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Journal Articles

Valence control of charge and orbital frustrated system YbFe$$_{2}$$O$$_{4}$$ with electrochemical Li$$^{+}$$ intercalation

Murase, Satoshi*; Yoshikawa, Yumi*; Fujiwara, Kosuke*; Fukada, Yukimasa*; Teranishi, Takashi*; Kano, Jun*; Fujii, Tatsuo*; Inada, Yasuhiro*; Katayama, Misaki*; Yoshii, Kenji; et al.

Journal of Physics and Chemistry of Solids, 162, p.110468_1 - 110468_6, 2022/03

 Times Cited Count:0 Percentile:0(Chemistry, Multidisciplinary)

We report a trial of the valence control for mixed valence iron triangular oxide YbFe$$_{2}$$O$$_{4}$$ in order to develop an effective technique to control the frustration of charges in strongly correlated electron systems. The electro-chemical doping of Li$$^{+}$$ into YbFe$$_{2}$$O$$_{4}$$ was examined on the cell type sample similar to the Li-ion secondary battery cell. Systematic change of the lattice constant, Fe-Fe and Fe-Yb distance were observed with Li doping. Maximum value of the doping was over 300 mAh/g. An EXAFS experiment indicated that Li positioned between Yb octahedron layer (U-layer) and Fe-bipyramidal layer (W-layer). However, detailed change of iron valence state of YbFe$$_{2}$$O$$_{4}$$ was not clearly observed because of the superimpose of the signal from iron metal nano particles in XANES observation. The results indicate that the electrochemical method might be one of the potential technique to control the frustration of charges in YbFe$$_{2}$$O$$_{4}$$.

Journal Articles

Analysis of glass behavior of Lu$$_{2}$$Fe$$_{3}$$O$$_{7}$$ with distributed equivalent circuit model

Fukada, Yukimasa*; Fukuyama, Ryota*; Fujiwara, Kosuke*; Yoshii, Kenji; Shigematsu, Kei*; Azuma, Masaki*; Ikeda, Naoshi*

Journal of the Physical Society of Japan, 90(2), p.024710_1 - 024710_6, 2021/02

 Times Cited Count:2 Percentile:45.66(Physics, Multidisciplinary)

We report an analysis of the dielectric glasslike state of the spin- and charge-ordered system Lu$$_{2}$$Fe$$_{3}$$O$$_{7}$$, which has structural and physical properties analogous to those of the electronic ferroelectrics ${it R}$Fe$$_{2}$$O$$_{4}$$ (${it R}$: rare earth). Aging and memory effects of resistivity were found in the electric impedance response. We performed a numerical analysis with equivalent electric circuits that have a logarithmic Gaussian distribution of resistance and capacitance. The distribution parameters well explained the glassy nature of the electric and dielectric properties between 100 and 200 K and the distribution variations of charge- and magnetic-ordered domains underlying the glass nature.

Journal Articles

Crystallographical and morphological changes in charge-ordering transition of RFe$$_{2}$$O$$_{4}$$ (R: Y, Lu) investigated by transmission electron microscopy

Horibe, Yoichi*; Mori, Shigeo*; Ikeda, Naoshi*; Yoshii, Kenji; Maeno, Hiroshi*; Murakami, Yasukazu*

Ferroelectrics, 584(1), p.20 - 30, 2021/00

 Times Cited Count:1 Percentile:16.71(Materials Science, Multidisciplinary)

Temperature dependence of charge-ordered crystal structures and domain structures in RFe$$_{2}$$O$$_{4}$$ (R: Y and Lu) was investigated by energy-filtered transmission electron microscopy, combined with conventional transmission electron microscopy. The presence of three-dimensional to two-dimensional charge ordering transition were observed in both RFe$$_{2}$$O$$_{4}$$ on heating. Furthermore, real-space images obtained with the energy-filtered transmission electron microscopy revealed that YRFe$$_{2}$$O$$_{4}$$ has less anisotropic nanometer-scale charge-ordered domains than LuRFe$$_{2}$$O$$_{4}$$. These findings in RFe$$_{2}$$O$$_{4}$$ indicate the importance of the interchange interactions between Fe-O bilayers in addition to those within bilayers in the structural phase transitions associated with charge ordering in this system.

Journal Articles

Dielectric and magnetocaloric study of TmCrO$$_{3}$$

Yoshii, Kenji; Ikeda, Naoshi*

Journal of Alloys and Compounds, 804, p.364 - 369, 2019/10

 Times Cited Count:11 Percentile:64.01(Chemistry, Physical)

Dielectric and magnetocaloric measurements are carried out for the chromite TmCrO$$_{3}$$. This oxide was reported to be multiferroic below the N$'e$el temperature ($$T_{rm N}$$) of 125 K, likely due to a structural transformation. The dielectric response shows large dielectric constants below 300 K. However, from the analyses of loss tangent, AC conductivity and dielectric modulus, this behavior is rooted in hopping of charge carriers rather than electric dipoles, as proposed for some other chromites. No dielectric anomaly is found at $$T_{rm N}$$. The magnetocaloric effect shows that the magnetic transitions at $$T_{rm N}$$ as well as the spin reorientation temperature are of a second order. This result strongly suggests the absence of magnetostructural transition at $$T_{rm N}$$ in accord with no observation of ferroelectric transition at this temperature.

Journal Articles

Absence of a polar phase in perovskite chromite $$R$$CrO$$_{3}$$ ($$R$$=La and Pr)

Yoshii, Kenji; Ikeda, Naoshi*; Shimojo, Yutaka; Ishii, Yoshinobu*

Materials Chemistry and Physics, 190, p.96 - 101, 2017/04

 Times Cited Count:15 Percentile:53.53(Materials Science, Multidisciplinary)

Magnetic and dielectric properties have been studied for LaCrO$$_{3}$$, PrCrO$$_{3}$$, and their solid solution La$$_{0.5}$$Pr$$_{0.5}$$CrO$$_{3}$$, belonging to a family of ferroelectricorthochromite series $${it R}$$CrO$$_{3}$$ ($${it R}$$: rare earths). The magnetic measurements confirm that the material shows canted antiferromagnetic ordering at 240-288 K. Neutron diffraction patterns could be fitted with the centrosymmetric $${it Pnma}$$, which is different from the non-centrosymmetric structure proposed for the ferroelectric phase of NdCrO$$_{3}$$. The large dielectric constants are likely due to the hopping of charge carriers as proposed previously for other chromites.

Journal Articles

Observation of momentum-resolved charge fluctuations proximate to the charge-order phase using resonant inelastic X-ray scattering

Yoshida, Masahiro*; Ishii, Kenji; Naka, Makoto*; Ishihara, Sumio*; Jarrige, I.*; Ikeuchi, Kazuhiko*; Murakami, Yoichi*; Kudo, Kazutaka*; Koike, Yoji*; Nagata, Tomoko*; et al.

Scientific Reports (Internet), 6, p.23611_1 - 23611_8, 2016/03

 Times Cited Count:1 Percentile:12.41(Multidisciplinary Sciences)

Journal Articles

Observation of all-in type tetrahedral displacements in nonmagnetic pyrochlore niobates

Torigoe, Shuhei*; Ishimoto, Yutaro*; Aoishi, Yuhei*; Murakawa, Hiroshi*; Matsumura, Daiju; Yoshii, Kenji; Yoneda, Yasuhiro; Nishihata, Yasuo; Kodama, Katsuaki; Tomiyasu, Keisuke*; et al.

Physical Review B, 93(8), p.085109_1 - 085109_5, 2016/02

 Times Cited Count:5 Percentile:28.22(Materials Science, Multidisciplinary)

Journal Articles

Elemental substitution effects in multiferroic ${it R}$Fe$$_{2}$$O$$_{4}$$ (${it R}$: rare earths)

Yoshii, Kenji; Funae, Takeshi*; Mizumaki, Masaichiro*; Ejiri, Hiroki*; Ikeda, Naoshi*; Saito, Hiroyuki; Matsumura, Daiju

Physica Status Solidi (C), 12(6), p.841 - 844, 2015/06

 Times Cited Count:1 Percentile:42.33

We report the effects of elemental substitutions in multiferroic ${it R}$Fe$$_{2}$$O$$_{4}$$ ($$R$$: Y, Ho-Lu, In). The substitution by nonmagnetic Ga$$^{3+}$$ at the Fe site, which has not been reported so far, shows a drastic decrease in the ferrimagnetic transition temperature ($$T_{rm N}$$). This is plausibly owing to the suppression of magnetic interactions between Fe ions, based on our previous results of other substituted systems such as ${it R}$FeCoO$$_{4}$$. Dielectric constants near room temperature were comparable to those of $$R$$Fe$$_{2}$$O$$_{4}$$. The suppression of dielectric loss in this system is suitable to application. The ${it R}$-site substitution was also attempted by the large R$$^{3+}$$ ions such as Dy$$^{3+}$$. The solubility limit was up to about 10% of ${it R}$ ions, as confirmed by XRD and EXAFS measurements. $$T_{rm N}$$ was raised by 5-10 K for Dy$$^{3+}$$ substitution.

Journal Articles

Temperature and polarization dependence of Fe L$$_{3}$$-edge X-ray absorption spectra of LuFe$$_{2}$$O$$_{4}$$

Agui, Akane; Mizumaki, Masaichiro*; Kuroda, Tomoko*; Kawai, Masahiro*; Nagata, Tomoko*; Ikeda, Naoshi*; Uozumi, Takayuki*

Journal of Electron Spectroscopy and Related Phenomena, 197, p.13 - 16, 2014/12

 Times Cited Count:4 Percentile:26.53(Spectroscopy)

In this paper, we report on the study of the temperature dependence of Fe L$$_{3}$$-edge X-ray absorption spectra (XAS) of LuFe$$_{2}$$O$$_{4}$$. In the charge ordered state the valence of Fe is in Fe$$^{2+}$$ and Fe$$^{3+}$$. And the Fe L$$_{3}$$-edge XAS spectra have double peak structure which is attributed the Fe$$^{2+}$$ and Fe$$^{3+}$$ state. In high temperature, the double peak structure becomes indistinct because the thermal excited state overlaps while the Fe valence keeping the integer number.

Journal Articles

Current-induced enhancement of magnetic anisotropy in spin-charge-coupled multiferroic YbFe$$_{2}$$O$$_{4}$$

Yoshii, Kenji; Matsumura, Daiju; Saito, Hiroyuki; Kambe, Takashi*; Fukunaga, Mamoru*; Muraoka, Yuji*; Ikeda, Naoshi*; Mori, Shigeo*

Journal of the Physical Society of Japan, 83(6), p.063708_1 - 063708_4, 2014/06

 Times Cited Count:4 Percentile:36.23(Physics, Multidisciplinary)

We report the change of magnetic properties of multiferroic YbFe$$_{2}$$O$$_{4}$$, caused by cooling in the presence of an electrical current. The magnetization measured after the cooling becomes smaller by about 10-20% than that after cooling without a current. The current also affects the magnetic anisotropy below about 100 K; the magnetic coercivity is increased by about 10-20%. These phenomena may arise from a coexistence of ferromagnetic and antiferromagnetic domains, or a disturbance in the formation of charge-ordered domains. From the applied viewpoint, the enhancement of anisotropy by an electrical current offers a method for stabilizing magnetization other than the well-known method, i.e., exchange bias.

Journal Articles

Magnetic properties of R$$_{2}$$Fe$$_{3}$$O$$_{7}$$ (R=Yb and Lu)

Yoshii, Kenji; Ikeda, Naoshi*; Fukuyama, Ryota*; Nagata, Tomoko*; Kambe, Takashi*; Yoneda, Yasuhiro; Fukuda, Tatsuo; Mori, Shigeo*

Solid State Communications, 173, p.34 - 37, 2013/11

 Times Cited Count:3 Percentile:16.32(Physics, Condensed Matter)

We have investigated the magnetic properties of R$$_{2}$$Fe$$_{3}$$O$$_{7}$$ (R=Yb and Lu), which belongs to the homologous family of electronic ferroelectric RFe$$_{2}$$O$$_{4}$$. Magnetization measurements show ferrimagnetic ordering at the Neel temperature (T$$_{N}$$) of about 270 K, which is slightly higher than that of RFe$$_{2}$$O$$_{4}$$ (T$$_{N}$$ about 230-250 K). Observation of spin glass and exchange bias shows a coexistence of ferromagnetic and antiferromagneticinteractions, similarly to RFe$$_{2}$$O$$_{4}$$. This situation gives rise to a complex magnetic change and a broad peak of magnetic entropy change. Some characteristics, such as refrigeration temperatures higher than in RFe$$_{2}$$O$$_{4}$$, seem to offer a possibility of this system to applications.

Journal Articles

Magnetic properties of single crystalline YbFe$$_{2}$$O$$_{4}$$

Yoshii, Kenji; Mizumaki, Masaichiro*; Matsumoto, Keisuke*; Mori, Shigeo*; Endo, Naruki; Saito, Hiroyuki; Matsumura, Daiju; Kambe, Takashi*; Ikeda, Naoshi*

Journal of Physics; Conference Series, 428, p.012032_1 - 012032_5, 2013/04

 Times Cited Count:13 Percentile:96.92

We have investigated a single crystal of multiferroic YbFe$$_{2}$$O$$_{4}$$. Its magnetic transition temperature was 250 K. The magnetization along the c-axis was much larger than that within the ab plane, indicating the Ising character of this system. The field-cooled magnetization became negative below 10 K. This was explained in terms of an antiparallel coupling between Yb and Fe moments. Magnetocaloric effects were also observed. The change of entropy was found to show a broad peak with a width of 100 K, which is favorable to application.

Journal Articles

Magnetoelectric effect driven by magnetic domain modification in LuFe$$_{2}$$O$$_{4}$$

Kambe, Takashi*; Fukada, Yukimasa*; Kano, Jun*; Nagata, Tomoko*; Okazaki, Hiroyuki*; Yokoya, Takayoshi*; Wakimoto, Shuichi; Kakurai, Kazuhisa; Ikeda, Naoshi*

Physical Review Letters, 110(11), p.117602_1 - 117602_5, 2013/03

 Times Cited Count:24 Percentile:76.55(Physics, Multidisciplinary)

Journal Articles

Exchange bias in multiferroic $$R$$Fe$$_{2}$$O$$_{4}$$ ($$R$$=Y, Er, Tm, Yb, Lu and In)

Yoshii, Kenji; Ikeda, Naoshi*; Nishihata, Yasuo; Maeda, Daisuke*; Fukuyama, Ryota*; Nagata, Tomoko*; Kano, Jun*; Kambe, Takashi*; Horibe, Yoichi*; Mori, Shigeo*

Journal of the Physical Society of Japan, 81(3), p.033704_1 - 033704_4, 2012/03

 Times Cited Count:10 Percentile:56.51(Physics, Multidisciplinary)

Exchange bias (EB) behavior has been observed for multiferroic $$R$$Fe$$_{2}$$O$$_{4}$$ ($$R$$=Y, Er, Tm, Yb, Lu and In). The materials with the small $$R$$$$^{3+}$$ ions ($$R$$=Tm, Yb, Lu and In) exhibit large EB fields ($$_sim^{>}$$ 1 kOe) below $$sim$$100-150 K. This property is rooted in a magnetically glassy state, arising from the competition between ferro- and antiferromagnetic domain interactions. In addition, the exchange bias field tends to be more enhanced for smaller $$R$$$$^{3+}$$ ions. Hence, the EB is controlled by the substitution at the $$R$$-site in this series.

Journal Articles

Magnetic and dielectric study of Bi$$_{2}$$CuO$$_{4}$$

Yoshii, Kenji; Fukuda, Tatsuo; Akahama, Hiroshi*; Kano, Jun*; Kambe, Takashi*; Ikeda, Naoshi*

Physica C, 471(21-22), p.766 - 769, 2011/11

 Times Cited Count:17 Percentile:59.23(Physics, Applied)

We have investigated the magnetic and dielectric properties of Bi$$_{2}$$CuO$$_{4}$$, which has the same chemical formula as that of the parent materials of high-Tc superconductors, R$$_{2}$$CuO$$_{4}$$ (R: rare earths). Magnetic measurements showed that this oxide exhibits an antiferromagnetic transition at around 40 K, owing to the localized Cu$$^{2+}$$ spins. Dielectric constants were found to be about 100 at room temperature, which are smaller than those of R$$_{2}$$CuO$$_{4}$$ (about 10000 at room temperature). The imaginary part of dielectric response showed the activation energy of about 0.1 eV, suggesting that the dielectric response is brought about by a transfer of Cu-3d electrons.

Journal Articles

Multiferroic character and magnetic phase of LuFe$$_{2}$$O$$_{4}$$

Oishi, Daisuke*; Hayakawa, Hironori*; Akahama, Hiroshi*; Ikeda, Naoshi*; Kambe, Takashi*; Matsuo, Yoji*; Kimizuka, Noboru*; Kano, Jun*; Yoshii, Kenji

Ferroelectrics, 415(1), p.51 - 56, 2011/10

 Times Cited Count:5 Percentile:26.24(Materials Science, Multidisciplinary)

The variation of AC dielectric constant in the function of the DC magnetic fields was found in low oxygen vacant LuFe$$_{2}$$O$$_{4}$$ single crystal in which the electric polarization arise from the polar charge ordering. These magneto-electric coupling should be explained by a novel mechanism where the boundary motion of the polar charge ordered domain is affected by the magnetic (spin) domain boundary motion.

Journal Articles

Doping effect on charge ordered structure in Mn-doped YbFe$$_{2}$$O$$_{4}$$

Matsumoto, Keisuke*; Koyama, Tsukasa*; Mori, Shigeo*; Yoshii, Kenji; Kambe, Takashi*; Ikeda, Naoshi*

IOP Conference Series; Materials Science and Engineering, 18(9), p.092047_1 - 092047_4, 2011/09

 Times Cited Count:1 Percentile:54.93

Changes of charge ordered (CO) structure by partial substitution of Mn for Fe in YbFe$$_{2}$$O$$_{4}$$ were investigated by a transmission electron microscope (TEM), incombination with conventional dielectric measurement. It is revealed that partial substitution of Mn$$^{2+}$$ for Fe$$^{2+}$$ in YbFe$$_{2}$$O$$_{4}$$ destroyed drastically the CO structure with the wave vector of q=$$<$$1/3 1/3 1/2$$>$$. Consequently polar clustering structure giving rise to honeycomb-shaped diffuse streaks was found in YbFeMnO$$_{4}$$. The random distribution of polar clustering structure gives rise to characteristic broad dielectric dispersion.

Journal Articles

Collapsing processes of charge ordered structure in charge- and spin- frustrated ferrite YbFe$$_{2}$$O$$_{4}$$

Matsumoto, Keisuke*; Koyama, Tsukasa*; Mori, Shigeo*; Yoshii, Kenji; Ikeda, Naoshi*

Journal of Physics; Conference Series, 320, p.012085_1 - 012085_5, 2011/09

 Times Cited Count:0 Percentile:0.03

In order to clarify the stability of charge ordered structure (CO) in charge- and spinfrustrated ferrite YbFe$$_{2}$$O$$_{4}$$, we have investigated changes of the CO structure by partial substitution of Mn$$^{2+}$$ for Fe$$^{2+}$$ in YbFe$$_{2}$$O$$_{4}$$ by a transmission electron microscope (TEM), incombination with conventional dielectric measurement. It is revealed that subtle substitution of Mn$$^{2+}$$ for Fe$$^{2+}$$ in YbFe$$_{2}$$O$$_{4}$$ destroyed drastically the CO structure with the wave vector of q=$$<$$1/3 1/3 1/2$$>$$ and, instead, induced polar clustering structure characterized by honeycomb shaped diffuse scatterings in the reciprocal space. The formation of polar clustering structure should be responsible for the characteristic dielectric dispersion.

Journal Articles

Direct observation of low-temperature superstructure in spin- and charge-frustrated ferrite YFe$$_{2}$$O$$_{4-delta}$$

Horibe, Yoichi*; Ikeda, Naoshi*; Yoshii, Kenji; Mori, Shigeo*

Physical Review B, 82(18), p.184119_1 - 184119_5, 2010/11

 Times Cited Count:9 Percentile:41.67(Materials Science, Multidisciplinary)

The low-temperature superstructure of YFe$$_{2}$$O$$_{4-delta}$$ was carefully investigated by transmission electron microscopy. We found that the unique superstructure at about 100 K is characterized by $$bar{1}$$/14 2/7 1/14-type superlattice reflection spots, suggesting the presence of charge reordering process. The low-temperature high-resolution images clearly show superlattice modulations in Y-O layers as well as Fe-O layers. The modification of intra-bilayer charge interactions due to lattice distortions in Y-O layers is discussed to play a crucial role in the stabilization of long-periodic superstructures at low temperatures.

Journal Articles

Magnetic and dielectric study of R$$_{0.5}$$Sr$$_{0.5}$$MnO$$_{3}$$ (R = Gd, Tb and Dy)

Yoshii, Kenji; Hiramitsu, Yusuke*; Okajima, Yuka*; Yoneda, Yasuhiro; Nishihata, Yasuo; Mizuki, Junichiro; Nakamura, Akio; Shimojo, Yutaka; Ishii, Yoshinobu*; Morii, Yukio; et al.

Materials Research Bulletin, 45(11), p.1574 - 1580, 2010/10

 Times Cited Count:12 Percentile:38.58(Materials Science, Multidisciplinary)

Magnetic and dielectric properties of perovskite manganites R$$_{0.5}$$Sr$$_{0.5}$$MnO$$_{3}$$ (R = Gd, Tb and Dy) have been investigated. DC and AC magnetic measurements showed short-range glassy magnetic ordering at Tg about 40 K. Such ordering was observed by neutron diffraction and is ascribable to the size mismatch of R$$^{3+}$$ and Sr$$^{3+}$$ settled randomly at the same crystallographic site. Dielectric constants for each material were about 1000-10000 between about 50 K and 300 K and showed broad maximums above Tg. Dielectric dispersion showed poor coherency of the motion of polar regions, plausibly because of the size-mismatch effect; both the magnetic and dielectric properties of this system are governed by the randomness at the R/Sr site. The tan$$delta$$ and EXAFS data suggest that the dielectric response is rooted in a transfer of the Mn-3d electrons.

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