Maximum energy product at elevated temperatures for hexagonal strontium ferrite (SrFe12O19) magnet

Park, Jihoon; Hong, Yang‐Ki; Kim, Seong‐Gon; Kim, Sungho; Liyanage, Laalitha; Lee, Jaejin; Lee, Wonchoel; Abo, Gavin S.; Hur, Kang-Heon; An, Sungyong

doi:10.1016/j.jmmm.2013.11.032

Cited by 51 publications

(7 citation statements)

References 34 publications

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“…For improved description of 3 d electrons in iron ions, the generalized gradient approximation with Coulomb and exchange interaction effects (GGA+U) were employed, where an on-site potential is added to introduce intra-atomic interactions between the strongly correlated electrons33. We employed an effective value ( U eff ) equal to the difference between the Hubbard parameter U and the exchange parameter J 34. To study how the results depend on U eff , three values (3.4, 6.7, and 10.4 eV) on Fe atoms were adopted on the basis of many rigorous calculations of barium hexaferrites313536.…”

Section: Methodsmentioning

confidence: 99%

Calculation of exchange integrals and Curie temperature for La-substituted barium hexaferrites

Zhao

Sun

et al. 2016

Sci Rep

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As the macro behavior of the strength of exchange interaction, state of the art of Curie temperature Tc, which is directly proportional to the exchange integrals, makes sense to the high-frequency and high-reliability microwave devices. Challenge remains as finding a quantitative way to reveal the relationship between the Curie temperature and the exchange integrals for doped barium hexaferrites. Here in this report, for La-substituted barium hexaferrites, the electronic structure has been determined by the density functional theory (DFT) and generalized gradient approximation (GGA). By means of the comparison between the ground and relative state, thirteen exchange integrals have been calculated as a function of the effective value Ueff. Furthermore, based on the Heisenberg model, the molecular field approximation (MFA) and random phase approximation (RPA), which provide an upper and lower bound of the Curie temperature Tc, have been adopted to deduce the Curie temperature Tc. In addition, the Curie temperature Tc derived from the MFA are coincided well with the experimental data. Finally, the strength of superexchange interaction mainly depends on 2b-4f1, 4f2-12k, 2a-4f1, and 4f1-12k interactions.

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Section: Methodsmentioning

confidence: 99%

Calculation of exchange integrals and Curie temperature for La-substituted barium hexaferrites

Zhao

Sun

et al. 2016

Sci Rep

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“…Still, hardly any recent works have revisited the SFO magnetic structure in depth employing state-of-the-art experimental techniques. From the theoretical side, and since the early work of Fang et al 9 where Gorter’s prediction 10 on the ferrimagnetic arrangement of the Fe sublattices was confirmed via ab initio calculations, M-type hexaferrites (M = Ba,Sr) have been extensively studied 11 – 18 A number of properties have been derived in these works including, among others, the electronic gap, the saturation magnetization ( ) and the MMs on the Fe ions together with their associated spin-resolved density of states (DOS), the MCA 13 , 15 , 16 as well as exchange couplings ( Js ) subsequently employed in the estimation of 12 , 19 or the evolution of with temperature 14 . In addition, a large effort has been put in exploring substitutional elements either for the M-ion (La 11 , 15 , 19 , Pb 17 , Pr 15 , Nd 15 ) or the Fe ions (Al 16 , Zn–Sn 13 ) in order to improve the material’s magnetic performance.…”

Section: Introductionmentioning

confidence: 99%

An ab initio study of the magnetic properties of strontium hexaferrite

Tejera-Centeno

Gallego

Cerdá

2021

Sci Rep

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The magnetic properties of $${\text{SrFe}}_{12}{\text{O}}_{19}$$ SrFe 12 O 19 , a paradigmatic hexaferrite for permanent magnet applications, have been addressed in detail combining density functional theory including spin–orbit coupling and a Hubbard U term with Monte Carlo simulations. This multiscale approach allows to estimate the Néel temperature of the material from ab initio exchange constants, and to determine the influence of different computational conditions on the magnetic properties by direct comparison versus available experimental data. It is found that the dominant influence arises from the choice of the Hubbard U term, with a value in the 2–3 eV range as the most adequate to quantitatively reproduce the two most relevant magnetic properties of this material, namely: its large perpendicular magnetocrystalline anisotropy and its elevated Néel temperature.

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“…For example, the substitution of La [6,7], Sm [8], Pr [9] and Nd [10] in the SFO increased coercivity moderately while the substitution of Zn-Nb [11], Zn-Sn [12][13][14] and Sn-Mg [21]. Park et al have calculated the exchange interaction of SFO from the differences of the total energy of different collinear spin configurations [22]. In spite of the importance of substituted SFO, only a few theoretical investigations have been done.…”

Section: Introductionmentioning

confidence: 99%

Site occupancy and magnetic properties of Al-substituted M-type strontium hexaferrite

Dixit

Nandadasa

Kim

et al. 2015

Journal of Applied Physics

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We use first-principles total-energy calculations based on density functional theory to study the site occupancy and magnetic properties of Al-substituted M -type strontium hexaferrite SrFe12−xAlxO19 with x = 0.5 and x = 1.0. We find that the non-magnetic Al 3+ ions preferentially replace Fe 3+ ions at two of the majority spin sites, 2a and 12k, eliminating their positive contribution to the total magnetization causing the saturation magnetization Ms to be reduced as Al concentration x is increased. Our formation probability analysis further provides the explanation for increased magnetic anisotropy field when the fraction of Al is increased. Although Al 3+ ions preferentially occupy the 2a sites at a low temperature, the occupation probability of the 12k site increases with the rise of the temperature. At a typical annealing temperature (> 700 • C) Al 3+ ions are much more likely to occupy the 12k site than the 2a site. Although this causes the magnetocrystalline anisotropy K1 to be reduced slightly, the reduction in Ms is much more significant. Their combined effect causes the anisotropy field Ha to increase as the fraction of Al is increased, consistent with recent experimental measurements.[4] decreased coercivity. However, the coercivity of the M-type hexaferrites is not increased significantly by these cation substitutions, and is still much smaller than that of Nd-Fe-B magnet [15].Al substitution in the M-type hexaferrite has been more effective in enhancing coercivity [16][17][18][19][20]. Particularly, Wang et al synthesized Al-doped SFO SrFe 12−x Al x O 19 (SFAO) with Al content of x = 0 − 4 using glycinnitrate method and subsequent annealing in a temperature over 700 • C obtaining the largest coercivity of 17.570 kOe, which is much larger than that of SFO (5.356 kOe) and exceeds even the coercivity of the Nd 2 Fe 17 B (15.072 kOe) [1]. Wang and co-workers also observed that the coercivity of the SFAO increases with increasing Al concentration at a fixed annealing temperature. These results call for a systematic understanding, from first principles, of why certain combinations of dopants lead to particular results. This theoretical understanding will be essential in systematically tailoring the properties of SFO.

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Maximum energy product at elevated temperatures for hexagonal strontium ferrite (SrFe12O19) magnet

Cited by 51 publications

References 34 publications

Calculation of exchange integrals and Curie temperature for La-substituted barium hexaferrites

Calculation of exchange integrals and Curie temperature for La-substituted barium hexaferrites

An ab initio study of the magnetic properties of strontium hexaferrite

Site occupancy and magnetic properties of Al-substituted M-type strontium hexaferrite

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