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The effect of refractory (Zr, Hf) elements on the magnetocaloric property of Mn-based alloys
Accepted Manuscript The effect of refractory (Zr, Hf) elements on the magnetocaloric property of Mn-based alloys
A.Y. Lee, S.Y. Kim, Y.D. Kim, M.H. Lee PII: DOI: Reference:
S0169-4332(19)30302-2 https://doi.org/10.1016/j.apsusc.2019.01.271 APSUSC 41670
To appear in:
Applied Surface Science
Received date: Revised date: Accepted date:
30 July 2018 26 December 2018 29 January 2019
Please cite this article as: A.Y. Lee, S.Y. Kim, Y.D. Kim, et al., The effect of refractory (Zr, Hf) elements on the magnetocaloric property of Mn-based alloys, Applied Surface Science, https://doi.org/10.1016/j.apsusc.2019.01.271
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
The effect of refractory (Zr, Hf) elements on the magnetocaloric property of Mnbased alloys a,b
A. Y. Lee , S. Y. Kima, Y. D. Kimb and M. H. Leea,* a
Advanced Process and Materials R&D Group, Korea Institute of Industrial Technology, 21999, Incheon, Republic of KOREA b
Department of Materials Science and Engineering, Hanyang University, 04763, Seoul, Republic of
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KOREA
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Abstract
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This study was investigated the effect of additional elements on the magnetocaloric property in MnFeXPGe (X=Zr, Hf) alloys. The magnetocaloric property of alloys depending on the decrease of the
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additional element was enhanced about 7.52J/kgK and 94.84J/kg at 242K in the Mn1.2Fe0.79Zr0.01P0.6Ge0.4 alloy. We were able to deduce that the magnetocaloric property was affected by the strong magneto-
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crystalline anisotropy resulting from high volume % of main phase (≥50%). The strong magnetocrystalline anisotropy was induced by the homogeneous dendritic structures and distinct main peak with
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(112̅0) plane in Mn1.2Fe0.8-x(Zr,Hf)xP0.6Ge0.4 (x=0.01, 0.05, 0.1 at.%) alloys.
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crystalline anisotropy
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Keywords: Magnetocaloric effect, Magnetic entropy change, Crystallographic anisotropy, Magneto-
*Corresponding author: Min-Ha Lee Tel.: +82-32-850-0424, Fax: +82-32-850-0410 E-mail: [email protected]
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1. Introduction Recently, there are many efforts to improve the earth environment. Specifically, refrigerants in cooling devices are changed an eco-friendly materials such as carbon dioxide or liquefied petroleum gas [1-3]. Among eco-friendly refrigerants, solid state magnetic materials have been interesting [4-5]. The magnetic materials such as MnFe-based magnetocaloric alloys, particularly MnFePGe alloys, have a lot
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of advantages i.e. large magnetocaloric effect, rare-earth free, and low cost. There were many experiments to enhance the magnetocaloric property by adding the constitute elements in MnFePGe
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alloys [6-9] and to demonstrate the relationship between magnetic properties such as magnetization or
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magnetic flux density and crystallographic orientation in FeCrNi or electrical steel alloys [10-11]. The magnetocaloric property such as Curie temperature and magnetic entropy change could be changed by
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concentrations of the constitute elements because that is influenced by the magnetic interactions dependence of variation of occupied atom sites and subsequently lattice parameters in conventional MnFePGe(Si) alloys [12-13]. Although there existed half-Heusler alloys with MNiSn (M=Hf, Ti, Zr) as
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thermoelectric materials [14], up to now, there is no report that the effect of Zr or Hf element addition on the magnetocaloric property in MnFePGe alloys. Moreover, the effect of crystallographic orientation on
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the magnetocaloric property in MnFePGe alloys is still unexplored.
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In this study, we investigated the effect of variation and concentration of additional elements implementing large magnetocaloric effect by tuning the refractory (Zr, Hf) elements in MnFePGe alloys. In addition, the effect of anisotropy of crystalline phases on the magnetocaloric property of
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MnFe(Zr,Hf)PGe alloys was also evaluated.
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2. Material and methods
The Mn1.2Fe0.8-xMxP0.6Ge0.4 (M=Zr, Hf, x=0.01, 0.05, 0.1 at.%) alloys were fabricated by using Mn2P (2N), Fe (4N), Zr (2N), Hf (3N), and Ge (5N) elements. The final ribbon samples were prepared by melt spinning under argon atmosphere after arc melting. The melt-spun ribbons went through heat treatment for 24 hours at 1373K in high vacuum (10-5Torr) and cooled in the chamber. The micro and crystal structure were analyzed by field emission scanning electron microscope (FE-SEM, Quanta 200 FEG) with X-ray energy dispersive spectroscopy (EDS), electron backscattered diffraction (EBSD), and X-ray diffraction (XRD, PANalytical, X’Pert PRO) with Cu-Kα radiation, respectively. In addition, the 2
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magnetocaloric effect was analyzed at constant and varying magnetic field (0.01T and 0 to 2T) by vibration sample magnetometer (VSM, Quantum design Inc.). Furthermore, the magnetic entropy change (ΔSm) and the relative cooling power (RCP) were calculated by using the Maxwell relation and Gschneidner and Pecharsky method, respectively [15].
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3. Results and discussion In SEM images of Figure 1, the alloys show dendritic structures except the H3 sample with cellular
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structures. Particularly, homogeneous microstructures from more uniform distributions of phases were
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exhibited in the Z1, Z2, and H1 samples. The homogeneity of microstructures could be changed depending on the contents of constituent elements and consequently affected the magnetocaloric
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properties [16]. All samples were separated into bright and dark areas marked as white and red colors arrow, respectively. According to EDS mapping in Figure 1, the bright and dark regions represented Gerich and P-rich areas, respectively. However, the H3 sample was occurred Fe-rich compositions in overall
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areas and observed Hf-rich areas in the cellular structures (marked as white color arrow). The chemical composition of each region marked as arrows in Figure 1 is summarized in Table 1. These results were
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consisted with XRD patterns in Figure 2. The main phases were identified as Ge6Fe3Mn4 (hexagonal,
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p6/mmm) and HfFe6Ge6 (hexagonal, p6/mmm), and the secondary phase was analyzed by Mn1.9P (hexagonal, p6̅2𝑚). Interestingly these two main phases were indicated as the minority phase in conventional MnFePGe alloys (hexagonal Fe2P-type, p6̅2𝑚) [17-19]. The major peak of main phase of
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MnFe(Zr,Hf)PGe samples varied depending on the concentration of additional Zr and Hf elements. J. Yang et al. [20] also reported that the effect of additional elements on phase formation and microstructure.
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They demonstrated the change of major peak and inhomogeneous microstructures depending on the increase of additional elements. As mentioned above, these variations are influenced by the atom sites and lattice parameters which varied to substitution of additional elements. Therefore, the critical peak with (112̅0) and (1̅21̅3) planes in the Ge6Fe3Mn4 and HfFe6Ge6 phases, respectively, became dominant as shown in the Z1 and H1 samples. On the other hand, the dominant peak of the Z3, H2, and H3 samples was exhibited the {21̅1̅9} plane in the Ge6Fe3Mn4 and HfFe6Ge6 phases. In case of the Z2 sample, the main peaks were indicated the (21̅1̅3) and (0001) planes in the Ge6Fe3Mn4 and Mn1.9P phases, respectively. However, the other peaks included the (21̅1̅9) plane were existed with significantly strong 3
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intensity. In Figure 3, the orientation images indicated color mapping is shown with phase mapping and pole figure. Those EBSD images shown in Figures 3(a) ~ 3(f) were analyzed for crystallographic anisotropy of MnFe(Zr,Hf)PGe alloys. The pole figure image in Figure 3(g) presented that the orientations of MnFe(Zr,Hf)PGe alloys shown large magnetocaloric effect were aligned to near the dotted line crossed
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the [31̅2̅1] and [31̅2̅0] orientations represented by sky-blue and green colors. The crystallographic anisotropy was higher in the Z1, Z2, and H1 samples with homogeneous microstructures and critical main
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peak of the Ge6Fe3Mn4 or HfFe6Ge6 phases with (112̅0) or {1̅21̅3} planes. Furthermore, especially the
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Z1 sample with the highest crystallographic anisotropy was correlated to the behavior of larger volume % of the Ge6Fe3Mn4 main phase. The phase volume % in each sample is summarized in Table 2. In addition,
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the crystallographic anisotropy was decreased by increase content of additional Zr and Hf elements. It was reported that the magnetic properties of alloys were influenced by the crystallographic anisotropy [10-11]. In Figure 4, the magnetocaloric properties of the Z1, Z2, and H1 samples with
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homogeneous microstructures, critical main peak of the Ge6Fe3Mn4 or HfFe6Ge6 phases with (112̅0) or {1̅21̅3} planes, and strong crystallographic anisotropy were larger than those of the Z3, H2, and H3
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samples. Nevertheless, the Z2 sample was indicated the strong crystallographic anisotropy and the main
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peak of the Ge6Fe3Mn4 phase with (21̅1̅3) plane, the magnetocaloric properties were lower than those of the Z1 and H1 samples. It is considered that another peak of the Mn1.9P phase with (0001) plane was coexisted with the main peak of the Ge6Fe3Mn4 phase with (21̅1̅3) plane. Moreover, the peak of the
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Ge6Fe3Mn4 phase with (21̅1̅9) plane was observed with considerable intensity rather than that in the Z1 and H1 samples. It was reported that magnetic materials have an easy and hard magnetization axes when
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magnetic field is applied. These magnetic materials could be easily and quickly magnetized if structures of those are became critical oriented texture with easy magnetization axes. That is called magnetocrystalline anisotropy [21-22]. In the MnFe(Zr,Hf)PGe alloys, it was suggested that the (112̅0) and {1̅21̅3} planes were crystal texture with easy magnetization direction rather than the (0001) and (21̅1̅9) planes. Therefore, the magneto-crystalline anisotropy of Z1 and H1 samples was higher than that of Z2 sample as well as the other samples and sequently the magnetocaloric properties were enhanced.
4. Conclusions 4
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The conventional MnFePGe alloys are promising candidates as non-rare earth element based magnetocaloric materials. In this study, the magnetocaloric properties of MnFePGe alloys were tuned by controlling the additional elements (Zr and Hf) in the Mn-based compound. In the case of Mn1.2Fe0.79Zr0.01P0.6Ge0.4 alloy with low concentration of additional element, the magnetocaloric properties were the largest at about 7.52J/kgK and 94.84J/kg at 242K among the other alloys with
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increased additional elements. The enhanced magnetocaloric property of Mn1.2Fe0.79M0.01P0.6Ge0.4 (M=Zr, Hf) alloys was due to the strong magneto-crystalline anisotropy resulting from large volume % (≥50%) of
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distinct main peak of the Ge6Fe3Mn4 phase with the (112̅0) plane.
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the Ge6Fe3Mn4 main phase, which was mainly influenced by homogeneous dendritic microstructures and
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Acknowledgements
This work was supported by the Industrial Technology Innovation program, as funded by the Ministry
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of Trade, Industry & Energy (MOTIE), Republic of Korea through the Korea Evaluation Institute of Industrial Technology (KEIT) (No.10053101). This research was also financially supported by the Ministry of Trade, Industry and Energy (MOTIE) and Korea Institute for Advancement of Technology
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(KIAT) through the International Cooperative R&D program (No. N0001713).
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Fig. 1. The SEM images obtained from (a) Z1, (b) Z2, (c) Z3, (e) H1, (f) H2, and (g) H3 content alloys, respectively, and EDS mapping of (d) Z1, (h) H1, and (i) H3 in the Mn 1.2Fe0.8-x(Zr,Hf)xP0.6Ge0.4 (x=0.01, 0.05, 0.1) alloys.
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Fig. 2. The XRD patterns with phase peaks (red peak: Ge 6Fe3Mn4 phase (JCPDS #00-030-0581), blue peak: HfFe6Ge6 phase (JCPDS #00-047-1209), green peak: Mn1.9P phase (JCPDS #01-079-1436)) and crystal orientations in the Mn1.2Fe0.8-x(Zr,Hf)xP0.6Ge0.4 (x=0.01, 0.05, 0.1) alloys.
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Fig. 3. The EBSD images with phase mapping of red (Ge 6Fe3Mn4 [(a) Z1, (b) Z2, and (c) Z3 samples] and HfFe6Ge6 [(d) H1, (e) H2, and (f) H3 samples] phases) and green colors (Mn 1.9P phase in all samples) and (g) pole figure with distribution of crystal orientations in each sample.
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Fig. 4. (a) Temperature curve dependence of magnetization and (b) temperature curve dependence of magnetic entropy change in the Mn1.2Fe0.8-x(Zr,Hf)xP0.6Ge0.4 (x=0.01, 0.05, 0.1) alloys. The insets in (a) and (b) are curves of Z3 and H3 samples.
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Table 1. The chemical compositions indicated the arrow in the Figure 1 by analyzing the EDS. P Zr Mn Fe Hf Ge
Z1 (Zr0.01)
Z2 (Zr0.05)
Z3 (Zr0.1)
H1 (Hf0.01)
H2 (Hf0.05)
H3 (Hf0.1)
White
Red
White
Red
White
Red
White
Red
White
Red
White
Red
Blue
0.20 0.15 20.17 27.49 51.99
17.08 0.24 37.65 37.27 7.77
0.05 0.41 19.88 28.86 50.81
16.20 0.00 39.15 35.89 8.75
3.14 3.92 22.89 26.18 43.87
16.86 0.00 42.50 32.67 7.97
0.23 17.43 29.27 2.73 50.34
16.31 37.99 36.33 1.88 7.49
0.10 14.74 32.59 1.45 51.12
16.55 30.16 39.46 6.43 7.39
15.29 10.49 41.33 30.44 2.44
0.10 10.19 38.53 1.75 49.43
16.09 27.27 45.00 2.03 9.61
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wt.%
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Table 2. The magnetocaloric properties and the phase volume % in the Figure 3. Phase Vol.% TC RCP |△SM| Alloys (K) (J/kg) Ge Fe Mn HfFe 6 3 4 6Ge6 (J/kgK) Z1 (Zr0.01) 242 7.52 94.84 55 (50:3:2) Z2 (Zr0.05) 227 6.14 69.64 22 (15:5:2) Z3 (Zr0.1) 187 0.15 5.91 64 (38:21:5) H1 (Hf0.01) 237 6.99 86.89 34 H2 (Hf0.05) 177 1.91 40.59 21 (11:10) H3 (Hf0.1) 402 0.007 0.16 79 (50:14:5:4:3:2:1)
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Mn1.9P 45 (27:17:1) 78 (66:12) 36 (15:13:5:3) 66 (42:18:6) 79 (22:18:18:12:6:3) 21 (8:8:3:1:1)
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Graphical Abstract We investigated the effect of refractory (Zr, Hf) elements on the magnetocaloric property of Mn-based alloys. The alloys with low content (0.01 at.%) of additional element, especially Zr element, were improved the magnetocaloric property. The enhanced magnetocaloric property was influenced by the strong magneto-crystalline anisotropy. In addition, the strong anisotropy was induced by distinct main peak with (112̅0) plane. Therefore, controlling of refractory elements and magneto-crystalline
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anisotropy is important to obtain enhanced magnetocaloric materials.
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Highlights ▶ Alloys with low content of additional Zr, Hf elements were improved the magnetocaloric property.
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▶ Magnetocaloric properties of alloy with Zr element were higher than those of alloy with Hf element.
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▶ The magneto-crystalline anisotropy was affected the magnetocaloric property.
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▶ The strong anisotropy was influenced by distinct main peak with critical crystal orientation.
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A.Y. Lee, S.Y. Kim, Y.D. Kim, M.H. Lee PII: DOI: Reference:
S0169-4332(19)30302-2 https://doi.org/10.1016/j.apsusc.2019.01.271 APSUSC 41670
To appear in:
Applied Surface Science
Received date: Revised date: Accepted date:
30 July 2018 26 December 2018 29 January 2019
Please cite this article as: A.Y. Lee, S.Y. Kim, Y.D. Kim, et al., The effect of refractory (Zr, Hf) elements on the magnetocaloric property of Mn-based alloys, Applied Surface Science, https://doi.org/10.1016/j.apsusc.2019.01.271
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
The effect of refractory (Zr, Hf) elements on the magnetocaloric property of Mnbased alloys a,b
A. Y. Lee , S. Y. Kima, Y. D. Kimb and M. H. Leea,* a
Advanced Process and Materials R&D Group, Korea Institute of Industrial Technology, 21999, Incheon, Republic of KOREA b
Department of Materials Science and Engineering, Hanyang University, 04763, Seoul, Republic of
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KOREA
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Abstract
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This study was investigated the effect of additional elements on the magnetocaloric property in MnFeXPGe (X=Zr, Hf) alloys. The magnetocaloric property of alloys depending on the decrease of the
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additional element was enhanced about 7.52J/kgK and 94.84J/kg at 242K in the Mn1.2Fe0.79Zr0.01P0.6Ge0.4 alloy. We were able to deduce that the magnetocaloric property was affected by the strong magneto-
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crystalline anisotropy resulting from high volume % of main phase (≥50%). The strong magnetocrystalline anisotropy was induced by the homogeneous dendritic structures and distinct main peak with
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(112̅0) plane in Mn1.2Fe0.8-x(Zr,Hf)xP0.6Ge0.4 (x=0.01, 0.05, 0.1 at.%) alloys.
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crystalline anisotropy
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Keywords: Magnetocaloric effect, Magnetic entropy change, Crystallographic anisotropy, Magneto-
*Corresponding author: Min-Ha Lee Tel.: +82-32-850-0424, Fax: +82-32-850-0410 E-mail: [email protected]
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1. Introduction Recently, there are many efforts to improve the earth environment. Specifically, refrigerants in cooling devices are changed an eco-friendly materials such as carbon dioxide or liquefied petroleum gas [1-3]. Among eco-friendly refrigerants, solid state magnetic materials have been interesting [4-5]. The magnetic materials such as MnFe-based magnetocaloric alloys, particularly MnFePGe alloys, have a lot
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of advantages i.e. large magnetocaloric effect, rare-earth free, and low cost. There were many experiments to enhance the magnetocaloric property by adding the constitute elements in MnFePGe
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alloys [6-9] and to demonstrate the relationship between magnetic properties such as magnetization or
SC
magnetic flux density and crystallographic orientation in FeCrNi or electrical steel alloys [10-11]. The magnetocaloric property such as Curie temperature and magnetic entropy change could be changed by
NU
concentrations of the constitute elements because that is influenced by the magnetic interactions dependence of variation of occupied atom sites and subsequently lattice parameters in conventional MnFePGe(Si) alloys [12-13]. Although there existed half-Heusler alloys with MNiSn (M=Hf, Ti, Zr) as
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thermoelectric materials [14], up to now, there is no report that the effect of Zr or Hf element addition on the magnetocaloric property in MnFePGe alloys. Moreover, the effect of crystallographic orientation on
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the magnetocaloric property in MnFePGe alloys is still unexplored.
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In this study, we investigated the effect of variation and concentration of additional elements implementing large magnetocaloric effect by tuning the refractory (Zr, Hf) elements in MnFePGe alloys. In addition, the effect of anisotropy of crystalline phases on the magnetocaloric property of
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MnFe(Zr,Hf)PGe alloys was also evaluated.
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2. Material and methods
The Mn1.2Fe0.8-xMxP0.6Ge0.4 (M=Zr, Hf, x=0.01, 0.05, 0.1 at.%) alloys were fabricated by using Mn2P (2N), Fe (4N), Zr (2N), Hf (3N), and Ge (5N) elements. The final ribbon samples were prepared by melt spinning under argon atmosphere after arc melting. The melt-spun ribbons went through heat treatment for 24 hours at 1373K in high vacuum (10-5Torr) and cooled in the chamber. The micro and crystal structure were analyzed by field emission scanning electron microscope (FE-SEM, Quanta 200 FEG) with X-ray energy dispersive spectroscopy (EDS), electron backscattered diffraction (EBSD), and X-ray diffraction (XRD, PANalytical, X’Pert PRO) with Cu-Kα radiation, respectively. In addition, the 2
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magnetocaloric effect was analyzed at constant and varying magnetic field (0.01T and 0 to 2T) by vibration sample magnetometer (VSM, Quantum design Inc.). Furthermore, the magnetic entropy change (ΔSm) and the relative cooling power (RCP) were calculated by using the Maxwell relation and Gschneidner and Pecharsky method, respectively [15].
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3. Results and discussion In SEM images of Figure 1, the alloys show dendritic structures except the H3 sample with cellular
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structures. Particularly, homogeneous microstructures from more uniform distributions of phases were
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exhibited in the Z1, Z2, and H1 samples. The homogeneity of microstructures could be changed depending on the contents of constituent elements and consequently affected the magnetocaloric
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properties [16]. All samples were separated into bright and dark areas marked as white and red colors arrow, respectively. According to EDS mapping in Figure 1, the bright and dark regions represented Gerich and P-rich areas, respectively. However, the H3 sample was occurred Fe-rich compositions in overall
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areas and observed Hf-rich areas in the cellular structures (marked as white color arrow). The chemical composition of each region marked as arrows in Figure 1 is summarized in Table 1. These results were
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consisted with XRD patterns in Figure 2. The main phases were identified as Ge6Fe3Mn4 (hexagonal,
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p6/mmm) and HfFe6Ge6 (hexagonal, p6/mmm), and the secondary phase was analyzed by Mn1.9P (hexagonal, p6̅2𝑚). Interestingly these two main phases were indicated as the minority phase in conventional MnFePGe alloys (hexagonal Fe2P-type, p6̅2𝑚) [17-19]. The major peak of main phase of
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MnFe(Zr,Hf)PGe samples varied depending on the concentration of additional Zr and Hf elements. J. Yang et al. [20] also reported that the effect of additional elements on phase formation and microstructure.
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They demonstrated the change of major peak and inhomogeneous microstructures depending on the increase of additional elements. As mentioned above, these variations are influenced by the atom sites and lattice parameters which varied to substitution of additional elements. Therefore, the critical peak with (112̅0) and (1̅21̅3) planes in the Ge6Fe3Mn4 and HfFe6Ge6 phases, respectively, became dominant as shown in the Z1 and H1 samples. On the other hand, the dominant peak of the Z3, H2, and H3 samples was exhibited the {21̅1̅9} plane in the Ge6Fe3Mn4 and HfFe6Ge6 phases. In case of the Z2 sample, the main peaks were indicated the (21̅1̅3) and (0001) planes in the Ge6Fe3Mn4 and Mn1.9P phases, respectively. However, the other peaks included the (21̅1̅9) plane were existed with significantly strong 3
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intensity. In Figure 3, the orientation images indicated color mapping is shown with phase mapping and pole figure. Those EBSD images shown in Figures 3(a) ~ 3(f) were analyzed for crystallographic anisotropy of MnFe(Zr,Hf)PGe alloys. The pole figure image in Figure 3(g) presented that the orientations of MnFe(Zr,Hf)PGe alloys shown large magnetocaloric effect were aligned to near the dotted line crossed
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the [31̅2̅1] and [31̅2̅0] orientations represented by sky-blue and green colors. The crystallographic anisotropy was higher in the Z1, Z2, and H1 samples with homogeneous microstructures and critical main
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peak of the Ge6Fe3Mn4 or HfFe6Ge6 phases with (112̅0) or {1̅21̅3} planes. Furthermore, especially the
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Z1 sample with the highest crystallographic anisotropy was correlated to the behavior of larger volume % of the Ge6Fe3Mn4 main phase. The phase volume % in each sample is summarized in Table 2. In addition,
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the crystallographic anisotropy was decreased by increase content of additional Zr and Hf elements. It was reported that the magnetic properties of alloys were influenced by the crystallographic anisotropy [10-11]. In Figure 4, the magnetocaloric properties of the Z1, Z2, and H1 samples with
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homogeneous microstructures, critical main peak of the Ge6Fe3Mn4 or HfFe6Ge6 phases with (112̅0) or {1̅21̅3} planes, and strong crystallographic anisotropy were larger than those of the Z3, H2, and H3
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samples. Nevertheless, the Z2 sample was indicated the strong crystallographic anisotropy and the main
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peak of the Ge6Fe3Mn4 phase with (21̅1̅3) plane, the magnetocaloric properties were lower than those of the Z1 and H1 samples. It is considered that another peak of the Mn1.9P phase with (0001) plane was coexisted with the main peak of the Ge6Fe3Mn4 phase with (21̅1̅3) plane. Moreover, the peak of the
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Ge6Fe3Mn4 phase with (21̅1̅9) plane was observed with considerable intensity rather than that in the Z1 and H1 samples. It was reported that magnetic materials have an easy and hard magnetization axes when
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magnetic field is applied. These magnetic materials could be easily and quickly magnetized if structures of those are became critical oriented texture with easy magnetization axes. That is called magnetocrystalline anisotropy [21-22]. In the MnFe(Zr,Hf)PGe alloys, it was suggested that the (112̅0) and {1̅21̅3} planes were crystal texture with easy magnetization direction rather than the (0001) and (21̅1̅9) planes. Therefore, the magneto-crystalline anisotropy of Z1 and H1 samples was higher than that of Z2 sample as well as the other samples and sequently the magnetocaloric properties were enhanced.
4. Conclusions 4
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The conventional MnFePGe alloys are promising candidates as non-rare earth element based magnetocaloric materials. In this study, the magnetocaloric properties of MnFePGe alloys were tuned by controlling the additional elements (Zr and Hf) in the Mn-based compound. In the case of Mn1.2Fe0.79Zr0.01P0.6Ge0.4 alloy with low concentration of additional element, the magnetocaloric properties were the largest at about 7.52J/kgK and 94.84J/kg at 242K among the other alloys with
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increased additional elements. The enhanced magnetocaloric property of Mn1.2Fe0.79M0.01P0.6Ge0.4 (M=Zr, Hf) alloys was due to the strong magneto-crystalline anisotropy resulting from large volume % (≥50%) of
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distinct main peak of the Ge6Fe3Mn4 phase with the (112̅0) plane.
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the Ge6Fe3Mn4 main phase, which was mainly influenced by homogeneous dendritic microstructures and
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Acknowledgements
This work was supported by the Industrial Technology Innovation program, as funded by the Ministry
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of Trade, Industry & Energy (MOTIE), Republic of Korea through the Korea Evaluation Institute of Industrial Technology (KEIT) (No.10053101). This research was also financially supported by the Ministry of Trade, Industry and Energy (MOTIE) and Korea Institute for Advancement of Technology
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(KIAT) through the International Cooperative R&D program (No. N0001713).
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Fig. 1. The SEM images obtained from (a) Z1, (b) Z2, (c) Z3, (e) H1, (f) H2, and (g) H3 content alloys, respectively, and EDS mapping of (d) Z1, (h) H1, and (i) H3 in the Mn 1.2Fe0.8-x(Zr,Hf)xP0.6Ge0.4 (x=0.01, 0.05, 0.1) alloys.
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Fig. 2. The XRD patterns with phase peaks (red peak: Ge 6Fe3Mn4 phase (JCPDS #00-030-0581), blue peak: HfFe6Ge6 phase (JCPDS #00-047-1209), green peak: Mn1.9P phase (JCPDS #01-079-1436)) and crystal orientations in the Mn1.2Fe0.8-x(Zr,Hf)xP0.6Ge0.4 (x=0.01, 0.05, 0.1) alloys.
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Fig. 3. The EBSD images with phase mapping of red (Ge 6Fe3Mn4 [(a) Z1, (b) Z2, and (c) Z3 samples] and HfFe6Ge6 [(d) H1, (e) H2, and (f) H3 samples] phases) and green colors (Mn 1.9P phase in all samples) and (g) pole figure with distribution of crystal orientations in each sample.
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Fig. 4. (a) Temperature curve dependence of magnetization and (b) temperature curve dependence of magnetic entropy change in the Mn1.2Fe0.8-x(Zr,Hf)xP0.6Ge0.4 (x=0.01, 0.05, 0.1) alloys. The insets in (a) and (b) are curves of Z3 and H3 samples.
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Table 1. The chemical compositions indicated the arrow in the Figure 1 by analyzing the EDS. P Zr Mn Fe Hf Ge
Z1 (Zr0.01)
Z2 (Zr0.05)
Z3 (Zr0.1)
H1 (Hf0.01)
H2 (Hf0.05)
H3 (Hf0.1)
White
Red
White
Red
White
Red
White
Red
White
Red
White
Red
Blue
0.20 0.15 20.17 27.49 51.99
17.08 0.24 37.65 37.27 7.77
0.05 0.41 19.88 28.86 50.81
16.20 0.00 39.15 35.89 8.75
3.14 3.92 22.89 26.18 43.87
16.86 0.00 42.50 32.67 7.97
0.23 17.43 29.27 2.73 50.34
16.31 37.99 36.33 1.88 7.49
0.10 14.74 32.59 1.45 51.12
16.55 30.16 39.46 6.43 7.39
15.29 10.49 41.33 30.44 2.44
0.10 10.19 38.53 1.75 49.43
16.09 27.27 45.00 2.03 9.61
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wt.%
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Table 2. The magnetocaloric properties and the phase volume % in the Figure 3. Phase Vol.% TC RCP |△SM| Alloys (K) (J/kg) Ge Fe Mn HfFe 6 3 4 6Ge6 (J/kgK) Z1 (Zr0.01) 242 7.52 94.84 55 (50:3:2) Z2 (Zr0.05) 227 6.14 69.64 22 (15:5:2) Z3 (Zr0.1) 187 0.15 5.91 64 (38:21:5) H1 (Hf0.01) 237 6.99 86.89 34 H2 (Hf0.05) 177 1.91 40.59 21 (11:10) H3 (Hf0.1) 402 0.007 0.16 79 (50:14:5:4:3:2:1)
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Mn1.9P 45 (27:17:1) 78 (66:12) 36 (15:13:5:3) 66 (42:18:6) 79 (22:18:18:12:6:3) 21 (8:8:3:1:1)
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Graphical Abstract We investigated the effect of refractory (Zr, Hf) elements on the magnetocaloric property of Mn-based alloys. The alloys with low content (0.01 at.%) of additional element, especially Zr element, were improved the magnetocaloric property. The enhanced magnetocaloric property was influenced by the strong magneto-crystalline anisotropy. In addition, the strong anisotropy was induced by distinct main peak with (112̅0) plane. Therefore, controlling of refractory elements and magneto-crystalline
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anisotropy is important to obtain enhanced magnetocaloric materials.
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Highlights ▶ Alloys with low content of additional Zr, Hf elements were improved the magnetocaloric property.
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▶ Magnetocaloric properties of alloy with Zr element were higher than those of alloy with Hf element.
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▶ The magneto-crystalline anisotropy was affected the magnetocaloric property.
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▶ The strong anisotropy was influenced by distinct main peak with critical crystal orientation.
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