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T. Harano,
G. Shibata,
K. Ishigami,
Y. Takashashi,
V. K. Verma,
V. R. Singh,
T. Kadono,
A. Fujimori,
Y. Takeda,
T. Okane,
Y. Saitoh, H. Yamagami,
T. Koide,
H. Yamada,
A. Sawa,
M. Kawasaki,
Y. Tokura,
A. Tanaka
[show abstract]
[hide abstract]
ABSTRACT: The coercivity of La1–xSrxMnO3 thin films can be enhanced by Ru substitution for Mn. In order to elucidate its mechanism, we performed soft x-ray absorption and magnetic circular dichroism measurements at the Ru M2,3 and Mn L2,3 edges. We found that the spin direction of Ru and Mn are opposite and that Ru has a finite orbital magnetic moment. Cluster-model analysis indicated that the finite orbital magnetic moment as well as the reduced spin moment of Ru result from local lattice distortion caused by epitaxial strain from the SrTiO3 substrate in the presence of spin-orbit interaction.
Applied Physics Letters 06/2013; 102(22):222404. · 3.84 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,
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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Yuan-Hua Lin,
M. Kobayashi,
Rongjuan Zhao,
G. S. Song,
Ce-Wen Nan,
Shun Li,
Wen-Sheng Yan,
J. I. Hwang,
Y. Ooki,
A. Fujimori,
Y. Takeda,
S. I. Fujimori,
K. Terai,
T. Okane,
Y. Saitoh, H. Yamagami,
Chen Gao
[show abstract]
[hide abstract]
ABSTRACT: We report p-type LiyNi0.97-yMn0.03O thin films (LNMO) via a simple solution method on silicon substrates. Magnetization measurements reveal that room-temperature tunable ferromagnetism can be observed in these LNMO thin films. The Mn L2,3 x-ray absorption and core-level photoelectron spectra indicate that Mn consists of the Mn2+ and Mn3+ components. The O K-edge x-ray absorption spectroscopy reveals that the majority of holes introduced by the Li doping have mainly O 2p character, and the hole concentration can be enhanced by almost two orders of magnitude by the Li doping, which can tune magnetism and TC. This ferromagnetic behavior in these LNMO thin films may be ascribed to the effective carrier-induced ferromagnetism (p-d exchange interaction through the O 2p band).
Phys. Rev. B. 05/2011; 83(19).
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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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[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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G. S. Song,
M. Kobayashi,
J. I. Hwang,
T. Kataoka,
M. Takizawa,
A. Fujimori,
T. Ohkouchi,
Y. Takeda,
T. Okane,
Y. Saitoh, H. Yamagami,
F.-H. Chang,
L. Lee,
H.-J. Lin,
D. J. Huang,
C. T. Chen,
S. Kimura,
M. Funakoshi,
S. Hasegawa,
H. Asahi
[show abstract]
[hide abstract]
ABSTRACT: The electronic structure of the magnetic semiconductor Ga1−xCrxN, and the effect of Si doping on it have been investigated by photoemission and soft x-ray absorption spectroscopy. We have confirmed that Cr in GaN is predominantly trivalent when substituting for Ga and that Cr 3d states appear within the band gap of GaN just above the N 2p-derived valence-band maximum. As a result of Si doping, downward shifts of the core levels (except for Cr 2p) and the formation of new states near the Fermi level were observed, which we attribute to the upward chemical-potential shift and the formation of a small amount of Cr2+ species caused by electron doping. Possibility of Cr-rich cluster growth by Si doping are discussed based on the spectroscopic and magnetization data.
Phys. Rev. B. 06/2008; 78(3).
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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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M Kobayashi,
Y Ishida,
J I Hwang,
G S Song,
A Fujimori,
C S Yang,
L Lee,
H-J Lin,
D J Huang,
C T Chen,
Y Takeda,
K Terai,
S-I Fujimori,
T Okane,
Y Saitoh, H Yamagami,
K Kobayashi,
A Tanaka,
H Saito,
K Ando
[show abstract]
[hide abstract]
ABSTRACT: The electronic structure of the Cr ions in the diluted ferromagnetic semiconductor Zn1-xCrxTe (x=0.03 and 0.15) thin films has been investigated using x-ray magnetic circular dichroism (XMCD) and photoemission spectroscopy (PES). Magnetic-field (H) and temperature (T) dependences of the Cr 2p XMCD spectra correspond well to the magnetization measured by a SQUID magnetometer. The line shape of the Cr 2p XMCD spectra is independent of H, T and x, indicating that the ferromagnetism originated from the same electronic states of the Cr ion. A cluster-model analysis indicates that although there are two or more kinds of Cr ions in the Zn1-xCrxTe samples, the ferromagnetic XMCD signal originated from Cr ions substituted for the Zn site. The Cr 3d partial density of states extracted using Cr 2p→3d resonant PES shows a broad feature near the top of the valence band, suggesting strong s,p–d hybridization. No density of states is detected at the Fermi level, consistent with their insulating behavior. Based on these findings, we conclude that the double-exchange mechanism cannot explain the ferromagnetism in Zn1- xCrxTe.
New Journal of Physics 05/2008; 10(5):055011. · 4.18 Impact Factor
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M Kobayashi,
Y Ishida,
J. I. Hwang,
G. S. Song,
A. Fujimori,
C S Yang,
L Lee,
H J Lin,
D. J. Huang,
C T Chen,
Y Takeda,
S. -I. Fujimori,
T. Okane,
Y Saitoh, H Yamagami,
K Kobayashi,
A Tanaka,
H Saito,
K Ando
[show abstract]
[hide abstract]
ABSTRACT: The electronic structure of the Cr ions in the diluted ferromagnetic semiconductor Zn$_{1-x}$Cr$_x$Te ($x=0.03$ and 0.15) thin films has been investigated using x-ray magnetic circular dichroism (XMCD) and photoemission spectroscopy (PES). Magnetic-field ($H$) and temperature ($T$) dependences of the Cr $2p$ XMCD spectra well correspond to the magnetization measured by a SQUID magnetometer. The line shape of the Cr $2p$ XMCD spectra is independent of $H$, $T$, and $x$, indicating that the ferromagnetism is originated from the same electronic states of the Cr ion. Cluster-model analysis indicates that although there are two or more kinds of Cr ions in the Zn$_{1-x}$Cr$_x$Te samples, the ferromagnetic XMCD signal is originated from Cr ions substituted for the Zn site. The Cr 3d partial density of states extracted using Cr $2p \to 3d$ resonant PES shows a broad feature near the top of the valence band, suggesting strong $s$,$p$-$d$ hybridization. No density of states is detected at the Fermi level, consistent with their insulating behavior. Based on these findings, we conclude that double exchange mechanism cannot explain the ferromagnetism in Zn$_{1-x}$Cr$_{x}$Te.
05/2008;
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M. Kobayashi,
Y. Ooki,
M. Takizawa,
G. S. Song,
A. Fujimori,
Y. Takeda,
K. Terai,
T. Okane,
S.-I. Fujimori,
Y. Saitoh, H. Yamagami,
M. Seki,
T. Kawai,
H. Tabata
[show abstract]
[hide abstract]
ABSTRACT: By means of photoemission and x-ray absorption spectroscopy, we have studied the electronic structure of ( Ni , Zn , Fe , Ti )<sub>3</sub> O <sub>4</sub> thin films, which exhibits a cluster glass behavior with a spin-freezing temperature T<sub>f</sub> of ∼230 K and photoinduced magnetization (PIM) below T<sub>f</sub> . The Ni and Zn ions were found to be in the divalent states. Most of the Fe and Ti ions in the thin films were trivalent ( Fe <sup>3+</sup>) and tetravalent ( Ti <sup>4+</sup>) , respectively. While Ti doping did not affect the valence states of the Ni and Zn ions, a small amount of Fe <sup>2+</sup> ions increased with Ti concentration, consistent with the proposed charge-transfer mechanism of PIM.
Applied Physics Letters 03/2008; · 3.84 Impact Factor
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M Kobayashi,
J. I. Hwang,
G. S. Song,
Y. Ooki,
M. Takizawa,
A. Fujimori,
Y Takeda,
S. -I. Fujimori,
K Terai,
T. Okane,
Y Saitoh, H Yamagami,
Y. -H. Lin,
C. -W. Nan
[show abstract]
[hide abstract]
ABSTRACT: The electronic structure of Li-doped Ni$_{1-x}$Fe$_x$O has been investigated using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). The Ni $2p$ core-level PES and XAS spectra were not changed by Li doping. In contrast, the Fe$^{3+}$ intensity increased with Li doping relative to the Fe$^{2+}$ intensity. However, the increase of Fe$^{3+}$ is only $\sim 5%$ of the doped Li content, suggesting that most of the doped holes enter the O $2p$ and/or the charge-transferred configuration Ni $3d^8\underline{L}$. The Fe 3d partial density of states and the host valence-band emission near valence-band maximum increased with Li content, consistent with the increase of electrical conductivity. Based on these findings, percolation of bound magnetic polarons is proposed as an origin of the ferromagnetic behavior.
12/2007;
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M Kobayashi,
Y. Ooki,
M. Takizawa,
G. S. Song,
A. Fujimori,
Y Takeda,
K Terai,
T. Okane,
S. -I. Fujimori,
Y Saitoh, H Yamagami,
M Seki,
T Kawai,
H Tabata
[show abstract]
[hide abstract]
ABSTRACT: By means of photoemission and x-ray absorption spectroscopy, we have studied the electronic structure of (Ni,Zn,Fe,Ti)$_{3}$O$_{4}$ thin films, which exhibits a cluster glass behavior with a spin-freezing temperature $T_f$ of $\sim 230$ K and photo-induced magnetization (PIM) below $T_f$. The Ni and Zn ions were found to be in the divalent states. Most of the Fe and Ti ions in the thin films were trivalent (Fe$^{3+}$) and tetravalent (Ti$^{4+}$), respectively. While Ti doping did not affect the valence states of the Ni and Zn ions, a small amount of Fe$^{2+}$ ions increased with Ti concentration, consistent with the proposed charge-transfer mechanism of PIM.
12/2007;
