Effect of nitrogen on the magnetization and 57Fe hyperfine field of NdFe10V2Ny

Journal of Magnetism and Magnetic Materials 140-144 (1995) 1021-1022

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Effect of nitrogen on the magnetization and 57Fe hyperfine field of NdFel0V2Ny T. Goto a,*, y . Takahashi a, S. Abe b a Faculty of Engineering, Tohoku Gakuin University, Tagajo 985, Japan b IMR, Tohoku Unicersity, Sendai 980, Japan Abstract

In the compounds NdFel0V2Ny, nitrogen atoms do not occupy only the 2b-sites but also other sites at nitrogen content y > 1 and the crystal begins to transform into an amorphous-like solid. The 57Fe hyperfine field is strongly enhanced upon nitrogenation and at higher nitrogen content of y > 2, most of the iron atoms are expected to have a moment approximately equal to that in bcc iron.

Ternary RFe12_xM x compounds (R = rare earth, M = Ti, V, Cr, Mn, Mo, Si, W and A1, 1 ~
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Fig. 1. X-ray diffraction patterns of NdFel0V 2 Ny.

ior near y = 1. From this result we consider that nitrogen atoms occupy the 2b-sites at the first step of nitrogenation procedure, then occupy other sites upon further nitrogenation. The magnetization curves of NdFel0V2Ny ( y = 1.01) are shown in Fig. 3. The values of magnetization per

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Nitrogen Content, y * Corresponding author. Fax: [email protected].

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Fig. 2. Relative change in unit cell volume, /IV~ Vo, with nitrogen content y, where V0 is the unit cell volume for y = 0.

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!". Goto et al. /Journal of Magnetism and Magnetic Materials 140-144 (1995) 1021-1022

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Fig. 3. Magnetization curves of NdFeloV2Ny (y = 1.01) at 300 and 77 K in magnetic fields parallel and perpendicular to the aligned direction. The broken curve indicates the magnetization curve for y = 0 at 77 K.

formula unit at H = 150 kOe are 18.9 and 19.1/z B at 300 and 77 K, respectively. On the other hand, the magnetizations for y = 0 are 14.4 and 15.3/x n at 300 K and 77 K, respectively. The variation of M6ssbauer spectrum at 300 K with nitrogen content is shown in Fig. 4. The distributions of the hyperfine field corresponding to these spectra were calculated using the Hesse-Rubartsch method [5]. The simulation spectra obtained from the hyperfine field distributions are also shown by the solid curves in Fig. 4. As seen in Fig. 4, a new subspectrum with large hyperfine field of about 330 kOe appears upon nitrogenation and the intensity increases with increasing nitrogen content. This

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Fig. 5. Change in the averaged 57Fe hyperfine field and iron moment upon nitrogenation. large hyperfine field becomes more dominant for the sample with y = 2.1, and its value is approximately equal to that of bcc iron. Therefore, it is expected that the 57Fe hyperfine fields at all the iron sites in this nitride will be approximately equal to the field in bcc iron, when the compound is further nitrogenated. Such a magnetic state of iron may be caused by weakened crystal binding upon nitrogenation. The average hyperfine fields and the iron moment deduced from them using a relation of 150 k O e / / z B are shown in Fig. 5 as a function of nitrogen content. These curves show an anomalous behavior near y = 1, similar to the variation of unit cell volume with nitrogen content. The neodymium moment at 300 K, which is deduced from the saturation magnetization and the average iron moment, is 1.6/z n for y = 0, and 2.4p, B for y = 1.01. In conclusion, in the NdFemV2Ny compounds, nitrogen atoms occupy the 2b-sites for y < 1, then occupy other sites upon further nitrogenation. As a result, the crystal binding would be weakened and the crystal begins to transform into an amorphous-like solid. In such a crystalline state, the iron moment is approximately equal to the moment of bcc iron. References

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Fig. 4. 57Fe Mossbauer spectra of NdFel0VzNy at 300 K. Solid curves indicate the calculated spectra.

[1] K.H.J. Bushchow and D.B De Mooij, The Concerted European Action on Magnets (Elsevier, Amsterdam, 1989) p. 63. [2] J.M.D. Coey and H. Sun, J. Magn. Magn. Mater. 87 (1990) L 251. [3] Y.C. Yang, X.D. Zhang, L.S. Kong, Q. Pan, S.L. Ge, J.L. Yang, Y.F. Ding, B.S. Zhang and C.T. Ye, Solid State Commun. 78 (1991) 313. [4] Y.C. Yang, X.D. Zhang, S.L. Ge, Q. Pan, L.S. Kong, H. Li, J.L. Yang, B.S. Zhang, Y.F. Ding and C.T. Ye, J. Appl. Phys. 70 (1991) 6001. [5] J. Hesse and A. Rubartsch, J. Phys. E 4 (1971) 401.