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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:38.77(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:2 Percentile:11.91(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:97.61

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:23 Percentile:77.7(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:58.4(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:16 Percentile:59.6(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:27.56(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:0 Percentile:0.09

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

Evidence for appearance of an internal field in the ordered state of CeRu$$_2$$Al$$_{10}$$ by $$mu^+$$SR

Kambe, Shinsaku; Chudo, Hiroyuki; Tokunaga, Yo; Koyama, Takehide*; Sakai, Hironori; Ito, Takashi; Ninomiya, Kazuhiko; Higemoto, Wataru; Takesaka, Tomoaki*; Nishioka, Takashi*; et al.

Journal of the Physical Society of Japan, 79(5), p.053708_1 - 053708_3, 2010/05

 Times Cited Count:53 Percentile:88.41(Physics, Multidisciplinary)

We report zero-field $$mu$$$$^{+}$$SR measurements made at J-PARC on CeRu$$_2$$Al$$_{10}$$. Below the phase transition temperature $$T_0sim27$$K, a clear modulation of $$mu$$$$^{+}$$ polarization due to an internal field is observed, indicating that magnetic ordering takes place. Compared with the internal field expected from the effective magnetic moment in the disordered state, the observed internal field at the $$mu$$$$^{+}$$ site is quite small. This indicates that the ordered Ce magnetic moment is small ($$sim10^{-2}$$$$mu$$$$_{rm B}$$) and/or the nearest pair of Ce magnetic moments are mutually anti-parallel. The $$T$$-dependence of the internal field is somewhat peculiar, suggesting that another ordering is taking place as well.

Journal Articles

Magneto-electric effect in charge-ordered LuFe$$_{2}$$O$$_{4}$$

Kambe, Takashi*; Komatsu, Takuma*; Michiuchi, Takamasa*; Hayakawa, Hiroki*; Oishi, Daisuke*; Hanasaki, Noriaki*; Yoshii, Kenji; Ikeda, Naoshi*

Journal of Physics; Conference Series, 200, p.012077_1 - 012077_4, 2010/02

 Times Cited Count:4 Percentile:83.16

A magneto-electric effect (ME) was observed in a charge-ordered ferroelectric LuFe$$_{2}$$O$$_{4}$$. The dielectric response in a three-dimensional charge-ordered phase is strongly influenced by magnetic field, especially around the ferri-magnetic ordering temperature. We also show the relation between the oxygen stoichiometry and the ME signal character above the magnetic transition temperature.

Journal Articles

Structural characterization and dielectric properties of hexagonal Lu(Fe,Ti)O$$_{3}$$

Matsuo, Yoji*; Hoshiyama, Takuya*; Mori, Shigeo*; Yoshii, Kenji; Michiue, Yuichi*; Kambe, Takashi*; Ikeda, Naoshi*; Brown, F.*; kimizuka, noboru*

Japanese Journal of Applied Physics, 48(9), p.09KB04_1 - 09KB04_3, 2009/10

 Times Cited Count:1 Percentile:5.74(Physics, Applied)

We have investigated an average crystal structure and microstructures in LuFe$$_{0.56}$$Ti$$_{0.44}$$O$$_{3}$$ by the transmission electron microscopy (TEM), in combination with the dielectric measurements. In this work, high-qualitypolycrystalline samples of LuFe$$_{0.56}$$Ti$$_{0.44}$$O$$_{3}$$ were successfully synthesized in air by the conventional solid state reaction. The average crystal structure at room temperature is characterized by the hexagonal structure (space group: $$P$$6$$_{3}$$ cm). Dielectric measurements revealed that LuFe$$_{0.56}$$Ti$$_{0.44}$$O$$_{3}$$ shows broad dielectric dispersion around 570 K, which should originate from the formation of the polar domain structures on the nanometer scale.

Journal Articles

Stoichiometric study of the dielectric and magnetic properties in charge frustrated system LuFe$$_{2}$$O$$_{4}$$

Michiuchi, Takamasa*; Yokota, Yusuke*; Komatsu, Takuma*; Hayakawa, Hironori*; Kuroda, Tomoko*; Maeda, Daisuke*; Matsuo, Yoji*; Mori, Shigeo*; Yoshii, Kenji; Hanasaki, Noriaki*; et al.

Ferroelectrics, 378(1), p.175 - 180, 2009/00

 Times Cited Count:18 Percentile:62.21(Materials Science, Multidisciplinary)

We have synthesized the samples of LuFe$$_{2}$$O$$_{4}$$, which shows the ferroelectricity due to charge ordering of Fe ions, under several different reducing conditions using a CO$$_{2}$$-CO flow. The reducing condition was changed by changing a flow ratio of CO$$_{2}$$ and CO. It was found that the flow ratio of CO$$_{2}$$/CO of about 5 provided the sample with the highest magnetic transition temperature of 240-250 K. This sample showed the dielectric constant of 10000 at room temperature. The imaginary part of the dielectric response offered the activation energy of 0.4-0.5 eV, which is slightly larger than that reported previously (about 0.3 eV). We will perform further investigation of the physical properties of this sample to clarify full details and their origin of LuFe$$_{2}$$O$$_{4}$$.

Journal Articles

A Cu NQR study in a $$d$$-electron heavy-fermion system, CaCu$$_{3}$$Ru$$_{4}$$O$$_{12}$$

Kato, Harukazu*; Tsuruta, Takuya*; Nishioka, Takashi*; Matsumura, Masahiro*; Sakai, Hironori; Kambe, Shinsaku

Journal of Physics and Chemistry of Solids, 68(11), p.2187 - 2190, 2007/11

 Times Cited Count:7 Percentile:37(Chemistry, Multidisciplinary)

Cu nuclear quadrupole resonance (NQR) studies have been carried out for CaCu$$_{3}$$Ru$$_{4}$$O$$_{12}$$,which has been suggested to show a heavy-fermion-like behavioral though it possess no f electron. A Lorentzian shape of the Cu NQR line with a narrow width implies that no magnetic ordering appears, at least, down to 5 K. The spin-lattice relaxation rate of the Cu nuclei probes a change of the Cu 3$$d$$ electron nature, resulting in the Fermi liquid state at a low temperature. These facts strongly support that the heavy fermion picture is available in the concerned compound.

Journal Articles

Cu NMR study in a heavy-electron system, CaCu$$_3$$Ru$$_4$$O$$_{12}$$

Kato, Harukazu*; Tsuruta, Takuya*; Nishioka, Takashi*; Matsumura, Masahiro*; Sakai, Hironori; Kambe, Shinsaku

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.251 - 253, 2007/03

Cu NMR measurements have been carried out for CaCu$$_3$$Ru$$_4$$O$$_{12}$$, which shows a heavy-fermion-like behavior although it posseses no f electron moment. The field-sweep spectrum observed can be understood as a powder pattern of a Cu nucleus affected by the quadrupole interaction with no axial symmetry. The quadrupole parameters and the Knight shift of Cu are evaluated.

Oral presentation

Magnetocapacitance of electronic ferroelectric LuFe$$_{2}$$O$$_{4}$$

Komatsu, Takuma*; Kambe, Takashi*; Michiuchi, Takamasa*; Hayakawa, Hironori*; Oishi, Daisuke*; Hanasaki, Noriaki*; Ikeda, Naoshi*; Yoshii, Kenji

no journal, , 

LuFe$$_{2}$$O$$_{4}$$ is a ferroelectric material arising from the real-space ordering of Fe charges below 330 K. In this paper, we measured the magnetic-field dependence of dielectric response in this material. We report a change of dielectric constant depending on the measurement temperature and applied magnetic field.

Oral presentation

Dielectric properties on charge ordered ferroelectrics LuFe$$_{2}$$O$$_{4}$$

Ikeda, Naoshi*; Kambe, Takashi*; Komatsu, Takuma*; Michiuchi, Takamasa*; Hayakawa, Hironori*; Hanasaki, Noriaki*; Yoshii, Kenji; Matsuo, Yoji*; Mori, Shigeo*

no journal, , 

A review will be given on the new type of ferroelectric material LuFe$$_{2}$$O$$_{4}$$. This oxide becomes ferroelectric below about 330 K, owing to the charge-ordered arrangement of Fe ions on a triangular lattice: This is a novel mechanism of ferroelectricity. We discuss the experimental results obtained from resonant X-ray diffraction, dielectric response, polarization and magnetization to show some interesting properties of this new ferroelectric oxide.

Oral presentation

Charge ordering state in the electronic ferroelectric LuFe$$_{2}$$O$$_{4}$$ studied by use of synchrotron radiation

Kubota, Masato*; Hayakawa, Hironori*; Oishi, Daisuke*; Akahama, Yuji*; Yoshii, Kenji; Kambe, Takashi*; Ikeda, Naoshi*

no journal, , 

Charge-ordered state of electronic ferroelectric LuFe$$_{2}$$O$$_{4}$$ was studied by use of synchrotron radiation. We have performed X-ray diffraction measurements at Fe K- and L-edges for a single-crystal LuFe$$_{2}$$$$_{4}$$ with applying currents at around room temperature. It was observed that the charge-ordered state changed depending on parameters such as the current density and the direction of current. We will discuss detailed results of experiments and at the conference.

Oral presentation

Magnetic properties and electronic properties of LuGaFeO$$_{4}$$

Kuroda, Tomoko*; Fukuyama, Ryota*; Kitamura, Satoshi*; Matsuo, Yoji*; Ikeda, Naoshi*; Kambe, Takashi*; Agui, Akane; Kimizuka, Noboru*

no journal, , 

no abstracts in English

Oral presentation

Successive charge-ordering transition in YFe$$_{2}$$O$$_{4}$$

Maeda, Daisuke*; Fukuyama, Ryota*; Kitamura, Satoshi*; Funae, Takeshi*; Matsuo, Yoji*; Ikeda, Naoshi*; Kambe, Takashi*; Kimizuka, Noboru*; Yoshii, Kenji

no journal, , 

We have investigated the successive phase transition in YFe$$_{2}$$O$$_{4}$$, which shows charge-ordering-induced ferroelectricity below about 330 K. This material has been reported to show complex phase transitions below 330 K. In this work we have studied the structure and physical properties of YFe$$_{2}$$O$$_{4}$$ synthesized in a variety of preparation conditions, and have found that slight changes of the conditions led to drastic alternations of physical properties. Details of the results will be shown at the conference.

Oral presentation

Applied-electric-field dependence of charge ordered phase in the trianglular-lattice system LuFe$$_{2}$$O$$_{4}$$

Hayakawa, Hironori*; Kubota, Masato*; Oishi, Daisuke*; Akahama, Yuji*; Matsuo, Yoji*; Ikeda, Naoshi*; Kambe, Takashi*; Kimizuka, Noboru*; Yoshii, Kenji

no journal, , 

We have investigated the change of charge-ordered state in LuFe$$_{2}$$O$$_{4}$$ caused by an applied electric field. The application of the field above a threshold led to a drastic decrease in resistivity; this behavior corresponds to the change of charge-ordered structure observed using synchrotron radiation. More details will be shown at the conference.

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