Magnetic Proporties of Intermetallic Compounds of Praseodymium with the Metals of Iron and Renium Subgroup

Introduction

One of the major problems of inorganic chemistry is the creation of new materials that meet the requirements of modern science and technology.

Materials made of intermetallic compounds of rare earth metals with iron triads are of particular interest from both the practical and theoretical point of view. Since the rare earth metals refer to 4f- as well as the elements of the iron subgroup to 3d-transition metals, than the atoms of these elements have inner orbital with unpaired electrons that causes the occurrence of the magnetic moments. Compounds formed by rare earth metals with iron triad have complex magnetic structures resulting in strong magnetic properties.

However, the widespread use of magnetic materials created of intermetallic compounds of the rare earth metals with metals of the iron subgroup is limited by their extreme fragility and low technology. Therefore, the search of ways of strengthening intermetallic compounds of rare earth metals and improvement of their adaptability is an extremely urgent task.

Analysis of the available data in the literature allows doing an assumption that the addition of rhenium to the rare earth intermetallic compounds improve their technological characteristics and stabilize their magnetic properties. Therefore, a systematic study of new complex compositions with praseodymium, rhenium and iron triad is very reasonable and promising.

According to the law discovered by O.Kubashevsky [1], the enthalpy of formation of intermetallides of iron triad metals grows in the modulus along Fe-Co-Ni series owing to increase of acceptor abilities of elements d – band in this series. As a result the number of formed intermetallides and their stability should increase at transition from Me-Fe systems to Me-Co and Me-Ni as occurs in Pr-Fe and Pr-Co systems [2]. O.Kubashevsky’s law isn’t obeyed at interaction of rhenium with iron, cobalt and nickel, namely, the number of intermetallide compounds decreases for Re-Fe and Re-Co systems [3].

Taking into account the value of statistical criteria of Vozdvizhensky [4] it is possible to offer that interactions between rhenium and metals of iron subgroup are rather simple. This is confirmed by formation of solid solutions of rhenium with hexagonal modification of cobalt.

 Material and Method

The research of alloys by means of  complex methods of the physical and chemical analysis has allowed to establish the character of  interaction in the ternary Pr-Co-Fe and Pr-Co-Re systems at 870 K [5]. The obtained results being in agreement with each other show that the interaction of components in studied systems, mainly is defined by the processes occurring in binary systems.

The analysis of the presented literary material allows to conclude that interactions of praseodymium with iron and cobalt essentially differs from interaction in Pr-Co-Re and  Pr-Co-Fe systems at 870 K.

In the studied systems we discovered practically all binary inter-metallide compounds, except Pr₅Со₁₉ and PrRe₂ that are found in the binary limiting systems stable at 870 K. In the ternary Pr-Co-Fe system at 870  the continuous series of solid solutions PrСо₂ and PrRe₂, Pr₂Со₁₇ and Pr₂ Fe₁₇is formed.

Hume-Rothery [6] formulated three conditions of formation of a continuous series of solid solutions: 1) the crystal structure belongs to one structural type, 2) the sizes of atoms differ not greatly (the differences in values of atomic radii shouldn’t exceed 10-12 %), 3) metals are of similar chemical nature. Fulfillment of the above-stated conditions promotes to the formation of a continuous series of solid solutions in Pr-Co-Fe system.

Result and Discussion

The location of homogeneity areas of a continuous number of  solid solutions along isoconcentrates of Pr and a continuous change of  lattice periods of their homogeneity area proves that there is a formation of solid solutions by replacement of one 3d-elements in a crystal lattice. Non-obeying of one of the conditions of a continuous number of solid solutions leads to the formation of the limited solid solutions which area of existence varies in the investigated systems in very wide limits.

The extension of homogeneity areas of the limited solid solutions on the basis of binary phases with identical stoichiometric structures in ternary system is defined basically by the dimensional factor. Thus solubility of the third component in the initial binary phases is greater if there is less distinction in the sizes of replaced and replacing atoms (fig. 1). The change of parameters of lattices in PrСо₃, Pr₂Со₇, PrСо₅ compounds shows that solubility of the third component in Pr-Co-Fe system is greater than in  Pr – Co – Re and Pr – Fe-Re (fig. 2) systems. Within the separate system the solubility of the third component in compounds with various stoichiometric content can’t be explained unambiguously by the properties of compounds – solvents, i.e. by thermodynamic structure or stoichiometry. The dimensional factor in this case plays a minor role in comparison with other factors. The established dependence of a solubility limit upon the constant concentration of 3d – electrons in phases of PrСо₃, Pr₂Со₇, PrСо₅ allows to assume that stability of the binary compounds R_xM_y with crystal structures derived from the compounds of CaCu₅ type is defined by 3d – electronic concentration [7].  The solubility of rhenium in binary inter-metallides of praseodymium with cobalt and iron is insignificant, possibly, owing to the influence of the dimensional factor of r_Fe = 0,126nm, r_Re = 0,137nm. Research of rhenium influence on the stabilization of binary inter-metallide compounds of praseodymium with cobalt and iron by means of a complex methods of the physical and chemical analysis has shown that rhenium dissolution occurs by statistical replacement of 3d – transitive metal atoms  with atoms of rhenium. Since magnetic properties of these inter-metallides are defined by presence of exchange interaction in the sublattice of metals of Fe triad, then dissolution of magnetic-inactive atoms of Rе in these inter-metallides should change magnetic behavior of these phases.

Study of phase structure is taken as a theoretical basis for research and a choice of alloys possessing optimum magnetic properties. On the basis of the analysis of  literary and experimental data it became possible to assume that alloys from area PrСо₅, Pr₂Ме₁₇ and new ternary inter-metallide compounds ψ should possess high magnetic characteristics. Therefore the study of magnetic properties of alloys from homogeneity areas of these compounds is of great importance since such alloys can be used as magnetic materials.

Figure 1: Isothermal cross-section for Pr-Co-Re system at 870 K. Click here to View figure

Figure 2: Isothermal section for Pr-Fe-Re system at 870 K. Click here to View figure

 

Results of the magnetic analysis for Pr-Co-Fe system in cuts of Pr₂Ме₁₇ and 16,6 ат. % Pr in the homogeneity area of  the inter-metallide compound PrСо₅  show that  the magnetic saturation and the residual induction decrease and coercive force grows. The further replacement of cobalt atoms by magnetic-active atoms of iron leads to increase in magnetic saturation and residual induction. These properties follow from the gradual filling of 3d – band.  As it is above mentioned  the compounds Pr₂Со₁₇ and Pr₂Fe₁₇ form a continuous number of solid solutions. The saturation magnetization coincides with the maximum of the lattice periods and microhardness [8]. The results of the magnetic analysis for Pr-Co-Fe system are represented in the tab.1.

Results of researches show that alloys of these solid solutions are characterized by ferrimagnetic  ordering [9].

Doping with iron increases the saturation magnetization and residual induction. The low values ​​of coercive force are explained by lattice defects, oxidation of the alloy surface, as well as brittleness and low adaptability of these intermetallic compounds. Therefore more refractory alloys of rhenium must improve manufacturability of these intermetallic compounds. The results of the magnetic analysis for Pr-Co-Re system are represented in the tab.2. According to the research results substitution of Co atoms by magneto-inactive Re atoms leads to the decrease of the saturation magnetization and residual induction, but the coercive force of Re system increases monotonically. The reason for such an increase of the coercive force of alloys is the change of the phase composition.

In the Pr-Fe-Re system the study of the Re effect on the magnetic properties of intermetallic compounds Pr₂Fe₁₇ and new ternary intermetallic compounds ψ showed that in homogeneity area their saturation magnetization, residual induction and coercive force increase monotonically [10]  (Table 3.).

Table 1: The results of magnetic analysis of Pr-Co-Fe system with a constant content of Pr –16.6 at.% and in section of Pr₂Co₁₇ – Pr₂Fe₁₇, in the field of 20 kA/m.

№	Alloy composition,  аt.%			Saturation magnetization, T.	Residual induction, T.	Coercive force, A/m.
	Pr	Co	Fe
1 2 3 4 5 6 7 8 9 10 11 12	16,6 16,6 16,6 10,5 10,5 10,5 10,5 10,5 10,5 10,5 22,2 12,5	83,4 80,0 40,0 80,0 60,0 50,0 30,0 20,0 10,0 0 77,8 10,0	0 3,4 43,4 9,5 29,5 39,5 59,5 69,5 79,5 89,5 0 77,5	1,4090 1,1350 1,3500 1,1740 1,2510 1,4410 1,4530 1,4400 1,1720 0,9880 0,8400  0,1055	0,1135 0,0680 0,0890 0,0767 0,0830 0,0995 0,0785  0,0785 0,0780  0,0475  0,1870  0,0575	10348,0    11940,0    10348,0    10188,8      9950,0    12099,2    10984,8    10348,0    10984,8      9552,0    27860,0    11940,0

 

Table 2: The results of magnetic analysis of Pr-Co-Re system with constant content of Pr-16.6 at.% and 10.6 at.% in the field of 20 kA/m.

№	Alloy composition,  аt.%			Saturation magnetization, T.	Residual induction, T.	Coercive force, A/m.
	Pr	Co	Re
1 2 3 4 5 6 7 8 9 10 11 12	16,6 16,6 16,6 16,6 16,6 10,6 10,6 10,6 10,6 10,6 10,6 10,6	83,4 75,0 70,0 60,0 50,0 89,4 85,0 80,0 70,0 65,0 55,0 40,0	0 8,4 13,4 23,4 33,4 0 4,4 9,4 19,4 24,4 34,4 49,4	1,3300 0,8085 0,7870 0,5100 0,3500 1,4000 1,1335 0,8790 0,8130 0,4850 0,3900 0,5440	0,2480 0,2120 0,2180 0,1660 0,0740 0,0870 0,0792 0,1165 0,2930 0,1770 0,0815 0,1387	29054,0   29133,6  45372,0  49352,0  76416,0    7164,0    7482,4  26745,6  75620,0  86366,0  79202,0  46008,8

 

Table : The results of magnetic analysis of Pr-Fe-Re system with a constant content of Pr- 10.6 and 8.0 at.%. in the field of 20 kA/m.

№	Alloy composition,  аt.%			Saturation magnetization, T.	Residual induction, T.	Coercive force, A/m.
	Pr	Fe	Re
1 2 3 4 5 6 7 8	10,5 10,5 10,5 10,5 8,0 8,0 8,0 8,0	89,5 84,5 79,5 74,5 77,0 72,0 67,0 62,0	0 5,0 10,0 15,0 15,0 20,0 25,0 30,0	0,5000 0,7000 0,2000 0,4000 0,1000 0,4000 0,7000 0,9000	0,0550 0,0600 0,0410 0,0700 0,0510 0,0800 0,0850 0,0900	15920 31840   6368  7562  7960 19900 31840 36616

 

Conclusion

Alloys of phase area  Pr₂Me₁₇  in the Pr-Co-Fe and PrCo₅ + Pr₂Co₇ + ε (Co, Re) system with optimal combination of magnetic properties (saturation magnetization, residual induction, coercive force) can be recommended for the production of magnetic materials

References

1.  Kubaschewski, O.; Chart, T.C. J. Inst. Metals. 1965, 93, 329-338
2. Moffat W.G. The handbook of binary phase diagrams. General Electric Comp. 1981
3. Parthe E.; Moreau J.M. J. Rare-earth metals. 1977, 53, 1-24
4. Vozdvijenski V.M. Forecast of binary phase diagrams. М.: Metallurgy. 1975, 224.
5.  Spabekova R.S.; Sokolovskaya E.M.; Vetoshkin I.D.; Kazakova E.F. Phase structure and properties of alloys of the system praseodymium-cobalt-iron. Herald of Moscow State University. 1992, 33, №3.
6. Hume-Rothery W. Factors influencing stability of metal phases. Collection of  articles: Stability of phases in metals and alloys. М.: World. 1970, 197-199.
7. Sokolovskaya E.M.; Vetoshkin I.D.; Kazakova E.F.; Spabekova R.S. Formation of intermetallides  in praseodymium-iron-cobalt system. VI Conference on a crystal chemistry of inorganic and coordination compound. 1992, 227.
8.  Sokolovskaya E.M.; Vetoshkin I.D.; Kazakova E.F.; Spabekova R.S. Phase structure and properties of alloys of the system  Pr- Со- Re. Herald of Moscow State University. 1992, 33, №6, 551-555.
9.  Spabekova R.S. Study of magnetic saturation and residual induction of the system praseodymium -cobalt-iron (Pr–Co–Fe) at 870К. Science and Knowledge of South Kazakhstan. 2008, 4 (69), 57-61.
10. Spabekova R.S., Chamza A.K., Umurzahova Zh.V. Structure and stability of praseodymium compounds with transition metals. “Key problems of modern physics”. Materials of the international scientific conference. Almaty.  2012.  .75-78.

---

This work is licensed under a Creative Commons Attribution 4.0 International License.