Journal of Magnetism and Magnetic Materials 262 (2003) 441–444 Influence of Ti and V substitution for Al on the properties of Nd60Fe30Al10 alloys N Chau*, N.H Luong, C.X Huu, N.T Thep, H.D Anh Center for Materials Science, National University of Hanoi, 334 Nguyen Trai, Thanh Xuan, Hanoi, Viet Nam Abstract Systems with compositions Nd60Fe30Al10ÀxTix and Nd60Fe30Al10ÀxVx (x ¼ 2; 4, 6, 8, and 10) have been prepared by arc melting and copper mold suction-casting The cast surface of the samples is partially crystalline At increasing the Ti or V content, the crystalline fraction in the samples increases and for x ¼ 10; the alloys are fully crystalline Melting temperatures also increase with increasing Ti or V content in the samples All samples, some of them in a partly crystalline state, exhibit good hard magnetic properties at room temperature With increasing Ti or V content, the magnetization continuously decreases, whereas both the coercivity and the Curie temperature increase Thermomagnetic curves measured for all samples at low field exhibit an interesting shape The temperature dependence of the coercivity of the samples has been determined r 2003 Published by Elsevier Science B.V PACS: 75.50.Bb; 75.50 Lk; 75.50.Vv Keywords: Magnetization; Hard magnetic materials; Crystallization–amorphous systems; Rare-earth alloys Recently, Inoue et al [1–3] prepared bulk amorphous alloys of the type Ln–Fe–Al (Ln=Nd, Pr) by a copper mold casting technique These alloys have generated considerable interest in both fundamental research and applications because they exhibit a large coercivity at room temperature Unlike the magnetic ribbons, in which the amorphous state can be only obtained by cooling from the melt with very high cooling rates of about 106 K/s, the amorphous state in the bulk alloys occurs at cooling rates as low as 1–102 K/s However, the authors of Refs [4–8] pointed out that it is difficult to prepare samples with a fully amorphous state from these alloys According to *Corresponding author Tel./fax: +84-4-858-9496 E-mail address: chau@cms.edu.vn (N Chau) Inoue et al [2,3], the hard magnetic properties occur in the alloys Ln–Fe–Al only when they are in the bulk amorphous state The same authors of Refs [4–8] have shown that the hard magnetic properties also persist in partially crystalline bulk samples The effects of B substitution for Al [7] and Co substitution for Al [8] have been studied This work presents the influence of Ti and V substitutions for Al in the alloy Nd60Fe30Al10, on its structure and magnetic properties Two alloy systems with compositions Nd60Fe30Al10ÀxTix (x ¼ 2; 4, 6, and 10) and Nd60Fe30Al10ÀxVx (x ¼ 2; 4, 6, and 10) have been prepared by arc-melting a mixture of highpurity elements in an argon atmosphere After melting all elements together, the samples were prepared by suction-casting of the molten alloy 0304-8853/03/$ - see front matter r 2003 Published by Elsevier Science B.V doi:10.1016/S0304-8853(03)00075-1 N Chau et al / Journal of Magnetism and Magnetic Materials 262 (2003) 441–444 20 x=2 x=4 x=6 x=8 x = 10 M (emu/g) 10 -10 -20 -14.0 -10.5 -7.0 -3.5 (a) 3.5 7.0 10.5 14.0 H (kOe) 20 10 M (emu/g) into a water-cooled copper mold The structure of the as-cast samples was examined with X-ray diffraction using a Bruker D5005 apparatus The composition was checked by EDS included in the JEOL 5410 LV SEM The thermal stability of the alloys has been determined by DSC using a TA Instruments SDT 2960 Magnetization and hysteresis loops were measured using a Digital Measurement Systems VSM model DMS 880 X-ray diffraction patterns of samples of both alloy systems show that the cast surfaces of all samples are crystalline, probably due to crystallization originating from the copper mold wall To study the variation of crystallinity with respect to the position in the sample, we have taken X-ray diffraction patterns at depths of d ¼ 0:2 and 0.4 mm beneath the surface of the samples The results show that with increasing depth the samples essentially remain crystalline, although the crystallinity fraction somewhat decreases Quantitative analysis by EDS reveals that the alloys have the intended nominal compositions The DSC curves of all samples have been determined The samples with lower Ti content show an exothermic peak associated with crystallization With increasing Ti concentration the crystallization transition becomes less clear and the sample with x ¼ 10 does not show any crystallization transition It indicates that the sample Nd60Fe30Ti10 is fully crystalline In the samples with lower V content a supercooled, partially amorphous state exists Nd60Fe30V10 is also fully crystalline We find that the melting temperature of the studied samples clearly increases with increasing Ti or V content The authors of Ref [9] pointed out that the addition of Co significantly enhances the glass-forming ability of Nd70ÀxFe20Al10Cox alloys Our observation here is in agreement with the results obtained in Ref [7] for Nd60Fe30Al10ÀxBx alloys in which the glass-forming ability decreases with increasing B content Fig shows the hysteresis loops of Nd60Fe30Al10ÀxTix (Fig 1a) and Nd60Fe30 Al10ÀxVx (Fig 1b) samples at room temperature We see that with increasing Ti or V content, both the magnetization measured at maximum field and x=2 x=4 x=6 x=8 x = 10 -10 -20 -15 -10 -5 (b) H (kOe) 10 15 Fig Hysteresis loops of the Nd60Fe30Al10ÀxTix (a) and Nd60Fe30Al10ÀxVx (b) samples at room temperature for different x-values 16 10000 Oe 5000 Oe 2500 Oe 1000 Oe 14 12 M (emu/g) 442 10 500 Oe 100 Oe 300 350 400 450 T (K) 500 550 600 Fig Thermomagnetic curves of Nd60Fe30Al6V4 measured at different applied fields the remanence decrease whereas the coercivity increases Thermomagnetic curves of the samples were measured at temperatures up to 620 K At low fields, the Hopkinson effect is clearly seen Fig N Chau et al / Journal of Magnetism and Magnetic Materials 262 (2003) 441–444 443 called irreversibility temperature, Tr (oTC ) Both the ZFC and FC MðTÞ curves resemble each other substantially in the range of TXTr ; implying the irreversibility of magnetization In addition, the low field ZFC MðTÞ curves clearly show a cusp at a so-called spin freezing (or spin–glass transition) temperature, Tg ; where a maximum magnetization is attained, as demonstrated in Fig presents a representative series of thermomagnetic curves for Nd60Fe30Al6V4 Note that crystalline fraction in this V substituted sample is rather high The occurrence of a Hopkinson effect here indicates that the magnetic anisotropy decreases rapidly with increasing temperature and the magnetic saturation can be easily reached at low magnetic fields due to a rotation of domain moments From Fig and from the thermomagnetic measurements at low field we derived the composition dependence of the magnetic characteristics of the samples as presented in Table One can see from Table that in both systems of samples, the Curie temperature increases with increasing Ti or V content substituted for Al Hysteresis loops are measured from low to high temperatures The available maximum field is not enough to saturate the samples, i.e the hysteresis loops are minor loops However, the coercivity increases rapidly with decreasing temperature For example, HC of Nd60Fe30Al8Ti2 is 8.5 kOe at 201 K and 0.5 kOe at 390 K whereas HC of Nd60Fe30Al8V2 is 8.35 kOe at 240 K and 0.46 kOe at 390 K Field-cooled (FC) and zero-field-cooled (ZFC) curves have been assessed for all samples Fig shows representative data, for Nd60Fe30Al6Ti4 (Fig 3a) and Nd60Fe30Al6V4 (Fig 3b) It is interesting to note that these curves are clearly separated from each other at low temperatures This remarkable feature of magnetic properties in two series of samples indicates the appearance of short-range ferromagnetic interactions This is confirmed by observing spin-glass-like behavior at low temperature and in low field ranges In low applied fields, both the ZFC and FC magnetization curves split at a temperature below the so- This research is performed within the project 420101 of the Vietnam National Program for Fundamental Sciences and the Vietnamese—US 3.6 M (emu/g) FC 2.4 1.2 Z FC 0.0 120 220 (a) 320 420 520 400 500 T (K) M (emu/g) FC ZFC 100 200 (b) 300 T (K) Fig FC and ZFC curves measured in a field of 20 Oe for Nd60Fe30Al6Ti4 (a) and Nd60Fe30Al6V4 (b) Table Composition dependence of magnetic characteristics X Ms (emu/g) Mr (emu/g) HC (Oe) TC (K) Nd60Fe30Al10ÀxTix Nd60Fe30Al10ÀxVx 10 10 18.8 12.6 3100 465 14.1 9.6 3310 472 14.1 9.4 3390 483 12.6 8.2 3650 485 9.8 5.6 4540 497 18.8 9.8 2600 462 17.4 11.5 3450 465 16.0 10.5 3655 468 16.1 10.5 4103 475 16.8 11.0 4300 483 444 N Chau et al / Journal of Magnetism and Magnetic Materials 262 (2003) 441–444 Cooperation project supported in part by the US National Science Foundation References [1] A Inoue, T Zhang, A Takeuchi, IEEE Trans Mag 33 (1997) 3814 [2] A Inoue, T Zhang, W Zhang, A Takeuchi, J Inst Met 37 (1996) 99 [3] A Inoue, T Zang, A Takeuchi, Sci Rep., RITU A 44 (1997) 261 [4] Y Li, J Ding, S.C Ng, X.Z Wang, J Magn Magn Mater 187 (1998) 273 [5] J Ding, Y Li, X.Z Wang, J Phys D 32 (1999) 713 [6] N Chau, N.H Luong, D.T.K Anh, C.X Huu, Proceedings of the Third Vietnamese-German Seminar on Physics and Engineering, Ho Chi Minh City, 3–8 April 2000, p 133 [7] N Chau, N.H Luong, C.X Huu, N.X Phuc, N.H Dan, J Magn Magn Mater 242–245 (2002) 1314 [8] N.H Dan, N.X Phuc, V.H Ky, N.M Hong, N Chau, N.H Luong, C.X Huu, R.W McCallum, L.H Lewis, L.D Tung, MRS Symp Proc 674 (2001) U.2.6.1 [9] G.J Fan, W Loser, S Roth, J Eckert, L Schuetz, J Mater Res 15 (2000) 1556 ... show that with increasing depth the samples essentially remain crystalline, although the crystallinity fraction somewhat decreases Quantitative analysis by EDS reveals that the alloys have the intended... nominal compositions The DSC curves of all samples have been determined The samples with lower Ti content show an exothermic peak associated with crystallization With increasing Ti concentration the. .. diffraction patterns of samples of both alloy systems show that the cast surfaces of all samples are crystalline, probably due to crystallization originating from the copper mold wall To study the variation