High Coercive Force Research Articles

新高保磁力Cu-Mn-Sb系合金の磁性について

Magnetic properties of Cu-Mn-Sb alloys containing 4.98∼59.80% of Mn and 10.03∼79.71% of Sb have been measured. It has been found that the alloys consisting of about 17∼40%Mn, 10∼54%Sb and 9∼65%Cu show high coercive forces when tempered at 150°∼650°C after chill casting and the alloy consisting of 22.04%Mn, 33.00%Sb and the rest Cu exhibits the highest coercive force, IHC, of 2000 Oe and a residual intensity of magnetization, Ir, of 12 G. Further it has been determined by means of electron microscopic observation and X-ray analysis that these alloys of high coercive force contain many acicular fine particles of ferrimagnetic compound Mn2Sb dispersed in the matrices of nonmagnetic compound CuMnSb and nonmagnetic αCu phase. The high coercivity of these alloys is probably caused by the anisotropy energy of these small particles composed of a single magnetic domain.

Measurements on permanent magnets made from misch metal-cobalt alloy powders

Powders of a misch metal-cobalt alloy of type (MM)Co 5 were prepared and consolidated in various ways to study the effects of particle size, plastic deformation during milling, and pressure applied during compacting on the permanent magnet properties. Vibration grinding yields particles with high coercive force ( M H_{c} = 4180 Oe) but which align very poorly in a field. Mortar-ground powders have high magnetic anisotropy combined with much lower, but strongly particle-size dependent H c . Ballmilling, a method suitable for production in quantity, constitutes a satisfactory compromise. Pressing ballmilled powder in a field with 3400 kg/cm2pressure and no binder gave optimum results. A magnet having M H_{c} = 2010 Oe, B H_{c} = 1620 Oe, B_{r} = 4060 G, and (BH)_{\max} = 2.34 MG.Oe was obtained. Details of the static and recoil behavior for this magnet are reported.

Stress induced magnetic anisotropy in natural single crystals of hematite

Abstract The stress induced anisotropy has been determined for several natural crystals of hematite for compressions of up to 300 Kg/cm2 along the trigonal axis and along different directions within the basal plane. The induced anisotropy is predominantly uniaxial, but substantial higher harmonics are present for compressions along the trigonal axis. It is larger for compressions within the basal plane in accordance with the magnetostriction experiments of Urquhart and Goldman. Stress induced anisotropy as a possible explanation of the high coercive forces of hematite powders is discussed, as shape and intrinsic crystalline anisotropy are negligible.

Magneto-optic and Magnetic Properties of NdCo5, Nd2Co17, and Co Films

NdCo 5 , Nd2Co17, and Co films have been prepared by vapor deposition in ultrahigh vacuum using the alternate layer deposition technique. The substrates were held at −116°C during deposition. A subsequent heat treatment caused a diffusion of the layers and formed the intermetallic compounds. Direct-current Kerr hysteresis loops were plotted during the anneal. The coercive force was measured as a function of temperature to determine when the diffusion was completed. It was found that the films had to be heated above 600°C to form the compounds. At 25°C all films exhibited large coercive forces of 535, 270, and 210 Oe for NdCo5, Nd2Co17, and Co, respectively, but Hc decreased rapidly with increasing temperature. X-ray analysis indicated that all films had a strong fiber texture with the c axis normal to the film. It is assumed that isotropic planar stress and a perpendicular anisotropy cause the high coercive forces at lower temperatures. For all films the optical constants n, k, and the Voigt parameters Q0 and q were measured in vacuo below 10−9 Torr in the wavelength range 400–650 mμ. (Q0 and q are the modulus and the phase of the complex quantity Q which is the off-diagonal component of the complex permittivity tensor.) These measurements show that with increasing rare-earth content the magneto-optic amplitude Q0 decreases.

Ferro-, Antiferro-, and Superparamagnetic Behavior of Fe-Al Alloys

In agreement with measurements of Sato and Arrott, and of Kouvel, we also found anomalous magnetic properties of Fe-Al alloys containing more than 28 at.%. Al. In order to investigate the different properties of these alloys in more detail, we have measured the temperature dependence of magnetization, susceptibility, anisotropy, rotational hysteresis, and coercive force of monocrystalline and polycrystalline specimens (containing 28 to 50 at.% Al) between 1.5° and 300°K. The following results have been found: a maximum of rotational hysteresis at about 12°K, high coercive forces and high unidirectional and uniaxial anisotropy in the temperature region below 40°K, magnetization creeping between 4° and 50°K, and superparamagnetic-like behavior at higher temperatures. These results may be interpreted by assuming the existence of two phases one of which is ferromagnetic, the second antiferromagnetic below 40°K. For T∼40°K, the domains of one phase, and for lower temperatures, the domains of both phases interact.

Coercivity of Mischmetal-Cobalt Alloy Powders

A single-phase alloy of the type MMCo5 prepared by fusing cobalt with cerium-rich mischmetal (MM: 54.5 w% Ce, 26 La, 13 Nd, 5 Pr) is the cheapest of several new candidate materials for fine-particle permanent magnets. Results of experiments with powders produced by mechanical grinding and tempering are reported. The coercive force is limited by crystal imperfections introduced during milling. Maximum values of MHc are between 2500 and 4600 Oe, depending upon the milling conditions and the magnetizing field. Vibration grinding produces higher Hc than ballmilling, but ballmilled powders align better in a field (loop squareness Mr/Mp≈0.9 vs 0.7). Vacuum annealing at 300°–400°C improves the coercivity somewhat (3770 to 4600 Oe); higher temperatures reduce Hc drastically. Mortar grinding under liquid nitrogen yields considerably higher coercive forces than grinding at room temperature.

A Domain-Boundary Model for a High Coercive Force Material

The coercive force of aligned Co5 (rare earth) powders, while always much less than 2K/M, varies greatly with magnetizing field, even up to 50 kOe. The remanence is much more nearly constant. The coherent rotation model for noninteracting particles is not adequate to describe this behavior. A model is presented based on the idea that domain boundaries may be present and move easily, but that a sufficiently large field will drive them out so that they must be renucleated. Two experimental findings support this model. First, the measured rotational hysteresis integral value depends on whether or not a large field is applied before each measurement, as the model predicts. Second, magnetization jumps corresponding to nucleation have been directly observed in single particles. Calculations of the behavior of aggregates based on this single-particle model show the type of variation of coercive force and remanence that has been observed.

The vibrating head magnetometer--Instrument for the measurement of magnetic transitions in high coercive force films

The magnetization pattern recorded in high coercive force media, such as magnetic tapes or discs, is measured with the vibrating head magnetometer (VHM) by vibrating a recording head parallel to the surface of the medium and along the track length. The VHM can be used with small, irregular-shaped samples. It can be used to measure precisely the shape of recorded magnetic transitions. Application of the VHM to the precise location of dropouts on prerecorded samples and to the alignment of a recording head with respect to a prerecorded track is described. Measurements have been made with the VHM of the half peak width and relative peak signal of isolated transitions in Co alloy films. The half peak width was found to be proportional to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(t/H_{c})^{0.5}</tex> .

ALNICO-II

Abstract ALNICO II is a general purpose permanent magnet alloy recommended for applications where better magnetic properties than Alnico I are desired. It is a high coercive force, high energy magnetic alloy. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on heat treating and machining. Filing Code: Fe-31. Producer or source: Allegheny Ludlum Corporation.

Thin evaporated films with high coercive force

A technique allowing the preparation by vacuum evaporation of a material useable as a storage medium in digital magnetic recording is described. It consists of the evaporation of successive chromium and cobalt layers on a substrate, the nature of which seems indifferent. The coercive force can be adjusted from 200 to 600 Oe by adjusting the cobalt layer thickness. Superimposing identical double layers of chromium-cobalt allows one to obtain the required amount of flux. Such a multiple layered film gives properties identical to those of a homogeneous magnetic material with a coercive force between 200-600 Oe and an induction better than 10 000 gauss. These properties are isotropic. High squareness of the hysteresis cycle, with Mr/Ms > 0.95, is achieved.

Vibrating head magnetometer--Instrument for measurement of the magnetization pattern stored in high coercive force films

Vibrating head magnetometer--Instrument for measurement of the magnetization pattern stored in high coercive force films

Effect of Molybdenum Addition on the Properties of a New Magnet Alloy &amp;ldquo;Malcolloy&amp;rdquo; in the Co&amp;ndash;Al System

Four years ago the present authors discovered a new magnet alloy “Malcolloy” having a high coercive force, and determined the effect of nickel additions on its properties, the highest coercive force thus obtained being 1500 Oe. In this paper, the effect of molybdenum addition on the properties of Co–Al alloys, has been studied and found that the coercive force of the alloys increases generally by the addition of molybdenum: An alloy containing 80.51% cobalt, 13.96% aluminium and 5.53% molybdenum shows a coercive force of 1600 Oe, a residual magnetic flux density of 2750 G and maximum energy product of 1.34×106 G·Oe, when tempered at 600°C for 20 hr after water-quenching from 1380°C. These alloys consist of many ferromagnetic elongated particles about 400 Å in mean diameter which are dispersed in the matrix of a nearly nonmagnetic β′ phase. Therefore, it may be concluded that the high coercivity of these alloys is mainly due to the presence of the fine particles of a single magnetic domain.

The magnetic properties of tirupati sandstone formation from godavary valley, India

The magnetic properties of Tirupati red sandstones of Middle Cretaceous age from Godavary Valley, India, have been investigated. The results of studies on the Qn ratio, remanent coercive force, Curie temperature and chemical demagnetization tests are reported. The rocks were found to have a Qn ratio varying from 0.5 to 14, a high remanent coercive force of the order of 2000–6000 Oe and a Curie temperature of nearly 680°C. The NRM of the rocks seems to be a chemical remanent magnetization with hematic being responsible for the various properties observed.

Preparation and hard magnetic properties of Co-Zn-P films for high-density recording

The digital recording density of magnetic media can be improved by the development of thin ferromagnetic coatings having a high coercive force. An experimental study of the influence of zinc on the coercive force of chemically reduced cobalt-phosphorus films is presented. Incorporation of zinc increases the coercive force of cobalt-phosphorus films on Mylar substrates by a factor of 2 to 60. Cobalt-zinc-phosphorus films exhibited coercivities ranging from 300 to 1200 Oe, depending on the preparation conditions. The influence of substrate and solution parameters, such as hypophosphite ion concentration, zinc concentration, and pH are discussed with respect to the hysteresis properties of the films. The influence of zinc on the coercivity is attributed to increased magnetic isolation of the cobalt particles and to a modification of particle size.

SIMONDS #81

Abstract SIMONDS #81 is a cobalt, tungsten, chromium permanent magnet steel that is capable of developing moderately high coercive force along with high residual induction when it is in the hardened condition. Strong magnetic fields can be achieved with fairly short magnets and the configuration desired can be obtained with castings or by fabrication from rolled bars, sheets or plates. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, and machining. Filing Code: SA-202. Producer or source: Simonds Steel Division, Simonds Saw &amp; Steel Company.

EFFECT OF MILLING METHODS ON BARIUM FERRITE POWDER FOR THE PRODUCTION OF PERMANENT MAGNETS

Tests have been carried out on the ball-milling of barium ferrite powder in four types of mill, embodying different principles of crushing. The results are compared on the basis of time taken and energy consumed to produce a powder of given fineness and high coercive force.

Domain tip propagation logic

A new thin film technique is described which has implications for use in a network of all-magnetic logic. The technique, called domain tip propagation logic (DTPL), makes use of the controlled growth of domains within low coercive force channels imbedded in a film element of generally high coercive force. Information is stored within regions of the low coercive force channels in the form of domains of reversed magnetization and propagated through the channels under the influence of an applied field by expansion of the domains at the domain tips. The direction of domain tip propagation can be controlled and the mutual interaction between domain tips within channels brought into proximity of each other. The direction of domain tip propagation is sensitive to the magnitude and direction of the applied field. This has made it possible to design new types of thin film shift registers which are of essentially unlimited length and high storage density and speed. Experimental DTPL shift registers with linear bit densities of 100 bits per inch have been constructed and operated with 300-ns clock pulses. As a result of these tests, it appears that the construction of multimegacycle DTPL shift registers with storage densities of the order of several thousands of bits per square inch is feasible. Magnetostatic interactions between channeled domain tips make any combinational operation possible and lead quite naturally to the construction of all the usual logic elements in a variety of ways. Information transfer is possible with what is essentially unlimited fan-out so that there is no need for regeneration in building up large complexes of logic. The restriction of reversal of the magnetization to small regions of film permits a high density of memory and logic elements. The principles of operation of various devices utilizing DTPL are described, as well as the techniques of device fabrication. Some of the static and dynamic properties of channeled domain tips which are pertinent to the operation of the devices presented will be discussed.

Demagnetization theory for longitudinal recording

The reproduce head flux function for a longitudinally, sinusoidally magnetized tape is calculated on the assumption that the tape first demagnetizes irreversibly and then remagnetizes reversibly. In contrast to previous work, wherein all changes were considered reversible, the present calculation leads to a nonvanishing loss at short wavelengths. The loss is, however, quite small for conventional γFe 2 O 3 tape, ranging from 4.5 dB to 8 dB for the cases of incontact reproduction with magnetic and nonmagnetic heads, respectively. It is concluded that little justification exists for the use of higher coercive force tape materials with the present values of tape remanence, and that tapes with the highest possible oxide packing fraction will always give the highest ouput.

Magnetic Properties Observed During Vacuum Deposition of Permalloy Films

The quasistatic magnetic properties of vacuum-deposited Permalloy films of zero magnetostrictive composition were continuously monitored during deposition and substrate heating and cooling period in an evaporator equipped with a laser-operated Kerr magneto-optic hysteresigraph and a quenchable substrate holder in the temperature range of −196° to ∼400°C as a function of thickness up to ∼2000 Å. Films deposited at liquid-nitrogen temperature exhibit low (∼3 Oe) coercive force, with a very square loop, at thicknesses as low as 25 Å; this decreases rapidly with thickness increase. Films deposited at elevated temperature, for example 300°C, exhibit high (&amp;gt;20 Oe) coercive force with a very rounded loop when first observable at about 100-Å thickness. This, however, plummets downward sharply near 150-Å thickness, the loop meanwhile becoming square. The room-temperature coercive force of films deposited at high temperatures is more than that measured during deposition, while that of films deposited at liquid-nitrogen temperature drops as the film attains room temperature. In general, no change in Hc is observed upon exposing the fresh film to air at room temperature. The 2000-Å low-temperature films (deposited at −196°C) exhibit a well-defined uniaxial anisotropy of ∼6 Oe. This anisotropy field decreases monotonically on heating after deposition. At room temperature, Hk becomes ∼4.5 Oe. Upon further heating, Hk decreases to &amp;lt;1 Oe at 335°C. At 350°C a new easy axis with Hc∼1 Oe is rapidly induced by the applied magnetic field along the previous hard axis. This coercivity increases to &amp;gt;2 Oe when the film is cooled to room temperature. Smaller changes in Hk are observed upon cooling in films deposited at temperatures above 200°C. Some results on anisotropy spectrum are discussed.

The Palaeomagnetism of Hematites of the Veldurti Area, Cuddapah Basin, India

Summary The palaeomagnetism of thirty-five samples from the hematite deposits of Veldurti (1536N, 78E) of Precambrian age has been studied. Most samples show upward dips and reverse polarization. The mean direction for thirty samples showing consistent direction of magnetization is 133 E, - 37. The inferred pole position for this group is situated at 45 N and 27 W. The magnetic mineral responsible for magnetization of these samples seems to be hematite. The magnetization is very stable with high coercive force. These observations are consistent with a position for India in the northern hemisphere at the time of magnetization of the deposits.