1995 Fiscal Year Final Research Report Summary
Methods of Test for Rare Earth Magnet Materials
| Project/Area Number |
06650784
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Structural/Functional materials
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| Research Institution | Tohoku Institute of Technology |
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Principal Investigator |
NAKAGAWA Yasuaki Tohoku Institute of Technology, Faculty of Engineering, Professor, 工学部, 教授 (10005944)
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| Co-Investigator(Kenkyū-buntansha) |
KATO Hiroaki Tohoku University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (40177465)
OHBA Katsuhiko Tohoku Institute of Technology, Faculty of Engineering, Professor, 工学部, 教授 (50085388)
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| Project Period (FY) |
1994 – 1995
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| Keywords | rare earth magnet / test method for permanent magnets / magnetization curve / demagnetizing factor |
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| Research Abstract |
(1) Magnetization measurements by an induction method without a closed magnetic circuit
The methods for testing permanent magnet materials stipulated in the industrial standards are closed magnetic circuit methods which employ a loop tracer using an iron-core electromagnet. If the coercivity exceeds the highest magnetic field generated by the electromagnet, full hysteresis curves cannot be obtained. In the present work, higher magnetic fields were produced by a high-power water-cooled magnet, and the magnetization was measured by an induction method with an open magnetic circuit. The absolute value of magnetization was obtained by calculation, and calibrated by pure nickel samples.
(2) Demagnetizing factors determined by the magnetization of soft magnetic materials
In the open magnetic circuit method, the demagnetizing field should be corrected. The correction for cylindrical samples is rather difficult because of the non-uniformity of magnetization. For soft magnetic materials, however, mean demagnetizing factors can be determined from the gradient of initial magnetization curve. We determined these factors using pure nickel cylinders with various dimension rations, although the application of this correction to hard magnetic materials is doubtful.
(3) Magnetization measurements for various permanent magnet materials
Rare earth magnet materials such as sintered or bonded Sm-Co and Nd-Fe-B were provided by a number of manufacturers. Magnetizations of cylindrical samples with 10 mm in diameter and 2 mm, 3.5 mm, 7 mm or 14 mm in length were measured. The magnetization curves for the samples with different dimension ratios become almost identical after the correction using the demagnetizing factors determined by nickel samples. It should be emphasized, however, that the demagnetizing correction for hard magnetic materials is not justified in principle, and so the dimensions of the sample should be specified when the data obtained are used as industrial standards.
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