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

Shin-Ichi Ohkoshi,Asuka Namai,Hiroko Tokoro,Syunsuke Oka,Waka Tarora,Marie Yoshikiyo,Kosuke Nakagawa,Tomomichi Nasu,Masaya Komine,Yasuto Miyamoto,Kenta Imoto

doi:10.1038/srep14414

Shin-Ichi Ohkoshi, Asuka Namai + Show 9 more

Open Access

https://doi.org/10.1038/srep14414

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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 × 106 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.

Highlights

Nanometer-size ε -Fe2O3 was prepared from a precursor, in which ferrihydrite Fe10O14(OH)[2] nanoparticles were embedded in SiO2 matrix
We describe 18 samples sintered at a large range of temperatures: 250 °C (S-250), 500 °C (S-500), 731 °C (S-731), 902 °C (S-902), 924 °C (S-924), 951 °C (S-951), 979 °C (S-979), 1002 °C (S-1002), 1020 °C (S-1020), 1032 °C (S-1032), 1044 °C (S-1044), 1061 °C (S-1061), 1063 °C (S-1063), 1104 °C (S-1104), 1142 °C (S-1142), 1198 °C (S-1198), 1213 °C (S-1213), and 1295 °C (S-1295)
X-ray powder diffraction (XRPD) patterns of the sintered samples and the precursor are shown in Fig. 1 and Supplementary Fig. S1

Summary

Introduction

In the sintering temperature range up to 700 °C, which is the region of the Fe10O14(OH)2 → γ -Fe2O3 transition, the d value is almost constant around 3–4 nm (Fig. 1, middle). The magnetic hysteresis loops of ε -Fe2O3 for S-951–S-1198 with random orientation at 300 K show that the Hc values are 0.4 kOe (S-951), 0.7 kOe (S-979), 2.1 kOe (S-1002), 3.4 kOe (S-1020), 4.7 kOe (S-1032), 8.3 kOe (S-1044), 11.9 kOe (S-1061), 12.8 kOe (S-1063), 17.3 kOe (S-1104), 20.3 kOe (S-1142), and 20.9 kOe (S-1198) (Fig. 2a, Supplementary Fig. S3).

Results

Conclusion