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Nanometer-size hard magnetic ferrite exhibiting high optical-transparency and nonlinear optical-magnetoelectric effect.

Ohkoshi S, Namai A, Imoto K, Yoshikiyo M, Tarora W, Nakagawa K, Komine M, Miyamoto Y, Nasu T, Oka S, Tokoro H - Sci Rep (2015)

Bottom Line: Additionally, we have observed magnetization-induced second harmonic generation (MSHG).The nonlinear optical-magnetoelectric effect of the present polar magnetic nanocrystal was quite strong.These findings have been demonstrated in a simple iron oxide, which is highly significant from the viewpoints of economic cost and mass production.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.

ABSTRACT
Development of nanometer-sized magnetic particles exhibiting a large coercive field (Hc) is in high demand for densification of magnetic recording. Herein, we report a single-nanosize (i.e., less than ten nanometers across) hard magnetic ferrite. This magnetic ferrite is composed of ε-Fe2O3, with a sufficiently high Hc value for magnetic recording systems and a remarkably high magnetic anisotropy constant of 7.7 × 10(6) erg cm(-3). For example, 8.2-nm nanoparticles have an Hc value of 5.2 kOe at room temperature. A colloidal solution of these nanoparticles possesses a light orange color due to a wide band gap of 2.9 eV (430 nm), indicating a possibility of transparent magnetic pigments. Additionally, we have observed magnetization-induced second harmonic generation (MSHG). The nonlinear optical-magnetoelectric effect of the present polar magnetic nanocrystal was quite strong. These findings have been demonstrated in a simple iron oxide, which is highly significant from the viewpoints of economic cost and mass production.

No MeSH data available.


Crystallographically oriented nanometer-sized ε-Fe2O3.(a) XRPD pattern of the crystallographically oriented S-1020 nanocrystal (average particle size = 8.2 nm) film. Grey dots and red line represent the observed and calculated patterns, respectively. The inset is the unit sphere illustration of the 3D distribution of the direction of the crystallographic a-axis of ε-Fe2O3 nanoparticles shown by red dots. The magnetic field was applied along the Z axis of the unit sphere. (b) The magnetic hysteresis loop of the crystallographically oriented S-1020 nanocrystal film measured in the applied magnetic field (H0) parallel to the easy-axis at 300 K. The red line is a guide to the eye.
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f3: Crystallographically oriented nanometer-sized ε-Fe2O3.(a) XRPD pattern of the crystallographically oriented S-1020 nanocrystal (average particle size = 8.2 nm) film. Grey dots and red line represent the observed and calculated patterns, respectively. The inset is the unit sphere illustration of the 3D distribution of the direction of the crystallographic a-axis of ε-Fe2O3 nanoparticles shown by red dots. The magnetic field was applied along the Z axis of the unit sphere. (b) The magnetic hysteresis loop of the crystallographically oriented S-1020 nanocrystal film measured in the applied magnetic field (H0) parallel to the easy-axis at 300 K. The red line is a guide to the eye.

Mentions: In addition, we prepared oriented nanocrystal thin film, which was obtained by dispersing the nanocrystals in a vehicle matrix under external magnetic field. The XRPD pattern of the S-1020 shows that the nanocrystals oriented along the crystallographic a-axis, perpendicular to the film (Fig. 3a). The magnetic hysteresis loop at 300 K shows that the ε-Fe2O3 nanocrystal with the size of 8.2 nm exhibits a large coercive field of 5.2 kOe (Fig. 3b, Supplementary Fig. S6), which meets the Hc value criterion for magnetic memory media. The magnetic measurement of the oriented S-1142 film was also conducted. The Hc value of the magnetic hysteresis loop and the natural resonance frequency of 182 GHz, reported in our previous works723, indicate that the magnetic anisotropy constants of Ka and Kb in orthorhombic symmetry are 7.7 × 106 erg cm−3 and 1.2 × 106 erg cm−3, respectively. Therefore, it is clarified that ε-Fe2O3 has remarkably high magnetic anisotropy compared with other ferrites such as BaFe12O19. The origin of such a small dp value and large K values can be explained by the following factors: (i) a strong magnetic anisotropy due to non-zero orbital angular momentum, L ≠ 0, through a strong hybridization between Fe and O, and (ii) remnants of the magnetic anisotropy due to the polar crystal structure.


Nanometer-size hard magnetic ferrite exhibiting high optical-transparency and nonlinear optical-magnetoelectric effect.

Ohkoshi S, Namai A, Imoto K, Yoshikiyo M, Tarora W, Nakagawa K, Komine M, Miyamoto Y, Nasu T, Oka S, Tokoro H - Sci Rep (2015)

Crystallographically oriented nanometer-sized ε-Fe2O3.(a) XRPD pattern of the crystallographically oriented S-1020 nanocrystal (average particle size = 8.2 nm) film. Grey dots and red line represent the observed and calculated patterns, respectively. The inset is the unit sphere illustration of the 3D distribution of the direction of the crystallographic a-axis of ε-Fe2O3 nanoparticles shown by red dots. The magnetic field was applied along the Z axis of the unit sphere. (b) The magnetic hysteresis loop of the crystallographically oriented S-1020 nanocrystal film measured in the applied magnetic field (H0) parallel to the easy-axis at 300 K. The red line is a guide to the eye.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4594123&req=5

f3: Crystallographically oriented nanometer-sized ε-Fe2O3.(a) XRPD pattern of the crystallographically oriented S-1020 nanocrystal (average particle size = 8.2 nm) film. Grey dots and red line represent the observed and calculated patterns, respectively. The inset is the unit sphere illustration of the 3D distribution of the direction of the crystallographic a-axis of ε-Fe2O3 nanoparticles shown by red dots. The magnetic field was applied along the Z axis of the unit sphere. (b) The magnetic hysteresis loop of the crystallographically oriented S-1020 nanocrystal film measured in the applied magnetic field (H0) parallel to the easy-axis at 300 K. The red line is a guide to the eye.
Mentions: In addition, we prepared oriented nanocrystal thin film, which was obtained by dispersing the nanocrystals in a vehicle matrix under external magnetic field. The XRPD pattern of the S-1020 shows that the nanocrystals oriented along the crystallographic a-axis, perpendicular to the film (Fig. 3a). The magnetic hysteresis loop at 300 K shows that the ε-Fe2O3 nanocrystal with the size of 8.2 nm exhibits a large coercive field of 5.2 kOe (Fig. 3b, Supplementary Fig. S6), which meets the Hc value criterion for magnetic memory media. The magnetic measurement of the oriented S-1142 film was also conducted. The Hc value of the magnetic hysteresis loop and the natural resonance frequency of 182 GHz, reported in our previous works723, indicate that the magnetic anisotropy constants of Ka and Kb in orthorhombic symmetry are 7.7 × 106 erg cm−3 and 1.2 × 106 erg cm−3, respectively. Therefore, it is clarified that ε-Fe2O3 has remarkably high magnetic anisotropy compared with other ferrites such as BaFe12O19. The origin of such a small dp value and large K values can be explained by the following factors: (i) a strong magnetic anisotropy due to non-zero orbital angular momentum, L ≠ 0, through a strong hybridization between Fe and O, and (ii) remnants of the magnetic anisotropy due to the polar crystal structure.

Bottom Line: Additionally, we have observed magnetization-induced second harmonic generation (MSHG).The nonlinear optical-magnetoelectric effect of the present polar magnetic nanocrystal was quite strong.These findings have been demonstrated in a simple iron oxide, which is highly significant from the viewpoints of economic cost and mass production.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.

ABSTRACT
Development of nanometer-sized magnetic particles exhibiting a large coercive field (Hc) is in high demand for densification of magnetic recording. Herein, we report a single-nanosize (i.e., less than ten nanometers across) hard magnetic ferrite. This magnetic ferrite is composed of ε-Fe2O3, with a sufficiently high Hc value for magnetic recording systems and a remarkably high magnetic anisotropy constant of 7.7 × 10(6) erg cm(-3). For example, 8.2-nm nanoparticles have an Hc value of 5.2 kOe at room temperature. A colloidal solution of these nanoparticles possesses a light orange color due to a wide band gap of 2.9 eV (430 nm), indicating a possibility of transparent magnetic pigments. Additionally, we have observed magnetization-induced second harmonic generation (MSHG). The nonlinear optical-magnetoelectric effect of the present polar magnetic nanocrystal was quite strong. These findings have been demonstrated in a simple iron oxide, which is highly significant from the viewpoints of economic cost and mass production.

No MeSH data available.