Presentation Information
[P2-65]Synthesis of La-Co highly co-substituted M-type Sr ferrite under high oxygen pressure using hot isostatic pressurization method
*Takeshi WAKI1, Shinji NAKAI1, Hiroto OHTA2, Masaki KATO2, Yoshikazu TABATA1, Hiroyuki NAKAMURA1 (1. Department of Materials Science and Engineering, Kyoto Universityaterial (Japan), 2. Doshisya University (Japan))
Keywords:
ferrite magnet,La-Co cosubstitution,High oxygen pressure,magnetic anisotropy
M-type ferrite AFe12O19 (A = Sr2+, Ba2+,...) is the base material of current ferrite magnets. It is known that La-Co co-substitution enhances both coercivity and remanent magnetization. This is due to the introduction of Co2+. When La-Co co-substituted M-type Sr ferrite is synthesized in air, the introduction of La3+ causes some of the Fe3+ to become Fe2+, and the La-Co isotopic substitution is no longer valid. The upper limit of Co2+ substitution is only about 0.25. We have reported that increasing the oxygen pressure suppresses the generation of Fe2+ and raises the upper limit of Co substitution, and that the magnetic anisotropy improves accordingly. At a pressure of PO2 = 387 atm, LaFe11CoO19, the limit of La-Co isotopic substitution, can be synthesized, but the sample has not yet been single-phased. In this study, we investigated the temperature and oxygen partial pressure conditions for the synthesis of La-Co highly co-substituted M-type Sr ferrite Sr1-xLaxFe12-xCoxO19 (x = 0.7-1), aiming for single-phase synthesis of the sample. The magnetic properties of the single-phase samples were also evaluated.
Samples were synthesized by the solid-phase reaction method: SrCO3, La2O3, Fe2O3, and Co3O4 were used as starting materials, and after a preliminary reaction in an oxygen stream, final heat treatment was performed using a hot isostatic pressurizer at 1200-1400°C, PO2 = 48-387 atm, reaction time 1-2 h. The obtained samples were identified by powder XRD. Magnetization measurements were performed with a SQUID magnetometer at T = 5--300 K and H = 0--70 kOe. We used field-oriented samples and applied magnetic field in the direction of the hard axis.
In the XRD pattern of the x = 1 sample synthesized at PO2 = 194 atm and at 1350°C, there was no M phase and hematite, orthoferrite, and spinel were observed. At 1400°C, there were M phase, but it did not reach a single phase. On the other hand, the XRD pattern for x = 0.9 shows M phase from 1200°C, and the diffraction of hematite, orthoferrite, and spinel decreased with increasing temperature, and M phase became single-phase at 1350°C. Hard-axis magnetization measurements showed that x = 0.9 sample did not saturate even at H = 70 kOe at the lowest temperature, indicating enhanced magnetic anisotropy. As the temperature is increased, a kink appears, and the anisotropic magnetic field was estimated by SPD method and found to be enhanced to HA = 40 kOe at T = 300 K (HA = 18.5 kOe for SrFe12O19). The sample with x = 0.8, finely powdered by ball milling and heat-treated to remove strain, showed a high coercivity of 8.5 kOe in the unoriented and fixed condition.
Samples were synthesized by the solid-phase reaction method: SrCO3, La2O3, Fe2O3, and Co3O4 were used as starting materials, and after a preliminary reaction in an oxygen stream, final heat treatment was performed using a hot isostatic pressurizer at 1200-1400°C, PO2 = 48-387 atm, reaction time 1-2 h. The obtained samples were identified by powder XRD. Magnetization measurements were performed with a SQUID magnetometer at T = 5--300 K and H = 0--70 kOe. We used field-oriented samples and applied magnetic field in the direction of the hard axis.
In the XRD pattern of the x = 1 sample synthesized at PO2 = 194 atm and at 1350°C, there was no M phase and hematite, orthoferrite, and spinel were observed. At 1400°C, there were M phase, but it did not reach a single phase. On the other hand, the XRD pattern for x = 0.9 shows M phase from 1200°C, and the diffraction of hematite, orthoferrite, and spinel decreased with increasing temperature, and M phase became single-phase at 1350°C. Hard-axis magnetization measurements showed that x = 0.9 sample did not saturate even at H = 70 kOe at the lowest temperature, indicating enhanced magnetic anisotropy. As the temperature is increased, a kink appears, and the anisotropic magnetic field was estimated by SPD method and found to be enhanced to HA = 40 kOe at T = 300 K (HA = 18.5 kOe for SrFe12O19). The sample with x = 0.8, finely powdered by ball milling and heat-treated to remove strain, showed a high coercivity of 8.5 kOe in the unoriented and fixed condition.
