Rotational Hysteresis Integral Research Articles

Effect of Factors on Coercivity in Sr–La–Co Sintered Ferrite Magnets

We varied the composition and sintering temperature of Sr-La-Co ferrite magnets to analyze the effects of various important factors on coercivity (H cJ). We examined the effects of crystal grain size and distribution, the mechanism of magnetization reversal, the degree of crystal grain orientation (OD), and the anisotropy field (H A) on H cJ. We proposed an equation based on the experimental results that expresses the measured H cJ and considers these effects as H cJ = C t(0.4/R h) OD (H A - H d - H in), where C t, R h, H d, and H in are the crystal grain size effects on H cJ of sintered magnet, rotational hysteresis integral corresponding to the mechanism of magnetization reversal, demagnetizing field of shape anisotropy, and interaction field between crystal grains, respectively. We found that apart from the volume ratio for single-domain crystal grains and H A, the mechanism of magnetization reversal had significant effects on H cJ for Sr-La-Co sintered ferrite magnets.

Effect of orientation on the thermal stability in advanced metal particulate tapes

The effects of the degree of particle orientation on the normalized magnetization decay and activation volume (Vact) were investigated for advanced data recording tapes prepared from ultrafine metal particulate (MP) composite. In this study, the mean volume of particles (Vphy) for advanced MP tapes varied between 1.7 and 5.3×10−18cm3, inclusive of a surface oxide layer. In MP tape with a larger Vphy (=5.3×10−18cm3), increasing the orientation ratio (OR) for improved recording characteristics was found to decrease the normalized magnetization decay. However, the OR values had little effect on the normalized magnetization decay of MP tape with a smaller Vphy (=1.7×10−18cm3). This may be attributed to the existence of a few particles approaching the theoretical superparamagnetic limit of 0.7×10−18cm3. In order to decrease the normalized magnetization decay, it is particularly important to increase Hc, which improves the anisotropy constant and the distribution of anisotropy field (HA) for advanced data recording tapes with very small Vphy. The value of Vact in the low reverse field, which is a major factor affecting media noise, decreased as OR increased regardless of Vphy. Also, Vact of both tapes decreased as the reverse field decreased in the range of 1.2kOe or less. Vact of an assembly of ultrafine particles was dependent on the distributions of HA and volume of particles, also the value of rotational hysteresis integral that related to the deterioration in the mechanism of magnetization reversal giving rise to an incoherent rotation.

Effects of thin Cr interlayer on time decay of magnetization and magnetization reversal for CoCrTaPt thin film media

The effect of thin Cr interlayer on the time decay of magnetization and magnetization reversal for CoCrTaPt/Cr/CoCrTaPt media is presented. The time decay of magnetization was measured at various reverse magnetic fields. The maximum magnetic viscosity coefficient which occurs around the remanent coercivity increases with increasing interlayer thickness, which implies the degradation of thermal stability. The activation volume decreases with increasing Cr interlayer thickness. Both torque magnetometer and the law of approach to saturation methods were used to measure the magnetic anisotropy. The results show a decrease in anisotropy with increasing interlayer thickness which may explain the degradation of thermal stability. The distribution of rotational hysteresis losses (W/sub r/) were measured and the rotational hysteresis integral (R/sub h/) was found to decrease with increasing Cr interlayer thickness which may be caused by reduction of the magnetic interaction.

Magnetic Characterization of Bacterial Magnetic Particles

Mossbauer measurement, chemical analysis (ratio of Fe 2+ to total Fe content), analyses of the rotational hysteresis loss (Wr) and the magnetic viscosity coefficient (Sv) for bacterial magnetic particles covered with organic thin films (BMPs) were investigated and compared with the results for Fe 3 O 4 fine particles prepared by a chemical coprecipitation method. The calculated value of the saturation magnetization (Js) of BMPs was found to be 1.06x10.4 Wb m/kg (84.7 emu/g) using Mossbauer spectroscopy and chemical analysis. The Wr/Js versus H curve for BMPs had a stronger peak than that of Fe 3 O 4 fine particles (Sample C1). The rotational hysteresis integrals (Rh) for BMPs and Fe 3 O 4 fineparticles were 1.12 and 0.62, respectively. It is believed that they have different magnetization reversal mechanisms. The Sv value of BMPs at 127A/m was 50% smaller than that of the Fe 3 O 4 fine particles (C1). The diameter (Dact) of the activation volume (minimum volume for magnetization reversal) calculated from Sv, and the critical diameter (Dc) obtained by considering the superparamagnetic behavior for BMPs, were 39 and 22 nm, respectively. As the Fe 3 O 4 fine particles (C1) have smallerDact(31 nm) and Dc(18 nm), it may be concluded that BMPs is magnetically more stable than Fe 3 O 4 fine particles (C1).

Magnetocrystalline anisotropy constants, rotational hysteresis energy and magnetic domain structure in UFe 6Al 6, UFe 9AlSi 2 and ScFe 10Si 2 intermetallic compounds

The magnetic torque, T, was applied to determine the anisotropy constants K 1 and K 2 of the UFe 6Al 6, UFe 9AlSi 2 and ScFe 10Si 2 compounds. The mechanism of magnetization reversal processes in these compounds was investigated on the basis of the analysis of the rotational hysteresis energy, W r and rotational hysteresis integral, R, calculated from the magnetic torque curves. Applying the powder pattern method, magnetic domain structures were observed. Moreover, the fundamental parameters of the domain structure were determined.

Synthesis and magnetic properties of electrodeposited metal particles on anodic alumite film

Elongated metal particles have been prepared by depositing transition metals into the pore channels of anodic aluminum oxide (alumite), with well-defined pores that build up into uniform and parallel channels. The highest coercivity for freshly prepared α-Fe particles in the alumite substrate reached 2700 Oe in the easy direction. The remanance curves of alumite films containing electrodeposited metals (Fe and Co) were measured to study the magnetostatic interaction of the particles. The possible reversal mechanisms of the metal particles in the alumite substrates were examined by the rotational hysteresis integral and the angular variation of the coercivity.

Evolution from soft to hard magnetic behavior in Co-based devitrified glassy alloy

From the amorphous alloy 6030V having the composition Co71.5Fe1.5Mo1Mn4Si13B9, a series of devitrified specimens with increasingly coarser microstructure and magnetic hardening is produced by annealing. From the features of the coercivity, the squareness ratio, the rotational hysteresis integral, and the magnetic interactions we infer that the magnetic hardening is due initially (Ta<600 °C) to a strengthening of the pinning effect of the precipitates on the domain walls, and then (Ta≳600 °C) to the formation of single-domain Co crystallites where the magnetization reversal mode is of incoherent type.

磁性細菌ＡＭＢ‐１から分離した磁性微粒子の磁気的性質

The experimental results on Mossbauer measurement, chemical analysis (a ratio of Fe2+ to total Fe content), analyses of the rotational hysteresis loss (Wr) and the measurement of magnetic viscosity coefficient (Sv) for bacterial magnetic particles (BMP, particle diameter D=25-65 nm) were compared with those of Fe3O4 particles (D=18-45 nm) prepared by the chemical coprecipitated method. The value of saturation magnetization (Js) calculated from Mossbauer spectrum and the results of chemical analysis for BMP was 1.06×10-4 Wb m/kg. The curves of Wr/Ms versus H for BMP showed more sharp peaks than those of Fe3O4 particles. The rotational hysteresis integral (Rh) of BMP and Fe3O4 particles were 1.12 and 0.62, respectively. It was considered that they have different magnetization reversal mechanism. Sv value of BMP was 127 A/m, which was 50% smaller than that of Fe3O4 particles. The diameter (Dact) of activation volume (minimum unit volume of magnetization reversal) calculated from Sv and the critical diameter (Dc) obtained by considering the superparamagnetic behavior of BMP, were 39 and 22 nm, respectively. On the other hand, Fe3O4particles had smaller Dact (31nm) and Dc (18nm). It maybe concluded that the magnetic stability of BMP is better than that of Fe3O4 particles.

Magnetic properties and rotational hysteresis of Fe3O4 and γ-Fe2O3 particles ∼ 250 nm in diameter

We report the magnetic properties for dispersed, spherical Fe3O4 and γ-Fe2O3 particles ∼ 250 nm in diameter in the temperature range T = 4.2–294 K. For Fe3O4, hysteresis properties show anomalies at 130 K, where the magnetocrystalline anisotropy constant K1 vanishes; the ratio Hc/Is (Hc = coercive force, Is = saturation magnetization) follows a linear relationship with K1/Is2 between 130 and 294 K. Below the Verwey transition temperature TV (∼ 120 K, the hysteresis properties depend on whether the sample is cooled in a strong magnetic field or in zero field; no magnetic anomalies were observed for γ-Fe2O3 particles, generated by oxidizing the Fe3O4 particles under study. The rotational hysteresis integral at 294 K is ∼ 0.7 for both compounds, pointing to a coherent-type magnetization reversal for assumed uniaxial single-domain particles (SDPs); however, the reduced saturation remanence is only ∼ 0.2, far below that for SDPs. Possible models for the particle magnetization modes are discussed.

極薄磁性層を有する塗布型磁気記録媒体用メタル粒子の構造と磁気特性について

Metal particles, which are developing as advanced thin layer metal particulate media, have a coercive force of 167 to 191kA/m and a particle length of 60 to 80 nm. The particle form and its inner structure were examined with high resolution transmission electron microscopy and magnetic properties of these magnetic media. The particle length distribution which was defined as the standard deviation divided by the average length, was improved about 0.6 times of conventional metal particles.The coercive force decreased with increasing particle length as well as aspect ratio(length/width). The value of rotational hysteresis integral was close to 1.1 with increasing the content of metal particles consisted of a single metal crystallite.Larger content of single crystal metal particles or smaller number of metal crystallites in a metal particle seems to cause magnetization reversal similar to the coherent mode and large coercive force of 167kA/m or above. The enhanced characteristics of metal particle for extremely thin layer metal particulate media were achieved by the improvement of particle size and the particle size distribution of starting materials, and also the higher densification in the metal manufacturing processes.There is still great room for improvement in the properties of metal particles which may be contributed to the extremely high density magnetic recording.

Rotational hysteresis and magnetization curling of FeAl thin films obtained by magnetron sputtering

Magnetic characteristics (magnetization, magnetic anisotropy, rotational hysteresis energy loss, rotational hysteresis integral) of Fe 100− x Al x films have been measured (for x = 18.2 and 24.2) to further make clear the effect of atomic ordering on their macroscopic properties. The results are discussed in terms of the presence of a fine-domain DO 3 ordered phase, dispersed within a disordered α matrix. The rotational hysteresis loss dependence W r = f( H) shows a two-peak shape and anisotropy fields have been inferred corresponding to the two phases. The shape anisotropy energy of the dispersed ordered domains (5.5 × 10 7 erg/cm 3), as well as of the matrix (≤ 1.5 × 10 4 erg/cm 3) have been evaluated. The volume fractions of the ordered domains were calculated as 0.19% and 0.23% for x = 18.2 and 24.2 respectively. The experimental results suggest that the changes in magnetization of the investigated films occur mainly by curling mechanism.

Magnetic Aftereffect and Magnetization Reversal of Sr-Ferrite Fine Particles

the magnetic aftereffect constant (S v ), the anisotropy field (H A ) distribution and the rotational hysteresis integral (R h ) were measured for M-type hexagonal strontium ferrite (SrM) fine particles with various average particle diameters (D) and coercive forces (H cJ ). The relations between S v , the activation volume (v), H cJ , H A , and R h were studied, as well as the effect of milling. S v is constant and independent of the magnetic field. In S v varies in proportion to In H cJ , and the relation H cJ ?v?2 was found to obtain in SrM particles not extensively subjected to milling. S v increases and v decreases for SrM fine particles (D=0.3 ?m) whose H A is widely distributed by milling, even though H cJ decreases markedly. S v and v are related to the distribution of H A . As H cJ increases, R h and v decrease, which indicates that the magnetization reversal mechanism of SrM fine particles approaches that of a coherent rotation mode.

Rotational Hysteresis Work and Rotational Hysteresis Integral of Polycrystalline Permanent Magnets

AbstractThe possible information on the magnetization processes of the grains available from the rotational hysteresis work and the rotational hysteresis integral of polycrystalline samples is investigated. A combined theoretical model for the switching field of the grains is considered, and numerical computations are carried out for different values of the model parameters. Especially, the influence of different orientations of the rotational plane of the applied field is studied.

Ｓｒフェライト微粒子の磁気余効と磁化反転機構

The magnetic after effect constant (Sv), the distribution of the anisotropy field (HA), and the rotational hysteresis integral (Rh) were measured for M-type hexagonal strontium ferrite (SrM) fine particles having various average particle diameter (D) and coercive force (HcJ). The relationships between Sv, the activation volume (v), HcJ, HA, and Rh were studied, as well as the milling effects. Sv is constant and independent of the magnetic field. ln Sv vary in proportion to ln HcJ, and the relation HcJ∝v-2 is obtained in SrM particles which were subjected to less milling effect. Sv increases and v decreases for SrM fine particles (D=0.3μm) whose HA is widely distributed by milling, even though HcJ decreases markedly. Sv and v are related to the distribution of HA. As HcJ increases, Rh and v decreases, which in dicates that magnetization reversalmechanism of SrM line particles approaches to that of the coherent rotation mode.

Magnetic evaluation of intergranular interactions in thin-film media by rotational hysteresis loss analysis

Magnetic torque analysis has been carried out for CoNiPt, CoCrTa/Cr and CoCrPt/Cr thin-film media. The magnetic field H grain k, where the rotational hysteresis loss vanishes, remained almost constant in each material, independent of the coercive force H c. Only in the CoCrTa media no clear correlation between the rotational hysteresis integral and H c was observed.

SUBSTITUTION EFFECTS ON THE CHARACTERISTICS OF Ba FERRITE PARTICLES

By investigating substitution effects on the properties of Ba ferrite particles for magnetic recording media, it has been found that Zn substituted particles have a rather small SFD(switching field distribution) compered with Co substituted particles. In particular, Co-Zn-Nb substituted Ba ferrite particles with a small amount of Co and a large amount of Zn are promising materials, exhibiting a small SFD and a small temperature coefficient of coercivity. The Zn-rich parricles have been found by torque measurement to be single-domain particles and have a uniaxial magnetocrystalline anisotropy not only at room temperature but also at low temperature. The Zn-rich particles have a small K2 in comparison with K1, while Co-rich particles have a comparatively large K2, especially at low temperature. From these results, it can be said that the Zn-rich particles have an idial uniaxial magnetocrystalline anisotropy. By the measurement of rotational hysteresis integral and angular depedance of coercivity, it has been found that the magnetization reversal for a medium using the Zn-rich particles is incoherent but more coherent than for a medium using Co-rich particles. It has been found that recording media using the Zn-rich particles of Co-Zn-Nb substitution system exhibiting a small SFD show excellent recording performance, especially in a short wavelength range.

Magnetization reversal mechanism evaluated by rotational hysteresis loss analysis for the thin film media

Rotational hysteresis loss analysis has been carried out for CoCrTa, CoNiPt, and CoCrPt thin-film media to evaluate the influence of microstructure on coercive force through the measurement of magnetic anisotropy. In each medium, the magnitudes of H/sub k//sup grain/ defined as a magnetic field where rotational hysteresis loss W/sub r/ diminishes remain almost a constant value independently of the values of coercive force. With increasing coercive force, the magnitude of the coercive force gradually becomes smaller than that of the switching field of magnetization H/sub p/ evaluated by torque analysis. Through the analysis of H/sub k//sup grain/ and H/sub p/, it is suggested that the coercive force in each examined medium is strongly dependent on the degree of intergranular exchange coupling and/or magnetostatic interactions. While on CoNiPt and CoCrPt media coercive force depends on the rotational hysteresis integral, no correlation between them was observed in CoCrTa films. >

Magnetization Reversal Mechanism in γ-Fe2O3 Thin Films

Magnetization reversal was studied in Co-Ti-Cu doped γ-Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> thin films, prepared by sputtering and heat treatment. The crystal grain size dependence of the coercivity suggested that the fanning mode is the most likely mechanism of reversal. The coercivity decreases with decreasing grain size because thermally activated magnetization reversal takes place. Rotational hysteresis integrals for the films ranged from 1.47 to 1.58, equal to those for the fanning mode.

Experimental investigation of Fe-(SiO2) granular films

Fe-(SiO2) granular films were fabricated by sputtering with a mosaic target. The fractional area of iron on the target was varied from 0.29 to 0.42. The volume fraction of iron was found from the saturation magnetization to be within 0.03 of that predicted by the target composition. The sample coercivities ranged from Hc = 130 to 950 Oe at room temperature and 690 to 2390 Oe at 77 K. Characteristics relevant for recording media were investigated for the highest-coercivity sample. The squareness values for hysteresis loops measured in and out of the plane of the film, Mr/Ms = 0.54 and 0.43, respectively, indicate that the granules have a uniaxial anisotropy and the easy axes tend to lie more in the plane of the film. The rotational hysteresis was measured at room temperature; the rotational hysteresis integral was calculated to be Ir = 1.56. Because the magnetization reversal is assisted by thermal fluctuation, the low temperature value of Ir was estimated by scaling the measured value by the ratio of the coercivities measured at 77 K and at room temperature. The value of Ir ≊ 0.6 is closest to the theoretical value for the coherent rotation mechanism. The relative decay of magnetization between 30 and 3600 s had a maximum value of ΔM/Ms = 0.10 for a reversal field near Hc. This value falls within the range of the values reported for conventional particulate media, which suggests that a stable transition can be recorded in this material.

ROTATIONAL HYSTERESIS MEASUREMENTS ON ALUMITE PERPENDICULAR MEDIA

Rotational hysteresis energy loss measurements have been performed to support the analysis of the magnetization processes of Fe- and Co-alumite perpendicular recording media. Two measurement techniques gave comparable results within error limits. The rotational hysteresis integral is severly lowered by the demagnetizing field. Normalizing the integral with the remanent magnetization instead of the saturation magnetization gives for Fe-alumite values indicating the curling mode, which was also proved by other measurement techniques. The half width value D(1/H)50 is introduced in the rotational loss graph. This value is an estimate for the dispersion of anisotropy axes and in our case it its proportional to the diameter of the Fe-needles. The in-plane loss is very low for the Fe-alumite samples, whereas it is high for the Co-alumite. In the well aligned Fe-alumite, rotation around the easy-axis does not give rise to an energy loss because no anisotropy is present in the rotation plane to cause irreversible magenetization jumps. The crystal anisotropy of fcc-Fe is small compared to the shape anisotropy of the particles. The high in-plane loss measured for Co-alumite is thought to originate from the dispersion of hcp-axes in the Co-needles.