Journal of the Korean Physical Society, Vol 62, No 12, June 2013, pp 1715∼1719 Magnetocaloric Effect in Fe-Ni-Zr Alloys Prepared by Using the Rapidly-quenched Method Nguyen Huy Dan,∗ Nguyen Huu Duc, Tran Dang Thanh, Nguyen Hai Yen and Pham Thi Thanh Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam Ngac An Bang and Do Thi Kim Anh Hanoi University of Science, 334 Nguyen Trai, Hanoi, Vietnam The-Long Phan and Seong-Cho Yu† Chungbuk National University, Cheongju 361 - 763, South Korea (Received 31 May 2012, in final form 21 July 2012) Fe90−x Nix Zr10 (x = 0, 5, 10, 15, 20 and 25) ribbons with various thicknesses were prepared by using a melt-spinning technique The Curie temperature, TC , of the alloys dramatically decreased from ∼960 K to room temperature at high quenching rates When the alloys had an amorphous structure, their TC strongly depended on the Ni concentration The maximum entropy change, |∆Sm |max , with ∆H = 12 kOe, of the alloys was around J·kg−1 K−1 at room temperature On the other hand, the full width at half maximum the entropy-change peak was quite large, ∼ 85 K, which was suitable for applications in magnetic refrigerators at room temperature PACS numbers: 75.30.Sg, 07.20.Mc, 75.50.Kj Keywords: Magnetocaloric effect, Refrigeration, Amorphous magnetic materials DOI: 10.3938/jkps.62.1715 I INTRODUCTION The giant magnetocaloric effect (GMCE) in materials is of interest in research virtue of its potential applications in the field of magnetic refrigeration Magnetic refrigeration is based on the principle of magnetic entropy change in materials under a varying magnetic field The application of magnetocaloric materials in refrigerators has the advantages of avoiding environmental pollution (unlike the refrigerators using compressed gases), improving the cooling efficiency (saving energy), reducing noise, and fitting some special cases The main problems to be addressed to improve the practical applications of magnetocaloric materials are: i) creating the GMCE in a low field, because creating a large magnetic field in civil devices is very difficult, ii) taking the magnetic phase transition temperature (working temperature) of materials with the GMCE to room temperature, and iii) extending the working temperature range (range with the GMCE) for materials to be cooled to a large temperature range In addition, some other properties of materials, such as the heat capacity, electrical conductivity, thermal conductivity, durability, price, etc., also need to be ∗ E-mail: † E-mail: dannh@ims.vast.ac.vn scyu@chungbuk.ac.kr addressed for the application of GMCE materials Along with the goal of saving energy and protecting the environmental, searches for magnetocaloric materials with capabilities for applications in magnetic refrigeration at room temperature are increasingly of interest in research Notably, the results obtained for Gd-containing magnetocaloric alloys (GdSiGe, GdCo .) [1, 2] have shown capabilities for extensive applications of magnetic refrigeration technology A number of devices using magnetic refrigerants have been experimentally produced with Gd-containing magnetocaloric alloys However, Gd-containing alloys have very high costs due to the scarcity of raw materials and the strict manufacturing technology In addition, Gd-containing alloys not satisfy a number of other requirements such as strength and thermal conductivity Besides Gdcontaining alloys, some of other magnetocaloric materials are of interest in studies on the mechanisms and possible applications These materials include As-containing alloys (MnAsSb, MnFePAs .) [3, 4], La-containing alloys (LaFeSi), Heusler alloys (CoMnSi, NiMnSn, NiMnGa .) [5,6] and ferromagnetic perovskite maganites [7,8] Recently, many researchers have focused on magnetocaloric materials with amorphous or nanocrystalline structures [9–12] The main advantages of amorphous or nanocrystalline materials are their capabilities -1715- -1716- Journal of the Korean Physical Society, Vol 62, No 12, June 2013 for the GMCE, low coercivity, high resistivity, roomtemperature magnetic phase transition and low cost, which are necessary requirements for practical applications Among this kind of GMCE materials, the Fe-Zrbased alloys have been attracting the attention of many scientists [13–19] In this work, we investigate the magnetocaloric effect in Fe-Ni-Zr alloys prepared by using the rapidly-quenched method II EXPERIMENTS AND DISCUSSION The alloys with nominal compositions of Fe90−x Nix Zr10 (x = 0, 5, 10, 15, 20 and 25) were prepared from pure metals (99.9%) of Fe, Ni and Zr An arc-melting method was first used to ensure the homogeneity of the alloys A melt-spinning method with various quenching rates was then used to fabricate the ribbon samples The variation of the quenching rate depended on such factors as the tangential velocity of the copper wheel, the hole in the quartz crucible, the injection pressure, etc The thickness (d) of the ribbon is commonly used to distinguish the quenching rate of the ribbon In this work, the ribbons with thicknesses of 15 and 30 µm were investigated The structure of the samples was examined by using powder X-ray diffraction (XRD) The magnetic properties of the samples were characterized by using magnetization measurements Figure shows XRD patterns of Fe90−x Nix Zr10 ribbons with various thicknesses Diffraction peaks corresponding to the crystalline phases of α-Fe, FeNi and NiZr2 are observed in these patterns However, the crystalline fraction in all the samples is small, i.e., the amorphous phase is dominant We can see that the diffraction peaks of the thinner (d = 15 m) ribbons, especially the ones with x = - 15, are very weak, which means these ribbons are almost amorphous The structural phase fraction strongly influences the magnetic properties of the alloys as presented below Thermomagnetization measurements was performed for Fe90−x Nix Zr10 ribbons with different thickness Figure presents reduced thermomagnetization curves for some typical ribbons The thermomagnetization curves of the ribbons with d = 30 µm manifest their multi-phase behaviors These ribbons have a magnetic phase transition in the temperature range of 250 - 500 K corresponding to the amorphous phase After the first transition, the magnetization of these ribbons does not decrease to zero, but maintains values characterizing the crystalline phase The magnetic transition in the temperature range of 250 - 500 K is thought to be of an amorphous nature because the ribbons prepared at a high quenching rate (their structure is fully amorphous) only have this transition As for the ribbons prepared at a low queching rate, their structure is partly crystalline (the lower the quenching rate, the higher the crystalline fraction) The magnetization of the ribbon prepared at temperature above 500 Fig XRD patterns of Fe90−x Nix Zr10 ribbons with d = (a) 30 µm and (b) 15 µm Fig (Color online) Reduced thermomagnetization curves in a magnetic field for 100 Oe of Fe90−x Nix Zr10 ribbons with d = 30 µm The inset shows the thermomagnetization curves in a magnetic field of 10 Oe of Fe90−x Nix Zr10 ribbons with d = 15 µm K is that of a crystalline phase, which has a Curie temperature higher than that of an amorphous phase, and its magnitude is directly proportional to the crystalline Magnetocaloric Effect in Fe-Ni-Zr Alloys Prepared · · · – Nguyen Huy Dan et al -1717- Table Influence of Ni concentration on the coercivity (Hc), Curie temperature (TC ), maximum entropy change (|∆Sm |max ), full width at half maximum (FWHM) of the entropy-change peak and refrigerant capacity (RC) of Fe90−x Nix Zr10 ribbons with d = 15 µm (∆H = 12 kOe) Ni (%) 10 15 Hc (Oe) 30 12 11 12 TC (K) 245 306 356 403 |∆Sm |max (J·kg−1 K−1 ) 0.93 1.09 1.02 0.95 Fig (Color online) Hysteresis loops at 300 K of Fe90−x Nix Zr10 ribbons with d = 15 µm The inset shows the magnetization at a field of 12 kOe vs Ni concentration in the samples fraction; i.e., it depends on the quenching rate The magnetization is then increased considerably by heating the ribbons This is due to the overall crystallization in the ribbons The magnetization of all the ribbons reaches zero after the last magnetic transition at a temperature of about 960 K As for the ribbons with d = 15 µm, their magnetization is almost zero after the first magnetic transition This is in agreement with the above structure analysis These ribbons are almost amorphous resulting in a single magnetic phase transition Thus, the quenching rate plays an important role in reducing the Curie temperature from a high value to a value in the room temperature region The quenching rate must be high enough to make the alloys fully amorphous in the solid state It should be noted that the Curie temperature of the amorphous phase is considerably raised with increasing Ni concentration in the alloy To the contrary, the Curie temperature of Fe90−x Mnx Zr10 ribbons is decreased with increasing Mn concentration [5] These different trends in the variation of the Curie temperature of the alloy can be understood in terms of the exchange interaction The exchange interaction of atoms in the alloy is enhanced by Ni, but reduced by Mn The effect of the Ni concentration on the Curie temperature has a sig- FWHM (K) 92 83 79 74 RC (J·kg−1 ) 86 90 81 70 Fig (Color online) Thermomagnetization curves in various magnetic field of Fe90−x Nix Zr10 ribbons with d = 15 µm The inset shows the magnetization vs magnetic field at 300 K obtained from virgin magnetization (dir.) and thermomagnetization (ind.) curves nificant meaning in controlling the working temperature of the magnetic refrigerants Figure shows the dependence of the magnetization on the external field and the Ni concentration of the ribbons with d = 15 µm We can see that, the ribbons have a soft magnetic feature and that their magnetization increases with increasing Ni concentration The results indicate that the addition of Ni can decrease the coercivity (see Table 1) and increase the saturation magnetization of the alloy These two effects of Ni improve its capacity for applications in magnetic refrigeration According to the obtained results, we selected four samples of Fe90−x Nix Zr10 (x = 0, 5, 10 and 15) ribbons with d = 15 µm to investigate their GMCE These samples showed a single magnetic phase transition at temperatures near room temperature, which is necessary for practical applications of magnetic refrigerants In this study, we calculate the magnetic entropy change, ∆Sm , based on thermomagnetization data (Fig 4) From the thermomagnetization curves for the samples in various magnetic fields, we can deduce the magnetization vs magnetic field, M (H), at various temperatures (Fig -1718- Journal of the Korean Physical Society, Vol 62, No 12, June 2013 Fig (Color online) Magnetization vs magnetic field at various temperatures an deduced from the thermomagnetization curves of Fe85 Ni5 Zr10 ribbons with d = 15 µm 5) This derivation was checked by comparing data (direct data) for a virgin magnetization curve with those (indirect data) deduced from the thermomagnetization curves (inset of Fig 4) We found that the data obtained from the two different ways agreed The ∆Sm was then determined from the M (H) data by using the following relation: H2 ∆Sm = H1 ∂M ∂T H dH (1) By using the proposed method to calculate the entropy change of magnetocaloric materials, we could save experimental time and expense This method is also useful for avoiding the effect of thermal fluctuations in the measurement systems Figure presents ∆Sm (T ) curves (∆H = 12 kOe) for the Fe90−x Nix Zr10 (x = 0, 5, 10 and 15) ribbons with d = 15 µm The maximum entropy change (|∆Sm |max ) of the alloy is nearly unchanged (∼1 J·kg−1 K−1 with ∆H = 12 kOe) while the full width at half maximum (FWHM) of the entropy change peak gradually decreases (from 92 K to 74 K) with increasing Ni concentration (see Table 1) The refrigerant capacity (RC) of the samples, which is defined as the product of the maximum entropy change (∆Smax ) and the full width at half maximum (FWHM) of the entropy change peak, was also calculated (see the inset of Fig 6) The RC of the alloy first increases and then decreases with increasing Ni concentration from to 15 at% Nevertheless, a maximum RC of about 90 J·kg−1 is achieved at a Ni concentration of at% for temperature around room temperature This RC of the Fe90−x Nix Zr10 alloys is higher than those of some amorphous and nanocrystalline alloys such as Finemet (Fe68.5 Mo5 Si13.5 B9 Cu1 Nb3 ), Nanoperm (Fe83−x Cox Zr6 B10 Cu1 , Fe91−x Mo8 Cu1 Bx ), HiT- Fig (Color online) ∆Sm (T ) curves (∆H = 12 kOe) of Fe90−x Nix Zr10 ribbons with d = 15 µm The inset indicates the refrigerant capacity (RC) vs Ni concentration of the alloy perm (Fe60−x Mnx Co18 Nb6 B16 ), and bulk amorphous alloys (Fex Coy Bz CuSi3 Al5 Ga2 P10 ) [6] Table present a summary of the influence of the Ni concentration on the coercivity (Hc ), Curie temperature (TC ), maximum entropy change (|∆Sm |max ), full width at half maximum (FWHM) of entropy change peak, refrigerant capacity (RC) of the Fe90−x Nix Zr10 (x = 0, 5, 10 and 15) ribbons with d = 15 µm In comparison with other materials, we can see that the Fe-Ni-Zr alloy is a good candidate for practical applications in magnetic refrigeration technology III CONCLUSION The Curie temperature of the Fe-Ni-Zr alloy can be regulated in the region of room temperature by choosing an appropriate quenching rate and Ni concentration The quite high maximum entropy change, |∆Sm |max > J·kg−1 K−1 for ∆H = 12 kOe, and the wide working range around room temperature, ∆T ∼ 85 K, reveal potential applications of the rapidly-quenched Fe-Ni-Zrbased alloys in magnetic refrigeration technology ACKNOWLEDGMENTS This work was supported by the National Foundation for Science and Technology Development (NAFOSTED) of Vietnam under grant number of 103.02-2011.23 and the Converging Research Center Program funded by the Ministry of Education, Science and Technology (2012K001431), South Korea A part of the work was Magnetocaloric Effect in Fe-Ni-Zr Alloys Prepared · · · – Nguyen Huy Dan et al done in the Key Laboratory for Electronic Materials and Devices, and Laboratory of Magnetism and Superconductivity, Institute of Materials Science, in Vietnam REFERENCES [1] V Provenzano, A J Shapiro and R D Shull, Nature 429, 853 (2004) [2] V K Pecharsky and K A Gschneidner, Phys Rev Lett 78, 4494 (1997) [3] O Tegus, B Fuquan, W Dagula, L Zhang, E Bră uck, P Z Si, F R de Boer and K H J Buschow, J Alloy Comp 396, (2005) [4] L G Medeiros, N A Oliveira and A 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decrease the coercivity (see Table 1) and increase the saturation