The coercive field and angular dependence of the coercive field of single-grain Nd2Fe14B permanent magnets are computed using finite element micromagnetics. It is shown that the thickness of surface defects plays a critical role in determining the reversal process. For small defect thicknesses reversal is heavily driven by nucleation, whereas with increasing defect thickness domain wall de-pinning becomes more important. This change results in an observable shift between two well-known behavioral models. A similar trend is observed in experimental measurements of bulk samples, where an Nd-Cu infiltration process has been used to enhance coercivity by modifying the grain boundaries. When account is taken of the imperfect grain alignment of real magnets, the single-grain computed results appears to closely match experimental behaviour.

1.
W.
Brown
, Jr.
,
Rev. Mod. Phys.
17
,
15
(
1945
).
2.
H.
Kronmüller
,
Phys. Status Solidi B
144
,
385
(
1987
).
3.
H.
Kronmüller
,
K.-D.
Durst
, and
M.
Sagawa
,
J. Magn. Magn. Mater.
74
,
291
(
1988
).
4.
T.
Woodcock
,
Y.
Zhang
,
G.
Hrkac
,
G.
Ciuta
,
N.
Dempsey
,
T.
Schrefl
,
O.
Gutfleisch
, and
D.
Givord
,
Scr. Mater.
67
,
536
(
2012
).
5.
D.
Givord
,
Q.
Lu
,
M.
Rossignol
,
P.
Tenaud
, and
T.
Viadieu
,
J. Magn. Magn. Mater.
83
,
183
(
1990
).
6.
D.
Givord
,
M.
Rossignol
, and
V. M.
Barthem
,
J. Magn. Magn. Mater.
258
,
1
(
2003
).
7.
H.
Kronmüller
,
K.
Durst
, and
G.
Martinek
,
J. Magn. Magn. Mater.
69
,
149
(
1987
).
8.
D.
Givord
,
P.
Tenaud
, and
T.
Viadieu
,
J. Magn. Magn. Mater.
72
,
247
(
1988
).
9.
D.
Elbaz
,
D.
Givord
,
S.
Hirosawa
,
F. P.
Missell
,
M. F.
Rossignol
, and
V.
VillasBoas
,
J. Appl. Phys.
69
,
5492
(
1991
).
10.
F.
Cebollada
,
M. F.
Rossignol
,
D.
Givord
,
V.
Villas-Boas
, and
J. M.
González
,
Phys. Rev. B
52
,
13511
(
1995
).
11.
G.
Rieger
,
M.
Seeger
, and
H.
Kronmüller
,
Phys. Status Solidi A
171
,
583
(
1999
).
12.
G.
Hrkac
,
T.
Woodcock
,
C.
Freeman
,
A.
Goncharov
,
J.
Dean
,
T.
Schrefl
, and
O.
Gutfleisch
,
Appl. Phys. Lett.
97
,
232511
(
2010
).
13.
H.
Sepehri-Amin
,
T.
Ohkubo
,
S.
Nagashima
,
M.
Yano
,
T.
Shoji
,
A.
Kato
,
T.
Schrefl
, and
K.
Hono
,
Acta Mater.
61
,
6622
(
2013
).
14.
M. E.
Schabes
and
H. N.
Bertram
,
J. Appl. Phys.
64
,
1347
(
1988
).
15.
H.
Schmidts
and
H.
Kronmüller
,
J. Magn. Magn. Mater.
94
,
220
(
1991
).
16.
17.
H.
Kronmüller
and
H. R.
Hilzinger
,
J. Magn. Magn. Mater.
2
,
3
(
1976
).
18.
D.
Suess
,
J.
Lee
,
J.
Fidler
, and
T.
Schrefl
,
J. Magn. Magn. Mater.
321
,
545
(
2009
).
19.
H.
Kronmüller
and
D.
Goll
,
Physica B
319
,
122
(
2002
).
20.
D.
Suess
,
Appl. Phys. Lett.
89
,
113105
(
2006
).
21.
R.
Grössinger
,
X. K.
Sun
,
R.
Eibler
,
K. H. J.
Buschow
, and
H. R.
Kirchmayr
,
J. Phys.
58
,
55
(
1986
).
22.
M.
Sagawa
,
S.
Fujimura
,
H.
Yamamoto
,
Y.
Matsuura
, and
S.
Hirosawa
,
J. Appl. Phys.
57
,
4094
(
1985
).
23.
T.
Schrefl
,
G.
Hrkac
,
S.
Bance
,
D.
Suess
,
O.
Ertl
, and
J.
Fidler
,
Handbook of Magnetism and Advanced Magnetic Materials
(
Wiley
,
2007
).
24.
J. M. D.
Coey
,
Magnetism and Magnetic Materials
(
Cambridge University Press
,
2004
).
25.
M.
Sharrock
,
J. Appl. Phys.
76
,
6413
(
1994
).
26.
A. J.
Newell
and
R. T.
Merrill
,
J. Appl. Phys.
84
,
4394
(
1998
).
27.
D.
Suess
,
J. Magn. Magn. Mater.
308
,
183
(
2007
).
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