6 March 2000
Investigators: R. D. Shull, L. J. Swartzendruber, L. H. Bennett, E. Della Torre, A. J. Shapiro, R. V. Drew, H. J. Brown, and D. E. Mathews
Objectives:
This main objective of this project is to improve the measurement process in magnetic materials in order to characterize these materials accurately and efficiently. This will enable industry to develop and produce new and better materials at lower cost.
Technical Description:
In collaboration with scientists from universities, industry, and other Divisions at NIST, magnetic materials important to the scientific and industrial communities are prepared and methods for the improved measurement of their properties are developed. Standard reference materials for the calibration of existing and planned instruments used in the measurement of magnetic properties are developed and produced. Methods for the improvement of flux pinning in superconducting materials are investigated in order to aid the industrial application of high temperature superconductors. Methods for the characterization of accommodation and aftereffect in magnetic recording and permanent magnetic materials are developed. Models are also developed for determining the most efficient methods to fully characterize magnetic materials, including their magnetostriction and time dependence.
Planned Outcome:
The expected results of this activity are fourfold: (1) improved characterization of magnetic recording media resulting in higher storage capacity and lower overall net cost per unit of storage, (2) improved characterization of permanent magnets, superconductors, and other industrial magnetic materials, resulting in more efficient and effective use of such materials, (3) improved calibration of magnetic measurement instruments giving NIST traceability at lower costs, and (4) facilitation of commerce in magnetic materials through improved agreement between producer and consumer on the measurements of magnetic properties at a lower cost.
Accomplishments:
Preparation, measurement, and analysis of a set of nickel spheres were completed. These spheres were issued as SRM 772a, a standard reference material intended for use in the calibration of magnetometers. A set of nickel disks was obtained for use as a standard reference material. Though they will not be as precise as the nickel spheres, the disks have the advantage that they are closer to the actual geometry used by a large number of laboratories who measure the magnetic properties of recording materials. They have the disadvantage that the user must measure the mass of the disk, whereas this is not necessary when using SRM 772a. Modifications to our absolute magnetometer that will enable the development of very low moment standards for use in high sensitivity instruments, such as alternating gradient magnetometers and SQUIDs, are planned. Critical currents were determined for a series of Bi2Sr2Cu2O8+x high temperature superconducting tapes. The effect of Al2O3 and carbon nanotube additions on the flux-pinning was investigated.
The ability of the Preisach-Arrhenius model to predict the change in magnetic stability with changes in temperature was investigated. For a commercially prepared magnetic particle tape it was found that, above 150 K, good agreement with the model obtains. However, below 150 K the results are at variance with the theory. Modifications to the theory which will improve its predictive capability over the entire temperature range have been developed.
A series of measurements have been made on the alloy system Zr3(Rh1-xPdx)4. This system is unique in that it exhibits rapid changes in its magnetic and superconducting properties over a narrow range of composition, the same range of composition in which incommensurate waves appear in the crystal structure. These results may have profound implications for theories of magnetism and superconductivity.
External Collaborations:
We are collaborating with several companies which produce magnetic measurement equipment and magnetic materials. We also collaborate with researchers at George Washington University, the State University of New York at Buffalo, and the University of Maryland.
Output:
Standard Reference Materials:
A nickel sphere for the calibration of magnetometers (such as vibrating sample magnetometers) was issued as SRM 772a.
Publications:
Della Torre, E., Swartzendruber, L. J., Bennett, L. H., and Rugkwamsook, P., "Experimental Test of the Preisach-Arrhenius Model with Temperature," accepted for publication in Physica B.
Della Torre, E. and Bennett, L. H., "A Preisach Model for Aftereffect," IEEE Trans. Magn. 34, 1276, 1998.
Swartzendruber, L. J., Bennett, L. H., Della Torre, E., Brown, H. J., and Judy, J. H., "Behavior of Magnetic Aftereffect Along a Magnetization Reversal Curve in a Metal Particle Recording Material," Mat. Res. Soc. Symp. Proc., 517, 355, 1998.
Della Torre, E., Bennett, L.H., and Swartzendruber, L. J., "Modeling Complex Aftereffect Behavior in Recording Materials using a Preisach-Arrhenius Approach," Mat. Res. Soc. Symp. Proc., 517, 291, 1998.
Reimers, A., and Della Torre, E., "Fast Preisach Based Magnetostriction Model for Highly Magnetostrictive Materials," accepted for publication by the IEEE Trans. Magn. 34, 3857, 1998.
Presentations:
Swartzendruber, L. J., "The Correlation between Magnetic and Mechanical Properties in Low Alloy Sheet Steel," ASNT Spring Meeting, Orlando, FL, March 1999.
6 March 2000