Magnetic Hardening Mechanism in Sintered R-Fe-B Permanent Magnets
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MAGNETIC HARDENING MECHANISM IN SINTERED R-Fe-B PERMANENT MAGNETS
M. SAGAWA AND S. HIROSAWA Sumitomo Special Metals Co.
Ltd.,
Mishimagun,
Osaka 618,
Japan
ABSTRACT The state-of-the-art description of the magnetic hardening mechanism in Recent experimental results the sintered Nd-Fe-B permanent magnet is given. concerning the coercivity-anisotropy (H -HA) correlation in B-rich Pr-Fe-B and Nd-Fe-B sintered magnets and the inhluence of the surface conditions of These results the sintered Nd-Fe-B magnets on the coercivity are reported. are interpreted in terms of theVoH versus c# H -NI plot, where I is the (R=Pr or Rdj anA N the effective spontaneous magnetization of R2 Fe14 demagnetization field coefficient.
INTRODUCTION It has been widely accepted that, in the new class of sintered permanent magnets based on the R Fe 4B inter-metallic compounds (R stands for rare earths), the coercivity is governed by nucleation of reversed domains H I, is related to the anisotropy [(1 and that the intrinsic coercivity, field, HA and the saturation magnetization, IS, of the matrix as [2-53
PoH cI= C0HA-NIS
(i)
The first term in the right side of the equation is the nucleation field of the reversed domains, and the second term arises to take into account the It is presumed that the conlocal stray fields at the nucleation sites. stants c and N are related to the microstructure of the sintered magnets. The purpose of this paper is to study how the constants c and N vary with the change in the composition and microstructure of the sintered Nd-Fe-B and This is the first step necessary for understanding the Pr-Fe-B magnets. magnetic hardening mechanism of the new magnets, leading to improvement of their magnetic properties.
COERCIVITY OF R 5Fe77B8 MAGNETS The HA-H relation in Nd1 Fe7 B sintered magnet has been studied from 8 and from concentration dependences of temperature dependences of H and H In the study, H. andH c in the (NdIxR x)-e-B sycsem (R=Tb, Dy and Er)t2]. tAe HA-HI relationship in the Nd-Fe-B system was compared with the Pr-Fe-B due to a spin reorientation system, •ecause in the latter a complication transition which is observed at 135K [6] in Nd Fe 4B does not exist and therefore a more straight-forward conclusion can e drawn from the Pr-Fe-B This method is applied in the present system than from the Nd-Fe-B system. study also. Figure 1 shows the temperature dependence of H I of PrA Fe77B8 and In spite of the distinct ifference in the Nd 15 Fe 77 B8 sintered magnets [2). anisotropy behavior of the two compounds mentioned above, the HcI-T curves No anomaly is observed at the spin reorienare very similar to each other.
Mat. Res. Soc. Symp. Proc. Vol. 96. ' 1987 Materials Research Society
162
8
10 o Pr15Fe77B8
-
* Ndl5Fe77B8 8-
-6
7-
-5 E
zU
U
4-
-
3 2 21-
a1 0
100
200
300
400
500
0
600
T (K) Fig.
1
Temperature dependence of the intrinsic coercivity of Pr and Nd 15Fe77B8 sintered magnets.
1 5 Fe 7 7
B8
tation temperature (T q) of Nd Fe 1B on the H -T curve for Nd Fe B8 This is an indicati
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