Magnetic properties of R2Fe14C (R=Dy or Er)_第1页
Magnetic properties of R2Fe14C (R=Dy or Er)_第2页
Magnetic properties of R2Fe14C (R=Dy or Er)_第3页
全文预览已结束

下载本文档

版权说明:本文档由用户提供并上传,收益归属内容提供方,若内容存在侵权,请进行举报或认领

文档简介

L179 Journal of Magnetism and Magnetic Materials 59 (1986) L179-L181 North-Holland. Amsterdam LETTER TO THE EDITOR MAGNETIC PROPERTIES OF R 2 Fe ,_,C (R = Dy or Er) A.T. PEDZIWIATR *, W.E. WALLACE Magnetics Technolog)/ Center and MEMS Department, Carnegie-Mellon Unioersrty, Pittsburgh, PA 15213. USA and E. BURZO Central Institute of Physics. P.O. Box MG-06, Bucharest, Romania Received IO February 1986 The Dy,Fe,C and EraFe,C compounds crystallize in a tetragonal structure of P4,/mnm-type. The compounds are ferrimagnetically ordered. The mean iron moments as well as the Curie temperatures are smaller than the values obtained in corresponding boron compounds. The easy direction of magnetization is along the c-axis for R = Dy and in the basal plane for R = Er The study of R-Fe-B alloys, where R is a rare earth or yttrium, has received considerable atten- tion in the last years, since permanent magnets produced from these materials surpass those of the samarium-cobalt type l. The intrinsic prop- erties of these materials are attributed to the R,Fe,B phase, which crystallizes in a tetragonal structure belonging to space group P4,/mnm 2-41. It has been suggested that in this structure boron can be replaced by carbon to some extent 5,6. An iron-rich phase having composition Gd,Fe,C was initially reported in the Gd-Fe-C system 5. This was later identified as Gd,Fe,C 6. However, no such carbide was found in the Ce-Fe-C system 7. The Curie point of Gd,Fe,C has recently been reported as 643 K and its saturation magnetization at 300 K is 12.4 8. It is of obvious interest to ascertain to what extent other tetragonal carbides are formed in the R-Fe-C systems. This phase has now been ob- served in the R-Fe-C systems with R = Dy or Er. The aim of this letter is to report the crystal * On leave from Institute of Physics, Jagiellonian University, Cracow, Poland. structure and magnetic properties of Dy,Fe,C and Er,Fe,C. The samples were prepared by melting the con- stituent elements in a water-cooled copper boat, by rf heating under a flowing ultra-high purity argon. The compounds were annealed for two weeks at 870C and then rapidly cooled to room temperature. The X-ray and thermomagnetic anal- ysis show the presence of only one phase having the Nd,Fe,B-type structure. The lattice parame- ters are given in table 1. These values are some- what smaller than those evidenced in the corre- sponding R,Fe,B compounds 8, probably due to the smaller radius of carbon as compared to that of boron. The c/a ratios determined in R,Fe,C compounds are 1.35, somewhat lower than c/a = 1.77 obtained for the R,Fe,B system. Magnetic measurements were performed in the temperature range 4.2-1100 K. Studies below room temperature were made by using a Faraday- type balance in external fields up to 20 kOe. The easy directions of magnetization were determined at 77 K and room temperature, respectively, in powdered samples aligned in wax. For Dy,Fe,C, uniaxial anisotropy was found, while for Er,Fe,C 0304-8853/86/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division) this is of planar type, A:, in the corresponding boron compounds O. The Curie points were de- tcrmined from the temperature dependence ol magnetization. at Iow external field. by using il Faraday-type balance. In fig. 1 ht have plotted the magnetization isotherms obtained at 4.2 K. For comparison. those of corresponding boron compounds are also given. The data were analyzed according to ap- proach to saturation law. M = M,( 1 - o/H ) + xi1 H, where M, is the spontaneous magnetization. x,) is a Pauli-type contribution and u is the coeffi- cient of magnetic hardness. The .4f,. LI and xi, values are given in table 1. The saturation magne- ti/.ations show an antiparallel coupling of R and FL sublattice moments, ;1s in rare earthLtransition metal compounds IO. The Pauli paramagnetic contributions are nearly the same for both Dy and Er compounds at-t: are nearly five times bigger than in the boron systems. Assuming that the rare earth moments are giLen b! the ,y./ values. we determined the iron sub- 1 4 8 12 16 20 External Field (koe) lattice ni;lgnetizations and the mean Iron mo- ments. .M, c. respectively. The M, values ;tirc 2.12 (R = Dy) :md 2.10 (R = Er). These ,:11- ues art: smaller bv = 107 than those obtained in R,Fe,B compknds. The above behavior is to be compared to that of Fe-B and Fe- C alloys. The composition dependence of the “Fe hvperfi nc field in crystalline and amorphous Fe- B :lllos has been reported 12 ;1s well LIS the magnctizaticn measurements in Fe C alloys I 31. From -Fc hyperfine field values the iron magnetic contribu- tions may be estimated II. For 7.14 at? B(C). which corresponds to 1 : 14 B(C) : Fe ratio. the iron magnetic moment in Fe C allovs i:, smaller by 10% than that in Fe- B alloys. These datil suggest that for both Fe -B (FsC) solid solutions and R,Fe,B(C). similar mechanisms ;ire involved in the variation of iron moments. A discussion concerning this matter has been provided elsewhere 141. Of course. in R T Fe, B compounds (g,-U2 J(J+l) A. T. Pedziwiatr et al. / Proper&s of R 2 Fe, JC Ll81 the situation is more complicated. As a result of various local environments, the Fe moments are dependent on the type of lattice sites 15. In fig. 2 we plotted the dependence of the Curie temperatures, T, on the De Gennes factor (gJ - 1)2J(J + 1) for R,Fe,B and R,Fe,C compounds with heavy rare earths. A linear de- pendence is shown. These data suggest that in addition to Fe-Fe exchange interactions which are nearly constant, a contribution from the inter- actions involving rare earths is also present. The T, values determined in R,Fe,C compounds are smaller, on the average, by = 40 K than those for the boron systems. This fact may be correlated with the slight decrease of the mean iron mo- ments. The temperature dependencies of the sponta- neous magnetizations for Dy,Fe,C and Er,Fe,C compounds are plotted in fig. 3. These are typical for ferrimagnetic ordering and according to NCels classification is of the P-type 16. Assuming a two-sublattice ferrimagnet, we estimated from the above data the parameters characterizing the ex- change interactions. The exchange fields acting on R sublattices are 2pr,Hexch = 370 K for R = Dy and = 220 K for R = Er. These are of the same order of magnitude as the overall crystal field splittings and consequently the ground state has a dominant contribution to the R magnetic mo- ment. Because of a smaller exchange field acting on the erbium sublattice, there is a more pro- nounced temperature dependence for ErzFe,C than for Dy,Fe,C. The exchange field acting on the iron sublattice is 2p,H, = lo3 K. Finally, we conclude that Dy,Fe,C and Er,Fe,C are formed in R-Fe-C systems. The easy axis of magnetization has the same direction as in the corresponding boron compounds. The mean iron moments as well as Curie temperatures are somewhat smaller than the values for the R,Fe,4B systems. Work is in progress dealing with the magnetic properties of R,Fe,B, _,C, alloys. 200 400 600 Temperature (K) Fig. 3. Thermal variation of Dy?Fe,C and Er,Fe,C magneti- zations. References 111 121 31 41 51 61 71 81 91 PO1 111 WI 1131 1141 P51 P61 J.D. Livingston, Proc. Eighth Intern. Workshop on Rare Earth Magnets and Their Applications, ed. K.J. Strnat, Dayton, Ohio (1985) p. 423. J.F. Herb& J.J. Croat, F.E. Pinkerton and W.B. Yelon, Phys. Rev. B29 (1984) 4176. C.B. Shoemaker, D.P. Shoemaker and R. Fruchart, Acta Cryst. 40 (1984) 1665. D. Givord, H.S. Li and J.M. Moreau, Solid State Com- mun. 50 (1984) 497. H.H. Stadelmaier and H.K. Park, Z. Metallkunde 72 (1981) 417. H.H. Stadelmaier and A. El Masry, Proc. Eighth Intern.

温馨提示

  • 1. 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
  • 2. 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
  • 3. 本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
  • 4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
  • 5. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,并不能对任何下载内容负责。
  • 6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
  • 7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。

评论

0/150

提交评论