Synthesis and Characterization of Permanent Magnetic Nanocomposites
Kunpeng Su, Xuehong Cui, Zhongwu Liu, and Dechang Zeng
Department of Metallic Materials Science and Engineering, School of Material Science and Engineering,
South China University of Technology, Guangzhou, 610640, China
Research Group for Magnetic Materials and Functional Thin Films http://www.mmff-scut.com
Melt-spun REFeB alloys
Introduction
-0.50
Experimental
1.6
140
1.4
120
1.2
100
1.0
80
0.8
Close symbols: Jr
60
40
P -27
C om position design
P -1
0
500
m agnetic m easurem ents
w et-chem ical
P-22
P-16
577.9C
624.9C
x=0
-0.06
400

-0.04
300~400K
300~473K
300~550K
-0.02
8
Fig.2 Correlation between jHC, Jr and (BH)max for melt spun NdFe-B based alloys with a wide range of compositions.
800
（ TemperatureC）
-0.03
2000
600
-0.05
10
12
14
Z (RE Content)
1. For melt spun REFeB alloys, upper limits of (BH)max (160-180 kJ/m3 or 19-21.5 MGOe) for are obtained
at the coercivity range 400-800 kA/m (Fig.2).
2. Nanopcomposite alloys have better thermal stability than single phase and RE-rich phase alloys (Fig.3)
3. Small additions have an important role in modifying the phase precipitation and the microstructure
(Fig.4).
 Fe3B
Pr2Fe23B3
Fe





Pr2Fe14B


b



Fig. 3 Temperature coefficiences of remanence () and
coercivity () for NdPr-FeCo-B alloys


30
 
40



50
a

60
70
80
2 (degree)
Fig.4 Top: DSC of RE-Fe-M-B Alloys with various Nb
addition; bottom: XRD patterns for alloys without (a)
and with (b) Nb addition
Bottom-up approach
←HCP
↖FCC
Fig.5 The photograph of as-cast rod of RE-Fe-Co-M-B BMG
Fig.8 Morphology for FeCo magnetic nanoparticles deposited by chemical methods before
(left) and after (right) heat treatment
intensity (counts)
400
300
200
100
30
60
90
2(degree)
Fig.6 XRD pattern of RE-Fe-Co-M-B as-cast rod,
showing amorphous structure
Fig.9 Morphology and XRD patterns for Nd–Fe-B/nano-Fe composite powders synthesized
by chemical synthesizing Fe nanoparticles on Nd–Fe-B powders
P -20
1.5
1.0
P-9
0.5
J (T)
P -23
P -14
0.0
-0.5
-1.0
C onstruction analysis
P-15
x=1
627.4C
-0.07
H , kA/m
j C
P -7
P -13
572.2C
2.0
P -7
P-12
1500
614.6C
P-5
suction casting
H eat T reatm ent
1000
x=2
579.3C
Single phase
-0.35
0.4
P -1
P-8
-0.40
RE-Rich
-0.30
0.6
Open symbols: (BH)max
Nanocomposite
Intensity
(BH)max, kJ/m
160
Jr, T
180
, %/K
Rapid quenched
RE-FeCo-B-(M) alloys 1.8
(Nd0.25Pr0.75)Z(Fe0.7Co0.3)94-zB6
Heat Flow
2.0
Suction cast magnets
The
nanocomposite magnets were synthesized by
various methods, as shown in Fig.1.
The Nd2Fe14B/-Fe nanocomposite alloys ribbons were
prepared by argon arc melting and melt spinning.
The Nd2Fe14B/Fe3B nanocomposite bulk magnets were
produced by devitrifying the bulk metallic glasses (BMGs)
with B-rich compositions of RE-Fe-Co-M-B. The BMG
precursors were prepared by suction casting.
Nd–Fe-B/nano-Fe Composite powders were synthesized
by
chemically
depositing
Fe
nanoparticles
on
11.5Nd81Fe1.9Co5.6B hard magnetic powders with a
average particle size of 100～200 µm. The Fe nanoparticle
synthesis employed wet chemistry method according to the
reaction: FeCl2 + NaBH4 +H2O→Fe(B) + NaCl + H2 +H2O [1].
The hard magnetic powders were immersed in the reaction
solution and acted as a substrate onto which the Fe
nanoparticles formed and deposited.
XRD, SEM and VSM were used to characterize the
microstructure and magnetic properties of experimental
materials.
m elt spinning
-0.45
, %/K
200
3
Since last decade, there has been great scientific
interest in the preparation and processing of nanocomposite
permanent magnets, due to the prediction of their high
theoretical magnetic properties [1,2]. The basic principle in
the nanocomposite magnet is to exchange couple a hard
magnetic phase with high coercivity (jHC) and a soft
magnetic phase with high magnetization (JS). The predicted
value of the maximum energy product (BH)max in this
composite system is about 120 MGOe, significantly higher
than that obtained so far in the superior single-phase system
NdFeB system, which is about 56 MGOe [3,4]. So the
exchange couple behavior is particularly a useful way to
develop superior permanent magnets. The most widely used
materials today are NdFeB alloy, SmCo alloy , FePt alloy
and hard ferrites in hard magnetic phase and Fe, Ni, Co,
Fe(Co) in soft magnetic phase.
So far, there are two routes to prepare such hard/soft
nanocomposite magnets. Most of the efforts followed “top
down” metallurgical routes, i.e., development of the
nanostructure through rapid solidification or high-energy
mechanical milling. The other route is “bottom up” approach
which assembles composite material by attaching soft
magnetic phase to hard magnetic phase [5].
We report here the recent work in SCUT China on the
nanocomposite magnetic magnets by these two routes,
including melt spinning, suction casting + annealing and
chemical deposition.
o
650 C/5min
o
700 C/5min
-1.5
P-16
-2.0
-1500
P-15
A nalysis and discuss
-1000
-500
0
500
1000
1500
H (kA/m)
1. The soft magnetic Fe, Co and FeCo spherical nanoparticles with mean sizes of 20-50
nm were synthesized. Nanospheres chains and hcp-structured nanorods can be
obtained by magnetic field assisted process and heat treatment, respectively.
2. The immersion of NdFeB micro-particles in the chemical solution of FeCl2+NaBH4
leads to the formation of NdFeB/nano-Fe composites, which provides a new
approach to realize exchange coupling in hard/soft magnets.
P -18
Process
O ptim ization
Fig .7 The hysteresis loops of rapidly solidified RE-Fe-M-B saloys
annealed at various temperatures
P -19
H igh Perform ance
M agnets
References
O ptim ization
Fig. 1 The Overview of Synthetic Routes
P -20
1. BMG rod with 2 mm in diameter was successfully prepared for
RE-Fe-Co-M-B alloys, which can be devitrified to
Nd2Fe14B/Fe3B nanocomposite magnet (Fig.5 and Fig.6).
2. High (BH)max (59.7 kJ/m3) can be achieved for these RE-FeCo-M-B alloys(Fig.7).
[1] R. Skomski, J.M.D. Coey, Phys. Rev. B 48 (1993) 15812.
[2] T. Schrefl, R. Fischer, J. Fidler, H. Kronmuller, J. Appl. Phys. 76 (1994) 7053.
[3 T. Schrefl, J. Fidler, H. Kronmuller, Phys Rev B 49 (1994) 6100.
[4] W. Rodewald, B. Wall, M. Katter, K. Uestuener, IEEE Trans. Magn. 38 (2002) 2955.
[5] Girija S. Chaubey, Vikas Nandwana,et.al ,Chem. Mater. 2008, 20, 475–478
华南理工大学材料科学与工程学院磁性材料与功能薄膜学术团队