2p X-ray Magnetic Circular Dichroism Research Articles

Electronic structures and magnetization reversal in Li0.5FeCr1.5O4

By employing temperature (T)-dependent soft x-ray magnetic circular dichroism (XMCD) in the Fe and Cr 2p absorption edges, the electronic structures of Li0.5FeCr1.5O4 spinel ferrite, which exhibits magnetization compensation, have been investigated. This work provides evidence that (i) both Fe and Cr ions are trivalent, (ii) most of Fe3+ ions occupy the A (Td) sites, while Cr3+ ions occupy the B (Oh) sites, (iii) the magnetic moments of Fe and Cr ions are coupled antiferromagnetically, and (iv) they are reversed at ∼255 K. The sum-rule analysis of Fe and Cr 2p XMCD spectra reveals that the orbital magnetic moments of Fe and Cr ions in Li0.5FeCr1.5O4 are much larger than those of metallic Fe and Cr, implying the large spin–orbit coupling and the non-fully occupied t2g orbitals of Fe3+ and Cr3+ ions. Based on these findings, we have provided a comprehensive model for the electronic and spin configurations of Fe and Cr ions in (Fe)A[Li0.5Cr1.5]BO4.

XMCD and PES study of a compensated-ferrimagnetic half-metal Mn3Ga

By employing soft X-ray magnetic circular dichroism (XMCD), soft X-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES), we have investigated the electronic structure of the candidate zero-moment half-metallic Mn3Ga. We have studied the ball-milled and annealed Mn3Ga powder samples that exhibit nearly zero magnetization. Mn 2p XAS revealed that Mn ions in Mn3Ga are nearly divalent for both of the Mn ions having the locally octahedral symmetry and those having the locally tetrahedral symmetry. The measured Mn 2p XMCD spectrum of Mn3Ga is very similar to that of ferrimagnetic MnFe2O4 having divalent Mn ions. The sum-rule analysis of the Mn 2p XMCD spectrum shows that both the spin and orbital magnetic moments of Mn ions in Mn3Ga are negligibly small, in agreement with the nearly compensated-ferrimagnetic ground state of Mn3Ga. The valence-band PES spectrum of Mn3Ga agrees well with the calculated density of states, supporting the half-metallic electronic structure of Mn3Ga.

Experimental evidence for mixed-valent Cr ions in half-metallic CrO2: Temperature-dependent XMCD study

By employing soft X-ray magnetic circular dichroism (XMCD) and soft X-ray absorption spectroscopy (XAS), we have investigated the temperature (T)-dependent valence and spin states of Cr ions in half-metallic ferromagnet CrO2 nanorod powder. The lineshape-analysis of both the Cr 2p XAS and XMCD spectra of CrO2 reveals that the Cr ions in bulk CrO2 have both Cr4+t2g2↑ and Cr3+t2g3↑ valence configurations. This work provides the direct experimental evidence for the Cr3+-Cr4+ mixed-valent states in bulk CrO2(Cr3.8+), demonstrating that the half-metallic ferromagnetism in CrO2 originates from the double-exchange interaction. The T-dependent intensity variation of the Cr 2p XMCD spectrum agrees well with the bulk magnetization M(T) and the Curie temperature, indicating that the measured Cr 2p XMCD data represent the intrinsic bulk ferromagnetism in CrO2, and support the above finding of the XMCD lineshape analysis.

Measuring spectroscopy and magnetism of extracted and intracellular magnetosomes using soft X-ray ptychography

Characterizing the chemistry and magnetism of magnetotactic bacteria (MTB) is an important aspect of understanding the biomineralization mechanism and function of the chains of magnetosomes (Fe3O4 nanoparticles) found in such species. Images and X-ray absorption spectra (XAS) of magnetosomes extracted from, and magnetosomes in, whole Magnetovibrio blakemorei strain MV-1 cells have been recorded using soft X-ray ptychography at the Fe 2p edge. A spatial resolution of 7 nm is demonstrated. Precursor-like and immature magnetosome phases in a whole MV-1 cell were visualized, and their Fe 2p spectra were measured. Based on these results, a model for the pathway of magnetosome biomineralization for MV-1 is proposed. Fe 2p X-ray magnetic circular dichroism (XMCD) spectra have been derived from ptychography image sequences recorded using left and right circular polarization. The shape of the XAS and XMCD signals in the ptychographic absorption spectra of both sample types is identical to the shape and signals measured with conventional bright-field scanning transmission X-ray microscope. A weaker and inverted XMCD signal was observed in the ptychographic phase spectra of the extracted magnetosomes. The XMCD ptychographic phase spectrum of the intracellular magnetosomes differed from the ptychographic phase spectrum of the extracted magnetosomes. These results demonstrate that spectro-ptychography offers a superior means of characterizing the chemical and magnetic properties of MTB at the individual magnetosome level.

Pd층의 두께 변화에 따른 [Co/Pd] 다층박막의 연엑스선 방사광 분광 연구

We have investigated the electronic structures of intermetallic multilayer (ML) films of [Co(2A)/Pd(xA)] (x: the thickness of the Pd sublayer; x = 1 A, 3 A, 5 A, 7 A, 9 A) by employing soft X-ray absorption spectroscopy (XAS) and soft X-ray magnetic circular dichroism (XMCD). Both Co 2p XAS and XMCD spectra are found to be similar to one another, as well as to those of Co metal, providing evidence for the metallic bonding of Co ions in [Co/Pd] ML films. By analyzing the measured Co 2p XMCD spectra, we have determined the orbital magnetic moments and the spin magnetic moments of Co ions in [Co(2A)/Pd(xA)] ML films. Based on this analysis, we have found that the orbital magnetic moments are enhanced greatly when x increases from 1 A to 3 A, and then do not change much for x ≥ 3 A. This finding suggests that the interface spin-orbit coupling plays an important role in determining the perpendicular magnetic anisotropy in [Co/Pd] ML films.

Spectroscopic study of Zn1−xCoxO thin films showing intrinsic ferromagnetism

Dilute magnetic semiconductors are widely studied due to their potential applications in spin-resolved electronics. We report the direct evidences of intrinsic ferromagnetism in the primarily ferromagnetic ZnO:Co thin films using near-edge X-ray absorption fine structure (NEXAFS) and soft X-ray magnetic circular dichroism (XMCD). The single phase Zn1−xCoxO thin films with nominal compositions (0.00 ≤ x ≤ 0.15) were synthesized by a spray pyrolysis technique, which exhibit room temperature ferromagnetism as revealed by alternating gradient force magnetometer (AGFM) measurements. The spectroscopic measurements indicate that most of Co dopants have substituted for Zn sites in ZnO matrix and they are present in divalent Co2+ (d7) state with tetrahedral symmetry according to the atomic multiplet calculations. The O 1s NEXAFS spectra suggest strong hybridization between O 2p and Co 3d electrons within ZnO matrix. The Co 2p XMCD measurements rule out the magnetism due to the presence of Co clusters, and show that Co–O–Co bonding provides localized magnetic moments leading to ferromagnetism.

Anomalous Magnetic Orientations of Magnetosome Chains in a Magnetotactic Bacterium: Magnetovibrio blakemorei Strain MV-1

There is a good deal of published evidence that indicates that all magnetosomes within a single cell of a magnetotactic bacterium are magnetically oriented in the same direction so that they form a single magnetic dipole believed to assist navigation of the cell to optimal environments for their growth and survival. Some cells of the cultured magnetotactic bacterium Magnetovibrio blakemorei strain MV-1 are known to have relatively wide gaps between groups of magnetosomes that do not seem to interfere with the larger, overall linear arrangement of the magnetosomes along the long axis of the cell. We determined the magnetic orientation of the magnetosomes in individual cells of this bacterium using Fe 2p X-ray magnetic circular dichroism (XMCD) spectra measured with scanning transmission X-ray microscopy (STXM). We observed a significant number of cases in which there are sub-chains in a single cell, with spatial gaps between them, in which one or more sub-chains are magnetically polarized opposite to other sub-chains in the same cell. These occur with an estimated frequency of 4.0±0.2%, based on a sample size of 150 cells. We propose possible explanations for these anomalous cases which shed insight into the mechanisms of chain formation and magnetic alignment.

철원소를 함유한 분자기반 생체물질 나노입자들의 연 x선 방사광 분광 연구

이 연구에서는 헬리코박터 파이로리 페리틴, 헴, <TEX>$NaM[Fe(CN)_6]{\cdot}H_2O$</TEX> 프러시안 블루(M=Co, Ni) 등의 분자기반 생체물질 나노입자들의 전자 구조를 연구하기 위하여 방사광을 광원으로 사용한 연 x선 광흡수 분광(soft x-ray absorption spectroscopy: XAS)과 연 x선 자기 원편광 이색성(soft x-ray magnetic circular dichroism: XMCD) 분광법 실험을 수행하였다. 이 연구로부터 페리틴 나노 입자들을 구성하고 있는 Fe 이온들은 모두 거의 3가 (<TEX>$Fe^{3+}$</TEX>)의 원자가 상태에 있으며, 프러시안 블루 나노 입자들 내의 Fe 이온들은 <TEX>$Fe^{2+}-Fe^{3+}$</TEX>의 혼합원자가 상태에 있다는 것을 알 수 있었다. 또한 페리틴 내의 <TEX>$Fe^{3+}$</TEX> 이온들은 한 종류의 대칭성을 가진 국소 구조를 가지며, Fe 이온들의 자기모멘트는 모두 한 방향으로 정렬되어 있다는 사실을 발견하였다. 그리고 프러시안 블루 나노 입자들의 Fe 이온의 국소적 결합은 주로 <TEX>$(CN)^-$</TEX> 리건드와의 결합에 의하여 결정된다는 것을 분광학적으로 알 수 있었다. By employing soft x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD), the electronic structures of molecule-based nano bioparticles, such as Helicobacter pylori ferritin (H. pylori ferritin), Heme, <TEX>$NaM[Fe(CN)_6]{\cdot}H_2O$</TEX>-type Prussian Blue (M=Co, Ni) analogue, have been investigated. The measured Fe 2p XAS spectra reveal that Fe ions are trivalent (<TEX>$Fe^{3+}$</TEX>) in H. pylori ferritins, while they are in the <TEX>$Fe^{2+}-Fe^{3+}$</TEX> mixed-valent states in <TEX>$NaM[Fe(CN)_6]{\cdot}H_2O$</TEX> Prussian Blue analogues (M=Co, Ni). According to the Fe 2p XMCD spectrum of high-state H. pylori ferritin, all the <TEX>$Fe^{3+}$</TEX> ions have the same local symmetry and their magnetic moments are aligned in the same direction. It is also found that the Fe 3d orbitals in <TEX>$NaM[Fe(CN)_6]{\cdot}H_2O$</TEX> have a strong covalent bonding to <TEX>$(CN)^-$</TEX> ligands, but with a very weak bonding to the 2p orbitals of O ligands.

방사광을 이용한 FeV2O4스피넬 산화물의 덩치상태와 분말상태의 전자구조 차이 연구

연 x선 광흡수 분광법(soft x-ray absorption spectroscopy: XAS)과 연 x선 자기 원편광 이색성(soft x-ray magnetic circular dichroism: XMCD)을 이용하여 스피넬 준강자성 산화물인 <TEX>$FeV_2O_4$</TEX>의 전자 구조를 연구하였다. Fe 2p XAS와 V 2p XAS 측정으로 부터 <TEX>$FeV_2O_4$</TEX>에서 Fe 이온과 V이온의 고유한 원자가는 각각 약 <TEX>$Fe^{2.3+}$</TEX>의 혼합원자가 상태와 약 <TEX>$V^{3+}$</TEX>의 상태임을 알 수 있었다. 실험적으로 측정된 Fe 2p XMCD의 신호는 거의 <TEX>$Fe^{2+}$</TEX> 상태에서 기인하였으며, <TEX>$Fe^{3+}$</TEX> 상태는 Fe 2p XMCD의 신호에 거의 기여하지 않는다는 사실이 발견되었다. 그러므로 <TEX>$FeV_2O_4$</TEX>의 자성 특성을 결정함에 있어서 자기적으로 정렬된 <TEX>$Fe^{2+}$</TEX> 상태 이온들이 중요한 역할을 한다고 생각된다. The electronic structure of ferrimagnetic spinel oxide of <TEX>$FeV_2O_4$</TEX> has been investigated by employing soft x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD). The Fe 2p and V 2p XAS spectra show that the valence states of Fe and V ions are <TEX>${\sim}Fe^{2.3+}$</TEX> mixed-valent states and <TEX>${\sim}V^{3+}$</TEX> states, respectively. In Fe 2p XMCD spectra, finite XMCD signals are observed for divalent <TEX>$Fe^{2+}$</TEX> states only, but not for <TEX>$Fe^{3+}$</TEX> states. This finding indicates that the magnetic moments of <TEX>$Fe^{2+}$</TEX> ions are ordered ferromagnetically but that those of <TEX>$Fe^{3+}$</TEX> ions are cancelled, implying that <TEX>$Fe^{2+}$</TEX> ions play an important role in determining magnetic properties of <TEX>$FeV_2O_4$</TEX>.

Phase separation in thermoelectric delafossite CuFe1−xNixO2 observed by soft x-ray magnetic circular dichroism

Electronic structures of Ni-doped CuFe1−xNixO2 delafossite oxides (0 ≤ x ≤ 0.03) have been investigated by employing soft x-ray magnetic circular dichroism (XMCD). Finite XMCD signals are observed for Fe, Ni, and Cu 2p states, and valence states of Cu, Fe, and Ni ions are nearly monovalent (Cu+), trivalent (Fe3+), and divalent (Ni2+), respectively, for all x ≤ 0.03. Tiny magnetic impurities could be detected by employing XMCD. Fe and Ni 2p XMCD signals are identified due to ferrimagnetic spinel impurities of CuFe2O4 and NiFe2O4. XMCD signals for Cu 2p states arise from divalent Cu2+ ions. Thermoelectrical properties are found to be very sensitive to the very little impurity phase present in delafossite oxides.

Soft x-ray synchrotron radiation spectroscopy study of CuFe1-xNixO2 (0≤ x ≤0.03) delafossite oxides

Electronic structures of Ni-doped CuFe1-xNixO2 delafossite oxides (x = 0, 0.015, and 0.03) have been investigated by employing soft x-ray absorption spectroscopy and soft x-ray magnetic circular dichroism (XMCD). It is found that the valence states of Cu, Fe, and Ni ions are nearly monovalent (Cu+), trivalent (Fe3+), and divalent (Ni2+), respectively, and that they do not change with x. In contrast, the Cu 2p XMCD signals, which arise from the Cu2+ states, increase with increasing x. This study suggests that the increasing XMCD signals are presumably related to the formation of ferrimagnetic spinel impurities in CuFe1-xNixO2.

Local electronic structure of Cr in the II–VI diluted ferromagnetic semiconductor Zn1-xCrxTe

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.

Soft x-ray magnetic circular dichroism study of weakly ferromagnetic Zn1−xVxO thin film

The authors performed a soft x-ray magnetic circular dichroism (XMCD) study of a Zn1−xVxO thin film, which showed a small ferromagnetic moment. Field and temperature dependences of V 2p XMCD signals indicated the coexistence of Curie-Weiss paramagnetic and antiferromagnetic V ions, quantitatively consistent with the magnetization measurements. The authors attributed the paramagnetic signal to V ions substituting for Zn sites, which are somewhat elongated along the c axis. A possible formation of ferromagnetically dead layers in the surface region of the film is also discussed.

Photoemission and soft X-ray absorption spectroscopy study of hole-doped CMR double perovskites

The electronic structures of Sr 2 - x K x FeMoO 6 ( x = 0 , 0.1 , 0.2 ) double perovskites have been investigated by employing photoemission spectroscopy (PES), soft X-ray absorption spectroscopy (XAS), and soft X-ray magnetic circular dichroism (XMCD) near the Fe 2 p absorption edge. The substitution of K + ions for Sr 2 + ions causes the increasing Fe 2 + component in the Fe 2 + – Fe 3 + mixed-valent states, but little difference in the Fe 2p XMCD spectra. As x increases, the photoemission intensity near the Fermi level decreases, which indicates the decreasing carriers and the decreasing bandwidth of the itinerant t 2 g ↓ states.

Photoemission, soft x-ray absorption, and magnetic circular dichroism spectroscopy study ofFe1−xCuxCr2S4 (0.1≤x≤0.5) spinel sulfides

The electronic and magnetic structures ofFe1−xCuxCr2S4 (0.1≤x≤0.5) spinel sulfides have been investigated systematically by performingphotoemission spectroscopy (PES), soft x-ray absorption spectroscopy(XAS), and soft x-ray magnetic circular dichroism (XMCD) measurementsusing synchrotron radiation. Cr and Cu ions are found to be nearly trivalent(Cr3+) andmonovalent (Cu+), respectively, and their valence states do not change withx. The Fe 2pXAS spectra of Fe1−xCuxCr2S4 are very similar to that of Fe metal, indicating that the Fe 3d electrons are stronglyhybridized to other valence electrons. The Fe and Cr 2p XMCD spectra show thatthe magnetic moments of Cr ions and Fe ions are aligned antiparallel to eachother and that both the Cr and Fe magnetic moments increase with increasingx. The valence-band PES study reveals that theCr3+ () 3d states are located at ∼1.5 eV below EF. The occupied Fe 3d states consist of the broad states, the states at ∼4 eV below EF, and the states very close to EF. The filled Cu 3d10 states lie at ∼2.5 eV below EF. This study suggests that the hybridized Fe and S 3p states near EF play an important role in determining the transport properties ofFe1−xCuxCr2S4 for x≤0.5.

Reactivity and magnetism of Fe/InAs(100) interfaces

Interface reaction and magnetism of epitaxially-grown Fe on InAs(100) are studied by core-level photoemission (As 3d and In 4d) and Fe 2p X-ray magnetic circular dichroism using synchrotron radiation. The reactivity of Fe/InAs(100) is relatively low compared to that of other interfaces involving deposition of 3d metals on III-V semiconductors. As a consequence, we observe a magnetic signal at Fe L2, 3 edges for the lowest thicknesses studied (1 ML). The atomic magnetic moment reaches a value close to that of the bulk α-Fe (2.2 μ B) for Fe coverages exceeding 5 ML. A ferromagnetic compound with approximate stoichiometry of FeAs is formed at the interface. The orbital magnetism represents between 12 and 20% of the total momentum, due to 3d density of states depletion and to crystal-field modification of the electronic levels. These properties make the Fe/InAs(100) interface very promising for spin-tunneling devices.