract: The stable carriers of the paleomagnetic record in rocks are commonly fine pseudo-single-domain (PSD) particles between about 1 and 20 μm in diameter. However, the underlying mechanism which determines PSD behavior has previously remained in debate. To study this problem, magnetic domain patterns have been observed with the Bitter method on particles of natural pyrrhotite and intermediate titanomagnetite in various magnetization states, including natural remanent magnetization (NRM), after alternating field demagnetization of the NRM and during high-field hysteresis. From these observations it is evident that two primary mechanisms govern high-field hysteresis behavior: (1) ‘bulk’ pinning of fully developed domain walls by intervening energy barriers, and (2) nucleation, the creation and expansion of walls into the particle volume to produce a fully developed domain structure. These observations demonstrate that nucleation can explain several important aspects of PSD behavior. Typically, multidomain particles are entirely governed by bulk wall pinning, since they readily develop walls whose dimensions are comparable to the particle diameter prior to or upon removal of a strong field. For these grains the average domain wall spacing is relatively insensitive to the particular magnetization state, being approximately proportional to r (r being the grain diameter), in accordance with equilibrium calculations. In contrast, particles that are at least partially controlled by nucleation fail to develop a discernable domain wall structure at saturation remanence. However, these same grains can easily accommodate walls in other magnetization states. It is found that nucleation can involve two physically distinct but sometimes experimentally inseparable processes: (1) initial creation of walls at surface imperfections, and (2) unpinning of minute wall fragments from strong potential energy ‘traps’ near the grain surface. When either process fails, a grain remains locked in a metastable, single-domain-like state at saturation remanence and requires application of a reverse field Hn, called the nucleation field, before walls appear. In pyrrhotite, the probability for nucleation failure rises with decreasing grain size and has been determined through observation to be given by f(w = 0) = 1.2 exp (−0.46 r)r being in micrometers). Such single-domain-like particles can thus contribute substantially to the saturation remanence in the PSD range. The nucleation field determined experimentally for pyrrhotite is given by Hn ≃ 1200/ r Oe. In many fine pyrrhotites, Hn is sufficiently strong to reverse completely the magnetization through a single Barkhausen jump of the nucleated wall. These observations thereby demonstrate that nucleation becomes increasingly more dominant as the particles become smaller, a manifestation of the random distribution of active nucleation sites. Nucleation may therefore account for much of the magnitude and grain size dependence of hysteresis parameters in the PSD range as well as resulting in a gradual transition between multidomain and PSD behavior. Fine particles completely controlled by nucleation during hysteresis behave in a strikingly parallel manner to classical single domains and are therefore quite appropriately described as being pseudo-single-domain.
128 citations
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01 Jan 1983
TL;DR: The magnetic susceptibility of diamagnetic materials has been shown to be at most 10−3 to 10−5 SI as discussed by the authors, where SI is the number of magnetic moments acquired per unit field applied.
Abstract: A magnetic field is produced by the movement of an electrical charge. So, at the lowest level, the movement of an electron results in the creation of a magnetic field. Electrons will normally spin about their axes and also orbit their nucleus and therefore have two types of motion that can produce magnetic fields. All substances can thus be regarded as being magnetic at an atomic level and can be classified into two types. In diamagnetic substances the electron shells are full and the precession of electron orbits when placed in a magnetic field results in the creation of a magnetic field in the opposite direction to the applied field. The magnetization acquired per unit field applied, the magnetic susceptibility, is small, less than 10−5 SI. In substances in which the electron shells are incomplete, paramagnetic materials, each atom has a magnetic moment due to the uncompensated electron spins. When placed in a magnetic field, the electron orbits precess but the magnetic moment is aligned in the same direction as the applied field and is generally stronger than that of diamagnetic substances, having susceptibilities of the order of 10−3 to 10−5 SI.
102 citations
TL;DR: In this article, normalized AF demagnetization curves of anhysteretic remanences (ARM's) produced by 1-, 10-and 40-Oe steady fields and of saturation isothermal remanence (IRM s ) in a suite of dispersed, unannealed magnetite powders with median sizes of 2, 4, 6, 10 and 14 μm (pseudo-single-domain or PSD size range) and 100μm (multidomain or MD size).
81 citations
TL;DR: In this article, the magnetic anisotropy constants for an aligned MnAlC magnet were measured from magnetization curves with the magnetic field parallel and perpendicular to the alignment axis.
Abstract: The magnetic anisotropy constants K1 and K2 have been measured for an aligned MnAlC magnet. The information is extracted from magnetization curves with the magnetic field parallel and perpendicular to the alignment axis. The anisotropy field HA =2(K1+2K2)/IS (IS is the saturation magnetization) was determined from a break point in a plot of the perpendicular magnetization against the inverse square of the field. K1 and K2 were then found from modified Sucksmith–Thomson plots. The data is used to calculate the 180° wall energies and widths and an estimate of the temperature coefficient of coercive field variation is made and compared with experiment.
44 citations
TL;DR: The magnetic properties of amorphous Fe92Zr8 and Fe90Zr10 alloys have been studied by 57Fe Mossbauer and magnetization measurements as discussed by the authors.
42 citations
TL;DR: In this article, the magnetic properties observed in porous glasses impregnated with metal carbonyls after exposure to light were discussed, and both superparamagnetic and single domain ferrimagnetic particles were found to be present, with the single domain particles having an exceedingly high coercive force.
Abstract: This article discusses the magnetic properties observed in porous glasses impregnated with metal carbonyls after exposure to light. In the photolyzed and consolidated glasses both superparamagnetic and single domain ferrimagnetic particles were found to be present, with the single domain particles having an exceedingly high coercive force. The concentration ratio between superparamagnetic and single domain particles depends strongly on temperature. An analysis of the observed phenomena is given.
39 citations
TL;DR: In this article, the angular variations of the magnetisation vector at a series of points across the strip have been calculated and the total energy of the model may be predicted for any combination of conductor angle, anisotropy skew and applied fields.
Abstract: Magnetoresistive sensors are made by photo-etching narrow linear folded tracks in vacuum-deposited permalloy film with uniaxial anisotropy. A large demagnetising field appears across each narrow strip in the resistive pattern: this and the presence of exchange energy, bias fields and the effects of anisotropy, combine to make the choice of optimum anisotropy and current flow directions complex. In the work described here the angular variations of the magnetisation vector at a series of points across the strip have been calculated. The inclusion of an exchange energy term allows the total energy to be determined and the behaviour of the model may be predicted for any combination of conductor angle, anisotropy skew and applied fields. Comparisons made with experimental values show close similarity of form but some quantitative discrepency. A simpler model, in which the permalloy film is assumed to be magnetised as a single domain and the magnetisation vector is constant across the strip is also evaluated.
32 citations
TL;DR: In this article, the Vogel-Fulcher law of superparamagnetism is applied to the magnetization changes of fine ferromagnetic particles. But the discussion is mainly concerned with magnetization change within particles.
32 citations
TL;DR: In this article, single-domain and pseudo-single-domain titanium-poor magnetite grains are present in silicic vitrophyre glass of an ash-flow tuff from western Nevada.
Abstract: Single-domain and pseudo-single-domain titanium-poor magnetite grains are present in silicic vitrophyre glass of an ash-flow tuff from western Nevada. Conventional transmission electron microscopy and analytical electron microscopy corroborate inferences, made solely from rock magnetic and remanence data, that the thermoremanent magnetization in the vitrophyre is carried by such grains. The magnetite grains vary in size, shape, and distribution throughout the glass. They probably crystal lized during violent eruption and welding of the ash flow, at temperatures well in excess of 600 °C.
22 citations
TL;DR: In this paper, the magnetization processes within the narrow domain laminae of amorphous ferromagnetic alloys have been investigated by means of the magneto-optical Kerr effect.
TL;DR: Amorphous Sm 1-x co x -films with uniaxial in-plane anisotropy with various Co-concentrations and various film thicknesses d ( 10nm \LEq d \leq 350nm ) have been prepared by flash-evaporation of SmCo-alloy powders.
Abstract: Amorphous Sm 1-x co x -films with uniaxial in-plane anisotropy with various Co-concentrations x (.67 \leq x \leq .91) and various film thicknesses d ( 10nm \leq d \leq 350nm ) have been prepared by flash-evaporation of SmCo-alloy powders. The saturation magnetization decreases linearly with x in the whole concentration range, whereas the coercive field increases linearly with x down to x\approx74 and then decreases. Drastic changes in all magnetic properties occur when at a given chemical composition the film thickness is reduced below d\approx50 nm. Head-on domains are separated by zig-zag walls whose amplitudes are analyzed as a function of the material parameters.
TL;DR: In this paper, a new statistical theory of domain wall pinning by a random array of inhomogeneities is outlined, where each pin site is characterized by its maximum pinning force f. The critical field H o required to unpin a 180° wall, in the absence of thermal activation, is found to be proportional to f 2ρ/γ where ρ is the volume density of pins and γ is the domain wall energy.
Abstract: A new statistical theory of domain wall pinning by a random array of inhomogeneities is outlined. Each pin site is characterized by its maximum pinning force f. The critical field H o required to unpin a 180° wall, in the absence of thermal activation, is found to be proportional to f2ρ/γ where ρ is the volume density of pins and γ is the domain wall energy. In an applied field H o the wall can be unpinned if an activation energy E is supplied thermally. Expressions for this energy are given for strong and weak pinning regimes. The use of these equations in interpreting the observed temperature dependence of coercive forces and magnetic viscosity results is discussed.
TL;DR: Magnetization distribution and behavior of magnetization in CoCr sputtered films of various thickness are studied by high-resolution Lorentz microscopy in this paper, where the authors show that magnetization reversal changes from the domain wall displacement mode in the 200 A thick film to the rotational mode in 1000 A thickness film.
Abstract: Magnetization distribution and behavior of magnetization in CoCr sputtered films of various thickness are studied by high-resolution Lorentz microscopy. The perpendicular component of magnetization increases with increasing film thickness, corresponding to the increase in the Q-value. The dominant mechanism of magnetization reversal changes from the domain wall displacement mode in the 200 A thick film to the rotational mode in the 1000 A thick film. In the 600 A thick film, elongated domains with a kind of cross-tie walls are formed perpendicular to an AC demagnetizing field in the film plane.
10 Nov 1983
TL;DR: In this article, the stability of reverse domains in thin films of magnetic materials having high coerciv-ity is investigated and it is shown that domains below a critical diameter are unstable and will collapse.
Abstract: The stability of reverse domains in thin films of magnetic materials having high coerciv-ity is investigated. It is shown that domains below a critical diameter are unstable and will collapse. To minimize this minimum domain diameter it is necessary to minimize domain wall energy while maximizing the product of magnetization times coercivity, M.Hc. Since M.Hc tends to be nearly a constant near the magnetic compensation temperature, it is concluded that domain wall energy a and the product M-Hcare critical parameters for assessing the use-fulness of a material for high density thermomagnetic recording applications.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: The magnetization process of ordered Au 4 V was measured at 4.2 K under long pulsed magnetic field up to 350 kOe as mentioned in this paper, where the saturation field H c and the saturation magnetization M 0 were determined to be 290kOe and 6.7 emu/g (1 μ B /V atom), respectively.
TL;DR: In this article, the magnetic domains of ball-milled small particles of the SmCo5 phase below several microns in size have been observed by the colloid-SEM (scanning electron microscope) method.
Abstract: Magnetic domains of ball-milled small particles of the SmCo5 phase below several microns in size have been observed by the colloid-SEM (scanning electron microscope) method, a modified Bitter method. Domains on the c plane of single-domain particles were found when the particle size decreased. Measurements show that sizes of two single-domain particles are 2.2 and 1.6 µm. These values are discussed with the theoretical critical sizes for the single-domain particles of SmCo5.
TL;DR: In this paper, three ferrofluids, consisting of suspensions of Fe3O4 particles of ≂100-200 A diameter in diester, hydrocarbon, and water have been investigated at temperatures 4.2-300 K by means of Mossbauer effect and magnetic measurements.
Abstract: Three ferrofluids, consisting of suspensions of Fe3O4 particles of ≂100–200 A diameter in diester, hydrocarbon, and water have been investigated at temperatures 4.2–300 K by means of Mossbauer effect and magnetic measurements. The magnetic data displays almost all the features observed in the spin glasses. The Neel model is used to explain the behavior of the fluids. From the temperature variation of the initial susceptibility and the isothermal remanence, K=(3.5±0.7)×105 erg/cc and D0=(80±5) A are obtained for the anisotropy constant and the median diameter, respectively, of the diester based ferrofluid. The ac susceptibility gives K=3×105 erg/cc and D0=92 A. For the water based ferrofluid measurements give K=1.5×105 erg/cc. Values obtained from Mossbauer measurements for K and D0 agree with those obtained from magnetization–susceptibility data.
TL;DR: In this paper, the irreversible magnetization in single-domain particles is treated on the basis of the Prigogine-de Groot theory in non-equilibrium thermodynamics, and an equation of gyromagnetic motion in the generalized form of the Landau-Lifshitz equation as well as expressions for heats evolved or absorbed during this process are derived.
TL;DR: The pseudo-binary Laves phases Pr x Sm 1-x Fe 2 were prepared and their magnetic properties were studied by the Mossbauer effect and magnetization measurements as discussed by the authors, and the usual single ion crystalline electric field model gave a good account of the magnetic anisotropy up to x = 0.42.
TL;DR: In this article, a numerical model of coercivity, for low magnetization materials, is discussed that uses the concept that a domain wall is trapped at inclusions in the magnetic material by the reduction in wall energy.
Abstract: In order to characterize magnetic materials properly, it is desirable to have models, based upon first principles if possible, of such material parameters as coercive force. Here, a numerical model of coercivity, for low magnetization materials, is discussed that uses the concept that a domain wall is trapped at inclusions in the magnetic material by the reduction in wall energy. With the choice of one adjustable parameter, reasonable results are obtained for such low magnetization materials as the ferrimagnetic garnets.
TL;DR: The magnetic properties of Co-Cr and Co-Mo films prepared by d.c. triode sputtering are discussed in this paper, where the magnetic domain structure of the films as observed by Lorentz electron microscopy is interpreted in terms of the deposition parameters and the properties of the film.
Abstract: The magnetic properties of Co-Cr and Co-Mo films prepared by d.c. triode sputtering are discussed. The films are found to have perpendicular magnetisation in certain composition ranges. The magnetic domain structure of the films as observed by Lorentz electron microscopy is interpreted in terms of the deposition parameters and the properties of the films. In particular the microstructure of the films is seen to have an overwhelming influence on the domain structure.
TL;DR: In this paper, the hysteresis behavior of isolated micro-sized magnetic particles can be investigated using a vibrating reed magnetometer with a sensitivity of about 10 -9 Acm 2.
TL;DR: In this paper, the effect of multiplicity was found to reduce connecivity by up to 20 percent, which was small compared with the intrinsic variation of the coercivity within a given sample, which is of the order of 300 percent.
Abstract: It is known that the acicular particles comprising a tape coating often occur as groups of a very few single particles lying side by side, i.e., "multiple particles." The coercivity of such multiple particles was calculated and compared with that of the constituent single particles. In general it was found that the effect of multiplicity was to reduce the connecivity by up to 20 percent, which is small compared with the intrinsic variation of the coercivity within a given sample, which is of the order of 300 percent.
TL;DR: In this paper, the magnetization distribution is considered in a thin ferromagnetic film of a thickness near the critical value, for which the continuous phase transition from the homogeneous magnetization state to the domain structure appears.
TL;DR: In this paper, the authors used the colloid-SEM (scanning electron microscope) method, a modified Bitter method, with magnifications from 10 000 x to 45 000 x.
Abstract: Magnetic domains of isolated small particles of the low-temperature phase of MnBi in the ball-milled state after sintering have been studied by the colloid-SEM (scanning electron microscope) method, a modified Bitter method, with magnifications from 10 000 x to 45 000 x. By decreasing the particle size, domain patterns characteristic of the single-domain particles were found. Observations show that the critical size for the single-domain particle is greater than 1 μm which is larger than the theoretical value of about 0·5 μm. This difference is discussed.
TL;DR: In this paper, the effect of the magnetic interaction between the magnetic carriers was estimated by a simple pair model, where the remanences of post depositional origin was assumed, and the intensity of remanence acquired during the consolidation of artificial sediments was measured as a function of the concentration of fine grain magnetites in a magnetite-talc mixture.
Abstract: The effect of the magnetic interaction between the magnetic carriers was estimated by a simple pair model, where the remanences of post depositional origin was assumed. The theory predicts a large concentration dependence of the intensity of the remanence for a very low concentration range (packing fraction ≤ 0.1%) if the magnetic particles are small and have a single domain structure. The effect decreases with the increase of the grain size. In order to check the validity of the theory, the intensity of the remanence acquired during the consolidation of artificial sediments was measured as a function of the concentration of fine grain magnetites in a magnetite-talc mixture. The result indicates the large concentration dependence of the remanence intensity. The validity of the various methods, which have been used to normalize the NRM in sediments to obtain the relative intensity change of the earth's magnetic field, was discussed on the basis of the present result.
TL;DR: In this article, the distribution of internal stress field of different regions in the amorphous ribbon is found, and the magnetic anisotropies in these regions are also calculated.