Structure, exchange interactions, and magnetic phase transition ofEr2Fe17−x

Abstract

We present the effect of aluminum substitution on the structure, exchange interactions, and magnetic phase transitions of the intermetallic compound Er 2 Fe 17 . All samples have a hexagonal Th 2 Ni 17 -type structure or a rhombohedral Th 2 Zn 17 -type structure. The replacement of Fe by Al results in an approximately linear increase in the unit-cell volumes at a rate of 9.3 Å 3 per Al atom. The Al atoms preferentially occupy 12k (18h) and 12j (18f ) sites at low Al concentration, while they prefer strongly to occupy 6c (4 f ) and 18f (12j) sites at high aluminum concentration. The Curie temperature is found to increase at first, form a maximum value at xϭ3, and then to decrease monotonically with increasing Al concentration. The exchange-coupling constant between 3d and 4 f sublattices, J RT , was obtained from fitting M -T curves for some of the samples. The intersublattice molecular-field coefficient n RT and hence the R-T exchange-coupling constant J RT have been also determined on the basis of magnetization curves at the compensation temperature. The exchange-coupling constant J RT shows almost no obvious composition dependence, while the exchange-coupling constant J TT is strongly dependent on the Al concentration. The composition dependence of the 3d sublattice exchange interaction is discussed in terms of bond lengths and atomic preferential occupancies. It is noteworthy that the substitution of Al has a significant effect on the magnetocrystalline anisotropies of both the Er sublattice and the Fe sublattice in Er 2 Fe 17Ϫx Al x compounds. The temperature and composition dependence of the easy magnetization direction suggests that the second-order crystal electric-field coefficient A 20 changes its sign from negative to positive with increasing Al concentration up to xϾ7. ͓S0163-1829͑98͒02721-0͔

Crystallographic and magnetic studies on iron-rich mixed rare-earth intermetallics (Nd/Tb)2(Fe/Al)17

“…Fig. 10 shows the magnetization of NdTbFe 17−y Al y compounds measured at 5 K. For y = 7, there exists an obvious jump in magnetization at 1.7 T. A similar feature was also observed in Er 2 Fe 8 Al 9 compound [23]. For y = 8, the magnetization does not reach a saturation up to 5 T. The saturation moments M S are derived from the M-1/H curves by extrapolating 1/H to zero and also listed in Table 2.…”

“…In Tb 2 Fe 17−y Al y compounds, a uniaxial anisotropy can be induced when y ≥ 6. In general, the anisotropy of R 2 Fe 17 compounds is mainly determined by the competition of iron sublattice and rare-earth sublattice anisotropies [23]. The total magnetocrystalline anisotropy can be written as: K 1,tot = K 1,R + K 1,Fe , where K 1,R is the contribution of the R sublattice to the anisotropy constant and K 1,Fe is the anisotropy constant of the Fe sublattice.…”

Syntheses and magnetic properties of Nd/sub 3/Co/sub 13-x/Ni/sub x/B/sub 2/ borides

“…The fact that this compound exhibits easy-plane anisotropy at room temperature restricts its possible application as permanent magnets. However, it has been shown [13]- [17] that the easy magnetization direction of R-T alloys can be modified by the introduction of M atom (M transition metal or metalloid metal). For example, low concentrations of Ga or Al substitution in Sm Fe results in a change in the easy magnetization direction from basal plane to -axis [13].…”

Structural and magnetic properties of iron-rich compounds in the Yb–Fe–Ga system

“…All investigated samples are ferromagnetic at room temperature and show similar properties compared to binary Yb 2 Fe 17 [1]. Their total mass magnetization is in the range of σ sample = 39-105 emu/g, whereas the values corrected for the magnetic impurity phase Fe 1 − x Ga x are in the range σ sample = 28.4-47.2 emu/g (see Table 4).…”

“…Iron-rich rare-earth (R) compounds and their substitution derivatives are of interest in view of their ferromagnetic properties ( [1] and references therein). Systematic studies of the aluminum substituted series R 2 Fe 17 − x Al x (R = Tb, Dy, Ho, Er) [2] and of the iron-rich corner of the ytterbium based Yb-Fe-Al phase diagram [3,4] have shown that the phase relations and structural properties change strongly as a function of both Al and R content.…”