The University of Tokyo, Japan
University Education. M.Sc.: 2010, The University of Tokyo. Professional Career. 2010-2011; JSPS Research fellowship for Young Scientists (DC1)., 2011-present; Assistant professor, Ohkoshi Laboratory, The University of Tokyo.
Our research group has reported ε-iron oxide (ε-Fe2O3) nanomagnets, which exhibits a large coercive field (Hc) of 20 kOe and high-frequency electromagnetic wave absorption due to zero-field ferromagnetic resonance at 182 GHz. Furthermore, we found that metal substitution of ε-Fe2O3 with non-magnetic ions, such as Al3+ or Ga3+, can control the absorption frequency from 182 GHz to 35 GHz. In this work, we studied the synthesis, crystal structure, magnetic properties, millimeter wave absorption properties and millimeter wave rotation of rhodium substituted ε-Fe2O3 (ε-RhxFe2−xO3) nanomagnets. ε-RhxFe2−xO3 nanomagnets were prepared by a chemical nanoscale synthesis using mesoporous silica as template. X-ray diffraction pattern and Rietveld analysis indicated that ε-RhxFe2−xO3 has an orthorhombic crystal structure with space group of Pna21. ε-RhxFe2−xO3 showed a large magnetic hysteresis loop at room temperature. The Hc value increased with rhodium substitution from 22 kOe (x= 0) to 27 kOe (x= 0.14). Furthermore, a crystallographically oriented sample recorded a gigantic Hc value of 31 kOe. Terahertz time domain spectroscopy system was used to measure electromagnetic wave absorption properties in the millimeter wave region, 30-300 GHz. ε-RhxFe2−xO3 showed high-frequency millimeter wave absorption. The observed resonance frequency (fr) was increased up to 209 GHz with rhodium substitution. The rotation angle and ellipticity were measured using a magnetized ε-Rh0.14Fe1.86O3 pellet sample. Irradiating millimeter wave causes the rotation angle to display a dispersive spectrum centered at fr= 209 GHz, and the minimum and maximum values are −10º and +10º at 196 GHz and 220 GHz, respectively, whereas the ellipticity exhibits a peak at fr with the value of +0.3. The present material should be useful for high frequency millimeter wave absorbers and rotators, since the frequency of the magnetic rotation corresponds to the highest frequency of windows of air.