DSpace at VNU: Influence of B content substituting for Al on the magnetic properties of Nd60Fe30Al10-xBx

Journal of Magnetism and Magnetic Materials 242–245 (2002) 1314–1316 Influence of B content substituting for Al on the magnetic properties of Nd60Fe30Al10ÀxBx Nguyen Chaua,*, Nguyen Hoang Luonga, Cao Xuan Huua, Nguyen Xuan Phucb, Nguyen Huy Danb a Center for Materials Science, National University of Hanoi, 334 Nguyen Trai, Hanoi, Viet Nam b Institute of Materials Science, NCST, Hoang Quoc Viet Road, Hanoi, Viet Nam Abstract The Nd60Fe30Al10ÀxBx (x ¼ 0; 2, 4, 6, and 10) alloys were prepared by copper mold casting using arc-melting Investigation shows that with increasing B content magnetization and remanence decrease while coercivity and Curie temperature increase The hard magnetic properties are achieved not only in the amorphous state but also in partly crystallizing state r 2002 Elsevier Science B.V All rights reserved Keywords: Magnetization; Hard magnetic materials; CrystallizationFamorphous systems; Rare-earth alloys Amorphous alloys are conventionally synthesized by rapidly quenching a melt below the glass transition temperature Tg ; therefore suppressing crystal nucleation and/or growth The ribbons prepared by rapid solidification are usually restricted with a thickness of about 20–50 mm Recently, it was found that multicomponent metallic alloys can be cast into bulk amorphous cylinders from the liquid state at cooling rate as low as 1–1001C/s with diameter of several milimeters The success of synthesizing these bulk amorphous alloys has been attributed, as proposed by Inoue et al [1], to the following three empirical rules for the achievement of large glass-forming ability: (1) multicomponent alloy systems consisting of more than three components, (2) significantly different atomic size ratios above about 12% among the main constituent elements, and (3) large negative heats of mixing among their main elements These new alloys are of significant technological importance, promising new engineering applications of bulk metallic glasses [2] Inoue et al [3] have extensively studied the glassforming ability of Nd90ÀxFexAl10 They found that the glass-forming ability for these alloys increases with *Corresponding author Tel./fax: +84-4-858-9496 E-mail address: chau@cms.edu.vn (N Chau) increasing iron content x and reaching a maximum for x ¼ 20; and decreases with further increase of the iron amount In the papers [1–3] the authors succeeded in finding Nd–Fe–Al and Pr–Fe–Al bulk amorphous alloys with hard magnetic properties at room temperature The aim of this paper is to present study of the influence of B content substituting for Al on the glassforming ability of Nd60Fe30Al10ÀxBx as well as the hard magnetic properties of these alloys Ternary Nd60Fe30Al10ÀxBx (x ¼ 0; 2, 4, 6, and 10) alloys were prepared by arc-melting in a mixture of Nd, Fe, Al and B with a purity of 99.9% in an argon atmosphere From the pre-alloyed ingots, the parallelepiped samples (dimensions   70 mm3) were prepared by suction-cast of the molten alloy into copper mold with water cooling The structure of as-cast samples was examined by X-ray diffractometer D5005, Bruker, using Cu-Ka radiation with the wavelength ( The composition of alloy was determined l ¼ 1:54056 A by energy dispersion spectrometer (EDS) included in scanning electron microscopy 5410LV, Jeol The thermal stability associated with crystallization and melting temperature was determined by differential scanning calorimetry (DSC) using apparatus SDT 2960, TA Instruments, with a heating rate of 201C/min Magnetization and hysteresis loops under an applied magnetic 0304-8853/02/$ - see front matter r 2002 Elsevier Science B.V All rights reserved PII: S - 8 ( ) - N Chau et al / Journal of Magnetism and Magnetic Materials 242–245 (2002) 1314–1316 field up to 13.5 kOe were measured by a vibrating sample magnetometer DMS 880, Digital Measurement Systems Fig shows the X-ray dispersion spectrum for Nd60Fe30Al10 sample measured by EDS This spectrum indicates the elements existing in our sample As can be seen in this figure, besides the three constituent elements Nd, Fe, Al, in the sample there is a small amount of oxygen which could be related to the purity of starting materials as well as to some oxidation during sample preparation The analysis based on the X-ray dispersion spectrum showed that the alloy has the nominal composition X-ray diffraction patterns taken from cast parallelepiped rods at cast surface indicate that cast surfaces of all rods prepared by suction-casting into copper molds with water cooling are largely crystalline, probably due to crystallization nucleations originating from copper mold wall To study the variation of crystallinity with respect to position within the samples, we have taken X-ray diffraction patterns at depth d ¼ 0:2 mm beneath 1315 the surface of the samples The results are shown in Fig X-ray diffraction scans reveal the broad peak around 2y ¼ 30:51; indicating the change of amorphous– crystalline character with increasing depth in the rods This is in agreement with results presented in Ref [4] for Nd60Fe30Al10 alloy Also, there could be a critical cooling rate which allows the samples to become bulk amorphous In order to investigate the influence of cooling rate of the melts on their atomic structure, we have remelt the ingots in quartz tubes (which initially have been evacuated with high vacuum and then filled with Ar gas) Then the remelts have been quenched in water, oil and air, corresponding to average estimated cooling rate of 1001C/min, 301C/min and 101C/min, respectively The X-ray diffraction analysis showed that the surface of the samples is partly crystalline but the sample quenched in the oil exhibits a more amorphization compared to other samples Thus it is very difficult to establish the optimal and uniform cooling rate for the melts to be in amorphous state in whole bulk samples regardless of the position within the samples The DSC curves for all as-cast samples show that with increasing B content the sharpness of the crystallization peak decreases In other words, large fraction of volume of the samples is already crystalline These results on the influence of B content on the amorphous character of the alloys are in good agreement with those obtained by X-ray diffraction analysis (see Fig 2) It is interesting to note that in the sample with x ¼ there exists a glass state before crystallization, and this state is not clearly seen in the DSC curves and disappearing with increasing B content Thus we observe the decrease of glassforming ability in Nd60Fe30Al10ÀxBx alloys with increasing x: The hysteresis loops of the Nd60Fe30Al10ÀxBx alloys have been measured at room temperature Representative hysteresis loops for the samples with x ¼ 6; and 10 are shown in Fig With increasing B content, both magnetization at 13.5 kOe and remanence decrease, Fig X-ray dispersion spectrum for as-cast Nd60Fe30Al10 alloy Fig X-ray diffraction patterns taken from cast rod at depth d ¼ 0:2 mm (from cast surface) of Nd60Fe30Al10ÀxBx alloys Fig Hysteresis loops of as-cast samples Nd60Fe30Al10ÀxBx (x ¼ 6; 8, 10) at room temperature 1316 N Chau et al / Journal of Magnetism and Magnetic Materials 242–245 (2002) 1314–1316 can be clearly seen, water quenched (with highest cooling rate) sample exhibits the best hard magnetic properties with coercivity Hc ¼ 3120 Oe compared to the value of Hc equal to 1980 and 1590 Oe for the samples cooled in oil and in air, respectively We note that the fraction of crystallization in this sample is higher According to Inoue et al [3], the hard magnetic properties at room temperature are obtained only for the bulk amorphous alloy However, as indicated above, in our case partly bulk amorphous samples always exhibit hard magnetic properties at room temperature Fig Hysteresis loops of Nd60Fe30Al10 prepared with different cooling rates from the melt whereas coercivity Hc increases It seems that the substitution of B for Al leads to the enhancement of hard magnetic, probably Nd2Fe14B, phase, causing the increase of Hc : Magnetization of the Nd60Fe30Al10ÀxBx samples has been measured as a function of temperature at kOe, showing that the Curie temperature increases with increasing B content Namely, Curie temperatures for samples with x ¼ 0; 2, 4, 6, and 10 are 477, 480, 480, 484, 486 and 494 K, respectively Fig shows hysteresis curves for Nd60Fe30Al10 prepared with different cooling rates for the melt As The authors are grateful to the Vietnam National Program for Natural Sciences for financial support Research performed within the Vietnamese-US cooperation project supported by the US National Science Foundation References [1] A Inoue, T Zhang, A Takeuchi, IEEE Trans Magn 33 (1997) 3814 [2] A Inoue, Mater Sci Eng A 226–228 (1997) 357 [3] A Inoue, T Zhang, A Takeuchi, Sci Rep RITU A 44 (1997) 261 [4] N.H Dan, N.X Phuc, V.H Ky, N.M Hong, N Chau, N.H Luong, C.X Huu, R.W McCallum, M.J Kramer, A.S O’Connor, K.W Dennis, L.H Lewis, L.D Tung, presented at the Materials Research Society Spring Meeting, SA, USA, April 16–20, 2001, submitted for publication  ... Al, in the sample there is a small amount of oxygen which could be related to the purity of starting materials as well as to some oxidation during sample preparation The analysis based on the X-ray... position within the samples The DSC curves for all as-cast samples show that with increasing B content the sharpness of the crystallization peak decreases In other words, large fraction of volume of. .. of the samples is already crystalline These results on the influence of B content on the amorphous character of the alloys are in good agreement with those obtained by X-ray diffraction analysis