The SmCo7-xTix, x = 0–0.56 bulk samples are prepared by arc melting. X-ray diffraction indicates that samples with 0.2\u3cx7-type structure phase and other minor phases appear for other values of x, which indicates that Ti helps stabilize the 1-7 phase. The lattice parameters ratio (c/a) increases with increasing Ti concentration. Room temperature saturation magnetization and Curie temperature decrease with increasing x. X-ray diffraction and magnetization measurements on aligned samples show that all samples studied have uniaxial anisotropy. The anisotropy field is found to increase with increasing x reaching a maximum of 175 kOe at x = 0.28 and then decreases for higher values of x. This anisotropy field is 20% higher than that of the same compound with Th2Zn17-type structure

Al-Omari, I.A.

Liu, J. Ping

Sellmyer, David J.

Zhou, Jian

English

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln David Sellmyer Publications Research Papers in Physics and Astronomy 5-1-2000 Structure and magnetic properties of SmCo7-xTix with TbCu7-type structure Jian Zhou University of Nebraska - Lincoln I.A. Al-Omari University of Nebraska - Lincoln J. Ping Liu University of Nebraska-Lincoln, pliu@uta.edu David J. Sellmyer University of Nebraska-Lincoln, dsellmyer@unl.edu Follow this and additional works at: https://digitalcommons.unl.edu/physicssellmyer  Part of the Physics Commons Zhou, Jian; Al-Omari, I.A.; Liu, J. Ping; and Sellmyer, David J., "Structure and magnetic properties of SmCo7-xTix with TbCu7-type structure" (2000). David Sellmyer Publications. 63. https://digitalcommons.unl.edu/physicssellmyer/63 This Article is brought to you for free and open access by the Research Papers in Physics and Astronomy at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in David Sellmyer Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Structure and magnetic properties of SmCo 7ÀxTixwith TbCu 7-type structureJ. Zhou,a) I. A. Al-Omari, J. P. Liu, and D. J. SellmyerBehlen Laboratory of Physics and Center for Materials Research and Analysis, University of Nebraska,Lincoln, Nebraska 68588-0111The SmCo72xTix , x50 – 0.56 bulk samples are prepared by arc melting. X-ray diffraction indicatesthat samples with 0.2,x,0.4 form a single disordered TbCu7-type structure phase and other minorphases appear for other values ofx, which indicates that Ti helps stabilize the 1-7 phase. The latticeparameters ratio (c/a) increases with increasing Ti concentration. Room temperature saturationmagnetization and Curie temperature decrease with increasingx. X-ray diffraction andmagnetization measurements on aligned samples show that all samples studied have uniaxialanisotropy. The anisotropy field is found to increase with increasingx reaching a maximum of 175kOe atx50.28 and then decreases for higher values ofx. This anisotropy field is 20% higher thanthat of the same compound with Th2Zn17-type structure. ©2000 American Institute of Physics.@S0021-8979~00!21308-X#I. INTRODUCTIONThe rare-earth~RE! transition-metal intermetallic com-pounds have been widely investigated for many years,among them the Sm–Co series compounds with 1-5 and 2-17crystal structures. These compounds have been used as sin-tered and bonded permanent magnets since the 1960s.1–3 Re-cently, attention has been focused on the TbCu7-type struc-ture Sm–Co intermetallic compounds because of theirpotential as high anisotropy magnetic materials.4–6 BothSmCo7 and Sm2Co17 can have the 1-7 type structure whenprepared appropriately. However, SmCo7 is unstable unless athird doping element such as Ti, Zr, Cu, etc. is added tosubstitute Co.TbCu7-type crystal structure could be indexed accordingto the CaCu5-type structure with significant deviations of thelattice constants and the x-ray peaks’ intensities. That is be-cause partial of the Ca sites are randomly substituted by apair of Cu in CaCu5-type structure. In Sm–Co compounds,SmCo7 and Sm2Co17 can form the TbCu7-type structure.Th2Zn17 structure can be formed if the substitution is or-dered. Khan7 found that Sm–Co with composition 1:5.4 hasthe TbCu7-type structure above 1100 °C. The magnetic prop-erties of these TbCu7-type Sm–Co alloys have been investi-gated by a few researchers. Saitoet al.4 studiedSm2~CoMn)17 with TbCu7-type disordered structure andfound that the anisotropy constant (Ku1) is about 1.2–1.4times larger than that for compounds with Th2Zn17-typestructure. Recently, Huanget al.6 studied SmCo72xZrx withTbCu7-type disordered structure and found that atT5300 K, these compounds exhibit anisotropy field as high as180 kOe forx50.5. Lefevreet al.8,9 also reported the exis-tence of TbCu7-type structure in Sm–Co–Zr ternary alloysprepared by arc melting. Disordered SmCo7 c mpound withTbCu7-type structure plays the role of a bridge betweenSmCo5 and Sm2Co17 compounds. It is natural to think thatthe 1:7 composition with 1-7 type structure may keep themerits of SmCo5 such as high anisotropy and of Sm2Co17such as large magnetization. However, a study ofSmCo72xZrx by Huanget al.6 showed that substituting Zrfor Co increase the anisotropy field and decrease the magne-tization. In this work, we focus our attention on the effects ofTi substituent on the structure and magnetic properties ofSmCo72xTix alloys.II. EXPERIMENTA series of samples based on RE-~Co,Ti! composition1:7 were prepared by arc melting. SmCo72xTix with x50,0.1, 0.2, 0.3, 0.35, 0.42, 0.56, and SmCo6.5 ~for comparison!with at least 99.9% pure elements were melted in a water-cooled copper boat under flowing argon. An extra amount ofSm ~8%–10%! was added to balance the loss of Sm due toevaporation. The alloys were melted several times to insurehomogeneity. The same samples were annealed at differenttemperatures between 650 and 950 °C in a sealed quartz tubeunder argon pressure. All these samples were wrapped sepa-rately in Ta foils to prevent oxidation. The as-cast materialwas ground in a mortar and the fine powder particles~,38mm! were subsequently mixed with epoxy and aligned in amagnetic field of 12 kOe for 24 h for magnetic anisotropymeasurements.The crystal structures of the samples are determined byusing x-ray diffraction. Loose powder samples were mea-sured to determine the saturation magnetization at room tem-perature. Vibrating sample magnetometer~VSM! with a hightemperature oven was used to measure the Curie tempera-ture. A SQUID magnetometer with maximum field of 55kOe was used to measure the magnetization of the alignedsamples.III. RESULTS AND DISCUSSIONFigure 1 shows the x-ray diffraction pattern of the as-cast SmCo72xTix and SmCo6.5. The pattern for SmCo7a!Author to whom correspondence should be addressed; electronic mail:jzhou@unlserve.unl.eduJOURNAL OF APPLIED PHYSICS VOLUME 87, NUMBER 9 1 MAY 200052990021-8979/2000/87(9)/5299/3/$17.00 © 2000 American Institute of PhysicsDownloaded 17 Nov 2006 to 129.93.16.206. Redistribution subject to AIP license or copyright, see http://jap.aip.org/jap/copyright.jspsample shows two phases, SmCo7 with the TbCu7-typestructure and Sm2Co17 with TbCu7-type structure. This indi-cates that the SmCo7 is unstable without the doping element,which is consistent with the results of Huanget al.,6 whileYang et al.5 reported single phase SmCo7 with TbCu7-typestructure for samples prepared by mechanical alloying. Forcomparison, a composition SmCo6.5 with 1-7 structure is pre-pared and presented with the results. X-ray diffraction forsamples withx50.2– 0.35 show the existence of TbCu7-typestructure. This means that Ti can help the formation of thestable structure. Forx.0.4, other minor phases, mainlySmCo3, appear with the 1-7 type structure. This behavior issimilar to that of the SmCo72xZrx series reported by Huanget al.6 Table I shows the changes in the lattice parameters~a!and ~c! due to the doping element Ti in SmCo72xTix com-pounds. The lattice parameter a decreases with increasing Ticoncentration, from 4.935 Å atx50 to 4.900 Å atx50.56,while c increases from 4.013 Å atx50 to 4.134 Å atx50.56 and hence the ratio (c/a) keeps increasing. X-raydiffraction for samples annealed at temperature between 650and 950 °C shows the Th2Zn17-type structure. This indicatesthat annealing does not help the formation of a singleTbCu7-type structure.VSM magnetic measurements show that all the samplesstudied are ferromagnetic. The room temperature saturationmagnetization (Ms) values for the different Ti concentra-tions are listed in Table I. It can be seen thatMs decreaseswith increasingx, where it drops from 102 emu/g forx50 – 84 emu/g forx50.56. Figure 2 shows theM –T curvesof SmCo72xTix . In this figure,Tc1 andTc2 indicate the Cu-rie temperatures for the 1:7 phase the 2:17 phase. The Curietemperature for the 1:7 phase decreases from 780 °C forx50 to 710 °C forx50.56. Forx.0.42, measurements showtrace of a small amount of SmCo3, which support our x-raydiffraction results. Forx values between 0.2 and 0.35, asingle 1-7 magnetic phase presents. The decrease in the Cu-rie temperature with increasingx indicates a weakening ofthe magnetic interactions. The metastable SmCo7 alloy de-composes into SmCo5 and Sm2Co17 above 700 °C.Field dependence of magnetization is investigated in thedirections parallel (M i) and perpendicular (M') to thealigning magnetic field direction~easy axis direction!. Figure3 shows the magnetization curves for SmCo6.65Ti0.35. Othermeasurements for different values ofx showed similar be-TABLE I. Lattice parameters~a! and ~c!, (c/a) ratio, phases present, Curie temperature (Tc), saturationmagnetization (Ms), and anisotropy field (HA) of SmCo72xTix compounds as a function of titanium concen-tration ~x!.x a ~Å! c ~Å! c/a PhasesTc1~°C!Ms~emu/g!HA~kOe!0 4.935 4.013 0.813 1:712:17780 102 1200.21 4.920 4.060 0.825 1:7 756 96 1560.28 4.897 4.056 0.828 1:7 745 94 1750.35 4.882 4.076 0.832 1:7 742 92 1680.42 4.872 4.074 0.835 1:711:3733 89 1600.56 4.900 4.134 0.842 1:711:3710 84FIG. 1. X-ray diffraction patterns for SmCo72xTix compounds.FIG. 2. M –T measurement of SmCo72xTix compounds under 1000 Oeapplied field.5300 J. Appl. Phys., Vol. 87, No. 9, 1 May 2000 Zhou et al.Downloaded 17 Nov 2006 to 129.93.16.206. Redistribution subject to AIP license or copyright, see http://jap.aip.org/jap/copyright.jsphavior. Extrapolation ofM' and M i curves were used toestimate the anisotropy field (HA). Table I shows theHAvalues of TbCu7-type SmCo72xTix as a function ofx. HAincreases with increasing Ti concentration reaching a maxi-mum of 175 kOe atx50.28 and then decreases for largervalues ofx. These results are similar to the results by Huanget al.6 for SmCo72xZrx compounds and comparable to theresults of Satyanarayanaet al.10 for Sm2Co172xTix com-pounds, whereHA increases from 90 to 125 kOe by increas-ing x from 0 to 0.5. This effect is important especially in thepreparation of commercial Sm~CoM)71z hard magnetic ma-terials. The HA value of the 1-7 structure structureSmCo6.79Ti0.21 is 20% larger than ourHA value for the samesample with the 2-17 type structure after annealing at 750 °C.The increase inHA is due to the change in the anisotropyconstantKu1 which is caused by the preferential occupationof the dumbbell sites by the doping elements as suggested byDeporteset al.11,12IV. CONCLUSIONSSamples of TbCu7-type structure SmCo72xTix have beenprepared and their crystal structures were determined byx-ray diffraction. Doping Ti can help stabilize TbCu7-typestructure in these alloys. The doping element is found todecreaseTc andMs for all values ofx, while increasing theanisotropy field for small values ofx. An anisotropy field ashigh as 175 kOe is obtained in these compounds which isabout 20% higher than that for the same samples with 2-17type structure. The basic results in this article help the un-derstanding of the effects of Ti substitution on the structureand magnetic properties of magnetic materials for high tem-perature applications.ACKNOWLEDGMENTThe authors would like to thank the AFOSR for the fi-nancial support under Grant No. AFOSR-F49620-98-1-0098.1K. J. Strnat, Ferromagnetic Materials~Elsevier Science, New York,1988!, Vol. 4, Chap. 2, pp. 131–209.2K. Kumar, J. Appl. Phys.63, R13 ~1988!.3H. R. Kirchmayr, J. Phys. D: Appl. Phys.29, 2763~1996!.4H. Saito, M. Takahashi, T. Wakiyama, G. Kidoand, and H. Nakagawa, J.Magn. Magn. Mater.82, 322 ~1989!.5J. Yang, O. Mao, and Z. Altounian, IEEE Trans. Magn.32, 4380~1996!.6M. Q. Huang, W. E. Wallace, M. McHenry, Q. Chen, and B. M. Ma, J.Appl. Phys.83, 6718~1998!.7Y. Khan, Phys. Status Solidi A21, 69 ~1974!.8A. Lefevre, L. Cataldo, M. Th. Cohen-Adad, and B. F. Mentzen, J. AlloysCompd.255, 161 ~1997!.9A. Lefevre, L. Cataldo, M. Th. Cohen-Adad, C. H. Allibert, and N. Valig-nat, J. Alloys Compd.241, 210 ~1996!.10M. V. Satyanarayana, H. Fujii, and W. E. Wallace, J. Appl. Phys.53, 2374~1982!.11J. Deportes, D. Givord, R. Lemaire, H. Nagai, and Y. T Yang, J. Less-Common Met.44, 273 ~1976!.12J. Deportes, D. Givord, J. Schweizer, and F. Tasset, IEEE Trans. Magn.12, 1000~1976!.FIG. 3. TypicalM –H loops for SmCo6.65Ti0.35 aligned sample at a tempera-ture of 300 K.5301J. Appl. Phys., Vol. 87, No. 9, 1 May 2000 Zhou et al.Downloaded 17 Nov 2006 to 129.93.16.206. Redistribution subject to AIP license or copyright, see http://jap.aip.org/jap/copyright.jsp

Structure and magnetic properties of SmCo\u3csub\u3e7-x\u3c/sub\u3eTi\u3csub\u3ex\u3c/sub\u3e with TbCu\u3csub\u3e7\u3c/sub\u3e-type structure

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Structure and magnetic properties of SmCo\u3csub\u3e7-x\u3c/sub\u3eTi\u3csub\u3ex\u3c/sub\u3e with TbCu\u3csub\u3e7\u3c/sub\u3e-type structure

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