141 results on '"Kay Kohn"'
Search Results
2. Effect of uniaxial stress cooling on the neutron magnetic scattering in a ZnCr2O4 single crystal
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Kiiti Siratori, Ayumu Hatanaka, Hideto Yanagihara, Masakazu Nishi, Kazuhisa Kakurai, Isao Kagomiya, Kenji Nakajima, Kay Kohn, and Eiji Kita
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Diffraction ,Magnetic domain ,Condensed matter physics ,Magnetic structure ,business.industry ,Scattering ,Chemistry ,General Chemistry ,Condensed Matter Physics ,Crystal ,Stress (mechanics) ,Optics ,General Materials Science ,Neutron ,business ,Single crystal - Abstract
For the determination of the magnetic structure, elimination of the magnetic domains is indispensable and the appropriate stress will be effective when the crystal has a structural transformation at T N . The effect of uniaxial stress cooling on the neutron magnetic scattering in a ZnCr 2 O 4 single crystal was studied. The pressure axis was set parallel to the [1 0 0] or [0 0 1], parallel or perpendicular to the diffraction plane, (0 0 1). The [1 0 0] pressure cooling increases one half-integer spots along the [1 0 0], whereas decreases others. The [0 0 1] pressure cooling increases two half-integer spots in the (0 0 1) plane, whereas decreases one half-integer spots.
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- 2007
3. Relation between ferroelectric and antiferromagnetic order in
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Naoshi Ikeda, Hiroyuki Kimura, Youichi Kamada, Yusuke Wakabayashi, Yoshihisa Ishikawa, Yukio Noda, Hiroshi Sawa, Kay Kohn, Yosikazu Fukuda, Satoru Kobayashi, and Toshihiro Osawa
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Physics ,Diffraction ,Phase transition ,Magnetic structure ,Condensed matter physics ,Neutron diffraction ,Condensed Matter Physics ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,Nuclear magnetic resonance ,Antiferromagnetism ,Electrical and Electronic Engineering ,Single crystal ,Diffractometer - Abstract
RMn 2 O 5 ( R = Y and rare earth) shows successive magnetic and ferroelectric phase transitions at about 45, 40, 39, 20 and 10 K. We have reinvestigated the magnetic structure of YMn 2 O 5 at the commensurate phase ( T = 25 K ) using a single crystal four-circle diffractometer in order to discuss the mechanism of magnetoelectric interaction and the origin of ferroelectricity. We also observed the lattice modulation vectors ( q L ) to compare the magnetic propagation vectors ( q M ) by synchrotron X-ray diffraction. Improved magnetic structure data are compared with the theory recently proposed.
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- 2006
4. Charge Ordering and Dielectric Dispersion in Mixed Valence Oxides RFe2O4
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Naoshi Ikeda, Kay Kohn, and Shigeo Mori
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Phase transition ,Valence (chemistry) ,Materials science ,Condensed matter physics ,media_common.quotation_subject ,Dielectric dispersion ,Frustration ,Dielectric ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Ion ,Charge ordering ,Hexagonal lattice ,media_common - Abstract
In a series of oxides RFe 2 O 4 (R = rare earth between Dy and Lu, or Y), equal numbers of Fe 2 + and Fe 3 + are located on a layer composed of two triangular nets stacked together. These oxides have several phase transitions where the arrangement of Fe 2 + and Fe 3 + ions transforms from one type to another. Unique dielectric properties of these oxides have been explained in connection with the charge ordering. Recent developments on the structure of the ordered phases are reviewed with comments on their correlation with the observed dielectric dispersion
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- 2005
5. Neutron Diffraction Study of Magnetic Ordering Associated with Ferroelectricity in TmMn2O5
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Hiroyuki Kimura, Yukio Noda, Satoru Kobayashi, and Kay Kohn
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Materials science ,Condensed matter physics ,Neutron diffraction ,General Physics and Astronomy ,Multiferroics ,Dielectric ,Ferroelectricity ,Sequence (medicine) - Abstract
We have studied magnetic orderings of a ferroelectric TmMn 2 O 5 by single-crystal neutron diffraction and dielectric measurements. Below T N1 = 44 K, TmMn 2 O 5 shows the sequence of magnetic phas...
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- 2005
6. Mössbauer Spectroscopy of Ferroelectric YMn2O5
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Midori Tanaka, Shin Nakamura, Satoshi Matsumoto, Kay Kohn, and Isao Kagomiya
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Materials science ,Magnetic moment ,Condensed matter physics ,Transition temperature ,General Physics and Astronomy ,Curie temperature ,Antiferromagnetism ,Dielectric ,Atmospheric temperature range ,Ferroelectricity ,Hyperfine structure - Abstract
We have investigated Mossbauer spectra of single crystal YMn 2 O 5 (with 1.5 mol % 57 Fe), which is simultaneously ferroelectric (the ferroelectric Curie temperature T CE =39 K and the second dielectric transition temperature T C2 =19 K) and antiferromagnetic ( T N =45 K) at low temperatures. In the temperature range of T C2 < T < T CE , the spectrum is composed of two different hyperfine sextets, indicating that the magnetic moments of Mn 3+ ions are in two different states. A half of them are oriented parallel to the a -direction, which is probably the easy direction, while the other half are forced to be oriented along the bisector of the b - and c -direction. A few evidences indicate that both A and B moments rotate at T C2 to form an incommensurate helical spin structure with bunching. We present a remark on a possible relation between the ferroelectric transition and the magnetic long-range order in this oxide.
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- 2005
7. Looking for Ferromagnetic Ferroelectrics
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Kay Kohn
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Materials science ,Condensed matter physics ,Ferromagnetism ,General Materials Science ,General Chemistry ,Condensed Matter Physics - Published
- 2005
8. Neutron Diffraction Study of Successive Magnetic Phase Transitions in Ferroelectric TbMn2O5
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Yukio Noda, Setsuo Mitsuda, Toshihiro Osawa, Kay Kohn, Hiroyuki Kimura, Satoru Kobayashi, and Noriaki Kasahara
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Permittivity ,Materials science ,Condensed matter physics ,Phase (matter) ,Neutron diffraction ,General Physics and Astronomy ,Magnetic phase ,Dielectric ,Anomaly (physics) ,Ferroelectricity ,Single crystal - Abstract
Neutron diffraction measurements have been performed on a single crystal of TbMn 2 O 5 to elucidate the interplay between magnetic ordering and ferroelectricity. On cooling below T N1 = 42 K, the system enters a lock-in commensurate magnetic (CM) state with the magnetic propagation vector q = (1/2,0,1/4) from a two-dimensionally modulated (2D) incommensurate magnetic (ICM) one with the temperature-dependent q = ( q x ,0, q z ). Unlike isomorphous YMn 2 O 5 and ErMn 2 O 5 where a 1D-ICM phase with q = ( q x ,0,1/4) appears and separates both 2D-ICM and CM phases, the CM phase coexists with the 2D-ICM one at temperatures between T = 36.5 and 37.8 K, associated with a kink and a sharp peak in the dielectric constant along the b axis. On further cooling, the system reenters an ICM state at T = 22.4 K whose q is pinned at (20/41,0,5/16) at low temperatures. The comparison between the temperatures of dielectric anomalies and magnetic phase transitions indicates that the formation of the CM ordering is related t...
- Published
- 2004
9. Reinvestigation of Simultaneous Magnetic and Ferroelectric Phase Transitions in YMn2O5
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Kay Kohn, Toshihiro Osawa, Yukio Noda, Hiroyuki Kimura, Satoru Kobayashi, and Isao Kagomiya
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Permittivity ,Phase transition ,Materials science ,Condensed matter physics ,Transition temperature ,Phase (matter) ,Neutron diffraction ,General Physics and Astronomy ,Magnetic phase transition ,Dielectric ,Ferroelectricity - Abstract
Magnetic ordering around the ferroelectric transition temperature T C1 of weakly ferroelectric YMn 2 O 5 has been reinvestigated by single-crystal neutron diffraction and dielectric measurements. Besides a two-dimensionally modulated incommensurate magnetic (2D-ICM) phase with the propagation vector q = ( q x ,0, q z ) and a lock-in commensurate magnetic (CM) one with q = (1/2,0,1/4) reported previously, we observed a 1D-ICM phase characterized by q = ( q x ,0,1/4) with q x ∼0.492 that appears in a narrow temperature interval of ∼1 K and separates the 2D-ICM and CM phases. Corresponding to the 2D-ICM-to-1D-ICM and 1D-ICM-to-CM phase transitions at T = 40.8 K and 40.0 K, a sharp peak and a shoulder in the dielectric constant along the b -axis were detected. These results suggest that the ferroelectricity appears simultaneously with the magnetic phase transition from the 2D-ICM to 1D-ICM phase in YMn 2 O 5 .
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- 2004
10. 2D-to-1D Modulated-to-Lock in Successive Magnetic Phase Transitions Associated with Ferroelectricity in ErMn2O5
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Hiroyuki Kimura, Yukio Noda, Isao Kagomiya, Kay Kohn, Toshihiro Osawa, and Satoru Kobayashi
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Physics ,Permittivity ,Condensed matter physics ,Phase (matter) ,Transition temperature ,Neutron diffraction ,General Physics and Astronomy ,Dielectric ,Anomaly (physics) ,Ferroelectricity ,Ion - Abstract
We report results of dielectric and neutron diffraction measurements in zero field on magnetic ordering of weakly ferroelectric ErMn 2 O 5 . Around the ferroelectric transition temperature of T C1 ∼38 K below T N1 = 44 K, we observed successive magnetic phase transitions from a two-dimensionally-modulated (2D) incommensurate magnetic (ICM) phase with the propagation vector q = ( q x ,0, q z ) to another 1D-ICM one with \(\mathbf{q} = (q_x,0,\frac{1}{4})\) at T = 39.1 K, and then to a commensurate magnetic (CM) phase with \(\mathbf{q} = (\frac{1}{2},0,\frac{1}{4})\) at T = 37.7 K. These two magnetic phase transitions (39.1 K and 37.7 K) were found to be associated with an anomaly in the dielectric constant along the b axis. In addition, we found that in the case of a rapid-cooling procedure a low-temperature ICM state characterized by \(\mathbf{q} = (\frac{1}{2},0,0.265)\) shows up and coexists with the CM phase below T N2 = 11.5 K where evolution of magnetic order of the Er ions is inferred from measureme...
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- 2004
11. The structural and electric properties of the perovskite system BaTiO3–Ba(Fe1/2Ta1/2)O3
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Xiping Jing, Jianhua Lin, Kay Kohn, Guobao Li, Fuhui Liao, Naili Di, Yoshiaki Uesu, Koh Saitoh, Shixiang Liu, Masami Terauchi, Shujian Tian, and Zhaohua Cheng
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Materials science ,Inorganic chemistry ,Analytical chemistry ,Space group ,Crystal structure ,Atmospheric temperature range ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Inorganic Chemistry ,Tetragonal crystal system ,Electron diffraction ,Electrical resistivity and conductivity ,Materials Chemistry ,Ceramics and Composites ,Physical and Theoretical Chemistry ,Perovskite (structure) ,Solid solution - Abstract
Compounds in the pseudo-binary BaTiO3-Ba(Fe1/2Ta1/2)O-3 system have been synthesized at 1500degreesC in air and characterized by X-ray and electron diffraction as well as impedance analysis and Mossbauer spectroscopy. The symmetry of Ba(Fe1/2Ta1/2)O-3 is found to be trigonal with the space group P3m1. Two solid solutions exist in the BaTi1-xFex/1Tax/1O3 system at room temperature. The first (SS1) is in the composition range 0 less than or equal to x less than or equal to 0.07 and is tetragonal, P4mm, while the second broader solid solution, (SS2) 0.12 less than or equal to x less than or equal to 1, is trigonal and has the space group P3ml. The conductivity becomes higher with reduced amount of Ti in the structure. The activation energy of conductivity differs between the two solid solutions, 0.80eV for SS1 and 0.30eV for SS2, which indicates different mechanisms. The maximum of the real part of the pemittivity recorded for compounds in SS1 decreases towards room temperature with increasing amount of Fe/Ta doping and a high dielectric constant of around 7000 is found for BaTi(0.94)Fc(0.03)Ta(0.03)O(3). (C) 2004 Elsevier Inc. All rights reserved.
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- 2004
12. Dielectric and Magnetic Properties of a Mixed Valence Oxide Fe 2 BO 4
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Kay Kohn, Shin Nakamura, and Nanayo Suda
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Valence (chemistry) ,Materials science ,Condensed matter physics ,Mössbauer effect ,Analytical chemistry ,Oxide ,Dielectric ,Condensed Matter Physics ,Magnetic susceptibility ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,Charge ordering ,Magnetization ,chemistry ,Mössbauer spectroscopy - Abstract
Low frequency dielectric dispersion was observed in a mixed valence oxide Fe 2 BO 4 . It suggests that the fluctuation of possible charge ordering of Fe 2+ and Fe 3+ is working. A few evidences of the ordering were obtained by Mossbauer spectroscopy.
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- 2003
13. Structure Transition and Charge Competition on YFe 2 O 4
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Kay Kohn, Shigeo Mori, Naoshi Ikeda, and Ryosuke Mori
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Materials science ,Condensed matter physics ,Magnetic moment ,media_common.quotation_subject ,Relaxation (NMR) ,Frustration ,Atmospheric temperature range ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,Magnetization ,Charge ordering ,Nuclear magnetic resonance ,Condensed Matter::Strongly Correlated Electrons ,Superstructure (condensed matter) ,Powder diffraction ,media_common - Abstract
We report the low temperature charge ordered structure and magnetic relaxation in nearly stoichiometric YFe 2 O 4 in which the charge frustration effect is considered to be dominant. The superlattice reflections have revealed the presence of four different phases with a triple, double, quadruple and septuplex charge-superstructure in the temperature range from room temperature to 130 K. The observed successive transitions have been proposed by a previous X-ray powder diffraction study. A slow relaxation of the superstructure was found at 130 K. Time dependence of the magnetic moment was observed at about 240 K to suggest a similar relaxation.
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- 2003
14. Mössbauer Spectrum and Spin Structure of Weakly Ferroelectric YMn 2 O 5 and HoMn 2 O 5
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Shin Nakamura, Satoshi Matsumoto, Midori Tanaka, Kay Kohn, and Isao Kagomiya
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Materials science ,Condensed matter physics ,Mössbauer effect ,Magnetic structure ,Magnetic moment ,Transition temperature ,Antiferromagnetism ,Curie temperature ,Condensed Matter Physics ,Néel temperature ,Ferroelectricity ,Electronic, Optical and Magnetic Materials - Abstract
Rare earth (R) manganese oxides RMn 2 O 5 are the ferroelectric crystals with Curie temperature between 25 and 39 K. They are at the same time antiferromagnetic below the Neel temperature slightly above their ferroelectric transition temperature. By applying Mossbauer spectroscopy to the samples with a small amount of 57 Fe, we concluded that Mn 3+ ions in ferroelectric YMn 2 O 5 and HoMn 2 O 5 are classified into two groups with different magnetic environments. We suggest a possibility that the long-range magnetic structure induces the spontaneous polarization.
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- 2003
15. Structure and Dielectric Properties of Ba 1 − x La x Ti 1 − x Cr x O 3 Ceramics
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Mamoru Fukunaga, Kay Kohn, Guobao Li, and Yoshiaki Uesu
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Tetragonal crystal system ,Materials science ,Analytical chemistry ,Curie temperature ,Orthorhombic crystal system ,Dielectric loss ,Crystal structure ,Dielectric ,Condensed Matter Physics ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,High-κ dielectric - Abstract
In order to develop useful lead-free ferroelectric materials based on BaTiO 3, Ba 1 m x La x Ti 1 m x Cr x O 3 ceramics were synthesized and their dielectric properties were studied. The crystal structure of Ba 1 m x La x Ti 1 m x Cr x O 3 changes in the sequence of tetragonal, cubic, rhombohedral and orthorhombic as x increases. Curie temperature T C decreases largely as x increases. The samples except for x = 0.003 show broad peak of high dielectric constant with small dielectric loss. The frequency dispersion like in relaxors is observed below room temperature with x = 0.08.
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- 2003
16. Magnetic Ordering of Rare Earth Ions and Magnetic-Electric Interaction of Hexagonal RMnO3(R=Ho, Er, Yb or Lu)
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Kay Kohn, Hisashi Sugie, and Nobuyuki Iwata
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Condensed Matter::Materials Science ,Paramagnetism ,Magnetization ,Materials science ,Condensed matter physics ,Magnetic domain ,Magnetic structure ,Magnetic moment ,Hexagonal crystal system ,Rare earth ions ,Physics::Optics ,General Physics and Astronomy ,Dielectric - Abstract
From magnetic, dielectric and magnetoelectric measurement, it is concluded that hexagonal HoMnO 3 , ErMnO 3 and YbMnO 3 undergo a magnetic phase transition at a low temperature where a magnetic lon...
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- 2002
17. Structure and Conductivity of Perovskites Sr1−xLaxTi1−xCrxO3
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Xiaojun Kuang, Shujian Tian, Yoshiaki Uesu, Fuhui Liao, Kay Kohn, Guobao Li, and Xiping Jing
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Diffraction ,Rietveld refinement ,Chemistry ,Inorganic chemistry ,Analytical chemistry ,Dielectric ,Crystal structure ,Conductivity ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Inorganic Chemistry ,Electrical resistivity and conductivity ,Materials Chemistry ,Ceramics and Composites ,Orthorhombic crystal system ,Physical and Theoretical Chemistry ,Solid solution - Abstract
The Sr1−xLaxTi1−xCrxO3 (0≤x≤1) system was synthesized at 1500°C for about 60 h. Their structures were analyzed by the use of powder X-ray diffraction data and Rietveld analysis software GSAS (General Structure Analysis System). Three solid solutions are found: cubic solid solution Sr1−xLaxTi1−xCrxO3 (0≤x≤0.168, space group Pm 3 m), rhombohedral solid solution Sr1−xLaxTi1−xCrxO3 (0.23≤x≤0.67, space group R 3 c) and orthorhombic solid solution Sr1−xLaxTi1−xCrxO3 (0.92≤ x≤1, space group Pnma). The conductivities of this series were measured mainly from 25 to 450°C. It was found that this series changed from dielectric material SrTiO3 to semiconductor LaCrO3 continuously. The highest conductive sample was found to be Sr1−xLaxTi1−xCrxO3 with x=0.92, whose conductivity at room temperature was about 5×10−3Ω−1cm−1.
- Published
- 2002
18. Dielectric Anomaly of ZnCr2O4at Antiferromagnetic Transition
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Y. Hata, Isao Kagomiya, Kay Kohn, Makoto Toki, and Eiji Kita
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Permittivity ,Materials science ,Condensed matter physics ,media_common.quotation_subject ,Neutron diffraction ,General Physics and Astronomy ,Frustration ,Dielectric ,Magnetic susceptibility ,Phenomenological model ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Néel temperature ,media_common - Abstract
Dielectric constant and magnetic susceptibility have been measured on a single crystal of ZnCr 2 O 4 , which is a typical example of magnetically frustrated systems. Two characteristic features are observed in the temperature dependence of dielectric constant. The first is a jump of dielectric constant at the Neel temperature, where an antiferromagnetic transition presumably of the first order occurs. The other feature is dielectric dispersion appearing below 70 K, where the presence of antiferromagnetic short-range order have been demonstrated by a neutron diffraction and a temperature dependence of magnetic susceptibility. The jump indicates the presence of the lattice distortion to relax the spin frustration which otherwise prevents magnetic long-range ordering. The origin of the dispersion is presumably related to the fluctuation of interfacial charge accompanied by magnetic fluctuation.
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- 2002
19. Structural Characterization of the Complex Perovskites Ba1−La Ti1−Cr O3
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Kay Kohn, Guobao Li, and Yoshiaki Uesu
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Diffraction ,Chemistry ,Rietveld refinement ,Inorganic chemistry ,Crystal structure ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Inorganic Chemistry ,Tetragonal crystal system ,Crystallography ,Lattice (order) ,Materials Chemistry ,Ceramics and Composites ,Orthorhombic crystal system ,Physical and Theoretical Chemistry ,Chemical composition ,Solid solution - Abstract
The series Ba 1− x La x Ti 1− x Cr x O 3 (0≤ x ≤1) was synthesized at 1400°C for about 60 h. Their structure was carefully analyzed by the use of powder X-ray diffraction and Rietveld analysis software GSAS (General Structure Analysis System). Four solid solutions are found in this series: tetragonal solid solution Ba 1− x La x Ti 1− x Cr x O 3 (0≤ x ≤0.029), cubic solid solution Ba 1− x La x Ti 1− x Cr x O 3 (0.0365≤ x ≤0.600), rhombohedral solid solution Ba 1− x La x Ti 1− x Cr x O 3 (0.700≤ x ≤0.873), and orthorhombic solid solution Ba 1− x La x Ti 1− x Cr x O 3 (0.956≤ x ≤1). There are corresponding two-phase regions between the adjacent two solid solutions. The detailed lattice parameters are presented. The relationship between the lattice parameters and the composition of the solid solutions is developed.
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- 2002
20. Dielectric and Structure Properties of Charge Competing System YFe 2 O 4
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Takahiro Akao, Kay Kohn, Masaichiro Mizumaki, Ryosuke Mori, and Naoshi Ikeda
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Diffraction ,Phase transition ,Materials science ,Condensed matter physics ,media_common.quotation_subject ,Frustration ,Charge (physics) ,Dielectric ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Ion ,Charge ordering ,Hexagonal lattice ,media_common - Abstract
YFe 2 O 4 m i ( i < 0.005), which is a member of charge-frustrated system RFe 2 O 4 was synthesized and investigated by the low-temperature synchrotron powder X-ray diffraction. The structure between 225K and 250K is the same with the three-dimensional charge ordered state of LuFe 2 O 4 . Below the charge ordering temperature, at least five different phase transitions were detected. Since the balance of competing interaction between ionic charge essentially dominates the presence of multi phases in frustrated system, the low oxygen deficiency in YFe 2 O 4 m i is considered as the origin of the multi phases in low temperature.
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- 2002
21. Structure and Ferroelectricity of RMn 2 O 5
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Kay Kohn, Isao Kagomiya, and Tomohiro Uchiyama
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Diffraction ,Crystallography ,Materials science ,Rietveld refinement ,Rare earth ,Antiferromagnetism ,Crystal structure ,Condensed Matter Physics ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,Ion - Abstract
We studied systematically the crystal structure of simultaneously ferroelectric and antiferromagnetic RMn 2 O 5 (R = Pr-Lu and Y, except Tm) oxides, based on powder X-ray diffraction and Rietveld analysis. We propose a simple picture of the change of the structure with the size of a rare earth ion.
- Published
- 2002
22. Calorimetric study of ferroelectromagnetic crystals, YMno3, ErMnO3, and LuMnO3
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Minoru Morita, Kay Kohn, Naoki Kamegashira, Mitsuru Itoh, and Tôru Kyômen
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education.field_of_study ,Phase transition ,Materials science ,Condensed matter physics ,Population ,Atmospheric temperature range ,Condensed Matter Physics ,Heat capacity ,Electronic, Optical and Magnetic Materials ,Crystal ,Antiferromagnetism ,education ,Schottky anomaly ,Excitation - Abstract
Heat capacities of ferroelectromagnetic crystals YMnO3, ErMnO3, and LuMnO3 were measured in a temperature range of 2–300 K and in some magnetic fields between 0 and 9 T. Heat capacity anomalies were observed at around 71, 79, and 84 K in YMnO3, ErMnO3, and LuMnO3 crystals, respectively, due to an antiferromagnetic phase transition. Schottky anomalies were observed in ErMnO3 crystal due to population changes among the energy levels of erbium ions. In the low temperature region and in zero magnetic field, a heat capacity term proportional to temperature was observed in YMnO3 and LuMnO3 crystals possibly due to an unusual magnetic excitation.
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- 2001
23. Calorimetric study of ferroelectromagnetic crystals, YMnO3 ErMnO3 and LuMnO3
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Toru Kyomen, Minoru Morita, Mitsuru Itoh, Kay Kohn, and Naoki Kamegashira
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Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Published
- 2001
24. Preparation and Characterization of EuO/BaO Bilayer Epitaxially Grown on SrTiO3Substrate
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Nobuyuki Iwata, T. Morishita, and Kay Kohn
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Materials science ,Reflection high-energy electron diffraction ,Electrical resistivity and conductivity ,Analytical chemistry ,General Physics and Astronomy ,Substrate (electronics) ,Coercivity ,Thin film ,Epitaxy ,Kikuchi line ,Molecular beam epitaxy - Abstract
We grew epitaxially single phase ferromagnetic EuO film on SrTiO 3 substrate by inserting BaO buffer layer with an orientation of EuO[100]//BaO[100]//SrTiO 3 [110] and EuO(001)//BaO(001)//SrTiO 3 (001). Compared with EuO film on MgO substrate, high quality of the film was obtained, demonstrated by appearance of Kikuchi line in RHEED pattern with less thickness, Laue oscillations around EuO(002) Bragg peak, lower full width of half maximum of rocking curve for EuO(002), and lower coercive field. The growth rate of EuO was between 8.0×10 -2 and 2.6×10 -1 A· s -1 , depending on the growth condition. Saturation magnetic moment 6.84(±0.31)µ B was obtained per europium atom. The oxygen deficiency of EuO film was estimated as less than 0.03% from the temperature dependence of resistivity. The highest resistivity detected was 2.55×10 11 Ω· cm at 83.8 K.
- Published
- 2000
25. Charge Frustration and Dielectric Dispersion in LuFe2O4
- Author
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Nobuyuki Myouga, Naoshi Ikeda, Hijiri Kitôh, Shunji Takekawa, Eri Takahashi, and Kay Kohn
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Arrhenius equation ,Permittivity ,Phase transition ,Materials science ,Condensed matter physics ,media_common.quotation_subject ,General Physics and Astronomy ,Frustration ,Dielectric ,Polarization (waves) ,Pyroelectricity ,symbols.namesake ,Charge ordering ,symbols ,media_common - Abstract
We report the dielectric anomaries at the phase transitions of Lu(Fe 2+ Fe 3+ )O 4 , which is considered as a charge and spin frustrated system. Dielectric constant shows a hump, just above the transition from the high temperature two-dimensional to the low temperature three-dimensional charge ordering. A few glassy behaviors were observed at this transition. The presence of spontaneous polarization in the low temperature phase was confirmed by the measurement of pyroelectricity. A step-wise increase of the dielectric constant with increasing temperature was observed between 150 K and 250 K as in other RFe 2 O 4 . These phenomena are explained by the presence of the polar domains with the ordering of Fe 2+ and Fe 3+ and the motions of the antiphase boundaries between them.
- Published
- 2000
26. Preparation and Magnetic Properties of EuO Thin Films Epitaxially Grown on MgO and SrTiO 3 Substrates
- Author
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Govind Pindoria, Nobuyuki Iwata, Tadataka Morishita, and Kay Kohn
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Materials science ,Reflection high-energy electron diffraction ,Nuclear magnetic resonance ,Ferromagnetism ,Magnetic moment ,Condensed matter physics ,General Physics and Astronomy ,Curie temperature ,Thin film ,Coercivity ,Epitaxy ,Molecular beam epitaxy - Abstract
Ferromagnetic EuO films were epitaxially grown on MgO and SrTiO 3 substrates aligned with EuO[100]//MgO[100], EuO(001)//MgO(001) and EuO[100]//SrTiO 3 [110], EuO(001)//SrTiO 3 (001). The single pha...
- Published
- 2000
27. Anisotropic growth kinetics in the geometrically frustrated isosceles triangular Ising antiferromagnetCoNb2O6
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T. Jogetsu, Kay Kohn, Shun–ichi Kobayashi, J. Miyamoto, H. Katagiri, and Setsuo Mitsuda
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Physics ,Condensed matter physics ,Kinetics ,Isosceles triangle ,Antiferromagnetism ,Ising model ,Anisotropic growth - Published
- 1999
28. Three-dimensional magnetic ordering in the quasi-one-dimensional Ising magnetCoNb2O6with partially released geometrical frustration
- Author
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Masayasu Ishikawa, Shun–ichi Kobayashi, Kay Kohn, Kazuo Miyatani, and Setsuo Mitsuda
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Base (group theory) ,Physics ,Condensed matter physics ,Geometrical frustration ,Antiferromagnetism ,Hexagonal lattice ,Ising model ,Neutron scattering ,Energy (signal processing) ,Magnetic field - Abstract
The formation of three-dimensional magnetic ordering has been studied on a quasi-one-dimensional magnet ${\mathrm{CoNb}}_{2}{\mathrm{O}}_{6}$ by mean-field calculations as well as neutron scattering measurements down to $T=1.5\mathrm{K}$ under magnetic fields up to ${H}_{\ensuremath{\parallel}c}\ensuremath{\sim}600\mathrm{Oe}.$ Measurements of a deviation of the magnetic Bragg scattering function from the delta function in the ordered state reveal a surprisingly rich variety of the magnetic formation arising from an isosceles triangular arrangement of the magnetic chain with competing interchain interactions in the $a\ensuremath{-}b$ plane. The competing interactions result in quasidegenerate ground states with different propagation wave numbers along the ${b}^{*}$ direction in the sinusoidally amplitude-modulated incommensurate magnetic (IC) phase. Our mean-field calculations qualitatively reproduce the complicated ${H}_{\ensuremath{\parallel}c}\ensuremath{-}T$ magnetic phase diagram and give evidence for a high degeneracy of ground states by calculating the ${H}_{\ensuremath{\parallel}c}\ensuremath{-}T$ dependence of the free energy curve in the propagation wave number space. In addition, a partial cancellation of the exchange field at the apex site from the base sites on the isosceles triangular lattice leads to a quasi-long-range ordering along the a axis in both IC and antiferromagnetic states where the correlation length along the a axis depends on the propagation wave number along the ${b}^{*}$ direction.
- Published
- 1999
29. Submillimeter Wave ESR Study of Magnetic Excitations in the Ising Ferromagnetic Chain CoNb2O6
- Author
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Sebastian Luther, Hitoshi Ohta, Kay Kohn, Hiroyuki Nojiri, Mitsuhiro Motokawa, Keigo Nagasaka, Susu Mu Okubo, Tomohiro Goto, and Takashi Kunimoto
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Physics ,Zeeman effect ,Condensed matter physics ,General Physics and Astronomy ,Zero field splitting ,Resonance (particle physics) ,law.invention ,symbols.namesake ,Ferromagnetism ,law ,Spin wave ,symbols ,Condensed Matter::Strongly Correlated Electrons ,Ising model ,Electron paramagnetic resonance ,Excitation - Abstract
Magnetic excitations in the Ising ferromagnetic chain CoNb 2 O 6 have been studied by submillimeter wave electron spin resonance in strong transverse magnetic fields. A distinct non-linear field dependence of the resonance branches and also zero field splittings have been observed. A large residual intensity of the spin-cluster resonance was found which was caused by the strong mixing among the different n -fold spin-clusters. In addition to a series of n -fold spin-cluster excitations, we also discovered a new set of spin-cluster excitation which can be attributed to non-integer n such as n ∼1.5 or n ∼2.5 for the first time. This effect is explained by the change of the quantization axis of the system in strong transverse magnetic fields. These new aspects of spin-cluster excitation show the significant effect of transverse magnetic fields on the magnetic excitation in an Ising ferromagnetic chain.
- Published
- 1999
30. Hybridized Mode of Phonon and Spin-Cluster Excitation in Quasi-One-Dimensional Magnet CoNb2O6
- Author
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M. Sato, Keigo Nagasaka, Kay Kohn, and Takashi Kunimoto
- Subjects
Materials science ,Condensed matter physics ,Phonon ,Magnet ,Lattice (order) ,General Physics and Astronomy ,Radiation ,Molecular physics ,Single crystal ,Spectral line ,Excitation ,Magnetic field - Abstract
Transmission measurements of far-infrared (FIR) polarized radiation have been performed in CoNb 2 O 6 single crystal. We have observed an absorption line at 9.7 cm -1 with a broad band from 9 to 25 cm -1 which should be attributed to the phonon of the lowest frequency below 30 cm -1 from the lattice dynamical analysis. As the temperature is decreased below 20 K and also as the magnetic field is applied up to 6 T, the absorption line with the band was intensively studied in magnetic fields as well as the various temperatures by using polarized FIR radiation field E parallel to the b - and c -axis. From the study, the band is attributed to the spin-cluster excitation (SCE) in the Ising-like chain. On the other hand, the absorption line also exhibits the variation as similar as SCE in magnetic fields. It concludes that the absorption line at 9.7 cm -1 is the hybridized mode of the B 3u mode of the phonon of the lowest frequency and SCE.
- Published
- 1999
31. Magnetic and Transport Properties of LaCo1-xNixO3-Comparison with La1-xSrxCoO3
- Author
-
Kay Kohn, Yoshihiko Kobayashi, Gen Shirane, Satoru Murata, Kichizo Asai, and John M. Tranquada
- Subjects
Magnetization ,Spin glass ,Materials science ,Magnetic structure ,Spin states ,Ferromagnetism ,Condensed matter physics ,Hall effect ,Seebeck coefficient ,General Physics and Astronomy ,Metal–insulator transition - Abstract
We have investigated magnetization, neutron scattering, resistivity, thermoelectric power and Hall effect in LaCo 1- x Ni x O 3 ( x =0.05 and 0.1) single crystals. At low temperatures, they show spin-glass behavior with a strong ferromagnetic correlation. Around 500 K, spin state transition from the intermediate spin state ( S =1) to the high spin state ( S =2) accompanied by an insulator-to-metal transition is observed as in undoped LaCoO 3 . These magnetic properties of LaCo 1- x Ni x O 3 are very similar to those previously reported for La 1- x Sr x CoO 3 . The low-temperature transport properties of both LaCo 1- x Ni x O 3 and La 1- x Sr x CoO 3 exhibit the characteristics of an insulator near the insulator-to-metal transition. The sign of the carrier is verified to be positive in both systems from the thermoelectric power measurement. However, the sign of the Hall coefficient of LaCo 1- x Ni x O 3 is negative. These transport properties are discussed in terms of small polaron hopping mechanism.
- Published
- 1999
32. Coexistence of Ferroelectricity and Antiferromagnetism in Rare Earth Manganese Oxide RMn2O5
- Author
-
Kay Kohn and Isao Kagomiya
- Subjects
Condensed Matter::Materials Science ,chemistry.chemical_compound ,Phase transition ,Materials science ,chemistry ,Condensed matter physics ,Rare earth ,Oxide ,Antiferromagnetism ,Dielectric ,Physics::Chemical Physics ,Manganese oxide ,Ferroelectricity - Abstract
Oxides of the group RMn2O5 (R=a rare earth or Y) are simultaneously ferroelectric and antiferromagnetic at low temperatures. The specific features of the phase transitions in this oxide are reviewed with a particular emphasis on the possible interactions between dielectric and magnetic properties.
- Published
- 1999
33. Ferroelectricity of SmMn2O5
- Author
-
Takahiro Fujita and Kay Kohn
- Subjects
Phase transition ,Magnetization ,Materials science ,Condensed matter physics ,Transition temperature ,Magnetoelectric effect ,Dielectric ,Condensed Matter Physics ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,Pyroelectricity - Abstract
We made the measurements of dielectric constant, pyroelectricity, magnetoelectric effect and magnetization of SmMn2O5 single crystals. From the results, we conclude that SmMn2O5 is ferroelectric below 35.5 K, and that it undergoes another phase transition at 28.8 K. The change in both electric and magnetic structures are supposed to occur at the lower transition temperature.
- Published
- 1998
34. Ferroelectric transitions of LuMn2O5
- Author
-
Kay Kohn and Isao Kagomiya
- Subjects
Spontaneous polarization ,Materials science ,Condensed matter physics ,Magnetic order ,Rare earth ,Magnetoelectric effect ,Curie temperature ,Condensed Matter Physics ,Ferroelectric crystal ,Ferroelectricity ,Electronic, Optical and Magnetic Materials - Abstract
LuMn2O5 with non-magnetic rare earth Lu is a ferroelectric crystal with the Curie temperature at 34 K, where a weak spontaneous polarization appears along the b-direction. It has characteristic features of improper ferroelectrics. We suppose that a possible order parameter is magnetic order.
- Published
- 1998
35. Magnetoelectric effect and rare earth magnetic ordering of ErMnO3
- Author
-
Kay Kohn and Nobuyuki Iwata
- Subjects
Range (particle radiation) ,Materials science ,Condensed matter physics ,Rare earth ,Oxide ,Magnetoelectric effect ,Physics::Optics ,Dielectric ,Condensed Matter Physics ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,Magnetic transitions ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,chemistry ,Polar - Abstract
We made dielectric, magnetic and magnetoelectric studies of a hexagonal ErMnO3. Our purpose is to make clear the magnetic-electric interaction phenomena expected in this oxide with both electric and magnetic long range ordering. The magnetic-electric interaction was demonstrated as the anomalies of dielectric constant along the polar axis at magnetic transitions. An additional spontaneous polarization and a large magnetoelectric effect were detected at low temperatures where a long range ordering of Er3+ moments was present.
- Published
- 1998
36. Magnetoelectric effect of TmMn2O5
- Author
-
Masanori Uga, Nobuyuki Iwata, and Kay Kohn
- Subjects
Condensed Matter::Materials Science ,Magnetization ,Materials science ,Condensed matter physics ,Phase (matter) ,Strong interaction ,Magnetoelectric effect ,Curie temperature ,Dielectric ,Condensed Matter Physics ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,Pyroelectricity - Abstract
Based on the measurements of pyroelectricity, dielectric constant, magnetization and magnetoelectric effect, we conclude that TmMn2O5 is ferroelectric below the Curie temperature of 36 K. There are two other transitions at 26 K and 6 K. The phase below 6 K undergoes a transition into another phase at about 5 kOe, possibly the reorientation of the Tm3+ moments. The dielectric properties change remarkably at this transition, indicating a strong interaction between electric and magnetic orders. Magnetic phase diagram at low temperatures is determined from the results of magnetic and dielectric measurement.
- Published
- 1998
37. Magnetic-field-induced transition of thulium manganese oxide TmMn2O5
- Author
-
Nobuyuki Iwata, Masanori Uga, and Kay Kohn
- Subjects
Materials science ,Condensed matter physics ,Magnetoelectric effect ,Physics::Optics ,chemistry.chemical_element ,Dielectric ,Condensed Matter Physics ,Manganese oxide ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Condensed Matter::Materials Science ,Paramagnetism ,Thulium ,chemistry ,Condensed Matter::Superconductivity ,Structural transition ,Anomaly (physics) - Abstract
We report the magnetic field dependence of dielectric constant and magnetoelectric effect of TmMn2O5 and YbMn2O5 single crystals. An anomalous change of magnetoelectric effect occurs at 5 kOe (TmMn2O5) or at 18 kOe (YbMn2O5) at 4.2 K, when an magnetic field is applied along the c-direction. The anomaly in YbMn2O5 is attributed to a transition between different magnetic structures. In TmMn2O5 an anomaly was also observed in dielectric constant. We propose a structural transition caused by a magnetic field.
- Published
- 1997
38. Low-temperature phase transition in ErMn2O5
- Author
-
Yasuharu Koyata and Kay Kohn
- Subjects
Magnetization ,Phase transition ,Materials science ,Condensed matter physics ,Phase (matter) ,Magnetoelectric effect ,Crystal structure ,Dielectric ,Condensed Matter Physics ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,Pyroelectricity - Abstract
From the measurements of dielectric constant, pyroelectricity, magnetoelectric effect and magnetization, we conclude that ErMn2O5 is ferroelectric below 37 K. In addition, magnetoelectric susceptibility increases remarkably with decreasing temperature below approximately 10 K, accompanied with the growth of magnetic long-range ordering of Er3+. We suppose that this magnetic ordering brings a change in the crystal structure, resulting in the change in spontaneous polarization. A magnetic-field-induced transition occurs between 10 and 30 kOe in this low-temperature phase.
- Published
- 1997
39. Ferroelectricity of holmium manganese oxide HoMn2O5with helical spin ordering
- Author
-
Kay Kohn, Masayasu Ishikawa, and Seiichi Kato
- Subjects
Permittivity ,Phase transition ,Materials science ,Condensed matter physics ,Transition temperature ,Magnetoelectric effect ,Orthorhombic crystal system ,Dielectric ,Condensed Matter Physics ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,Pyroelectricity - Abstract
We report the results of dielectric, pyroelectric, magnetoelectric and specific heat measurements of HoMn2O5 single crystals, concluding that this oxide is ferroelectric below 38 K. The direction of the spontaneous polarization is along the b-direction of the orthorhombic structure. The presence of the ferroelectric transition is demonstrated by a peak in the temperature dependence of dielectric constant and also a shoulder in specific heat. The transition is accompanied by an appearance of spontaneous polarization and the quadratic (in magnetic field) magnetoelectric effect, which can be switched by electric field applied during cooling the crystal through the transition temperature. The crystal undergoes another phase transition around 22 K. HoMn2O5, like other RMn2O5 oxides, has several features typical to improper ferroelectrics, such as small spontaneous polarization, a low peak height of dielectric constant at the transition temperature, etc. We suppose that the ferroelectricity of RMn2O5 i...
- Published
- 1997
40. Pressure Dependence of the 100 K Spin-State Transition in LaCoO3
- Author
-
Takashi Naka, Hiroki Takahashi, Takehiko Matsumoto, Kay Kohn, Osamu Yokokura, Kichizo Asai, Nobuo Môri, and Masaru Suzuki
- Subjects
Magnetization ,Materials science ,Volume (thermodynamics) ,Spin states ,Condensed matter physics ,Excited state ,General Physics and Astronomy ,Condensed Matter::Strongly Correlated Electrons ,Ground state ,Magnetic susceptibility ,Ambient pressure ,Spin-½ - Abstract
The pressure dependence of the 100 K spin-state transition in LaCoO 3 is investigated through magnetization measurement under pressures of up to 18.2 kbar. The energy gap, Δ, between the low-spin ground state and the excited magnetic state (intermediate spin) increases remarkably with increasing pressure. The linear part of the pressure dependence of Δ, which is dominant below 5 kbar, is interpreted consistently by the volume expansion due to the spin-state transition under ambient pressure. In the higher pressure region, a quadratic pressure dependence is dominant, which suggests a very steep volume dependence of the energy of the excited magnetic state under the highly compressed condition.
- Published
- 1997
41. Dipole glass behavior of RFe2O4
- Author
-
K. Siratori, Kay Kohn, K. Odaka, Naoshi Ikeda, and Eri Takahashi
- Subjects
Crystal ,Dipole ,Charge ordering ,Materials science ,Spin glass ,Condensed matter physics ,Transition dipole moment ,Hexagonal lattice ,Dielectric ,Condensed Matter Physics ,Dispersion (chemistry) ,Electronic, Optical and Magnetic Materials - Abstract
We report low frequency dielectric dispersions of ErFe2O4 in which equal numbers of Fe2+ and Fe3+ ions occupy the sites on a triangular lattice. The first dispersion observed between 200 K and 300 K is explained qualitatively on a model that spontaneous polarization is present in the crystal below the Verwey transition. The second dispersion at higher temperatures is characterized by a few glass-like features. It was interpreted by successive freezing of the local dipole moments accompanied by short-range ordering of Fe2+ and Fe3+ ions.
- Published
- 1997
42. Mössbauer study on the antiferromagnetic FeO synthesized under high pressure
- Author
-
Takuro Yoshikawa, Yasushi Kanke, Hideto Yanagihara, Eiji Kita, Yorihiko Tsunoda, Kiiti Siratori, and Kay Kohn
- Published
- 2013
43. Electric and Magnetic Low-Temperature Phase Transitions ofYbMn2O5
- Author
-
Kay Kohn, Nobuyuki Iwata, Akihiro Inomata, Hideki Nakamura, and Yasuharu Koyata
- Subjects
Permittivity ,Condensed Matter::Materials Science ,Phase transition ,Materials science ,Condensed matter physics ,Magnetic moment ,Magnetoelectric effect ,Physics::Optics ,General Physics and Astronomy ,Antiferromagnetism ,Dielectric ,Magnetic susceptibility ,Pyroelectricity - Abstract
We made measurements of dielectric constant, pyroelectric current, magnetic susceptibility and magnetoelectric effect of single crystals of YbMn 2 O 5 . From the results, we concluded that there were two phase transitions besides antiferromagnetic transition at approximately 40 K. The first transition at 32 K is characterized by a peak of dielectric constant, a kink of magnetoelectric polarization and an appearance of pyroelectricity below this temperature. It was considered to be electric in nature. The second one is at 6 K. It is also accompanied by another peak of dielectric constant, a steep rise of pyroelectricity and anomalies of both magnetic and magnetoelectric susceptibilities. We suppose that the ordering of Yb 3+ magnetic moments begins to develop at this temperature, involving a change in the crystal structure and then in spontaneous polarization. The low temperature phase has a magnetic field-induced transition which occurs at about 19 kOe at 4.2 K.
- Published
- 1996
44. Pyroelectric effect and possible ferroelectric transition of helimagnetic and
- Author
-
Kay Kohn and Akihiro Inomata
- Subjects
Spontaneous polarization ,Condensed matter physics ,Chemistry ,Electric field ,Inorganic chemistry ,Rare earth ,General Materials Science ,Orthorhombic crystal system ,Dielectric ,Condensed Matter Physics ,Polarization (waves) ,Ferroelectricity ,Pyroelectricity - Abstract
In a series of papers, we have reported the results of dielectric, magnetic and magnetoelectric studies of (R = rare earth between Nd and Lu, Y or Bi), proposing the possibility of ferroelectricity in these oxides, but the direct demonstration of ferroelectricity was lacking. In this paper we present the results of pyroelectric current measurements of and single crystals between 4.2 and 273 K. These results indicated the existence of spontaneous polarization at low temperatures. The spontaneous polarization was switched by an applied electric field. Its possible direction is along the b axis of an orthorhombic crystal. The supposed temperature dependence of spontaneous polarization was complicated except for the case of , suggesting a ferrielectric origin of the polarization.
- Published
- 1996
45. Magnetic Relaxation in Diluted Triangular Antiferromagnet LuFeMgO4
- Author
-
Kay Kohn, Etsuko Himoto, Naoshi Ikeda, and Midori Tanaka
- Subjects
Spin–spin relaxation ,Magnetization ,Materials science ,Condensed matter physics ,Thermoremanent magnetization ,Relaxation (NMR) ,Spin–lattice relaxation ,General Physics and Astronomy ,Thermal fluctuations ,Antiferromagnetism ,Magnetic susceptibility - Abstract
We observed a few magnetic relaxation phenomena in a LuFeMgO 4 single crystal, that is, the difference in the magnetization between field-cooled and zero-field-cooled specimens, the appearance of thermoremanent magnetization, and the frequency dependence of the cusp temperature of AC susceptibility. The observed relaxation was interpreted in terms of thermal fluctuations and freezing of the magnetic clusters which are supposed to exist in this substance.
- Published
- 1995
46. Magnetic Equations of State of Heisenberg Ferromagnets, EuS and Its Sr-Diluted Derivatives, in a High Field Region
- Author
-
Yasuaki Nakagawa, Kiiti Siratori, Kay Kohn, Hiroaki Kato, and Eiji Kita
- Subjects
Physics ,Paramagnetism ,Magnetization ,Curie's law ,Curie–Weiss law ,Condensed matter physics ,Heisenberg model ,General Physics and Astronomy ,Curie temperature ,Field strength ,Brillouin and Langevin functions - Abstract
Magnetization, M , of EuS and Eu 1- x Sr x S ( x ≤0.4) was measured below 90 K in an external magnetic field up to 150 kOe. It is shown that M in the paramagnetic region is well expressed by a Brillouin function for S =7/2, with an effective field H +λ M . Even at temperatures below asymptotic Curie temperature, magnetization approaches the Brillouin function with increasing field strength. Moreover, it is found that magnetization scaled by ( T - T c ) b can be expressed as a universal function of magnetic field scaled by ( T - T c ) b + c . Here, T c is the ferromagnetic Curie point. Scaling exponents, b and c , are very different from those in the critical region. The exponent c is about 1.15 and independent of x whereas b is 0.14 for EuS and decreases rapidly with increasing x, proportionally to T c .
- Published
- 1995
47. Disappearance of 2D Magnetic Character in Quasi-1D System CoNb2O6under Magnetic Field
- Author
-
Satoru Kobayashi, Kazuo Miyatani, Kouji Aga, Hajime Katagiri, Kay Kohn, Hideki Yoshizawa, Masayasu Ishikawa, and Setsuo Mitsuda
- Subjects
Paramagnetism ,Materials science ,Magnetic domain ,Ferromagnetism ,Magnetic structure ,Condensed matter physics ,Ferrimagnetism ,General Physics and Astronomy ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Magnetic susceptibility ,Magnetic field - Abstract
We report neutron scattering as well as ac susceptibility studies on the formation of magnetic ordering in a quasi-1D ferromagnetic chain system CoNb 2 O 6 in magnetic fields up to 600 Oe. At T =1.5 K, a noncollinear ferrimagnetic (FR) phase with up-up-down spin arrangement along the b axis is field-induced in the magnetic field above ∼300 Oe. Interestingly, the pronounced 2D magnetic character previously found in the noncollinear antiferromagnetic phase disappears in the FR phase. This is direct evidence that the 2D magnetic character is due to the cancellation of interchain exchange fields at an apex site of a 2D isosceles-triangular lattice where quasi-1D ferromagnetic chains lie.
- Published
- 1995
48. Magnetoelectric effect and low-temperature phase transitions in YMn2O5
- Author
-
Akinobu Ikeda and Kay Kohn
- Subjects
Phase transition ,Materials science ,Condensed matter physics ,Oxide ,Magnetoelectric effect ,Sense (electronics) ,Dielectric ,Condensed Matter Physics ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,Spontaneous polarization ,chemistry.chemical_compound ,chemistry ,Electric field - Abstract
A possibility of ferroelectricity has been proposed in some low temperature phases of the oxides of the series RMn2O5 (R = a rare earth from Nd to Lu, Y or Bi). YMn2O5 is unusual in this series, because Y3+ is non-magnetic. We made dielectric, magnetic and magnetoelectric measurements on single crystals of this oxide to detect two electric transitions at 39 K and 19 K. These transitions are accompanied with anomalies in the dielectric constant and the magnetic and the magnetoelectric susceptibilities. Particularly, the sign of the magnetoelectric susceptibility is switched below 19 K, depending on the sense of the electric field applied during cooling the sample down to 4.2 K. This fact indicates that YMn2O5 possesses spontaneous polarization at least below 19 K.
- Published
- 1995
49. Anisotropy of Dielectric Dispersion in ErFe2O4Single Crystal
- Author
-
Kiiti Siratori, Hijiri Kito, Kay Kohn, Naoshi Ikeda, and Jun Akimitsu
- Subjects
Permittivity ,Materials science ,Nuclear magnetic resonance ,Magnetic domain ,Condensed matter physics ,Dispersion relation ,Relaxation (NMR) ,Dispersion (optics) ,General Physics and Astronomy ,Dielectric ,Anisotropy ,Single crystal - Abstract
Dielectric dispersion was observed in a single crystal with the composition of ErFe 2 O 3.95 below magnetic transition temperature. It is characterized by a large dielectric constant of the order of 10 4 , and a Debye-type frequency dependence like in the polycrystalline samples of the same substance which we reported in a previous paper. Large anisotropy exists in the strength e s - e ∞ and the characteristic relaxation frequency of the dispersion. The strength is higher within the c -plane than along the c -axis, while the characteristic frequency is much larger along the c -axis than within the c -plane. The dielectric dispersion in the polycrystalline sample cannot be explained by a simple average of the single crystal results. The observed dispersion is qualitatively discussed with a model of domain wall motion on an assumption that ErFe 2 O 4 is a polar crystal.
- Published
- 1995
50. Magnetoelectric effect and low-temperature phase transitions of TbMn2O5
- Author
-
Kay Kohn and K Saito
- Subjects
Magnetization ,Phase transition ,Magnetic moment ,Condensed matter physics ,Chemistry ,Electric field ,Magnetoelectric effect ,Antiferromagnetism ,General Materials Science ,Dielectric ,Condensed Matter Physics ,Néel temperature - Abstract
We made dielectric, magnetic and magnetoelectric measurements on single-crystal samples of TbMn2O5, which was an antiferromagnet with the Neel temperature of approximately 40 K. From the results, we concluded that there were two groups of phase transitions at lower temperatures. The first group are three successive transitions at 29.3, 27.2 and 25.6 K, whose natures are probably electric. The crystal is polar below this temperature range, because the polarity of the magnetoelectric effect can be controlled by electric field cooling. Another transition exists at 8 K, where time inversion symmetry breaks. It is related to the ordering of Tb3+ magnetic moments.
- Published
- 1995
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