Abstract:We report the magnetism of fluorite Nd-Fe alloys containing 60-70 at% of Nd as a possible crystalline grain-boundary (GB) phase for Nd-Fe-B permanent magnets. Due to strong magnetic interactions between Nd and Fe, binary fluorite Nd-Fe alloys exhibit high Curie temperatures. The Curie temperature decreases significantly with the addition of Ga or Cu suggesting that these elements are indispensable for the demagnetization of the GB phase.
“…[9]. Very recently, an attempt has been made to calculate the exchange coupling constants in the crystalline Nd-Fe alloy as a candidate of crystalline GB phase of the Nd-Fe-B permanent magnet [23,24]. Results from this study strongly suggest that the crystalline Nd-Fe alloy is ferromagnetic, even though its Nd composition ratio is up to 67%.…”
We investigate the exchange coupling constant Jij in NdxFe1−x amorphous alloys with different compositions within the framework of first-principles calculation. We observed a strong atomicdependence of Jij and its fluctuations. We show that the composition strongly affects the distance dependence of Jij . Composition dependence of calculated Curie temperatures is modest for x < 0.5. To examine the effect of the local environment on the exchange couplings, we demonstrate combined analyses of the coordination structure and exchange coupling constants using the Gabriel graph. Our study reveals that the Curie temperatures are mostly dominated by the averaged Jij and coordination numbers determined by the pairs of neighboring atoms. We also observed that the exchange couplings between Fe-Fe and Fe-Nd become stronger with increasing the number of surrounding Nd atoms.
“…[9]. Very recently, an attempt has been made to calculate the exchange coupling constants in the crystalline Nd-Fe alloy as a candidate of crystalline GB phase of the Nd-Fe-B permanent magnet [23,24]. Results from this study strongly suggest that the crystalline Nd-Fe alloy is ferromagnetic, even though its Nd composition ratio is up to 67%.…”
We investigate the exchange coupling constant Jij in NdxFe1−x amorphous alloys with different compositions within the framework of first-principles calculation. We observed a strong atomicdependence of Jij and its fluctuations. We show that the composition strongly affects the distance dependence of Jij . Composition dependence of calculated Curie temperatures is modest for x < 0.5. To examine the effect of the local environment on the exchange couplings, we demonstrate combined analyses of the coordination structure and exchange coupling constants using the Gabriel graph. Our study reveals that the Curie temperatures are mostly dominated by the averaged Jij and coordination numbers determined by the pairs of neighboring atoms. We also observed that the exchange couplings between Fe-Fe and Fe-Nd become stronger with increasing the number of surrounding Nd atoms.
“…In addition, Ga is more effective than Cu to make Nd-Fe alloys paramagnetic at room temperature. The addition of Ga weakens the exchange interaction among Nd Fe as well as Fe Fe pairs, which results in the decrease in [ 74 ]. Figure 9.…”
Section: Finite-temperature Magnetism For Intergranular Phases In Nd-mentioning
confidence: 99%
“… Curie temperature for fluorite Nd-Fe- alloys as a function of the composition parameter . The figure is taken by permission from [ 74 ]. Copyright (2020) The Japan Society of Applied Physics …”
Section: Finite-temperature Magnetism For Intergranular Phases In Nd-mentioning
Development of high-performance permanent magnets relies on both the main-phase compound with superior intrinsic magnetic properties and the microstructure effect for the prevention of magnetization reversal. In this article, the microstructure effect is discussed by focusing on the interface between the main phase and an intergranular phase and on the intergranular phase itself. First, surfaces of main-phase grains are considered, where a general trend in the surface termination and its origin are discussed. Next, microstructure interfaces in SmFe
12
-based magnets are discussed, where magnetic decoupling between SmFe
12
grains is found for the SmCu subphase. Finally, general insights into finite-temperature magnetism are discussed with emphasis on the feedback effect from magnetism-dependent phonons on magnetism, which is followed by explanations on atomic arrangements and magnetism of intergranular phases in Nd-Fe-B magnets. Both amorphous and candidate crystalline structures of Nd-Fe alloys are considered. The addition of Cu and Ga to Nd-Fe alloys is demonstrated to be effective in decreasing the Curie temperature of the intergranular phase.
Development of high-performance permanent magnets relies on both the main-phase compound with superior intrinsic magnetic properties and the microstructure effect for the prevention of magnetization reversal. In this article, the microstructure effect is discussed by focusing on the interface between the main phase and an intergranular phase and on the intergranular phase itself. First, surfaces of main-phase grains are considered, where a general trend in the surface termination and its origin are discussed. Next, microstructure interfaces in SmFe 12 -based magnets are discussed, where magnetic decoupling between SmFe 12 grains is found for the SmCu subphase. Finally, general insights into finite-temperature magnetism are discussed with emphasis on the feedback effect from magnetism-dependent phonons on magnetism, which is followed by explanations on atomic arrangements and magnetism of intergranular phases in Nd-Fe-B magnets. Both amorphous and candidate crystalline structures of Nd-Fe alloys are considered. The addition of Cu and Ga to Nd-Fe alloys is demonstrated to be effective in decreasing the Curie temperature of the intergranular phase.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
