Evidence for domain wall pinning by a magnetic grain‐boundary phase in sintered Nd‐Fe‐B based permanent magnets

1988 ◽  
Vol 63 (8) ◽  
pp. 3321-3323 ◽  
Author(s):  
K. J. Strnat ◽  
H. F. Mildrum ◽  
M. Tokunaga ◽  
H. Harada
Keyword(s):  
Domain Wall ◽  
Grain Boundary ◽  
Permanent Magnets ◽  
Boundary Phase ◽  
Domain Wall Pinning

A HYBRID MODEL ON HYSTERESIS LOOP AND COERCIVITY IN NANOSTRUCTURED PERMANENT MAGNETS

2006 ◽  
Vol 05 (04n05) ◽  
pp. 627-631 ◽  
Author(s):  
M. J. SUN ◽  
G. P. ZHAO ◽  
J. LIANG ◽  
G. ZHOU ◽  
H. S. LIM ◽  
...  
Keyword(s):  
Thin Films ◽  
Domain Wall ◽  
Grain Boundary ◽  
Magnetic Moment ◽  
Permanent Magnets ◽  
Hysteresis Loops ◽  
Bulk Materials ◽  
Rotational Model ◽  
Moment Distribution ◽  
Coercivity Mechanism

A simplified micromagnetic model has been proposed to calculate the hysteresis loops of nanostructured permanent magnets for various configurations, including thin films, exchange-coupled double-layer systems and bulk materials. The reversal part of the hysteresis is based on the Stoner–Wohlfarth coherent rotational model and the coercivity mechanism is due mainly to the motion of the transition region (a domain wall like magnetic moment distribution in the grain boundary). The elements of nucleation and pinning models are also incorporated.

scholarly journals The study of domain-wall pinning by inhomogeneities in nanocrystalline permanent magnets

2003 ◽  
Vol 52 (3) ◽  
pp. 708
Author(s):  
Rong Chuan-Bing ◽  
Zhang Hong-Wei ◽  
Zhang Jian ◽  
Zhang Shao-Ying ◽  
Shen Bao-Gen
Keyword(s):  
Domain Wall ◽  
Permanent Magnets ◽  
Domain Wall Pinning

Magnetism of Nd–Fe films as a model of grain boundary phase in Nd–Fe–B permanent magnets

2015 ◽  
Vol 9 (1) ◽  
pp. 013002 ◽  
Author(s):  
Akimasa Sakuma ◽  
Tsuneaki Suzuki ◽  
Takahiro Furuuchi ◽  
Toshiyuki Shima ◽  
Kazuhiro Hono
Keyword(s):  
Grain Boundary ◽  
Permanent Magnets ◽  
Boundary Phase

scholarly journals Nanocompositional Electron Microscopic Analysis and Role of Grain Boundary Phase of Isotropically Oriented Nd-Fe-B Magnets

2017 ◽  
Vol 2017 ◽  
pp. 1-17 ◽  
Author(s):  
Gregor A. Zickler ◽  
Josef Fidler
Keyword(s):  
Domain Wall ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Magnetization Reversal ◽  
Coercive Field ◽  
Microscopic Analysis ◽  
Realistic Model ◽  
Boundary Phase ◽  
Electron Microscopic ◽  
The Impact

Nanoanalytical TEM characterization in combination with finite element micromagnetic modelling clarifies the impact of the grain misalignment and grain boundary nanocomposition on the coercive field and gives guidelines how to improve coercivity in Nd-Fe-B based magnets. The nanoprobe electron energy loss spectroscopy measurements obtained an asymmetric composition profile of the Fe-content across the grain boundary phase in isotropically oriented melt-spun magnets and showed an enrichment of iron up to 60 at% in the Nd-containing grain boundaries close to Nd2Fe14B grain surfaces parallel to the c-axis and a reduced iron content up to 35% close to grain surfaces perpendicular to the c-axis. The numerical micromagnetic simulations on isotropically oriented magnets using realistic model structures from the TEM results reveal a complex magnetization reversal starting at the grain boundary phase and show that the coercive field increases compared to directly coupled grains with no grain boundary phase independently of the grain boundary thickness. This behaviour is contrary to the one in aligned anisotropic magnets, where the coercive field decreases compared to directly coupled grains with an increasing grain boundary thickness, if Js value is > 0.2 T, and the magnetization reversal and expansion of reversed magnetic domains primarily start as Bloch domain wall at grain boundaries at the prismatic planes parallel to the c-axis and secondly as Néel domain wall at the basal planes perpendicular to the c-axis. In summary our study shows an increase of coercive field in isotropically oriented Nd-Fe-B magnets for GB layer thickness > 5 nm and an average Js value of the GB layer < 0.8 T compared to the magnet with perfectly aligned grains.

Magnetic coercivity

1987 ◽  
Vol 65 (10) ◽  
pp. 1194-1199 ◽  
Author(s):  
Paul Gaunt
Keyword(s):  
Statistical Theory ◽  
Domain Wall ◽  
Permanent Magnets ◽  
Domain Wall Pinning ◽  
Magnetic Hardening

The theory of magnetic hardening and its impact on the design of permanent magnets is presented. The statistical theory of domain-wall pinning by sample inhomogeneities is outlined, and its relevance to the latest generation of permanent magnets is discussed.

scholarly journals A Combined TEM/STEM and Micromagnetic Study of the Anisotropic Nature of Grain Boundaries and Coercivity in Nd-Fe-B Magnets

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Gregor A. Zickler ◽  
Josef Fidler ◽  
Johannes Bernardi ◽  
Thomas Schrefl ◽  
Ahmad Asali
Keyword(s):  
Domain Wall ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Coercive Field ◽  
Boundary Phase ◽  
Micromagnetic Simulations ◽  
Fe Content ◽  
Néel Domain Wall ◽  
High Resolution Tem ◽  
Numerical Finite Element

The nanoanalytical high resolution TEM/STEM investigation of the intergranular grain boundary phase of anisotropic sintered and rapidly quenched heavy rare earth-free Nd-Fe-B magnet materials revealed a difference in composition for grain boundaries parallel (large Fe-content) and perpendicular (low Fe content) to the alignment direction. This behaviour vanishes in magnets with a high degree of misorientation. The numerical finite element micromagnetic simulations are based on the anisotropic compositional behaviour of GBs and show a decrease of the coercive field with an increasing thickness of the grain boundary layer. The magnetization reversal and expansion of reversed magnetic domains primarily start as Bloch domain wall at grain boundaries parallel to thec-axis and secondly as Néel domain wall perpendicular to thec-axis into the adjacent hard magnetic grains. The increasing misalignment of grains leads to the loss of the anisotropic compositional behaviour and therefore to an averaged value of the grain boundary composition. In this case the simulations show an increase of the coercive field compared to the anisotropic magnet. The calculated coercive field values of the investigated magnet samples are in the order ofμ0HcJ=1.8 T–2.1 Tfor a mean grain boundary thickness of 4 nm, which agrees perfectly with the experimental data.

scholarly journals Ferroelectric domain wall pinning at a bicrystal grain boundary in bismuth ferrite

2008 ◽  
Vol 93 (14) ◽  
pp. 142901 ◽  
Author(s):  
Brian J. Rodriguez ◽  
Y. H. Chu ◽  
R. Ramesh ◽  
Sergei V. Kalinin
Keyword(s):  
Domain Wall ◽  
Grain Boundary ◽  
Bismuth Ferrite ◽  
Ferroelectric Domain ◽  
Domain Wall Pinning
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