Permanent magnetic properties of nano-composite Sm 2 Fe 15 Si 2 C /α- Fe with CuadditiveHong-wei Zhang, Shao-ying Zhang, Bao-gen Shen, and Chin Lin Citation: Journal of Applied Physics 85, 4660 (1999); doi: 10.1063/1.370439 View online: http://dx.doi.org/10.1063/1.370439 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/85/8?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Effects of V and Si additions on the coercivity and microstructure of nanocomposite Fe 3 B/Nd 2 Fe 14 Bmagnets J. Appl. Phys. 91, 9308 (2002); 10.1063/1.1474615 Investigation of magnetization reversal in Sm–Fe–Cu(Zr)–Ga–C nanocomposite magnets J. Appl. Phys. 87, 1410 (2000); 10.1063/1.372027 Enhancement of Curie temperature of the 2:17 phase in nanocomposite Sm 2 (Fe,Co) 15 Cr 2 C 2 / (Fe,Co)magnets J. Appl. Phys. 86, 3857 (1999); 10.1063/1.371299 Microstructure and magnetic properties of Sm 2 (Fe,Si) 17 C x /α- Fe nanocomposite magnets prepared underhigh pressure Appl. Phys. Lett. 74, 597 (1999); 10.1063/1.123157 Microstructure refinement and improvements of magnetic properties of two-phase exchange-coupled Sm 2 Fe 15Ga 2 C x /α- Fe nanocomposites by additional Zr Appl. Phys. Lett. 73, 1586 (1998); 10.1063/1.122212

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Permanent magnetic properties of nano-compositeSm2Fe15Si2C/a-Fe with Cu additive

Hong-wei Zhang,a) Shao-ying Zhang, and Bao-gen ShenState Key Laboratory of Magnetism, Institute of Physics & Centre for Condensed Matter Physics,Chinese Academy of Sciences, Beijing 100080, People’s Republic of China

Chin LinPhysics Department, Peking University, Beijing 100871, People’s Republic of China

The ribbons of nano-composite Sm2Fe15Si2C/a-Fe with Cu additive were prepared by melt spinningat substrate velocityv520 m/s. The analysis of x-ray diffraction patterns shows that the relativecontent ofa-Fe phase increases with increasing Fe percent in samples, and the average grain sizeof 2:17 carbides anda-Fe in the ribbons determined by the Scherrer method is about 50 and 30 nm,respectively. The ribbons exhibit a single hard magnetic phase behavior and remanenceenhancement, due to inter-grain exchange coupling between hard and soft magnetic phases. Theremanence increases with the increase of iron content in samples, while the coercivity decreasesrapidly. The highest maximum energy product around 10.7 MGOe was obtained forSm8Fe76Cu4Si8C4 ribbons. The reversible and irreversible magnetization portions were analyzedfrom the recoil loops, and an irreversible nucleation field around 4.8 kOe for hard magnetic phasewas observed in Sm8Fe76Cu4Si8C4 ribbons. © 1999 American Institute of Physics.@S0021-8979~99!56108-2#

Since it was found that a small substitution of Al, Ga,Cr, and Si for Fe could stabilize Sm2Fe17 with high carbonconcentration, much attention has been paid to obtaininggood permanent magnetic properties of these materials.1–4

Although high coercivities have been obtained by melt-spinning and mechanical alloying techniques, the low rema-nence limits achieving high energy product. For example, theintrinsic coercivity around 8.4 and 12.4 kOe has been ob-tained for melt-spun Sm2Fe15Si2C and Sm2Fe14CuSi2C,5 buttheir energy products achieved only about 7.56 and 7.2MGOe, respectively.

Recently, nano-composite permanent magnetic materi-als, which consist of a mixture of hard and soft magneticphase, have attracted considerable attention. Since these ma-terials show magnetic behavior with enhanced remanenceand reasonable high coercivity,7 they can be potentially usedas inexpensive magnets, and a theoretical maximum energyproduct up to 120 MGOe~;1 MJ/m3! has been predicted.8

In this article, the magnetic properties of nano-compositesSm2Fe15Si2C/a-Fe with a few percent of Cu additive wereinvestigated.

The alloys with nominal composition ofSm8.7Fe73.9Cu4.3Si8.7C4.3~A!, Sm8Fe76Cu4Si8C4~B!,Sm7.4Fe77.8Cu3.7Si7.4C3.7~C!, and a sample without an excessof Fe, Sm10Fe70Cu5Si10C5~D! were prepared by arc meltingthe constituent materials Sm, Fe, and Si~with a purity of atleast 99.9%! and Fe–C alloy~5.2 wt% C and 94.4% Fe!under high purified argon gas. The as quenched ribbons wereprepared by melt spinning at the substrate velocityv520 m/s for~A!, ~B!, and~C!, and atv515 m/s for~D!.

The structural studies were carried out by x-ray diffrac-tion ~XRD! in a Rigaku Rint 1400 using CuKa radiation.

The magnetic properties were measured along the directionparallel to the ribbons by a vibrating sample magnetometer~VSM! with a maximum field Hmax520 kOe at room tem-perature. Due to the specimens with dimensions of 4 mmlong, 1 mm wide, and 0.03 mm thick, the demagnetizationfactor of the specimens can be neglected.

Figure 1 shows the XRD patterns of the ribbons. Thesamples mainly consist of Th2Zn17 structure phase anda-Fe.The analysis of XRD patterns shows that the relative contentof a-Fe phase increases with the increase of Fe percent insamples, and noa-Fe phase exists in ribbons~D!. The grainsize of Sm2Fe15Si2C anda-Fe in ribbons determined by theScherrer method from XRD patterns is about 50 and 30 nm,respectively. The similar grain size of hard and soft magneticphase in Sm2Fe15Ga2Cx /a-Fe ribbons with additive Zr hasbeen observed by means of transmission electronmicroscopy.9

Figure 2 shows the hysteresis loops of the ribbons. Thehysteresis loops show a single hard magnetic phase behavior.The smooth demagnetization curves in two-phase compos-ites are due to the interaction of exchange coupling betweenthe magnetic soft phasea-Fe and the magnetic hard one,Sm2Fe15Si2C.7,8 The intrinsic coercivity iHc , remanenceMr , and maximum energy product (BH)max of ribbons~A!,~B!, ~C!, and ~D! are listed in Table I. It is found that theremanence increases with the increase of the content of Fe insamples, while the coercivities of ribbons decrease rapidly.The reduced remanenceMr /Ms is about 0.68, 0.72, 0.73,and 0.58 for ribbons~A!, ~B!, ~C!, and ~D!, respectively.Each of the values is higher than 0.5 of theoretical isotropicmagnet reduced remanence predicted by Stoner-Wolfarth.The remanence enhancement in ribbons~D! shows that inter-grain exchange coupling interaction cannot be negligible in ananocrystalline single phase magnet,10 but brightly smallera!Electronic mail: hwzhang@g203.iphy.ac.cn

JOURNAL OF APPLIED PHYSICS VOLUME 85, NUMBER 8 15 APRIL 1999

46600021-8979/99/85(8)/4660/3/$15.00 © 1999 American Institute of Physics

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than that in ribbons~A!, ~B!, and ~C! separately. The inter-grain exchange coupling in hard and soft magnetic phaseribbons is brightly stronger than that in single hard magneticphase ribbons, due to low anisotropy of soft phasea-Fe. Thehighest (BH)max around 10.7 MGOe was obtained in ribbons~B!. The hard magnetic properties of two-phase composite

permanent magnet are mainly governed by the microstruc-ture, especially by the size of softa-Fe.7,11 The size around30 nm ofa-Fe may be larger than the domain wall width ofhard Sm2Fe15Si2C. The size distribution of two phase may bebroader by direct melt-spinning technique. So, the value ofhighest energy product of the ribbons in this work is smallerthan that of Nd2Fe14B/a-Fe or Fe3B prepared by otherauthors.12,13 Figure 3 shows two typical recoil loops of rib-bons ~B! from which we have measured for a number ofstarting fields along the demagnetization curve of a previ-ously saturated sample. A comparatively high degree of re-versibility like the exchange spring mechanism is observedin the fields below coercivity. It originates from the revers-ible rotation of the magnetic soft phasea-Fe for fields notstrong enough to reverse the magnetic hard 2:17 carbide. Therelatively open recoil loops are indicative of irreversible be-havior. The local field whicha-Fe grain experiences is muchsmaller than the external field H, due toa-Fe grain beingsurrounded exclusively by hard magnetic Sm2Fe15Si2Cgrains. The irreversible behavior which occurred during re-coil loop can be explained asa-Fe particles passed throughan internal hysteresis loop.

From the investigations of reversible and irreversibleportion in the dc demagnetization curve, the nucleation fieldHn for reversing the magnetically hard phase could be ob-tained. Figure 4 shows a plot of the irreversible reduced por-tion Dmirrev.5@Mr2Md(H)#/2Mr and the reversible reduced

FIG. 1. The XRD patterns of ribbons~A!, ~B!, ~C!, and~D!.

FIG. 2. The hysteresis loops of ribbons~A!, ~B!, ~C!, and~D!.

TABLE I. The phase composition, intrinsic coercivity, remanence, and en-ergy product of ribbons~A!, ~B!, ~C!, and~D!.

Ribbons Phase iHc ~kOe! Mr ~emu/g! (BH)max ~MGOe!

A Th2Zn171a-Fe 7.0 79.9 9.0B Th2Zn171a-Fe 5.0 87.6 10.7C Th2Zn171a-Fe 2.3 91.1 6.5D Th2Zn17 11.4 58.5 7.2

FIG. 3. The two typical recoil loops of ribbons~B!.

4661J. Appl. Phys., Vol. 85, No. 8, 15 April 1999 Zhang et al.

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portion Dmrev.5M rev./Mr vs H for ribbons ~B!, whereMd(H) and Mr are the dc field demagnetization remanencein dc demagnetization curve and remanence after saturation,respectively. The irreversible nucleation field Hn of about 4.8kOe has been achieved according to the one-dimensional ho-mogenous magnetization rotation model.7 A local maximum

close to Hn has also been observed in the curve ofDmrev. vsH. The value ofDmrev. first increases with the increase of H,which may be caused by competition between inter-grainexchange interaction and external field, and then decreaseswith the increase of H higher than Hn because the hard mag-netic phase reverses the magnetization unrecoverably.

This work was supported by the State Key Project ofBasic Research and the National Natural Sciences Founda-tion of China.

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FIG. 4. The analysis of reversible and irreversible part of total magnetiza-tion versus H of ribbon~B!.

4662 J. Appl. Phys., Vol. 85, No. 8, 15 April 1999 Zhang et al.

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