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T Kataoka,
Y Sakamoto,
Y Yamazaki,
V R Singh,
A Fujimori,
Y Takeda, T Ohkochi,
S.-I Fujimori,
T Okane,
Y Saitoh,
H Yamagami,
A Tanaka,
D D Sarma
[show abstract]
[hide abstract]
ABSTRACT: a b s t r a c t We have studied the electronic structure of the molecular ferromagnet β-Mn phthalocyanine (β-MnPc) in a polycrystalline form, which has been reported to show ferromagnetism at T < 8.6 K, by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). From the experimental results and subsequent cluster-model calculation, we find that the ferromagnetic Mn ion in β-MnPc is largely in the 4 E g ground state arising from the (e g) 3 (b 2g) 1 (a 1g) 1 [(d xz,yz) 3 (d xy) 1 (d z 2) 1 ] configuration of the Mn 2+ state. Considering that the highest occupied molecular orbital (HOMO) of MnPc with the 4 E g ground state originates from the a 1g orbital of the Mn 2+ ion, it is proposed that a 1g –a 1g exchange coupling via the π orbitals of the phthalocyanine ring plays a crucial role in the ferromagnetism of β-MnPc.
Solid State Communications 01/2012; 152:806-809. · 1.65 Impact Factor
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T. Kataoka,
Y. Sakamoto,
Y. Yamazaki,
V. R. Singh,
A. Fujimori,
Y. Takeda, T. Ohkochi,
S. -I. Fujimori,
T. Okane,
Y. Saitoh,
H. Yamagami,
A. Tanaka
[show abstract]
[hide abstract]
ABSTRACT: We have studied the electronic structure of the molecular ferromagnet
$\beta$-Mn phthalocyanine ($\beta$-MnPc) in a polycrystalline form, which has
been reported to show ferromagnetism at T$<$8.6 K, by x-ray absorption
spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). From the
experimental results and subsequent cluster-model calculation, we find that the
ferromagnetic Mn ion in $\beta$-MnPc is largely in the $^4$$E$$_g$ ground state
arising from the ($e$$_{g}$)$^3$($b$$_{2g}$)$^1$($a$$_{1g}$)$^1$
[($d_{xz,yz}$)$^3$($d_{xy}$)$^1$($d_{z^{2}}$)$^1$] configuration of the
Mn$^{2+}$ state. Considering that the highest occupied molecular orbital (HOMO)
of MnPc with the $^4$$E$$_g$ ground state originates from the $a$$_{1g}$
orbital of the Mn$^{2+}$ ion, it is proposed that $a$$_{1g}$-$a$$_{1g}$
exchange coupling via the $\pi$ orbitals of the phthalocyanine ring plays a
crucial role in the ferromagnetism of $\beta$-MnPc.
01/2012;
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T Kataoka,
Y Yamazaki,
V. R. Singh,
Y Sakamoto,
A. Fujimori,
Y Takeda, T. Ohkochi,
S. -I. Fujimori,
T. Okane,
Y Saitoh,
H Yamagami,
A Tanaka,
M. Kapilashrami,
L. Belova,
K. V. Rao
[show abstract]
[hide abstract]
ABSTRACT: We have investigated the electronic structure of ZnO:Mn and ZnO:Mn,N thin
films using x-ray magnetic circular dichroism (XMCD) and
resonance-photoemission spectroscopy. From the Mn 2$p$$\rightarrow3d$ XMCD
results, it is shown that, while XMCD signals only due to paramagnetic
Mn$^{2+}$ ions were observed in ZnO:Mn, nonmagnetic, paramagnetic and
ferromagnetic Mn$^{2+}$ ions coexist in ZnO:Mn,N. XMCD signals of ZnO:Mn,N
revealed that the localized Mn$^{2+}$ ground state and Mn$^{2+}$ state
hybridized with ligand hole coexisted, implying $p$-$d$ exchange coupling. In
the valence-band spectra, spectral weight near the Fermi level was suppressed,
suggesting that interaction between magnetic moments in ZnO:Mn,N has localized
nature.
12/2011;
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T Kataoka,
Y Yamazaki,
V R Singh,
Y Sakamoto,
A Fujimori,
Y Takeda, T Ohkochi,
S.-I Fujimori,
T Okane,
Y Saitoh,
H Yamagami,
A Tanaka,
M Kapilashrami,
L Belova,
K V Rao
[show abstract]
[hide abstract]
ABSTRACT: We have investigated the electronic structure of ZnO:Mn and ZnO:Mn,N thin films using x-ray magnetic circular dichroism (XMCD) and resonance-photoemission spectroscopy. From the Mn 2p ! 3d XMCD results, it is shown that, while XMCD signals only due to paramagnetic Mn 2þ ions were observed in ZnO:Mn, nonmagnetic, paramagnetic, and ferromagnetic Mn 2þ ions coexist in ZnO:Mn,N. XMCD signals of ZnO:Mn,N revealed that the localized Mn 2þ ground state and Mn 2þ state hybridized with ligand hole coexisted, implying p-d exchange coupling. In the valence-band spectra, spectral weight near the Fermi level was suppressed, suggesting that interaction between magnetic moments in ZnO:Mn,N has localized nature. V C 2011 American Institute of Physics. [doi:10.1063/1.3643044] In the field of spintronics, it is essential to develop diluted magnetic semiconductors (DMSs) with ferromagnet-ism at room temperature. Theoretical study 1 based on Zen-er's p-d exchange model has predicted that wide-gap semiconductors such as Mn-doped ZnO (ZnO:Mn) are prom-ising candidates for room temperature ferromagnetic DMSs. However, experimental results obtained so far have not been mutually consistent, i.e., some studies 2–4 reported the obser-vation of intrinsic ferromagnetism, whereas others 5–7 reported the absence of ferromagnetism or extrinsic ferro-magnetism in these materials. Recently, there has been works 8,9 suggesting that structurally perfect ZnO:Mn DMSs do not exhibit ferromagnetic order. According to first-principles calculations, 10 if carriers are not doped into ZnO:Mn, antiferromagnetic superexchange interaction pre-dominates so that the ground state is an insulating antiferro-magnetic spin glass while ferromagnetism can be stabilized only by hole doping, e.g., through N substitution for O. These reports imply that hole doping is necessary for ferro-magnetism in ZnO:Mn. Indeed, ferromagnetism has been reported for N-doped ZnO:Mn (ZnO:Mn,N). 11,12 However, ferromagnetism has also been observed for n-type ZnO:Mn. 13 It is thus debatable whether ferromagnetism occurs only in a p-type ZnO:Mn or not. In order to clarify the above issue, x-ray magnetic circular dichroism (XMCD) is an ideal tool, because XMCD is an element specific probe and the line shapes of XMCD spectra are fingerprints of magnetically active components. In particular, from the mag-netic field dependence of XMCD signals, one can judge whether the XMCD signals come from ferromagnetism or not. 14 In this paper, we show the magnetic field dependence
Applied Physics Letters 01/2011; 99:132508. · 3.84 Impact Factor
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T. Kataoka,
M. Kobayashi,
Y. Sakamoto,
G. S. Song,
A. Fujimori,
F.-H. Chang,
H.-J. Lin,
D. J. Huang,
C. T. Chen, T. Ohkochi,
Y. Takeda,
T. Okane,
Y. Saitoh,
H. Yamagami,
A. Tanaka,
S. K. Mandal,
T. K. Nath,
D. Karmakar,
I. Dasgupta
[show abstract]
[hide abstract]
ABSTRACT: We have studied the electronic structure of Fe-doped ZnO nanoparticles, which have been reported to show ferromagnetism at room temperature, by x-ray photoemission spectroscopy, resonant photoemission spectroscopy, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism (XMCD). From the experimental and cluster-model calculation results, we find that Fe atoms are predominantly in the Fe <sup>3+</sup> ionic state with mixture of a small amount of Fe <sup>2+</sup> and that Fe <sup>3+</sup> ions are dominant in the surface region of the nanoparticles. It is shown that the room temperature ferromagnetism in the Fe-doped ZnO nanoparticles primarily originated from the antiferromagnetic coupling between unequal amounts of Fe <sup>3+</sup> ions occupying two sets of nonequivalent positions in the region of the XMCD probing depth of ∼2–3 nm .
Journal of Applied Physics 03/2010; · 2.17 Impact Factor
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H Yamagami, T Ohkochi,
S-i Fujimori,
T Toshimitsu,
A Yasui,
T Okane,
Y Saitoh,
A Fujimori,
Y Haga,
E Yamamoto,
S Ikeda,
Y Onuki
[show abstract]
[hide abstract]
ABSTRACT: Uranium ferromagnet UIr is well-known to a pressure-induced superconductor without an inversion symmetry. In order to clarify the U 5f states of ferromagnetically-ordered UIr below Tc ~ 46 K and at ambient pressure, we observed 5f-sensitive soft X-ray photoemission spectra (SXPES), and calculated the band structure by a relativistic LAPW method in a local-spin density approximation. The temperature-dependent angle-integrated SXPES near the Fermi energy show a definite energy-shift of the band structures below and above Tc. The exchange splitting of the 5f bands seems to be consistent with an itinerant band picture like Stoner model. Furthermore the angle-resolved SXPES are compared with the theoretical band structure to investigate the relationship between the band shift and the magnetism.
Journal of Physics Conference Series 02/2010; 200(1):012229.
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[show abstract]
[hide abstract]
ABSTRACT: We have investigated the electronic states of the uranium monochalcogenide US, which is a typical ferromagnetic uranium compound, using soft x-ray photoemission spectroscopy (SX-PES). In early ultraviolet photoemission spectroscopy studies, two peak structures of the U 5f states were observed and have been interpreted that one has an itinerant character around the Fermi level (EF) and the other located below EF has a character of localized U 5f electrons. In this study, the intrinsic bulk valence-band spectrum of US was first deduced by estimating the contribution of surface states to the valence-band spectrum using core-level photoemission spectra. We conclude that the electronic structure of US can be basically described by the itinerant nature of the U 5f electrons from comparison with theoretical valence-band spectra obtained by band-structure calculation in the local-density approximation. Comment: 5pages, 3figures. accepted to PRB as a rapid communication
09/2009;
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M. Kobayashi,
G. S. Song,
T. Kataoka,
Y. Sakamoto,
A. Fujimori, T. Ohkochi,
Y. Takeda,
T. Okane,
Y. Saitoh,
H. Yamagami,
H. Yamahara,
H. Saeki,
T. Kawai,
H. Tabata
[show abstract]
[hide abstract]
ABSTRACT: The electronic structure of the oxide semiconductor ZnO has been investigated using soft x-ray angle-resolved photoemission spectroscopy (ARPES). The obtained band dispersions within the k<sub>x</sub>-k<sub>y</sub> planes reflect the symmetry of the Brillouin zone and show no surface-state-derived flat bands. Band dispersions along the k<sub>z</sub> direction have also been observed. The obtained band dispersions qualitatively agree with band-structure calculations except for the bandwidth. The observations provide experimental evidence that soft x-ray ARPES enables us to study the bulk band structure of semiconductors.
Journal of Applied Physics 07/2009; · 2.17 Impact Factor
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T. Okane, T. Ohkochi,
Y Takeda,
S. -I. Fujimori,
A Yasui,
Y Saitoh,
H Yamagami,
A. Fujimori,
Y Matsumoto,
M Sugi,
N Kimura,
T Komatsubara,
H Aoki
[show abstract]
[hide abstract]
ABSTRACT: Angle-resolved photoelectron spectroscopy in the Ce 3d-4f excitation region was measured for the paramagnetic state of CeRu2Si2, CeRu2(Si0.82Ge0.18)2, and LaRu2Si2 to investigate the changes of the 4$f$ electron Fermi surfaces around the quantum critical point. While the difference of the Fermi surfaces between CeRu2Si2 and LaRu2Si2 was experimentally confirmed, a strong 4f-electron character was observed in the band structures and the Fermi surfaces of CeRu2Si2 and CeRu2(Si0.82Ge0.18)2, consequently indicating a delocalized nature of the 4$f$ electrons in both compounds. The absence of Fermi surface reconstruction across the critical composition suggests that SDW quantum criticality is more appropriate than local quantum criticality in CeRu2(Si[1-x]Ge[x])2. Comment: 4 pages, 5 figures
06/2009;
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M. Kobayashi,
Y. Ishida,
J. I. Hwang,
G. S. Song,
M. Takizawa,
A. Fujimori,
Y. Takeda, T. Ohkochi,
T. Okane,
Y. Saitoh,
H. Yamagami,
Amita Gupta,
H. T. Cao,
K. V. Rao
[show abstract]
[hide abstract]
ABSTRACT: The electronic structure of In2−xVxO3 (x=0.08) has been investigated by photoemission spectroscopy and x-ray absorption spectroscopy (XAS). The V 2p core-level photoemission and XAS spectra revealed that the V ion is in the trivalent state, which is the same valence state as that of In in In2O3. The V 3d partial density of states obtained by the resonant photoemission technique showed a sharp peak above the O 2p band. While the O 1s XAS spectrum of In2−xVxO3 was similar to that of In2O3, there were differences in the In 3p and 3d XAS spectra between the V-doped and pure In2O3. The observations give clear evidence for hybridization between the In-derived conduction band and the V 3d orbitals in In2−xVxO3.
Phys. Rev. B. 05/2009; 79(20).
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T Okane, T Ohkochi,
Y Takeda,
S-i Fujimori,
A Yasui,
Y Saitoh,
H Yamagami,
A Fujimori,
Y Matsumoto,
M Sugi,
N Kimura,
T Komatsubara,
H Aoki
[show abstract]
[hide abstract]
ABSTRACT: Angle-resolved photoelectron spectroscopy in the Ce 3d-->4f excitation region was measured for the paramagnetic state of CeRu2Si2, CeRu2(Si0.82Ge0.18)2, and LaRu2Si2 to investigate the changes of the 4f electron Fermi surfaces around the quantum critical point. While the difference of the Fermi surfaces between CeRu2Si2 and LaRu2Si2 was experimentally confirmed, a strong 4f-electron character was observed in the band structures and the Fermi surfaces of CeRu2Si2 and CeRu2(Si0.82Ge0.18)2, consequently indicating a delocalized nature of the 4f electrons in both compounds. The absence of Fermi surface reconstruction across the critical composition suggests that SDW quantum criticality is more appropriate than local quantum criticality in CeRu2(Si1-xGex)2.
Physical Review Letters 05/2009; 102(21):216401. · 7.37 Impact Factor
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T Kataoka,
M Kobayashi,
Y Sakamoto,
G. S. Song,
A. Fujimori,
F. -H. Chang,
H J Lin,
D. J. Huang,
C T Chen, T. Ohkochi,
Y Takeda,
T. Okane,
Y Saitoh,
H Yamagami,
A Tanaka,
S. K. Mandal,
T. K. Nath,
D. Karmakar,
I. Dasgupta
[show abstract]
[hide abstract]
ABSTRACT: We have studied the electronic structure of Zn$_{0.9}$Fe$_{0.1}$O nano-particles, which have been reported to show ferromagnetism at room temperature, by x-ray photoemission spectroscopy (XPS), resonant photoemission spectroscopy (RPES), x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). From the experimental and cluster-model calculation results, we find that Fe atoms are predominantly in the Fe$^{3+}$ ionic state with mixture of a small amount of Fe$^{2+}$ and that Fe$^{3+}$ ions are dominant in the surface region of the nano-particles. It is shown that the room temperature ferromagnetism in the Zn$_{0.9}$Fe$_{0.1}$O nano-particles is primarily originated from the antiferromagnetic coupling between unequal amounts of Fe$^{3+}$ ions occupying two sets of nonequivalent positions in the region of the XMCD probing depth of $\sim$ 2-3 nm. Comment: Single column, 12 pages, 8 figures, 1 table
04/2009;
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T Okane, T Ohkochi,
T Inami,
Y Takeda,
S -i Fujimori,
N Kawamura,
M Suzuki,
S Tsutsui,
H Yamagami,
A Fujimori,
A Tanaka,
D Aoki,
Y Homma,
Y Shiokawa,
E Yamamoto,
Y Haga,
A Nakamura,
Y =Ofinuki
Phys. Rev. B. 01/2009; 80(10):104419.
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Y Takeda,
M Kobayashi,
T Okane, T Ohkochi,
J Okamoto,
Y Saitoh,
K Kobayashi,
H Yamagami,
A Fujimori,
A Tanaka,
J Okabayashi,
M Oshima,
S Ohya,
P N Hai,
M Tanaka
[show abstract]
[hide abstract]
ABSTRACT: The magnetic properties of as-grown Ga1-xMnxAs have been investigated by the systematic measurements of temperature and magnetic field dependent soft x-ray magnetic circular dichroism (XMCD). The intrinsic XMCD intensity at high temperatures obeys the Curie-Weiss law, but a residual spin magnetic moment appears already around 100 K, significantly above the Curie temperature (T_{C}), suggesting that short-range ferromagnetic correlations are developed above T_{C}. The present results also suggest that the antiferromagnetic interaction between the substitutional and interstitial Mn (Mn_{int}) ions exists and that the amount of the Mn_{int} affects T_{C}.
Physical Review Letters 06/2008; 100(24):247202. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We have investigated the electronic states of the uranium monochalcogenide US, which is a typical ferromagnetic uranium compound, using soft x-ray photoemission spectroscopy (SX-PES). In early ultraviolet photoemission spectroscopy studies, two peak structures of the U 5f states were observed and have been interpreted that one has an itinerant character around the Fermi level (EF) and the other located below EF has a character of localized U 5f electrons. In this study, the intrinsic bulk valence-band spectrum of US was first deduced by estimating the contribution of surface states to the valence-band spectrum using core-level photoemission spectra. We conclude that the electronic structure of US can be basically described by the itinerant nature of the U 5f electrons from comparison with theoretical valence-band spectra obtained by band-structure calculation in the local-density approximation.
Phys. Rev. B. 80(16).
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T. Okane, T. Ohkochi,
T. Inami,
Y. Takeda,
S.-i. Fujimori,
N. Kawamura,
M. Suzuki,
S. Tsutsui,
H. Yamagami,
A. Fujimori,
A. Tanaka,
D. Aoki,
Y. Homma,
Y. Shiokawa,
E. Yamamoto,
Y. Haga,
A. Nakamura,
Y. Ōnuki
[show abstract]
[hide abstract]
ABSTRACT: X-ray magnetic circular dichroism (XMCD) experiments were performed at the Np M4,5 and the Ga K absorption edges of NpNiGa5 to investigate the temperature-dependent changes of magnetic properties of Np 5f and Ga 4p electron states. By the sum-rule analysis of the Np M4,5 XMCD data, the orbital magnetic moment μL and the spin magnetic moment μS were estimated for the Np 5f3 and 5f4 electronic configurations and their comparison to the previous magnetization and neutron-scattering experiments suggests that the 5f4 configuration is more likely than the 5f3 configuration in NpNiGa5. It was found that |μL/μS| tends to increase from the high-temperature low-moment ordered state to the low-temperature high-moment ordered state. The result of the Ga K XMCD indicates that the Ga 4p electrons are magnetically polarized and the temperature and magnetic-field dependences of the Ga 4p orbital moment are proportional to those of the magnetization measurements.
Phys. Rev. B. 80(10).
