Journal of Science: Advanced Materials and Devices (2017) 123e127 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Long-range ferromagnetism and magnetocaloric effects in rapidly quenched Ni50ÀxCoxMn50ÀyAly ribbons Nguyen Thi Mai a, b, Nguyen Hai Yen c, Pham Thi Thanh c, Tran Dang Thanh c, Dinh Chi Linh c, Vu Manh Quang d, Nguyen Mau Lam d, Nguyen Le Thi c, e, Nguyen Thi Thanh Huyen f, Do Thi Kim Anh b, Nguyen Huy Dan c, * a The College of Printing Industry, Phuc Dien, Bac Tu Liem, Ha Noi, Viet Nam Hanoi University of Science, Vietnam National University, 334 Nguyen Trai, Thanh Xuan, Ha Noi, Viet Nam Institute of Material Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Ha Noi, Viet Nam d Hanoi Pedagogical University, No 2, 32 Nguyen Van Linh, Phuc Yen, Vinh Phuc, Viet Nam e Hong Duc University, 565 Quang Trung, Dong Ve, Thanh Hoa, Viet Nam f Quang Ninh University of Industry, Yen Tho, Dong Trieu, Quang Ninh, Viet Nam b c a r t i c l e i n f o a b s t r a c t Article history: Received 15 February 2017 Received in revised form 17 February 2017 Accepted 19 February 2017 Available online 27 February 2017 Ni50ÀxCoxMn50ÀyAly (x ¼ and 9; y ¼ 17, 18 and 19) alloy ribbons were prepared by melt-spinning with a tangential velocity of copper wheel of 40 m sÀ1 X-ray diffraction patterns reveal multi-crystalline phase behavior in the fabricated ribbons The shape of thermomagnetization curves clearly depends on Co and Al concentrations The Curie temperatures (TC) of the alloy ribbons strongly increase with increasing the Co concentration and slightly decrease with increasing the Al concentration The martensitic-austenitic phase transition in the alloy ribbons can be manipulated by tuning Co and Al concentrations The maximum magnetic entropy change jDSmjmax of about 0.75 J kgÀ1 KÀ1 for a field change of 12 kOe at TC z 364 K was achieved for the Ni43Co7Mn32Al18 ribbon Critical analysis using the Arrott-Noaks and KouveleFisher methods demonstrates the existence of a long-range ferromagnetic order in this ribbon © 2017 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: Magnetocaloric effect Magnetic phase transition Heusler alloy Critical parameter Melt-spinning method Introduction The magnetocaloric effect (MCE) is defined as the heating or cooling of a magnetic material when a magnetic field is applied The MCE occurs in a magnetic solid as a result of the entropy variation due to the coupling of the magnetic spin system with the magnetic field Since the discovery of the MCE, it has been widely utilized in magnetic materials to reach low temperatures Nowadays, there is a great deal of interest in using the MCE as an alternative technology for refrigeration The magnetic refrigeration offers the prospect of an energy-efficient and environmentally friendly alternative to the common vapor cycle refrigeration technology used today [1e5] Among magnetocaloric materials, NieMn-based Heusler alloys are emerging as a promising candidate [6] Recently, Ni-Mn-based * Corresponding author E-mail address: dannh@ims.vast.ac.vn (N.H Dan) Peer review under responsibility of Vietnam National University, Hanoi alloys have been reported to exhibit the large magnetocaloric effects, including both the conventional and inverse magnetocaloric effects [7e9] Besides that, the shape memory effect and other interesting properties have also been observed [10e12] In the NiMn-Al Heusler alloys, the Neel temperature TN z 300 K was found to be virtually independent of composition [13] The Ni-MnAl alloys with their relatively low cost and high ductility are a potentially attractive candidate material as a magnetic refrigerant The partial substitution of Co for Ni in these alloys has been reported to have a strong effect on the martensitic-austenitic transformation which greatly enhanced the MCE [14e16] Despite some previous efforts [7,16e18], a clear understanding of the magnetocaloric effect and its association with the magnetic phase transition and magnetic interactions characterized by critical exponents in NiCo-Mn-Al alloys has not been reached To address this, we have systematically investigated the magnetic, magnetocaloric and critical properties of Ni50ÀxCoxMn50ÀyAly (x ¼ and 9; y ¼ 17, 18 and 19) rapidly quenched ribbons http://dx.doi.org/10.1016/j.jsamd.2017.02.007 2468-2179/© 2017 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) 124 N.T Mai et al / Journal of Science: Advanced Materials and Devices (2017) 123e127 Fig XRD patterns of Ni50ÀxCoxMn50ÀyAly ribbons with x ¼ (a) and x ¼ (b) Experimental Six alloy ingots with nominal compositions of Ni50ÀxCoxMn50ÀyAly (x ¼ and 9; y ¼ 17, 18 and 19) were prepared from pure elements (99.9%) of Ni, Co, Mn and Al using the arc-melting method in Argon gas The melt-spinning method was then used to fabricate the alloy ribbons with a tangential velocity of copper wheel of 40 m sÀ1 The structure of the alloys was investigated by powder X-ray diffraction (XRD) technique using CuKa radiation with measuring step of 0.02 at room temperature The magnetic properties and magnetocaloric effects of the alloys were characterized on a vibrating sample magnetometer with temperature range of 77e500 K and maximum magnetic field of 12 kOe Results and discussion The XRD patterns taken at room temperature (Fig 1) show that crystalline phases of L10 (face centered cubic), B2 (body centered cubic) and 10M (orthorhombic) are formed in the ribbons Most of the samples mainly contain B2 and L10 phases The 10M phase appears in the ribbons with high concentrations of Al and Co The change of the structure would probably affect magnetic and magnetocaloric properties of the alloys The magnetic properties of the samples were characterized by magnetization versus temperature (M-T) measurements (Fig 2a) The results show that the shape of M-T curves clearly depends on Co and Al concentrations For examples, the magnetization of the sample with x ¼ increased from ~0.7 emu/g for y ¼ 17 to ~7.7 emu/g for y ¼ 19 The Curie temperatures of the alloy ribbons strongly increased with increasing the Co concentration and slightly decreased with increasing the Al concentration By increasing the Co concentration from at.% to at.%, the Curie temperature (TC) strongly increased from ~364 K (for x ¼ and y ¼ 18) to ~ 394 K (for x ¼ and y ¼ 18) The magnetization of Ni50ÀxCoxMn33Al17 ribbons are also increased considerably with the substitution of Co for Ni The martensitic-austenitic phase transition in the alloy ribbons can be tuned by adjusting Co and Al concentrations In this series of samples, the Ni43Co7Mn32Al18 ribbon shows two strong magnetic phase transitions near a room temperature region Therefore, it was chosen as a representative one for analyzing magnetic and magnetocaloric properties The magnetocaloric effect in the ribbon was assessed by the magnetic entropy change (DSm) as functions of temperature and magnetic field using Maxwell relationship: ZH2 DSm ¼ H1 vM vT dH (1) H From a series of experimental curves M(T) (Fig 2b), the corresponding M(H) curves can be deduced (Fig 3a) Fig 3b shows DSm(T) curves of the Ni43Co7Mn32Al18 ribbon for different magnetic field changes (DH ¼ 1, 4, 8, and 12 kOe) For DH ¼ 12 kOe, the maximum magnetic entropy changes (jDSmjmax) are determined to be about 0.43 and À0.74 J kgÀ1 KÀ1 for the conventional (negative) and inverse (positive) magnetocaloric effects, respectively As Fig Thermomagnetization curves of Ni50ÀxCoxMn50ÀyAly (x ¼ and 9; y ¼ 17, 18 and 19) ribbons measured in a magnetic field of 100 Oe (a) and thermomagnetization curves of Ni43Co7Mn32Al18 ribbon measured in different magnetic fields (b) N.T Mai et al / Journal of Science: Advanced Materials and Devices (2017) 123e127 125 Fig Magnetic field dependence of the magnetization at different temperatures (a) and DSm (DH ¼ 1, 4, 8, and 12 kOe) versus temperature (inset shows the field dependence of jDSmjmax) (b) of the Ni43Co7Mn32Al18 ribbon expected, the jDSmjmax increases with increasing the magnetic field (the inset of Fig 3b) The temperature dependence of DSm for different applied field changes for the second-order phase transition of materials can be described by the so-called “universal master” curves [19e21] Based on the DSm(T) curves, the DSm =DSmax versus q plots are constructed White q value is determined by the formula: qẳ T TC ị=Tr1 TC ị; T TC Þ=ðTr2 À TC Þ; T TC T > TC (2) where Tr1 and Tr2 are the temperatures of the two reference points For the present study, they are selected as those corresponding to DSm Tr1;2 ị ẳ k:DSmax k ¼ 0:5Þ This choice of k does not affect the actual construction of the universal curve, as it implies only proportionality constant Fig 4a shows the universal master curve of the Ni43Co7Mn32Al18 ribbon All DSm(T) data are well collapsed onto a universal master curve, affirming the nature of second-order magnetic transition of the material This is an interesting property of second-order phase transition materials and is distinct from first-order phase transition materials It has been shown that the magnetic orders of materials exhibiting in a second-order magnetic phase transition can be assessed by the critical parameters using Arrott plots [22] The Arrott plots, H/M versus M2 (Fig 4b), were constructed from the M(H) data It can be observed that the M2eH/M curves are nonlinear at low magnetic field and linear at high magnetic field Values of the spontaneous magnetization (MS) and the inverse initial susceptibility (cÀ1 ) at different temperatures were derived from Arrott plots The critical parameters of b, g and TC relate to the two above quantities via the following equations: MS Tị ẳ M0 ịH c1 Tị ẳ H0 r M0 < 0; ε > 0; (3) (4) where M0, H0 and D are the critical amplitudes and ε ¼ ðT À TC Þ=TC is the reduced temperature The linear extrapolation from high field to the intercepts with the M2 and H/M axes gives the values of MS(T) and cÀ1 (T), respectively The critical parameters TC, b and g were obtained from fitting MS(T) and cÀ1 (T) data (Fig 5a) following the according formulas (3) and (4), while d was calculated by using the Widom scaling relation, equation d ¼ þ g=b (5) [23] The Ni43Co7Mn32Al18 ribbon possesses TC ¼ 364.21 ± 0.61 K, b ¼ 0.469 ± 0.048, g ¼ 0.951 ± 0.035 and d z 3.027 The critical parameters can be obtained more accurately by the KouveleFisher method [25] Like Arrott-Noakes method, MS(T) and cÀ1 ðTÞ are determined by plotting M1/b versus (H/M)1/g curves The critical parameters of b and g relate to the two above quantities by these equations: MS ẵdMS =dT1 ẳ T TC Þ=b Fig Universal master curves of DSm =DSmax versus q (a) and Arrott plots, M2-H/M (b) of the Ni43Co7Mn32Al18 ribbon (6) 126 N.T Mai et al / Journal of Science: Advanced Materials and Devices (2017) 123e127 Fig Temperature dependence of spontaneous magnetization MS(T) and inverse initial susceptibility cÀ1 ðTÞ (a) and KouveleFisher plots (b) for the Ni43Co7Mn32Al18 ribbon h À1 cÀ1 ðTÞ dc0 ðTÞ dT i1 ẳ T TC ị=g (7) The critical parameters TC, b and g obtained from fitting MS(T) and cÀ1 (T) data by using the according formulas (6) and (7) Fig 5b shows the KouveleFisher curves of the Ni43Co7Mn32Al18 ribbon with fitting results of TC z 364 K, b z 0.462 and g z 0.948 Based on the Widom scaling relation, the d value was calculated to be 3.051 Clearly, the critical parameter values determined from the KouveleFisher method are in good agreement with those obtained by the Arrott-Noakes fittings These critical parameters are quite close to those of the mean-field model (b ¼ 0.5, g ¼ and d ¼ 3) characterizing materials with long-range ferromagnetic interactions [24] In a previous study, it has been shown that Ni50Mn50ÀxSnx (x ¼ 13 and 14) alloy ribbons show a short-range ferromagnetic order for x ¼ 13 but a long-range ferromagnetic order for x ¼ 14 at temperatures just below Tc, indicating that that Sn addition tends to drive the system, in the austenitic ferromagnetic phase, from the short-range (x ¼ 13) to long-range (x ¼ 14) ferromagnetic order [16] The long-range ferromagnetism has recently been reported for Co50ÀxNixCr25Al25 (x ¼ and 5) alloys [17] In the present case, the presence of Co and Al seem to establish a longrange ferromagnetic order in the Ni43Co7Mn32Al18 ribbon, thus favoring the conventional (negative) magnetocaloric effect rather than the inverse (positive) magnetocaloric effect Nevertheless, a systematic study on effects of various Co and Al contents on the magnetic ordering and magnetocaloric effect in Ni50ÀxCoxMn33Al17 ribbons will be essential to fully understand their relationship Conclusion The rapidly quenched Ni50ÀxCoxMn50ÀyAly (x ¼ and 9; y ¼ 17, 18 and 19) ribbons exhibit multi-crystalline phases of the L10, B2 and 10M types The Curie temperature of the alloy ribbon strongly increases with increasing the Co-concentration and slightly decreases with increasing the Al-concentration For a field change of 12 kOe, the maximum magnetic entropy change of the Ni43Co7Mn32Al18 ribbon is about 0.43 and À0.74 J kgÀ1 KÀ1 for the negative and positive magnetocaloric effects, respectively This sample exhibits a long-range ferromagnetic order at temperatures just below the TC Acknowledgments This work was supported by the National Foundation for Science and Technology Development (NAFOSTED) of Viet Nam under Grant numbers of 103.02e2014.35 Part of the work was done in Key Laboratory for Electronic Materials and Devices and Laboratory of Magnetism and Superconductivity, IMS-VAST, Viet Nam References [1] O 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