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 CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 55, 2016 

A publication of 

 

The Italian Association 
of Chemical Engineering 
Online at www.aidic.it/cet 

Guest Editors: Tichun Wang, Hongyang Zhang, Lei Tian
Copyright © 2016, AIDIC Servizi S.r.l., 
ISBN 978-88-95608-46-4; ISSN 2283-9216 

Effect of Ho Doping and Annealing on Magnetostrictive 
Properties of Tb-Dy-Ho-Fe/Epoxy Composites 

Ran Zhao*a, b, Bowen Wanga, Shuying Caoa, Jie Xiaoc  
a
School of Electrical Engineering, Hebei University of Technology, Guangrong road No.8, Tianjin, China  

b
Jiangxi Province Key laboratory of Precision Drive & Control, Nanchang Institute of Technology, Tianxiang Road No.289, 

Nanchang, China 
c
School of Materials Engineering, Hebei University of Technology, Guangrong road No.8, Tianjin, China  

zhaoran@nit.edu.cn 

The effect of Ho-doping and annealing on magnetostriction and magnetostriction hysteresis of Tb-Dy-Ho-Fe/ 
epoxy composites was investigated in this paper. The polymer bonded (Tb0.15Ho0.85Fe1.9)x+(Tb0.3Dy0.7Fe1.9)1-x 
composites (x=0.21, 0.25 and 0.31) were prepared and annealed in a vacuum magnetic heat treatment 
furnace at 20, 80, 100 and 150 °C. The microstructure of the sample was then observed by optical 
microscopy. The magnetostricion of the composites was studied by a standard strain gauge technique. The 
research results showed that when the Ho content x=0.31, the composites exhibited large magnetostriction 
and small magnetostriction hysteresis. When annealing temperature is 100°C, the composites have a 
maximum magnetostriction at 695 ppm. 

1. Introduction 
In recent decades, giant magnetostrictive materials (Tb-Dy-Fe alloys) have attracted great attention due to 
their large magnetostriction (1500-2000 ppm) at room temperature (Claeyssen et al., 1999 and Squire, 2011). 
Compared to other smart materials, such as shape memory alloy and piezoelectric, it exhibits obvious 
advantages of applications in transducers and actuators (Shigenao et al., 2001, VANNESSA and 
CERROLAZA, 2013, Rajan et al., 2015, Morega et al., 2016). However, the high saturation magnetic field and 
large magnetostriction hysteresis has restricted its applications (Zhao et al., 1998). The investigations of 
magnetostrictive hysteresis have shown that the addition of Ho element to Tb-Dy-Fe alloys can reduce the 
hysteresis width and improve the magnetostriction in the low magnetic field (Busbridge and Piercy, 1999, 
Wang et al., 2014, 2015, 2015 and 2016). 
The excellent magnetostrictive properties of Tb-Dy-Ho-Fe alloys can be utilized with polymer bonding 
technology (Lim et al., 1999, Jonhson and Amirouche, 2008, Dong et al., 2011) to fabricate the Tb-Dy-Ho-
Fe/epoxy composites. This composites exhibits advantages of superior mechanical properties, high frequency 
performance and low cost. Thus, Tb-Dy-Ho-Fe/epoxy composites is hoped to find applications in high 
sensitivity magnetometers and ultrasonic transducers (Karafi et al., 2003, Wang and Feng, 2013). In 
summery, the research on the magnetostrictive properties of Tb-Dy-Ho-Fe/epoxy composites is of great 
significance.  
In this study, the effect of the Ho-doping and annealing temperature on the magnetostriction and 
magnetostriction hysteresis of Tb-Dy-Ho-Fe/epoxy composites was studied. And we fabricated the 
(Tb0.15Ho0.85Fe1.9)x+(Tb0.3Dy0.7Fe1.9)1-x/epoxy composites with different Ho content, and annealed the 
composites at different temperatures. Then we studied the magnetostriction and magnetostriction hysteresis, 
and the influence of annealing temperature on the magnetostriction of the composites. 

2. Experiments 
The magnetostrictive compounds were prepared from materials of the following purity: Tb, Dy, and Ho (99.9 
wt.%), Fe (99.8 wt.%). The (Tb0.15Ho0.85Fe1.9)x+(Tb0.3Dy0.7Fe1.9)1-x (x=0.21, 0.25 and 0.31) compounds were 

                               
 
 

 

 
   

                                                  
DOI: 10.3303/CET1655051

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Please cite this article as: Zhao R., Wang B.W., Cao S.Y., Xiao J., 2016, Effect of ho doping and annealing on magnetostrictive properties of 
tb-dy-ho-fe/epoxy composites, Chemical Engineering Transactions, 55, 301-306  DOI:10.3303/CET1655051   

301



 

 

melted in an arc furnace under high purity argon. The as-cast samples wrapped in Mo foil were sealed in a 
silica tube filled with high purity argon and were homogenized at 1000 °C for 24 h and at 950 °C for 120 h. 
The Tb-Dy-Ho-Fe alloys was crushed in absolute ethanol by a ball milling machine, into the particle size range 
of 75-180 μm. 
Double component epoxy resin (AB resin) was used as the matrix. Its working temperature is 200 °C. The 
mass fraction of A-component, B-component and magnetostrictive particles is 5:1: 100. Mixing process of the 
resin and magnetostrictive particles was operated in the glove box. Then the mixture was transferred to the 
mould, where it was compressed by the press machine at 2.5 MPa for 5 min. Finally, the mixture was cured at 
room temperature, made into 10×10×5 mm samples. This method was used to prepare the samples with Ho 
content of x=0.21, 0.31 and 0.25. 
The microstructure of the composites was observed using the optical microscope at first. And then the 
magnetostriction and the magnetostriction hysteresis of the samples were measured by the magnetic 
measurement system. The samples were annealed in a vacuum magnetic field heat treatment furnace, and 
the heating temperatures were 25, 80, 100 and 150 °C. At last, the annealed of the samples were tested and 
their magnetostriction curves were compared. 

3. Results and Discussion 
3.1 Microstructure 
The optical microscope was utilized to observe the microstructure of the composites. Figure 1 shows the 
microsructure of Tb0.25Dy0.45Ho0.31Fe1.9/epoxy composites.From the figure, we can see that the black part is 
the epoxy matrix, the white area is the magnetostrictive particle. The particles are uniformly distributed in the 
matrix, and the magnetostrictive particles are aligned in the direction of the long axis of the composites. The 
proposed composites has typical pseudo 1-3 structure. 

 

Figure 1: Optical micrograph of the Tb0.25Dy0.45Ho0.31Fe1.9/epoxy composites 

3.2 The effect of Ho content 
The influence of Ho element on the magnetostriction of Tb-Dy-Ho-Fe alloy has been researched in literature 
(JIANG et al., 2009, Wang et al., 2014) already. Therefore, it is reasonable to suppose that magnetocrystalline 
anisotropy constant K1 and magnetostrictive hysteresis decreases with increasing Ho content in range of 
0.1<x<0.6. In this section, the Tb-Dy-Ho-Fe/epoxy composites with different Ho content are tested to 
investigate whether this rule applicable to the magnetostrictive composites.  
Figure 2 exhibits the λ-H curves with varying Ho content. When x=0.21, the saturation magnetostriction λs is 
480 ppm. And the magnetostriction λ is 82 ppm at 100 kA/m, λ=220 ppm at 200 kA/m. Its saturation magnetic 
field is 760 kA/m. When x=0.25, the composite is saturated at 755 kA/m and λs is 514 ppm. In the meantime, 
its magnetostriction is 110 ppm at 100 kA/m, and λ=263 ppm at 200 kA/m. When x=0.31, the saturation 
magnetostriction and saturation magnetic field of the sample are 605 ppm and 750 kA/m, respectively. At 100 
kA/m applied magnetic field, its magnetostriction increase to 202 ppm, and λ=387 ppm when H is 200 kA/m. 
From Figure 2 we found an obvious growth that with the increasing of Ho content, λs of the composites is also 
increased, and the saturation magnetic field strength is decreased. In the low magnetic field (<100 kA/m), the 
composites’ magnetostriction is greatly improved when x=0.31. 
  

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Figure 2: The λ-H curves of (Tb0.15Ho0.85Fe1.9)x+(Tb0.3Dy0.7Fe1.9)1-x/epoxy composites with x=0.21, 0.25 and 
0.31 

The magnetostriction hysteresis width of (Tb0.15Ho0.85Fe1.9)x+(Tb0.3Dy0.7Fe1.9)1-x/epoxy composites was tested 
at 50, 100, 150 and 200 kA/m applied magnetic field, respectively. Its hysteresis characteristics are shown in 
Figure 2 and Figure 3. Figure 3 shows the variation of hysteresis width Wh with Ho content. When x=0.21, the 
maximum hysteresis width is 9.1 kA/m at 100 kA/m applied magnetic field. The maximum hysteresis width 
appears at 100 kA/m and its value is 7 kA/m when x=0.25. And when x=0.31, the maximum hysteresis width is 
3 kA/m at 150 kA/m. These events that the composites has the minimum hysteresis width when the Ho 
content is 0.31. The improvement in the hysteresis width by Ho element is particularly evident in the low 
magnetic field. 

 

Figure 3: The hysteresis width of (Tb0.15Ho0.85Fe1.9)x+(Tb0.3Dy0.7Fe1.9)1-x/epoxy composites with x=0.21, 0.25 
and 0.31 

In Figure 4, the ratio of magnetostriction to hysteresis width (λ/Wh) at megnetic field of 50, 100, 150, 200 kA/m 
are shown, which is determined by the measured magnetostriction and hysteresis width curves shown in 
Figure 2 and Figure 3. From Figure 4 it can be seen that the ratio rises with increasing x, and it shows a peak 
at 200 kA/m applied magnetic field. And this events that the Tb0.285Dy0.63Ho0.085Fe1.9/epoxy composites 
performs both large magnetostriction and narrow magnetostriction hysteresis. 

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Figure 4: The ratio of magnetostriction to hysteresis width (λ/Wh) of (Tb0.15Ho0.85Fe1.9)x+(Tb0.3Dy0.7Fe1.9)1-x 
/epoxy composites with x=0.21, 0.25 and 0.31 

3.2 The effect of annealing 
In order to investigate the influence of the annealing effect on the magnetostrictive performance, the magnetic 
field heat treatment experiments were performed on the composites. The annealing temperatures chosen 
were 20, 80, 100 and 150 °C. 

 

Figure 5: Magnetostriction curves after annealing at 25, 80, 100 and 150 °C (x=0.31) 

As annealed at 25 and 80 °C, the magnetostriction didn’t show obviously change. When the heating treatment 
temperature was 100 °C, the saturation magnetostriction reached 695 ppm. However, when the temperature 
was increased further to 150 °C, the magnetostrictive properties of the sample were greatly decreased, and 
the value was 550 ppm. As discussed in references (Or et al., 2003, Na et al., 2004 and Dong et al., 2010), 
there are several factors determining the magnetostrictive performance of the composites: the shape, size and 
magnetostriction of magnetostrictive particles, the young's modulus of the composites. In this The optimum 
annealing temperature has been found at 100 °C. At this temperature, the rich rare-earth phase (Tb, Dy, Ho) 
in Tb-Dy-Ho-Fe alloys will be reduced. Due to this, the magnetostriction performance will be improved. Also 
noted is that the residual thermal stress generated during the heat process will increase the saturation 
magnetostriction of the composites. Conversely, over-heating will reduce the performance of Tb-Dy-Ho-Fe 
particles in the composites, as well as the young's modulus of the composites. 

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4. Conclusions 
In this work, the influence of Ho content and annealing on the magnetostriction performance of the 
(Tb0.15Ho0.85Fe1.9)x+(Tb0.3Dy0.7Fe1.9)1-x/epoxy composites was studied. In order to find the optimum Ho content 
and heat treatment temperature, we fabricated the samples with Ho content at x=0.21, 0.25 and 0.31. And 
annealed these samples by a magnetic vacuum magnetic field heat treatment furnace with heating 
temperatures of 25, 80, 100 and 150 °C. We also experimented with the magnetostrictive performance, and 
found some patterns as follows: 
(1) The performances of magnetostrictive composites will be improved by Ho element. With increasing of x, 
the composites’ magnetostrictive hysteresis was reduced and the saturation magnetostirction was promoted. 
When x=0.31, a large magnetostriction (605 ppm) and narrow magnetostrictive hysteresis (Wh is 3 KA/m at 
150 KA/m applied magnetic field) were observed. Which illustrated that Ho-doping is beneficial to increasing 
the magnetostriction under low magnetic field and reducing the hysteresis width of Tb-Dy-Ho-Fe/epoxy 
composites. 
(2) An appropriate heat treatment temperature is helpful for the properties of magnetostrictive composites. 
When annealed at 100 °C, the saturation magnetostriction is increased to 695 ppm, and the magnetostriction 
property at low magnetic field is retained. However, it is noted that the over-heating in the heat treatment 
process will cause damages and decline the magnetostrictive performance of the Tb-Dy-Ho-Fe/epoxy 
composites. 

Acknowledgments  

This work was supported by National Natural Science Foundation of China under granted No.51171057 and 
University Science and Technology Key Program of Hebei Province under granted No.ZD201600. 

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