Theoretical Studies on the Magnetic Moments of Iron Nitrides Including Fe 16 N 2
- PDF / 608,874 Bytes
- 12 Pages / 420.48 x 639 pts Page_size
- 61 Downloads / 168 Views
THEORETICAL STUDIES ON THE MAGNETIC MOMENTS OF IRON NITRIDES IN-
CLUDING Fe16N2 AKIMASA SAKUMA AND YUTAKA SUGITA* Magnetic and Electronic Materials Research Laboratory, Hitachi Metals, Ltd., Mikajiri 5200, Kumagaya 360, Saitama, Japan "Central Research Laboratory, Hitachi Ltd., 1-280, Higashi-Koigakubo, Kokubunji, Tokyo, 185, Japan
ABSTRACT The spin-polarized band calculations for the iron nitrides, Fe 3N, Fe4N and Fel6N2, have been performed with use of LMTO-ASA method in the frame of local spin density functional formalism. The results show that the most distant Fe atoms from N have the largest magnetic moment. The central role of the N atom is to bring about the large magnetic moments through the lattice expansion. Concurrently, the N atoms promote an itinerancy of electrons and then in turn prevent the exchange-splitting. This results in an Fe16N2 with the lowest N concentration having the largest magnetic moments. Quantitatively, the obtained magnetic moments are in fair agreements with the experimental results except for Fe 1 6N2. The calculated magnetic moment of Fe16N2 is about 2.4 tLB/Fe, while the measured value is 1 reported as 3.5 Rt/Fe. The orbital magnetic moment of Fe16N2 is about 0.07 tB, which is too small to make up for the difference from the experimental value.
INTRODUCTION Until the early 1970's, iron nitrides had been investigated in terms of the itinerant electron magnetism of the transition metals including interstitial non-magnetic atoms [1-9]. The aim of the studies was focused on the establishment of the relationship between ferromagnetism and metal-nonmetal bonding. Since Kim and Takahashi [10] found a giant magnetic moment in the Fe-N film in 1972, the elements such as N, C and B in the transition metals have attracted concerns not only in the physical aspect but also in the development of magnetic materials for technological applications. They reported that the film consists of Fe and Fe16N2 whose structure was discovered previously by Jack [ 11 ]. Ever since, many attempts have been made to prepare the single phase Fe 1 6N2 with several techniques. Recently, Komuro et al. [121 have first grown a single crystal Fe16N2 film on lnGaAs epitaxially by MBE technique and demonstrated B. of the Fe16N2 to be 2.8-3.OT. Concurrently, Nakajima et al. [13,14] succeeded to construct the Fe16N2 film by ion implantation and measured the average magnetic moment of Fe atom is about 2.5 [tB. Although the data reported by several workers scatters so far, it is convincing that the magnetic moment of Fe16N2 exceeds one of bcc-Fe by far. The current controversial problems are the mechanism of the occurrence of such a large magnetic moment and how the magnetism of the Fe16N2 is related to that of both Fe-N with no site order of N atoms and other iron nitride compounds. There are four phases in the iron nitrides, c-Fe 2N, e-FeN (2 < x < 3), y'-Fe4 N and (x"Fe 6N2 whose structures were determined by Jack 111,151 previously. E-Fe N exhibits Mat. Res. Soc. Symp. Proc. Vol. 313. ©1993 Materials Research Societ
Data Loading...
