Micromagnetism and the microstructure of high-temperature permanent magnets

Journal Article · Wed Dec 01 04:00:00 EST 2004 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.1809250· OSTI ID:20658102

Goll, D; Kronmueller, H; Stadelmaier, H H ^[1]

---

1. Max-Planck-Institut fuer Metallforschung, Heisenbergstrasse 3, D-70569 Stuttgart (Germany)

Sm{sub 2}(Co,Cu,Fe,Zr){sub 17} permanent magnets with their three-phase precipitation structure (cells, cell walls, and lamellae) show two characteristic features which so far are difficult to interpret but which are the prerequisites for high-temperature applications: (1) The hard magnetic properties only develop during the final step of the three-step annealing procedure consisting of homogenization, isothermal aging, and cooling. (2) Depending on the composition and on the annealing parameters, the temperature dependence of the coercivity can be easily changed from the conventional monotonic to the recent nonmonotonic behavior showing coercivities up to 1 T even at 500 K. The magnetic hardening during cooling is due to the fact that the cell walls order chemically and structurally during the cooling process. From an analysis of electron diffraction patterns of the superimposed structures existing before and after cooling it could be proven that a phase transition from a phase mixture of defective phases 2:17, 2:7, and 5:19 to the ordered 1:5 phase takes place in the cell walls during cooling. The nonmonotonic temperature dependence of the coercivity is narrowly related to the magnetic hardening mechanism which can be either pinning or nucleation and results from the magnetic and microstructural properties of the cell walls. These properties have been determined quantitatively from hysteresis loop measurements and from high-resolution transmission electron microscopy and energy dispersive x-ray analysis. Due to the temperature dependence of the intrinsic magnetic properties, the nonmonotonic temperature dependence of the coercivity is found to be determined by repulsive pinning of domain walls at the cell walls at low temperatures, by attractive pinning of domain walls in the cell walls at intermediate temperatures, and by nucleation at high temperatures. This complex temperature behavior is also reflected in characteristic changes of the angular dependence of the coercivity and can be described quantitatively on the basis of micromagnetism.

• OSTI ID: 20658102
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 11 Vol. 96; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AGING
ANNEALING
CELL WALL
CHEMICAL ANALYSIS
COBALT ALLOYS
COERCIVE FORCE
COOLING
COPPER ALLOYS
CURIE POINT
ELECTRON DIFFRACTION
IRON ALLOYS
MAGNETIC PROPERTIES
MICROSTRUCTURE
PERMANENT MAGNETS
PHASE TRANSFORMATIONS
SAMARIUM ALLOYS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0400-1000 K
TRANSMISSION ELECTRON MICROSCOPY
ZIRCONIUM ALLOYS