E. A. Nesbitt

NEW PERMANENT MAGNET MATERIALS.

New permanent magnet materials containing rare‐earth elements (RE) have been discovered. For the most part, these alloys are based on the hexagonal intermetallic compounds, Co5RE. Replacement of cobalt with copper in some of these rare‐earth compounds results in solid materials with substantial permanent magnet properties. Coercive forces as high as 28,700 Oe have been obtained in heat‐treated samples of alloys in the Co5Sm–Cu5Sm system.

NEW PERMANENT MAGNET MATERIALS CONTAINING RARE-EARTH METALS.

Previously, most basic magnetic properties of the hexagonal intermetallic compounds involving the rare‐earth (RE) and 3‐d transition elements were reported in the literature. In addition, some of these compounds were investigated by various workers for permanent magnet properties by grinding ingots of the compounds into very fine powder. Recently, we discovered new permanent magnet materials which were based mostly on the hexagonal intermetallic compounds Co5RE. Replacement of cobalt with copper in some of these rare‐earth compounds resulted in solid materials having substantial permanent magnet properties. An outstanding feature of these alloys is their high value of intrinsic coercive force. High‐energy product alloys were found in the Co5−xCuxSm and Co5−xCoxCe systems with iron additions. Small pieces of Co3.5Fe0.4Cu1.35Sm exhibited BR=6450 G, BHC=4000 Oe, and (BH)m=9×105 G Oe. Also, small pieces of Co3.5Fe0.5CuCe exhibited BR=5100 G, BHC=3500 Oe, and (BH)m=5.2×106 G Oe. In general, these alloys are pr...

MnAlGe Films for Magneto‐Optic Applications

MnAlGe is a uniaxial ferromagnetic compound with a saturation 4πMs of 3600 G, and Curie temperature of 245°C. We have studied polycrystalline thin films of this compound formed on various substrates by getter sputtering. The optimum substrate temperature to obtain films with uniform magnetic properties was 500°C. Films prepared at this temperature have a substantial component of magnetization normal to the plane of the substrate, and a coercive force of approximately 2000 Oe. Information was written into films approximately 700‐A thick by Curie point writing or with a fine permanent magnet wire, and read with good optical contrast by means of the polar Faraday effect. The relatively low Curie temperature is advantageous in reducing the power required for Curie point writing for magneto‐optic memory or holographic applications.

Further Magnetic and Thermal Studies of Cast Rare‐Earth Permanent Magnets

Studies have been made of the effect of composition on the magnetic properties of arc‐cast alloys in the vicinity of Co3.5CuFe0.5Ce. The residual induction varies from 4000 to 6400 G with intrinsic coercive force values from approximately 5000 to 12 000 Oe. The maximum energy product values range from about 4 to 10×106 G Oe, the higher values generally associated with alloys of lower copper content. Freezing points of these alloys were determined for the first time using differential thermal analysis. Solidification occurs over a range of temperatures; initial freezing point decreases from 1177°C for a low copper alloy (Co3.94Cu0.5Fe0.56Ce) to 1124°C for a high copper alloy (Co2.63Cu2.0Fe0.36Ce). Several additional peaks were observed in the cooling curves after the initial freezing had occurred. These peaks are tentatively attributed to additional phases which are likely in view of the complexity of the Co–Ce and Cu–Ce binaries. The precipitation reaction at 400°C which was previously observed by metallo...

Cast Permanent Magnets of the Co5RE Type with Mixtures of Cerium and Samarium

Previous studies of the effect of composition on the magnetic properties of arc‐cast alloys in the vicinity of Co3.5CuFe0.5Ce yielded maximum energy products from 4 to 10×106 G Oe, residual inductions from 4000 to 6400 G, and intrinsic coercive forces from 5000 to 12 000 Oe. The partial substitution of samarium for cerium in alloys in this vicinity results in an improvement in permanent magnet properties, with maximum energy products from 4.6 to 12.3×106 G Oe, residual inductions 4300 to 7150 G, and intrinsic coercive forces from 4000 to 13 400 Oe. Freezing points of these alloys were determined using differential thermal analysis. The dependence of magnetic saturation on temperature was determined for several of these alloys from room temperature to 1.5°K. The saturation increases gradually with decreasing temperature without anomaly. The temperature coefficient of saturation magnetization between 25° and −100°C was found to be 0.1%/°C for the alloy Co3.5CuFe0.5Ce, 0.06%/°C for the alloy Co3.5Cu1.35Fe0.4...

Thin‐Film Surface Bias on Magnetic Bubble Materials

A method of reducing the external magnetic bias field to maintain stable cylindrical domains (magnetic bubbles) in uniaxial orthoferrites or garnets is presented. A thin film of a permanent magnetic material is sputtered onto a platelet inducing an exchange coupling interaction across the interface. This interaction manifests itself as an effective bias field which reduces the external applied field required to stabilize bubbles. So far the largest effective bias obtained has been about 25 Oe, using Co3.2Cu1.3Fe0.5Ce0.25Sm0.75 sputtered onto a 15‐μ‐thick platelet of Sm0.55Tb0.45FeO3. Dynamic properties do not seem to be appreciably altered for low‐speed operation in a T‐bar rotating field device.

Medium‐Coercive‐Force Permanent‐Magnet Alloys Based on the Co–Fe–Ti System

The magnetic properties of Co–Fe–Ti alloys in the vicinity of 80% Co‐11% Fe‐9% Ti were investigated. Saturation magnetization decreases nearly linearly with Ti additions, extrapolating to a zero value at about 15% Ti. Values of coercive force up to about 60 Oe could be developed by precipitation aging of arc‐melted alloys containing 8% Ti. Ductile alloys with Hc up to 45 Oe, however, were limited to 6% or less of Ti. For the latter, the coercive force was increased by cold‐working prior to the aging treatment. Wire specimens of an 85% Co‐12% Fe‐3% Ti alloy exhibited excellent squareness and low magnetostriction.

Effect of Processing on Permanent Magnet Materials Containing Rare‐Earth Metals

It is established that the new rare‐earth permanent magnet alloys containing copper show precipitation effects during heat treatment. Alloys drastically quenched from a high temperature had a comparatively low value of coercive force which increased substantially upon aging at a lower temperature. Also, upon aging, it was observed optically that a precipitate formed. These effects permit considerable latitude in the heat treatment of the alloys. Experiments on coarse powders showed that useful permanent magnet properties can be obtained with alloys in this form. Oriented coarse powder compacts which are stable in air having intrinsic coercive forces at 17 000 Oe have been made.

Intrinsic Magnetic Properties and Mechanism of Magnetization of Co‐Fe‐Cu‐R Permanent Magnets

The anisotropy constant Ku and the intrinsic coercive force MHc were determined in the temperature range 4.2° to 297°K on a single crystal of Co3.5Fe.5CuCe1.09. Also, a magnetization curve was obtained on a thermally demagnetized sample of this composition in which domain walls were present. It was necessary for the applied field to reach the value of the coercive force to substantially change the magnetization. As a result of these magnetic measurements and the direct observation of the precipitate particles by Leamy and Green using transmission electron microscopy, it appears that the magnetization process is governed by domain wall pinning.

Preparation and properties of sintered CoCuFeCe permanent magnets

Abstract Sintered directional permanent magnets of Co 3.8 Cu 0.9 Fe 0.5 Ce have been prepared with an energy product of 9.3 × 10 6 GOe, and intrinsic coercive force of 7000 Oe. Relatively low alignment fields, compacting pressures, sintering temperatures, and magnetizing fields were used. The magnets have a fine equiaxed microstructure, are crack free and mechanically strong.