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Title: Characterization of rare earth permanent magnets

Abstract

Recently developed alloys based either on ternary phases such as Nd{sub 2}Fe{sub 14}B (2--14) or on iron-rich pseudobinaries with the ThMn{sub 12}-structure combine excellent intrinsic magnetic properties with the appropriate microstructure for applications as hard magnetic materials. In order to understand the magnetic behavior of these materials, systematic microstructural characterization has been performed using microdiffraction, x-ray microanalyses and high resolution electron microscopy. The magnetic behavior of three types of NdFeB specimens, namely sintered, mechanically alloyed and melt-spun, is correlated to their microstructure. The effect of minority phases on the magnetization and the coercivity in these materials is investigated. The ease with which the nonmagnetic Nd-rich grain boundary phase decouples hard magnetic 2--14'' matrix grains depends on their average grain size which is related to the different preparation processes. 20 refs., 5 figs., 1 tab.

Authors:
;
Publication Date:
Research Org.:
Lawrence Berkeley Lab., CA (United States)
Sponsoring Org.:
USDOE; AVHFOUN; USDOE, Washington, DC (United States)
OSTI Identifier:
5412797
Report Number(s):
LBL-29553; CONF-901059-1
ON: DE91017010
DOE Contract Number:
AC03-76SF00098
Resource Type:
Conference
Resource Relation:
Conference: 11. international workshop on rare earth magnets and their applications and 6th international symposium on magnetic anisotropy and coercivity in rare earth-transition metal alloys, Pittsburgh, PA (United States), 21-24 Oct 1990
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; BORON ALLOYS; MAGNETIC PROPERTIES; MICROSTRUCTURE; IRON BASE ALLOYS; NEODYMIUM ALLOYS; SAMARIUM ALLOYS; TITANIUM ALLOYS; ANNEALING; COLD WORKING; GRAIN SIZE; INTERMETALLIC COMPOUNDS; PERMANENT MAGNETS; SINTERING; TRANSMISSION ELECTRON MICROSCOPY; ALLOYS; CRYSTAL STRUCTURE; ELECTRON MICROSCOPY; FABRICATION; HEAT TREATMENTS; IRON ALLOYS; MAGNETS; MATERIALS WORKING; MICROSCOPY; PHYSICAL PROPERTIES; RARE EARTH ALLOYS; SIZE; 360102* - Metals & Alloys- Structure & Phase Studies; 360104 - Metals & Alloys- Physical Properties

Citation Formats

Huetten, A., and Thomas, G. Characterization of rare earth permanent magnets. United States: N. p., 1991. Web.
Huetten, A., & Thomas, G. Characterization of rare earth permanent magnets. United States.
Huetten, A., and Thomas, G. 1991. "Characterization of rare earth permanent magnets". United States. doi:.
@article{osti_5412797,
title = {Characterization of rare earth permanent magnets},
author = {Huetten, A. and Thomas, G.},
abstractNote = {Recently developed alloys based either on ternary phases such as Nd{sub 2}Fe{sub 14}B (2--14) or on iron-rich pseudobinaries with the ThMn{sub 12}-structure combine excellent intrinsic magnetic properties with the appropriate microstructure for applications as hard magnetic materials. In order to understand the magnetic behavior of these materials, systematic microstructural characterization has been performed using microdiffraction, x-ray microanalyses and high resolution electron microscopy. The magnetic behavior of three types of NdFeB specimens, namely sintered, mechanically alloyed and melt-spun, is correlated to their microstructure. The effect of minority phases on the magnetization and the coercivity in these materials is investigated. The ease with which the nonmagnetic Nd-rich grain boundary phase decouples hard magnetic 2--14'' matrix grains depends on their average grain size which is related to the different preparation processes. 20 refs., 5 figs., 1 tab.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1991,
month = 6
}

Conference:
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  • The hard magnetic properties of rapidly quenched R-Fe-B alloys are reported. Energy products of these isotropic materials for R=Nd and Pr can exceed 14 MGOe with intrinsic coercivities greater than 15 kOe. Magnetic hardening is achieved by quenching directly from the melt or by annealing an over-quenched precursor; in both instances a finely crystalline microstructure of a R{sub 2}Fe{sub 14}B intermetallic phase develops. Microstructure-property relationships for materials prepared by both techniques are discussed.
  • Nd-Fe-B and Sm-Co permanent magnets have been irradiated with fission neutrons and gamma rays. Irradiated samples were periodically removed for room temperature measurements of the open-circuit remanence. Hysteresis loops were measured before and after irradiation. For neutron irradiation, two magnets showed a rapid loss of remanence, while a third decayed more slowly. Irradiation in the Omega West Reactor at Los Alamos with fast neutrons caused the fast-decay samples to have an initial loss of remanence of 1% for irradiation at 350 K to a fluence of 10/sup 15/ n/cm/sup 2/. Both SmCo/sub 5/ and Sm/sub 2/Co/sub 17/ magnets showed excellentmore » resistance to radiation-induced loss of remanence for neutron irradiation to a fluence of 2.6 x 10/sup 18/ n/cm/sup 2/. Results for gamma irradiation are presented and discussed in terms of possible mechanisms for radiation-induced loss of magnetic properties.« less
  • Precision high aspect-ratio micro molds constructed by deep x-ray lithography have been used to batch fabricate accurately shaped bonded rare-earth based permanent magnets with features as small as 5 microns and thicknesses up to 500 microns. Maximum energy products of up to 8 MGOe have been achieved with a 20%/vol. epoxy bonded melt-spun isotropic Nd2Fe14b powder composite. Using individually processed sub- millimeter permanent sections multipole rotors have been assembled. Despite the fact that these permanent magnet structures are small, their magnetic field producing capability remains the same as at any scale. Combining permanent magnet structures with soft magnetic materials andmore » micro-coils makes possible new and more efficient magnetic microdevices.« less
  • Quantifying the relationship between crystallographic texture and magnetic properties is highly desirable for the engineering high (BH){sub max} magnets. Existing techniques for the evaluation of texture in permanent magnets often rely upon magnetic remanence measurements. However, such determinations are strictly applicable only to assemblies of non-interacting particles, which nullifies the use of the Stoner-Wohlfarth criteria in texture determinations of ``exchange-spring`` magnets. New techniques in the determination of texture of bulk permanent magnets are being developed to overcome these inherent experimental difficulties. Crystallographic alignment studied by transmission synchrotron x-ray diffraction as a function of position within the sample reveals insights intomore » the development of texture with deformation level in thermomechanically-processed magnets. Information concerning texture may also be obtained by a different method based on paramagnetic susceptibility measurements. Such measurements also provide Curie temperature data, which is sensitive to chemical changes that may have occurred in the magnetic phase during processing.« less