Showing papers on "Coercivity published in 1982"

Properties of Ba ferrite particles for perpendicular magnetic recording media

Abstract: Fine Ba ferrite particles, suitable for coated perpendicular magnetic recording media, have been prepared. The particles, about 0.08 μm in average diameter, are thin hexagonal platelets with easy magnetization axes normal to their planes. Coercivity H c is controllable in a wide range, without significant reduction in magnetization, by Co and Ti substitution. The measured temperature dependences of H c and σ s showed stable characteristics. Good squareness ratio was obtained from an orientation capability measurement.

Ferromagnetic‐spin glass transition in Fe‐Zr amorphous alloy system

Abstract: Several kinds of Fe‐Zr amorphous ribbons have been prepared from the melt in an argon atmosphere, and the spin‐glass‐like behaviors have been investigated. The thermomagnetic history has been observed, and the freezing temperature monotonously decreases, in contrast to the Curie temperature, which increases and then goes through a maximum with increasing Zr content. Asymmetric hysteresis loops and the relaxation of remanence have also been found. The coercive force of Fe92Zr8 amorphous alloy drastically increases below 30 K, and the high‐field susceptibility of the present alloys are extremely large. These behaviors are explained in terms of the coexistence of ferromagnetic and antiferromagnetic states.

Synthesis of Fine Fe4N Powder and Its Magnetic Characteristics

Abstract: A pigment of Fe4N particles for magnetic recording was prepared by nitrogenizing acicular metal iron powder. The chemical treatment needed to obtain stoichiometric Fe4N powder was studied, and it was found that Fe4N powder was obtained when the Fe powder was heated at about 400°C in a mixture of H2–NH3 (65–80 vol.%). The Curie point of the powder coincided well with that of bulk Fe4N. The coercive force of Fe4N was 640 Oe, which is considerably smaller than that of the Fe powder used as the starting material. The dispersion of magnetic anisotropy was measured by a torque meter, and the decrease in the coercivity of nitrogenized iron powder was attributed to the exchange anisotropy of the surface layer.

Magnetic hardening of Pr‐Fe and Nd‐Fe alloys by melt‐spinning

Abstract: The dependence of the hard magnetic properties of melt‐spun Nd1−xFex (0.5⩽x⩽0.7) and Pr1−xFex (0.4⩽x⩽0.7) alloys on quench rate is reported; the latter was controlled by varying the substrate surface velocity (vs ) of the melt‐spinner. All of the alloys show an appreciable maximum in coercivity (Hci ) as a function of quench rate. For Nd1−xFex , a peak room temperature Hci of 8.65 kOe was found for a Nd0.5Fe0.5 alloy. Room‐temperature coercivities of ∼7.5 kOe were found in Pr1−xFex over the interval 0.6⩽x⩽0.7. The temperature dependence of the coercivity changed from a 1/T dependence for the most amorphous alloys to exponential for the alloys exhibiting maximum coercivity; coercivities as high as 78 kOe were found at 20 K. X‐ray data indicate that the coercive force results from an amorphous and/or very finely crystalline microstructure whose average particle size and/or intrinsic anisotropy varies as a function of quench rate. Crystallization studies, using differential scanning calorimetry and x‐ray dif...

General theory of the coercive force due to domain wall pinning

Abstract: Due to the nonlinear nature of the relevant mathematical equations, previous solutions to the geometrically simple problem of pinning of a 180° ferromagnetic domain wall by a single planar defect in an infinite medium contain the approximation of small deviations in the nature of the defect material relative to the host matrix. We have enlarged the theory of such domain wall pinning to include all magnitudes of deviation of the magnetic anisotropy Ki , magnetization Mi , and/or magnetic exchange energy Ai , characterizing the defect for all defect widths. In particular, we have obtained graphs for the resultant reduced coercive force hc = HcM1/K1 , due to such domain wall pinning, as a function of the dimensionless constants F = A2M2/A1M1 and E = A2K2/A1K1 and of the defect width, as well as graphs for the maximum obtainable coercive force as a function of F and E. (Here i = 1 represents the host material and i = 2 the defect.) As an example, we discuss these results in terms of applications to the Sm2(Co,Cu,Zr,Fe)17 hard magnetic materials.

Formation of Ba-ferrite films with perpendicular magnetization by targets-facing type of sputtering

Abstract: Ba-ferrite films have been prepared by means of Targets-Facing type of sputtering method which is very useful to prepare magnetic films at high rate without any bombardment of high energy particles such as γ-electrons and negative ions emitted from the targets and is favorable to obtain stoichiometric films of good quality. C-axis orientation of the films depends strongly on substrate temperature and crystal structure of substrate. C-axis well oriented BaM films are deposited on amorphous materials such as a-SiO 2 . The deposited films of 3000 A in thickness have ΔΘ 50 less than 1 degree, magnetic anisotropy constant of 3.2\times10^{6} erg/cc, saturation magnetization of 380 emu/cc and coercive force of 1.3 kOe. These films reveal much better c-axis orientation and surface smoothness than the films deposited by DC diode type of sputtering method and have almost the same composition as that of the targets.

Permanent magnet properties of rapidly quenched rare earth-iron alloys

Abstract: Recent studies have demonstrated the potential of producing rare earth-iron permanent magnets by rapid quench processing. High coercivity, unachievable by traditional powder-metallurgy methods, has been obtained either by crystallization of an amorphous or rapidly quenched precursor or by direct-quenching. Results obtained by both techniques on a variety of rare earth-iron alloys are discussed. In particular, melt-spun Nd-Fe and Pr-Fe alloys develop an appreciable maximum (7-9 kOe) in room temperature coercivity (H ci ) as a function of quench rate, which is controlled by varying the surface velocity of the melt-spinner substrate. Even higher H ci (>20 kOe) has been observed in Sm-Fe. Magnetic and crystallization properties suggest that the coercive force of these materials is related to the formation of one or more metastable rare earth-iron phases.

Hexagonal Ferrites from Melts and Aqueous Solutions, Magnetic Recording Materials

Abstract: Owing to their particular crystallographic properties, ferrimagnetic hexagonal ferrites exhibit a far greater coercive force than the conventional magnetic pigments. They therefore appear to be suitable for use in magnetic information storage procedures, some of which are novel and are at the development stage. Thus, magnetic tapes of high coercive force containing barium ferrite could be used as master tapes for copying magnetic information or for producing forgery-proof magnetic cards, if magnetic heads having high-order write fields were successfully developed. Moreover, platelet-like ferrite pigments in which the preferred direction of magnetic orientation is perpendicular to the plane of the platelet are of great interest for perpendicular magnetic recording. In this progress report, the crystal structures, magnetic characteristics of hexagonal ferrites, and chemical processes for their production are discussed. In particular, reactions in salt melts or under hydrothermal conditions produce finely divided pigments whose particles have a pronounced hexagonal, plate-like habit, a narrow particle size distribution, and advantageous magnetic properties. The magnetic properties of the pigments crystallized from salt melts may be adjusted by cation exchange.

Characteristics of RF-sputtered CoCr films

Abstract: The magnetization of the CoCr recording medium has been investigated by several methods. First the perpendicular hysteresis loops are analysed in the thickness range from 500 to 20,000 A. This provided evidence that the magnetization process is typefied by domain wall motion. Second the dependence of the coercivity on the film thickness has been determined. The dependence found can be explained if it is assumed, that the coercivity is caused by domain walls, impeded by the crystallite boundaries. Finally stand-still recording experiments have been performed, which confirm that magnetization takes place by the displacement of domain walls. The switching criterion in the writing process is best met by taking the field averaged over the film thickness.

Observation of Ferroelectric Hysteresis Loop of Fe 3 O 4 at 4.2 K

Abstract: The existence of ferroelectricity in magnetite has been established by determining the c -axis component of the spontaneous polarization at 4.2 K. The ferroelectric D - E hysteresis loop was observed by changing the applied electric field stepwise by 5 kV/cm at intervals of 10 s between -15 kV/cm and 15 kV/cm. It has been found that, at 4.2 K, the coercive field is extremely high and the electric leakage current is still prominent. The switching process of the polarization was observed at the d c field of 20 kV/cm.

Extended theory of the coercive force due to domain wall pinning

Abstract: We have enlarged the theory of ferromagnetic domain wall pinning by defects to include large as well as small deviations of the magnetic anisotropy, magnetization, and/or magnetic exchange energy of the defect, from the host material for all values of the defect width. In particular, we obtain results for the coercive force due to such pinning as a function of two dimensionless constants characterizing the defect and of the defect width. We also obtain results for the maximum obtainable coercive force in terms of these parameters. We discuss these results in terms of applications to the Sm2(Co, Cu, Zr, Fe)17 hard magnetic materials.

High density recording characteristics of sputtered γ‐Fe2O3 thin‐film disks

Abstract: Sputtered γ‐Fe2O3 thin films are attractive in practical application to high density magnetic recording. This paper presents basic processes of γ‐Fe2O3 thin‐film fabrication, magnetic properties, and high density recording characteristics of the films. The film is prepared by reactive sputtering of an iron alloy containing a small amount of Co, Ti, and/or Cu in an Ar‐O2 atmosphere on anodized Al alloy substrates and successive heat treatment. The film shows a high coercivity of 1000 Oe and a coercive squareness of 0.84 with the reduced thickness. The anodized Al alloy provides hard, smooth, and chemically stable substrates. The continuous γ‐Fe2O3 thin films show high recording density with an excellent signal to noise ratio (SNR). First, the recording characteristics of the film employed in practical disk storage with the areal recording density of 24 000 bit/mm2 are described. SNR improves as the average crystallite size decreases. It is shown that 35 dB can be obtained at the linear density of 1000 flux...

Magnetic properties of compositionally modulated thin films

Abstract: The magnetization density per cm3 of Ni‐content of compositionally modulated Cu–Ni thin films at 5 K was found to depend on the modulation wavelength (λ) and amplitude (A) and reached ∼90% of that of pure Ni. Short‐λ and low‐T studies on Cu–Ni showed an inter‐wavelength coupling of the moments of Ni‐rich regions that may depend on the thickness of the latter relative to that of the Cu‐rich regions. Evidence for xy‐like two‐dimensional ferromagnetism was also observed in Cu–Ni with λ containing only a few Ni‐rich planes. Coercivity and anisotropy were found to depend strongly on the modulation characteristics; the former increased sharply with decreasing λ while the latter had an oscillatory dependence.

Magnetization transitions in perpendicular magnetic recording

Abstract: A simple magnetic transition model is proposed for perpendicular recording with a single-pole head. It has been found that the amplitude of the transitions is proportional to the coercivity H c of the recording medium and is independent of the saturation magnetization M s if M_{s} \gsim (3/4\pi) H_{c} . Experimental proof using Co-Cr sputtered films is also given.

Biaxial magnetoelasticity in steels

Abstract: The effects of stress coaxial, transverse, and biaxial relative to applied field on magnetization, susceptibility, and domain wall configurations are derived and confirmed using rod, hollow cylinder, and hollow toroid steel samples. The effective stress σ=σ∥−σ⊥ is linearly proportional to pressure on 90° domain walls below residual stress and to changes in reluctance above residual stress. The equivalent field, Hσ=6.0(5) A/m, per MPa of stress was measured in excellent agreement with 6.2(4) A/m calculated from material parameters. The quantity dχ−1/dσ=9.0(6)×10−6/MPa was measured in good agreement with 8.3(5) calculated. A lower limit of reluctance due to inhomogeneities was observed. Magnetization increases with tension and compression allow measurement of ±90° domain wall fractions, f±=0.30±M/Ms, below the coercive field. Net magnetization changes from both walls generate magnetization hysteresis loops with stress cycling.

Thickness dependence of magnetic hysteretic properties of rf‐sputtered amorphous Tb–Fe alloy thin films

Abstract: The variation in the magnetic hysteretic properties of rf‐sputtered amorphous Tb–Fe thin films as a function of the nominal film thickness was investigated, using Kerr magneto‐optic and Hall effect measurements. The results on the thickness dependence of coercivity, polarity of the hysteresis loop, and Curie temperature of films prepared at the same sputtering condition indicate that there is a change in the ‘‘effective’’ film composition. This composition change is believed to be due to microstructure‐induced variations in the short‐range order during the film growth.

Metallic glasses having a combination of high permeability, low coercivity, low ac core loss, low exciting power and high thermal stability

Abstract: Metallic glasses having high permeability, low coercivity, low ac core loss, low exciting power, and high thermal stability are disclosed. The metallic glasses are substantially completely glassy and consist essentially of about 58 to 81 atom percent iron, from 1 to about 10 atom percent of at least one member selected from the group consisting of nickel and cobalt, about 1 to 6 atom percent of at least one member selected from the group consisting of chromium, molybdenum, vanadium, niobium, and zirconium, about 11 to 27.5 atom percent boron about 0.5 to 8 atom percent silicon, 0 to about 2 atom percent carbon, plus incidental impurities, the total of born, silicon and carbon present ranging from about 17 to 28 atom percent. The alloy is heat treated at a temperature and for a time sufficient to achieve stress relief without inducing precipitation of discrete particles therein. Such a metallic glass alloy is especially suited for use in devices requiring high response to weak magnetic fields, such as ground fault interrupters and current/potential transformers.

Chapter 3 The structure and properties of alnico permanent magnet alloys

Abstract: Publisher Summary The alnicos are an important group of permanent magnet alloys. They contain Fe, Co, Ni, and A1 with minor additions of Cu and Ti. This chapter discusses the structure and properties of alnico permanent magnet alloys. The relatively high coercivities of the alnicos are due to the shape anisotropy of Fe or Fe–Co rich single-domain particles, which are precipitated in a weakly ferromagnetic or nonferromagnetic Ni–Al rich matrix. After cooling from about 1200 °C at a controlled rate ≈30 °Cs –1 , the isotropic alnicos 1–4 are subsequently tempered for several hours at about 600–650 °C. The phase separation takes place by spinodal decomposition at 800–850 °C as the alloys are cooled. The final shapes and sizes of the particles are determined in the very early stages of the spinodal decomposition and microstructural investigations have shown that the Fe or Fe–Co rich particles are elongated parallel to the (100) directions in the matrix. The anisotropic alnicos 5, 6, 7, and the grain-oriented alnico 5DG are produced by controlled cooling from 1250 °C in a saturating magnetic field ≈200–300 kAm –1 and then tempered for several hours at about 600 °C. The high coercivity alnicos 8 and 9 are also cooled from about 1250 °C and then annealed isothermally in a saturating magnetic field ≈200–300 kAm –1 for a few minutes at about 820 °C after which they are given a two-stage tempering treatment usually for several hours at about 650 °C and then at 550 °C.

Demagnetization curves of four rare‐earth‐cobalt magnet types at temperatures 300–1000 K

Abstract: Intrinsic demagnetization curves and the temperature dependence of specific magnetization states were measured with a dc magnetometer on four types of sintered rare‐earth‐cobalt permanent magnets at temperatures from 300 to 1000 K. All magnetic properties vary reversibly with temperatures up to limits of 650–850 K, depending on the alloy. Precipitation‐hardened magnets of the 1–7 or the 1–5 types and the common sintered SmCo5 all exhibit quite different temperature characteristics. The MHc of 1–7 type magnets decreases gradually with increasing temperature. Its temperature dependence can be well described by a simple exponential function. The MHc of SmCo5 drops sharply with increasing temperature and becomes very small at about 750 K. The cerium magnet shows a distinct kink in MHc versus T at 550 K, separating two temperature regions in which clearly different mechanisms are responsible for the coercivity.

Plasma effects on the Co-Cr deposition in opposing targets sputtering method

Abstract: It is well known that Co-Cr films show a high perpendicular magnetic anisotropy, coercivity of 1000 oe or above and other properties suitable for perpendicular magnetic recording media. In this report, Co-Cr films, deposited by the bombardment of ions extracted from plasma using a new type of cathode sputtering apparatus with opposing targets, which will be called opposing targets sputtering hereafter, were investigated on morphology, crystal structure and magnetic properties. It was found that in the Co-Cr films of suitable magnetic properties for recording media, the morphology changes and the degree of C-axis orientation of Co-Cr hcp crystal, Δθ 50 is a constant value as low as about 3° with the increase of ion bombardment energy during deposition. Both morphology and the dependency of Δθ 50 on thickness of the Co-Cr films deposited by the opposing targets sputtering considerably differ from those by RF sputtering. There was no columnar structure observed in the cross section of the Co-Cr films suitable for perpendicular magnetic recording media prepared by the opposing targets sputtering, whereas columnar structure is reported to be observed clearly in the case of both RF sputtering and vacuum vapor deposition.

Properties of amorphous Co–Ta and Co–W films deposited by rf sputtering

Abstract: Magnetic and thermal properties of Co100−xTax(11≤x≤25) and Co100−xWx(13≤x≤25) amorphous films deposited by rf diode sputtering have been investigated. In both systems, structural changes of these films from crystalline to amorphous lead to a drastic decrease of their coercive force Hc and the absolute value of saturation magnetostriction λs, where λs is negative. Since magnetic properties and structure of the amorphous Co–Ta and Co–W films depend significantly on the argon gas pressure PAr, the PAr must be adjusted to the proper value during sputtering to obtain films with soft magnetic properties. Typical magnetic properties of Co–Ta and Co–W amorphous films are as follows: (i) Co–Ta: 4πMs≤11 kG, −λs≤2×10−6, Hc≤0.4 Oe. (ii) Co–W: 4πMs≤11 kG, −λs≤8×10−6, Hc≤4.0 Oe. The crystallization temperature Tx of the amorphous Co–Ta films is above 700 K and Tx increases with the increase of Ta content in the films. Tx of amorphous Co–W films is above 940 K. In this alloy system, however, structure relaxation occurs ...

The microstructure and magnetic properties of electroplated cobalt film for perpendicular magnetic recording

Abstract: In this work, the results of a systematic study of the correlation between the microstructure and magnetic hysteretic properties of electroplated Co films [1] are reported. Based on this study, the origin of the perpendicular easy magnetization in the film is confirmed to be associated with the combined effects of crytalline and shape anisotropy of the Co particles in the film. The variations of the demagnetizing field, H d , and coercivity, H c , which would affect the application of the film in perpendicular magnetic recording are also demonstrated by manipulating the interparticle separation through systematic changes in the plating parameters and the post plating treatments.

High coercivity Co and Co‐Ni alloy films

Abstract: A high coercivity and a high hysteresis loop squareness pure Co and Co‐Ni (up to 50 at %) alloy films have been prepared by a new process. The new process involves the films, including N, being sputter deposited in an atmosphere of Ar‐N2 mixture and annealed at temperature above 553 K. Most of the included N diffuses out from the film surface after annealing, and the films have a strong preferred orientation with the c axis parallel to the film plane. In Co70Ni30 alloy films, a high coercivity Hc of 1 kOe (80 kA/m) and a high hysteresis loop squareness S* of 0.95 are achieved. The values of Hc gradually decrease as the Ni/Co concentration ratio of the films departs from 30/70. There is a strong correlation between Hc and the preferred orientation of crystallites; Hc increases as the c axis orientation parallel to the film plane grows.

Magnetic domains in rare-earth cobalt permanent magnets

Abstract: The microstructure of two commercial 2:17 precipitation hardened rare-earth magnets has been examined and compared with the magnetic properties. Transmission electron microscope studies on Sm(Co,Fe,Cu,Hf) 7.25 , Hicorex 99C show a fine cellular microstructure with 2:17 rhombohedral cells surrounded by coherent 1:5 hexagonal cell boundaries. In Sm(Co,Fe,Cu,Zr) 7.22 , TDK REC-26 the cells are much coarser and 1:3 phase thin lamellae are superimposed on the cellular structure. X-ray energy dispersive analysis shows a higher Cu content in the cell boundaries. Lorentz electron microscopy shows "wavy" domain walls in both cases indicating that the domain walls are pinned at the cell boundaries. The higher Cu content of the cell boundaries dilutes the magnetic properties of the SmCo 5 phase and produces a large domain wall energy gradient across the cell boundary leading to the observed high coercivities.

Annealing effects and short-range ordering in the non-magnetostrictive amorphous alloy Co 58 Ni 10 Fe 5 Si 11 B 16

Abstract: Effects of isothermal and isochronal annealing on the coercive field and the effective magnetic anisotropy in the as-quenched and the stress relieved amorphous alloy Co58Ni10Fe5Si11B16 were investigated. The mechanisms of the deterioration of soft magnetic properties in non-magnetostrictive amorphous alloys by annealing at low temperatures,T a

Structure and magnetic-properties of y(co1-xmx)5 compounds

Abstract: The structures of the pseudobinary Y(Co1−xMx)5 compounds (M ≡ Ni, Cu, Al, Ti, V, Cr, Mn, Fe) and the magnetic properties of the Y(Co1−xNix)5 compounds in particular were investigated. It was found that a large homogeneous single-phase region with a CaCu5-type structure forms when M is nickel or copper. The homogeneous range becomes restricted when M is a metal other than nickel or copper. The experimental results are critically examined in terms of the atomic size effect and the electron concentration factors. It is believed that continuous substitution in the Y(Co1−xNixx)5 system is primarily due to the smaller atomic size and weaker magnetic moment of the nickel atoms. There are strong indications that the nickel atoms preferentially occupy the 2c sites of the cobalt atoms. The composition dependence of the lattice constants and the interatomic distances can be satisfactorily accounted for by the nickel atoms occupying the 2c rather than the 3g sites in the hexagonal CaCu5-type lattice. The composition dependence of the Curie temperatures and the temperature dependence of the magnetization of Y(Co1−xNix)5 compounds were studied. The intrinsic coercive force IHc at cryogenic temperatures is discussed in terms of the localized moment model. The composition dependence of IHc was analysed in detail by using the moment distribution function and other intrinsic parameters.