Microstructure and magnetization reversal of iron-rare-earth-boron permanent magnets

Thesis/Dissertation · Thu Jan 01 00:00:00 EST 1987

OSTI ID:5180665

Ramesh, R

Investigation of the microstructure and details of magnetization reversal of the new class of permanent magnets was undertaken to understand the inter-relationship between the microstructure and magnetic properties of the magnets. The overall microstructure consists of almost defect-free grains of the matrix Nd{sub 2}Fe{sub 14}B surrounded by a Nd-rich, oxygen-stabilized, fcc phase. Through examination of the virgin magnetization curve, the applied-field dependence of the intrinsic coercivity, and remanence, it was shown that the magnet behaves as a nucleation-controlled magnet. Since the interiors of the matrix grains are defect-free, domain-wall nucleation occurs due to defects at the grain boundaries and two-phase interfaces. One possible defect is oxygen which can be a cause for the large difference between the anisotropy field and the intrinsic coercivity, even in the case of an optimally treated magnet. The effect of post-sintering heat treatments upon the intrinsic coercivity and energy product was rationalized, based upon the above observations. Increase in the cooling rate after sintering leads to a decrease in the intrinsic coercivity due to the effect of quenching stresses, caused by thermal-expansion mismatch at the fcc phase-matrix interface.

• Research Organization: California Univ., Berkeley, CA (USA)
• OSTI ID: 5180665
• Resource Relation: Other Information: Thesis (Ph. D.)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
42 ENGINEERING
BORON ALLOYS
MAGNETIC PROPERTIES
IRON ALLOYS
NEODYMIUM ALLOYS
PERMANENT MAGNETS
MICROSTRUCTURE
COERCIVE FORCE
DEFECTS
OXYGEN
ALLOYS
CRYSTAL STRUCTURE
ELEMENTS
MAGNETS
NONMETALS
PHYSICAL PROPERTIES
RARE EARTH ALLOYS
360104* - Metals & Alloys- Physical Properties
420500 - Engineering- Materials Testing