Thermodynamics of SmCo5 compound doped with Fe and Ni: An ab initio study

Abstract

SmCo 5 permanent magnets exhibit enormous uniaxial magnetocrystalline anisotropy energy and have a high Curie temperature. However, a low energy product presents a significant drawback in the performance of SmCo 5 permanent magnets. In order to increase the energy product in SmCo 5 , we propose substituting fixed amount of cobalt with iron in a new magnet, SmFe 3 CoNi, where inclusion of nickel metal makes this magnet thermodynamically stable. We further discuss some basic theoretical magnetic properties of the SmCo 5 compound. IntroductionThree basic material parameters determine the intrinsic properties of hard magnetic materials: (i) spontaneous (saturation) magnetization, M s , (ii) Curie temperature, T c , and (iii) magnetocrystalline anisotropy energy (MAE), K 1 [1]. These three parameters all need to be large for the permanent magnet to be technologically suitable: T c ~ ≥ 550 K, M s ~ ≥ 1 MA/m, K 1 ~ ≥ 4 MJ/m 3 . The desired values of these properties can be achieved by combining transition-metal (TM) with rare-earth-metal (RE) atoms in various intermetallic compounds, where the RE atoms induce a large magnetic anisotropy while the TM atoms provide a large magnetization and high Curie temperature [1,2].SmCo 5 (in the hexagonal CaCu 5 -type structure) magnets exhibit enormous uniaxial MAE of K 1 ~ 17.2 MJ/m 3 , substantially higher than that of Nd 2 Fe 14 B (Neomax) magnets (K 1 ~ 4.9 MJ/m 3 ), and have almost twice the Curie temperature (T c ~ 1020 K) compared to Neomax (T c ~ 588 K) [3,4]. However, Nd 2 Fe 14 B currently dominates the world market for permanent magnets (~ 62 %) [5,6], since it possesses the highest energy performance measured by a record energy product (BH) max of 512 kJ/m 3 , more than twice as high as the energy product of SmCo 5 magnets, (BH) max of 231 kJ/m 3 [3,4]. Although SmCo 5 magnets are more suitable for high temperature applications than Neomax, due to their relatively low energy performance SmCo 5 magnets occupy only ~ 3% of the world market [5,6].From a cost stand point, it would be beneficial to substitute Co atoms with Fe, because Fe in the Earth's crust is ~ 2000 times more abundant than Co and consequently much cheaper. In addition, Fe is a ferromagnetic metal with a very large magnetization at room temperature (1.76 MA/m [3]). However, the SmFe 5 compound is thermodynamically unstable and does not appear in the equilibrium Sm-Fe phase diagram, although the alloy compound Sm(Co 1-x Fe x ) 5 with the CaCu 5 -type structure has been synthesized by the melt-spinning method for x = 0.0 -0.3 [7]. Furthermore, the Curie temperature for Sm(Co 1-x Fe x ) 5 alloys was found to increase from ~ 1020 K to ~ 1080 K when increasing x from 0.0 to 0.2 [8], in contrast to Sm 2 (Co 1-x Fe x ) 17 alloys which exhibit a monotonic decrease in Curie temperature with increasing Fe content [9].The fundamental purpose of the present study is to explore the effect of adding Ni to the SmCo 5 magnet in order to stabilize Sm(Co 1-x Fe x ) 5 alloys containing a sufficient amount of iron to boost the...

Thermodynamics and Magnetism of YCo5 Compound Doped with Fe and Ni: An Ab Initio Study

“…The implementation of these particular methods ensures that our results are rigorous and independent of technical implementations while employing the most advantageous attributes and durability strengths of each method. Related details of the ab initio [96,97] and the CALPHAD computational methods are outlined in Section 2. Results of the density-functional-theory (DFT) calculations of the ground state properties of the Y(Co-Fe-Ni) 5 alloys connected with CALPHAD calculations are outlined in Section 3.…”

“…For comparison, we also show (Figure 2b) the heat of formation calculated within the EMTO-CPA formalism [3,4] In order to understand the difference between Figure 2a,b, one needs to take into consideration several of the following arguments. Nickel metal forms the stable CaCu5-type compounds with both yttrium and samarium metals.…”

“…As we mentioned in the Introduction, the YFe 5 compound as well as the SmFe 5 compound (see refs. [3,4]) do not exist in the equilibrium Y-Fe and Sm-Fe phase diagrams, correspondingly, thus no experimental information about the heat of formation of these hypothetical compounds is available. However, the EMTO calculations show that that the heat of formation of the YFe 5 compound is positive, +6.46 mRy/atom, and is half of the calculated heat of formation of the SmFe 5 compound, +12.68 mRy/atom.…”

“…In our previous papers [3,4], we suggested a new economically effective permanent magnet, SmFe 3 CoNi, that was developed from the well-known SmCo 5 blueprint. More contemporary neodymium magnets of the Nd-Fe-B type are superior to the SmCo 5 magnet because of their greater maximum energy product emerging from their iron-rich stoichiometry.…”

“…For comparison, we also show (Figure 2b) the heat of formation calculated within the EMTO-CPA formalism [3,4] of the pseudo-binary SmFe3(Ni1-xCox)2 alloys where Fe atoms occupy all 3g-type sites and the occupation of the 2c-type sites continuously changes from pure Ni (the SmFe3Ni2 compound) to pure Co (the SmFe3Co2 compound). These calculations show that the pseudo-binary SmFe3(Ni1-xCox)2 alloys could remain stable until almost half of Ni atoms are replaced by Co atoms.…”