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The present study probes the effect of cation distributions in the structural, optical, electronic, and magnetic properties of mixed-valent inverse-spinel NiCo2O4 (NCO) nanoparticles (NPs). NCO NPs were prepared using the sol–gel combustion method and the grain size was obtained in the magnetic exchange length range assumed to be from single-ion anisotropy. The Raman and photoluminescence spectroscopies confirm the presence of an inverse-spinel structure with different oxidation states, and vibrating sample magnetometry clarifies the existence of ferromagnetism with the presence of magnetic anisotropy among the cations. These NPs annealed at a higher grain-growth temperature accumulate ferrimagnetic properties and produce magneto-crystalline anisotropy making NCO an assuring material for spintronic applications. A detailed x-ray absorption spectroscopy and x-ray magnetic circular dichroism studies reveal an indestructible correlation between the distribution of the present cations and the element-specific origin of ferrimagnetic behavior. Ni is found to be accountable for the magnetic moment and electronic conduction, whereas Co is associated mainly with the generation of the magnetic anisotropy even in the polycrystalline NP form. This describes the anti-ferromagnetic coupling between Co and Ni ions that is pivotal in demonstrating the exchange interaction between these cations. The above result signifies the site-dependent cation valence states for the magnetic properties, and the extent of growing conditions are related to such cation-site dysfunction. This depicts further tunability in NCO as a functional oxide material. [ABSTRACT FROM AUTHOR]

The burgeoning fields of spintronics and topological electronics require materials possessing a unique combination of properties: ferromagnetism, metallicity, and chemical stability. SrRuO3 (SRO) stands out as a compelling candidate due to its exceptional combination of these attributes. However, understanding its behavior under tensile strain, especially its thickness-dependent changes, remains elusive. This study employs machine-learning-assisted molecular beam epitaxy to investigate tensile-strained SRO films with thicknesses from 1 to 10 nm. This work complements the existing focus on compressive-strained SRO, opening a new avenue for exploring its hitherto concealed potential. Using soft x-ray magnetic circular dichroism, we uncover an intriguing interplay between film thickness, electronic structure, and magnetic properties. Our key findings reveal an intensified localization of Ru 4d t2g-O 2p hybridized states at lower thicknesses, attributed to the weakened orbital hybridization. Furthermore, we find a progressive reduction of magnetic moments for both Ru and O ions as film thickness decreases. Notably, a non-ferromagnetic insulating state emerges at a critical thickness of 1 nm, marking a pivotal transition from the metallic ferromagnetic phase. These insights emphasize the importance of considering thickness-dependent properties when tailoring SRO for next-generation spintronic and topological electronic devices. [ABSTRACT FROM AUTHOR]

Pointed magnetic elements are introduced as an improvement upon rectangular strips currently employed in composite element magnetic barcodes. The coercivity of these elements, as measured using the magneto-optic Kerr effect, is found to strictly adhere to a single power law relationship with the element width, where the power law exponent is dependent on the length of the pointed region and takes values between − 0.98 and − 0.91. The steeper gradients here, along with the absence of the crossover region seen in rectangular devices, present these structures as a strict improvement in terms of potential device applications. These improvements are found to be present for all structures where the pointed region is as long as, or longer than, the magnetic element is wide. The remanent magnetization configuration, imaged using photo-emission microscopy with contrast from x-ray magnetic circular dichroism (XMCD-PEEM), is compared to the results of micromagnetic simulations. It is found to cant inward in the pointed section of the strip, aligning with the edges of the point, pinning the magnetization and giving a consistent magnetization reversal behavior for all element widths investigated. [ABSTRACT FROM AUTHOR]

The present study is focused on the investigation at 400 K of the tetragonal-rutile phase of Cr-doped VO2 (CVO) thin films grown by pulsed laser deposition. Synchrotron-based x-ray measurements of both the surface-sensitive total electron yield (TEY) and bulk-sensitive total fluorescence yield (TFY) modes were used to investigate the pristine and Cr-doped VO2 (5%, 10%, 20%, and 30% of atomic weight). The structural analysis and purity of the crystalline phase of the as-deposited films are manifested via grazing incidence x-ray diffraction patterns, which confirm the tetragonal-rutile phase. The purity of the phase is also confirmed by the presence of Eg-mode phonons in the Raman spectra and its deconvolution reflects on the oxygen-mediated electronic/vibrational transitional effect. A clear hysteretic behavior obtained through vibrating sample magnetometry strongly suggests the ferromagnetic interaction in the thin films of CVO. The local-electronic property of the samples is examined using x-ray absorption spectroscopy (XAS) in TEY and TFY modes where the difference in the configured helicity photons resulted in the fine spectra of x-ray magnetic circular dichroism (XMCD). XAS and XMCD measurements performed at V L2,3 and Cr L2,3 edges explicitly demonstrate the ferromagnetism in the thin films of CVO. The strong hybridization between V 3d and Cr 3d states with O 2p states is evident from the spectra of the O K-edge, resulting in the onset of the cation-pair formation V5+–Cr3+, which is ferromagnetic by means of double-exchange interaction. The theoretical calculation of density functional theory made upon Vienna ab initio simulation package suggests that CVO is in a mixed state of a ferromagnetic-insulator and a half-metallic ferromagnet. [ABSTRACT FROM AUTHOR]

NiCo2O4 (NCO) films grown on MgAl2O4 (001) substrates have been studied using magnetometry and x-ray magnetic circular dichroism based on x-ray absorption spectroscopy and spin-polarized inverse photoemission spectroscopy with various thicknesses down to 1.6 nm. The magnetic behavior can be understood in terms of a layer of optimal NCO and an interfacial layer (1.2 ± 0.1 nm), with a small canting of magnetization at the surface. The thickness dependence of the optimal layer can be described by the finite-scaling theory with a critical exponent consistent with the high perpendicular magnetic anisotropy. The interfacial layer couples antiferromagnetically to the optimal layer, generating exchange-spring styled magnetic hysteresis in the thinnest films. The non-optimal and measurement-speed-dependent magnetic properties of the interfacial layer suggest substantial interfacial diffusion. [ABSTRACT FROM AUTHOR]

The spectroscopic g-factor of epitaxial thin film Yttrium Iron Garnet (YIG) has been studied using a combination of ferromagnetic resonance spectroscopy and x-ray magnetic circular dichroism. The values obtained by the two techniques are found, within experimental error, to be in agreement using Kittel's original derivation for the g-factor. For an insulating material with an entirely Fe3+ configuration, a spin mixing correction to Kittel's derivation of the spectroscopic g-factor, as recently shown by Shaw et al. [Phys. Rev. Lett. 127, 207201 (2021)] for metallic systems, is not required and demonstrates that the spin mixing parameter is small in YIG due to negligible spin–orbit coupling. [ABSTRACT FROM AUTHOR]

The intermetallic compound Fe 1 − x Co x Si has a helical magnetic order for 0.05 < x < 0.8 , whereas its orbital angular momentum contributing to the occurrence of a Dzyaloshinskii–Moriya interaction has not yet been verified. We applied soft x-ray magnetic circular dichroism spectroscopy on the Fe L 2 , 3 and Co L 2 , 3 edges below T c for Fe 0.75 Co 0.25 Si such that their orbital magnetic moments m orb were evaluated independently. The dichroic signals provide direct experimental evidence that m orb for both Fe and Co is coupled in a parallel manner with each spin counterpart m spin . The ratio of m orb to m spin is independently estimated as m orb / m spin ∼ 3 % for Fe and 9% for Co. By comparing the average of the two m spin values with the saturated magnetization using a commercial superconducting quantum interference device (SQUID) magnetometer, the hole number in the d bands for both Fe and Co is roughly estimated as approximately 1.5. This suggests that Fe and Co should be arranged closely for stabilizing the ferromagnetic moments. [ABSTRACT FROM AUTHOR]

Thin-film magnetization controlled by optical helicity has been recently reported. Although circularly polarized light has spin angular momentum, helicity-dependent all-optical magnetization switching is mediated by the stochastic thermal process, such as magnetic circular dichroism, and the effect of photon spin angular momentum is considered to be a secondary role. Conversely, the inverse Faraday effect in ferromagnetic thin films and photon spin angular momentum injection into heavy metal thin films have been observed, which can induce torque on metallic thin-film magnets. In this study, we show photon spin angular momentum driven magnetization dynamics in bilayers of Co/(Pt, Au) thin films with various thicknesses. The heavy metal Pt, Au, and ferromagnetic Co layer thickness dependencies of photon spin angular momentum driven torques are discussed in terms of field-like torque owing to the inverse Faraday effect and spin-transfer torque caused by photon spin angular momentum injection into the heavy metal layer with details of optical and magnetic properties. This study provides a better understanding of photon spin angular momentum induced magnetization dynamics in metallic thin-film heterostructures for efficient photon-driven magnetization manipulation. [ABSTRACT FROM AUTHOR]

BiFeO3 epitaxial films (tBFO = 1–10 nm) were grown on a LaSrMnO3 (tLSMO = 70 nm) buffer layer and capped with a Ru or Ru/Al layer. The BiFeO3 ultrathin film (tBFO = 3 nm) was confirmed to be continuous and flat over a wide area. Piezoelectric response and switching of spontaneous polarization were observed in the ultrathin films by switching-spectroscopy piezoelectric force microscopy measurements. Using the lock-in method with a modulation frequency of 10 Hz in x-ray absorption spectroscopy (XAS), a difference was observed between the left- and right-circularly polarized XAS signals of Fe L3 and L2 owing to x-ray magnetic circular dichroism (XMCD). The number of Fe L3 and L2 XMCD peaks indicated that a mixture of oxygen octahedron and tetrahedron (divalent and trivalent) structures might be formed. The tBFO dependence of XMCD revealed that approximately 1 nm thick ferro-like magnetic properties emerged on the BiFeO3 side of the BiFeO3/Ru interface. Ru may partially extract oxygen from BiFeO3, forming an oxygen tetrahedron structure. The BiFeO3/Ru bilayer exhibits both a piezoelectric response and ferro-like magnetism, which is promising as the basic structure of multiferroic tunnel junctions. [ABSTRACT FROM AUTHOR]

In order to understand the mechanism of the ferromagnetism in the ferromagnetic semiconductor Ga 1 − x Mn x As [(Ga,Mn)As], we have investigated the magnetic behavior on a microscopic level through systematic temperature (T)- and magnetic field (H)-dependent soft x-ray magnetic circular dichroism (XMCD) experiments at the Mn L 2 , 3 absorption edges. The T and H dependences of XMCD intensities have been analyzed using a model consisting of the ferromagnetic (FM), paramagnetic, and superparamagnetic (SPM) components. Intriguingly, we have found a common behavior for the ferromagnetic ordering process in (Ga,Mn)As samples with different Mn concentrations (4% and 10.8%) and different Curie temperature (T C ) values (65, 120, and 164 K). In particular, the SPM component develops well above T C , indicating that local FM regions are formed well above T C . The present findings indicate that the onset of ferromagnetic ordering is triggered by local electronic states around the substitutional Mn ions rather than uniform electronic states considered by mean-field theories. Insight into the most representative ferromagnetic semiconductor, (Ga,Mn)As, provided by the present study will be an important step in understanding the mechanism of ferromagnetic ordering in various ferromagnetic semiconductor families. [ABSTRACT FROM AUTHOR]

The layered van der Waals compounds ( MnBi 2 Te 4)( Bi 2 Te 3) were recently established as the first intrinsic magnetic topological insulators. We report a study on the epitaxial growth of (MnBi 2 Te 4) m (Bi 2 Te 3) n films based on the co-deposition of MnTe and Bi 2 Te 3 on BaF 2 (111) substrates. X-ray diffraction and scanning transmission electron microscopy evidence the formation of multilayers of stacked MnBi 2 Te 4 septuple layers and Bi 2 Te 3 quintuple layers with a predominance of MnBi 2 Te 4. The elemental composition and morphology of the films is further characterized by x-ray photoemission spectroscopy and atomic force microscopy. X-ray magnetic circular and linear dichroism spectra are comparable to those obtained for MnBi 2 Te 4 single crystals and confirm antiferromagnetic order in the films. [ABSTRACT FROM AUTHOR]

We studied the dynamic magnetization behavior of a hard-disk-drive (HDD) write head by using nano-beam x-ray magnetic circular dichroism (XMCD). The write head was operated by applying a square-wave write current with a frequency of 211.9 MHz to the coil of the write head, which was in synchronization with the fivefold frequency of the x-ray pulses. Snapshot images of the magnetization on the air-bearing surface of the write head were obtained with spatial and time resolutions of 100 nm and 50 ps, respectively, and temporal changes in the magnetization of the main pole and the shield were observed. When a square-wave write current with a transition time of 0.2 ns was applied, the magnetization reversal of the main pole was completed in 0.7 ns, and this reversal time was determined by the dynamic property of the write head. During the main pole reversal, the shield area showed spatially non-uniform magnetization patterns, and its response was slower than that of the main pole. These results show that the XMCD measurement setup developed in this study is a powerful tool for understanding the dynamic behavior of an HDD write head and contributes to the development of higher capacity HDDs. [ABSTRACT FROM AUTHOR]

Perpendicular magnetic anisotropy (PMA) in the Ta/CoFeB/MgO system has been studied using x-ray magnetic circular dichroism and vibrating sample magnetometry. The ratios of the orbital to spin magnetic moments of Co atoms in the Ta/CoFeB/MgO structures with PMA have been found to be enhanced by 100%, compared with the Ta/CoFeB/Ta structure without PMA. The orbital moments of Co are as large as 0.30 μ B , more than half of their spin moments in the perpendicularly magnetized Ta/CoFeB/MgO structures. The results indicate that the PMA observed in the CoFeB/MgO structures is related to the increased spin–orbital coupling of the Co atoms. This work offers experimental evidence of the correlation between PMA and the element-specific spin and orbital moments in the Ta/CoFeB/MgO systems. [ABSTRACT FROM AUTHOR]

Ferrimagnets close to the magnetic compensation are excellent candidates to spin-torque-based spintronic applications, as their small magnetizations allow lowering switching currents. Here, we studied the magnetic compensation of Mn4 − xNixN epitaxial films by performing x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at the L2,3 absorption edges of Mn and Ni atoms and compared them with those of Ni3FeN films. The XAS spectrum of the Ni3FeN films exhibits shoulders at approximately 2 eV above the Ni L2,3 main peaks, originating from orbitals hybridization between Ni 3d at face-centered (II) sites and N 2p at body-centered sites. However, such shoulders are not observed at the Ni L2,3 edges of the Mn4 − xNixN films (x = 0.1 and 0.25). These results indicate that the orbitals of Ni atoms do not hybridize with those of N atoms. Hence, Ni atoms preferentially occupy corner (I) sites, where hybridization is weak because of the relatively long distance between Ni at I sites and N atoms. The XMCD signals of Mn and Ni atoms reverse sign between x = 0.1 and 0.25. This shows that the directions of the magnetic moments carried by Mn and Ni atoms are reversed, indicating that the magnetic compensation occurs in the range 0.1 < x < 0.25. In addition, the signs of Mn(I) XMCD signals are opposite to those of Mn(II) and Ni for each composition. Thus, the magnetic moments of Ni atoms are aligned parallel to those of Mn(II) regardless of whether x is below or above the compensation point. [ABSTRACT FROM AUTHOR]

The magnetic property of a 0.7BiFeO3-0.3TbMnO3 composite has been studied in detail and compared with that of 0.8BiFeO3-0.2TbMnO3. The magnetic properties in 0.7BiFeO3-0.3TbMnO3 are improved in manifold compared to BiFeO3. An exchange bias (HEB) is observed in both the compositions of these antiferromagnetic composites, which varies between 5 and 180 Oe with a maximum at ∼275 K. Isothermal remanent magnetization measurements at room temperature indicate the presence of an interfacial layer of a 2-dimensional dilute uniaxial antiferromagnet in a uniform magnetic field (2D DAFF). The presence of exchange bias can be explained on the basis of a strong strain-mediated magnetoelectric coupling induced exchange interaction and the creation of a 2D DAFF layer at the interface. The properties of this layer are defined by canting and pinning of BiFeO3 spins at the interface with TbMnO3 due to Fe and Mn interaction. X-ray magnetic circular dichroism confirms the presence of canted antiferromagnetic ordering of BiFeO3, charge transfer between Mn ions, and different magnetically coupled layers that play a vital role in the exchange bias. [ABSTRACT FROM AUTHOR]

Induced Pt ferromagnetism in Fe 3 O 4 / Pt / Fe 3 O 4 epitaxial trilayer films has been investigated by means of X-ray magnetic circular dichroism (XMCD) at the Pt L 3 , 2 -edges at various temperatures from 300 K to 12 K , including the metal-insulator transition temperature of Fe 3 O 4 (T V ∼ 114 K). At all the temperatures, we observed clear XMCD signals due to Pt ferromagnetism, the amplitude of which was determined to be 0.39 μ B at 300 K and 0.52 μ B at 12 K for the sample with the Pt thickness of ∼ 2 nm. Interestingly, these values are comparable to or even greater than those in Pt/3 d -ferromagnetic-metal (Fe, Ni, Co, and Ni 81 Fe 19) junction systems. The results can be interpreted in terms of a possible Fe interdiffusion into the Pt layer and also possible Fe-Pt alloying due to its high-temperature deposition. [ABSTRACT FROM AUTHOR]

We have fabricated a device for microwave-assisted switching (MAS) experiments with perpendicularly magnetized CoCrPt-SiO2 granular film with anisotropy field Hk = 18.8 kOe. The device was carefully designed to be able to apply a microwave field of 0.95 kOe in amplitude continuously, allowing direct evaluation of microwave-assisted switching properties of the medium without any assumptions about time-dependent switching behavior. The coercivity of CoCrPt-SiO2 medium linearly decreases with increasing microwave frequency, and the maximum coercivity reduction ratio reaches 80% for hrf = 0.95 kOe at frf = 25 GHz after subtracting the effect of temperature rise due to microwave field application. The linear slope of coercivity against the frequency becomes steeper with increasing microwave field amplitude, which is a unique frequency and amplitude dependencies in granular media. Correlation length obtained by X-ray magnetic circular dichroism microscopy measurement decreases by applying a microwave field with higher frequency, suggesting that the magnetic clustering dimensions of the medium possibly depend on microwave frequency during microwave-assisted switching. [ABSTRACT FROM AUTHOR]

Magnetic skyrmions are topologically protected spin textures. They can exist in bilayer synthetic antiferromagnets and have some exotic behaviors in terms of dynamics. In this work, we theoretically studied the dynamics of magnetic skyrmions in antiferromagnetic-exchange coupled disks in terms of microwave response using micromagnetic simulations. It is well known that clockwise (CW)/counterclockwise (CCW) circular resonance modes of skyrmions can be excited when an in-plane microwave is applied to the system. We found three coupled excitation modes (CW-CW, CCW-CCW, and CW-CCW) in the presence of antiferromagnetic-exchange coupling and the type of excitation mode depends on the frequency of the in-plane microwave. Furthermore, the topological trajectories of excitation modes are elliptical. For the low frequency (less than 10 GHz) excitation, the trajectory is close to linear mode since the major axis of the ellipse is much larger than its minor axis. [ABSTRACT FROM AUTHOR]

We study the carrier transport and magnetic properties of group-IV-based ferromagnetic semiconductor Ge1-xFex thin films (Fe concentration x = 2.3%–14%) with and without boron (B) doping, by measuring their transport characteristics: the temperature dependence of resistivity, hole concentration, mobility, and the relation between the anomalous Hall conductivity versus conductivity. At relatively low x (=2.3%), the transport in the undoped Ge1-xFex film is dominated by hole hopping between Fe-rich hopping sites in the Fe impurity levels, whereas that in the B-doped Ge1-xFex film is dominated by the holes in the valence band in the degenerated Fe-poor regions. As x increases (x = 2.3%–14%), the transport in the both undoped and B-doped Ge1-xFex films is dominated by hole hopping between the Fe-rich hopping sites of the impurity band. The magnetic properties of the Ge1-xFex films are studied by various methods including magnetic circular dichroism, magnetization, and anomalous Hall resistance and are not influenced by B-doping. We show band profile models of both undoped and B-doped Ge1-xFex films, which can explain the transport and the magnetic properties of the Ge1-xFex films. [ABSTRACT FROM AUTHOR]

We explore the electronic and related properties of Cu2MnAl1–xGax with a first-principles, relativistic multiscattering Green function approach. We discuss our results in relation to existing experimental data and show that the electron-core hole interaction is essential for the description of the optical spectra especially in describing the X-ray absorption and magnetic circular dichroism spectra at the L2,3 edges of Cu and Mn. [ABSTRACT FROM AUTHOR]

We explore the electronic and related properties of Cu2MnAl1–xGax with a first-principles, relativistic multiscattering Green function approach. We discuss our results in relation to existing experimental data and show that the electron-core hole interaction is essential for the description of the optical spectra especially in describing the X-ray absorption and magnetic circular dichroism spectra at the L2,3 edges of Cu and Mn. [ABSTRACT FROM AUTHOR]

We report on the crystal growth as well as the structural and magnetic properties of Bi0.8Sb0.2 topological insulator (TI)/MnxGa1-x bi-layers grown on GaAs(111)A substrates by molecular beam epitaxy. By optimizing the growth conditions and Mn composition, we were able to grow MnxGa1-x thin films on Bi0.8Sb0.2 with the crystallographic orientation of Bi0.8Sb0.2(001)[1 ...1 0]// MnGa (001)[100]. Using magnetic circular dichroism (MCD) spectroscopy, we detected both the L10 phase (x < 0.6) and the D022 phase (x > 0.6) of MnxGa1-x. For 0.50 ≤ x ≤ 0.55, we obtained ferromagnetic L10-MnGa thin films with clear perpendicular magnetic anisotropy, which were confirmed by MCD hysteresis, anomalous Hall effect as well as superconducting quantum interference device measurements. Our results show that the BiSb/MnxGa1-x bi-layer system is promising for perpendicular magnetization switching using the giant spin Hall effect in TIs. [ABSTRACT FROM AUTHOR]

X-ray magnetic circular dichroism (XMCD) measurements of iron nano-islands grown on graphene and covered with a Au film for passivation reveal that the oxidation through defects in the Au film spontaneously leads to the formation of magnetite nano-particles (i.e., Fe3O4). The Fe nano-islands (20 and 75 monolayers; MLs) are grown on epitaxial graphene formed by thermally annealing 6H-SiC(0001) and subsequently covered, in the growth chamber, with nominal 20 layers of Au. Our X-ray absorption spectroscopy and XMCD measurements at applied magnetic fields show that the thin film (20 ML) is totally converted to magnetite, whereas the thicker film (75 ML) exhibits properties of magnetite but also those of pure metallic iron. Temperature dependence of the XMCD signal (of both samples) shows a clear transition at TV ≈ 120K consistent with the Verwey transition of bulk magnetite. These results have implications on the synthesis of magnetite nano-crystals and also on their regular arrangements on functional substrates such as graphene. [ABSTRACT FROM AUTHOR]

To investigate the possible sources of the switching field distribution in bit-patterned media, we applied a scanning hard-X-ray nanoprobe technique based on X-ray magnetic circular dichroism spectroscopy to an array of Co-Pt dots with the typical diameters of 200 nm. Element-specific magnetization curves at the Pt L3 edge were measured for individual dots isolated from each other, and the magnetization switching field (coercivity) values were determined for more than 100 individual dots. To assess the effect of dot diameters as a possible source of switching field distribution, a statistical analysis of the coercivity values and dot diameters measured for many dots was performed. The resulting switching field distribution had a mean of = 1:80 kOe and a standard deviation of σHSW=0.64 kOe. The relative deviation of σHSW/ = 36% was not in good agreement with the relative dispersion in a dot diameter of σD/ = 2:7%, and no clear correlation between the coercivity and dot diameter was observed. These results may suggest other possible sources of switching field distribution than dot diameter, such as dispersion in the c-axis orientation and in magnetocrystalline anisotropy. [ABSTRACT FROM AUTHOR]

X-ray magnetic circular dichroism (XMCD) is widely used for the characterization of magnetism of materials. However, information from XMCD related to the atomic, electronic, and magnetic structures is not fully utilized due to the lack of reliable theoretical tools for spectral analysis. In this work, the first-principles configuration interaction (CI) calculations for X-ray absorption spectra developed by the author were extended for the calculation of XMCD, where the Zeeman energy was taken into the Hamiltonian of the CI to mimic magnetic polarization in the solid state. This technique was applied to interpret the L2,3 XMCD from 3d transition metal complex oxides, such as NiFe2O4 and FeTiO3. The experimental XMCD spectra were quantitatively reproduced using this method. The oxidation states as well as the magnetic ordering between transition metal ions on crystallographically different sites in NiFe2O4 can be unambiguously determined. A first-principles analysis of XMCD in FeTiO3 revealed the presence of Fe3+ and Ti3+ ions, which indicates that the charge transfer from Fe to Ti ions occurs. The origin of magnetic polarization of Ti ions in FeTiO3 was also discussed. [ABSTRACT FROM AUTHOR]

We performed X-ray magnetic circular dichroism (XMCD) photoemission electron microscopy imaging to reveal the magnetic domain structure of anti-perovskite nitride Co3FeN exhibiting a negative spin polarization. In square and disc patterns, we systematically and quantitatively determined the statistics of the stable states as a function of geometry. By direct imaging during the application of a magnetic field, we revealed the magnetic reversal process in a spatially resolved manner. We compared the hysteresis on the continuous area and the square patterns from the magnetic field-dependent XMCD ratio, which can be explained as resulting from the effect of the shape anisotropy, present in nanostructured thin films. [ABSTRACT FROM AUTHOR]

An ultrahigh-vacuum-compatible setup for broad-band X-ray detected ferromagnetic resonance (XFMR) in longitudinal geometry is introduced which relies on a low-power, continuous-wave excitation of the ferromagnetic sample. A simultaneous detection of the conventional ferromagnetic resonance via measuring the reflected microwave power and the XFMR signal of the X-ray absorption is possible. First experiments on the Fe and Co L3-edges of a permalloy film covered with Co nanostripes as well as the Fe and Ni K-edges of a permalloy film are presented and discussed. Two different XFMR signals are found, one of which is independent of the photon energy and therefore does not provide element-selective information. The other much weaker signal is element-selective, and the dynamic magnetic properties could be detected for Fe and Co separately. The dependence of the latter XFMR signal on the photon helicity of the synchrotron light is found to be distinct from the usual x-ray magnetic circular dichroism effect. [ABSTRACT FROM AUTHOR]

We have studied the electronic and magnetic states of Co and Mn atoms at the interface of the Co2MnβSi (CMS)/MgO (β = 0.69, 0.99, 1.15, and 1.29) magnetic tunnel junction (MTJ) by means of x-ray magnetic circular dichroism. In particular, the Mn composition (β) dependences of the Mn and Co magnetic moments were investigated. The experimental spin magnetic moments of Mn, mspin(Mn), derived from x-ray magnetic circular dichroism weakly decreased with increasing Mn composition β in going from Mn-deficient to Mn-rich CMS films. This behavior was explained by first-principles calculations based on the antisite-based site-specific formula unit (SSFU) composition model, which assumes the formation of only antisite defect, not vacancies, to accommodate off-stoichiometry. Furthermore, the experimental spin magnetic moments of Co, mspin(Co), also weakly decreased with increasing Mn composition. This behavior was consistently explained by the antisite-based SSFU model, in particular, by the decrease in the concentration of CoMn antisites detrimental to the half-metallicity of CMS with increasing β. This finding is consistent with the higher tunnel magnetoresistance ratios which have been observed for CMS/MgO/CMS MTJs with Mn-rich CMS electrodes. [ABSTRACT FROM AUTHOR]

We performed x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at Fe L2,3 and N K-edges for Fe4N epitaxial films grown by molecular beam epitaxy. In order to clarify the element specific local electronic structure of Fe4N, we compared experimentally obtained XAS and XMCD spectra with those simulated by a combination of a first-principles calculation and Fermi's golden rule. We revealed that the shoulders observed at Fe L2,3-edges in the XAS and XMCD spectra were due to the electric dipole transition from the Fe 2p core-level to the hybridization state generated by σ* anti-bonding between the orbitals of N 2p at the body-centered site and Fe 3d on the face-centered (II) sites. Thus, the observed shoulders were attributed to the local electronic structure of Fe atoms at II sites. As to the N K-edge, the line shape of the obtained spectra was explained by the dipole transition from the N 1s core-level to the hybridization state formed by π* and σ* anti-bondings between the Fe 3d and N 2p orbitals. This hybridization plays an important role in featuring the electronic structures and physical properties of Fe4N. [ABSTRACT FROM AUTHOR]

Tailored parallel-stripe magnetic domains with antiparallel magnetizations in adjacent domains along the long stripe axis have been fabricated in an IrMn/CoFe Exchange Bias thin film system by 10 keV He+-ion bombardment induced magnetic patterning. Domain walls between these domains are of Néel type and asymmetric as they separate domains of different anisotropies. X-ray magnetic circular dichroism asymmetry images were obtained by x-ray photoelectron emission microscopy at the Co/Fe L3 edges at the synchrotron radiation source BESSY II. They revealed Néel-wall tail widths of 1 lm in agreement with the results of a model that was modified in order to describe such walls. Similarly obtained domain core widths show a discrepancy to values estimated from the model, but could be explained by experimental broadening. The rotation senses in adjacent walls were determined, yielding unwinding domain walls with non-interacting walls in this layer system. [ABSTRACT FROM AUTHOR]

We acquired direct measurements for in-plane and perpendicular-to-plane magnetic moments of Fe films using an x-ray magnetic circular dichroism technique with increase of the Fe thickness (up to 40Å) on the Ag(001) surface. Epitaxial Fe/Ag(001) films were grown in situ with the thickness varying from 2Å to 40Å, and the magnetic anisotropy was carefully investigated as a function of the film thickness. We found re-entrance of the in-plane magnetic anisotropy of the Fe film in ultrathin region. The results manifest that the epitaxial Fe/Ag(001) film undergoes two distinct spin reorientation transitions from in-plane to out-of-plane at the film thickness t≈9Å and back to in-plane at t≈18Å as t increases. [ABSTRACT FROM AUTHOR]

Recently, the graphene-based absorber captures much attention due to its bright potential. In this paper, a modeling study of graphene-based absorber is made for variable magnetostatic bias, i.e., the magnetic circular dichroism (MCD). A strong MCD signal about ΔA=0.94 is obtained in 7 T for a uniform graphene-based absorber. By periodically patterning subwavelength holes on the graphene, the structured absorber exhibits two obvious peaks induced by cavity resonance and localized resonance of meta-surface in 0 T, respectively. As the magnetic field increases, the absorption peaks show quite different electromagnetic response for the two kinds of circularly polarized lights. Two distinct MCDs signals of 0.711 at 2.02 THz and 0.91 at 2.49 THz in 7 T are observed. The results are well explained by a modified equivalent circuit model. [ABSTRACT FROM AUTHOR]

This report investigates the phase evolution pathway of magnetite nanocrystal synthesis on oxide-supported substrates. A template-free phase separation approach, which exploits the thermodynamic instability of ternary perovskite BiFeO3 and inherent volatility of bismuth oxide in low oxygen pressure and high temperature is presented. The formation of an intermediate hematite nanocrystal phase is found as a key step that controls the eventual size and morphology of the magnetite nanocrystals. X-ray absorption spectra measurements and X-ray magnetic circular dichroism confirm that the spectral fingerprints of the magnetite nanocrystals match with that of bulk crystals. Magnetic measurements show that magnetic anisotropy is directly attributed to the nanocrystal morphology. [ABSTRACT FROM AUTHOR]

We performed first-principles calculations for Cr3+ L2,3-edge x ray absorption near-edge structures (XANES) of Cr3+:α-Al2O3 (ruby) and α-Cr2O3 and magnetic circular dichroism (MCD) of Cr3+ L2,3-edge XANES of ruby using a relativistic multielectron method. In order to investigate the lattice relaxation effects for ruby, theoretical studies were carried out using the three types of model clusters, including the lattice relaxation effects. These theoretical XANES spectra for both ruby and α-Cr2O3 well reproduced the experimental XANES spectra. The lattice relaxation effects on the XANES spectra for ruby were very small, while the results of configuration analysis of the many-electron wave function indicated that the mixing between L2 and L3 edges was significantly large in Cr3+ L2,3-edge XANES spectra for both ruby and α-Cr2O3. In addition, XANES spectra showed that the L3-edge component significantly mixed in the L2-edge peaks, while the L3-edge component also significantly contributed to the intensity of L2-edge. The theoretical MCD spectra for ruby also well reproduced the experimental one. We also investigated the validity of the sum rules quantitatively by comparing the magnetic moments calculated from the theoretical spectra using the sum rules and those calculated directly from the explicit many-electron wave functions. The orbital moments by both methods were almost zero, and the spin moments had 10% difference between these methods. The results of the configuration analysis indicated that the magnitude of the mixing between L2 and L3 edges could be the major cause of this discrepancy. [ABSTRACT FROM AUTHOR]

Ferromagnetic (FM) material dependence of the uncompensated (UC) antiferromagnetic (AF) moments in AF/FM exchange biased bilayers has been studied using the x-ray magnetic circular dichroism technique in the AF/FM (AF = γ-Mn-Ir, FM = Ni-Co, Co-Fe, Fe-Ni) bilayers. The direction and magnitude of the UC-Mn moment change significantly when the composition of the FM layer changes. The crystal structure of the FM layer affects the magnitude of the UC-Mn moments. The UC-Mn moments and the FM moments of Fe-rich alloys prefer the anti-parallel alignment. Conversely, the UC-Mn moments align parallel to the FM moments in Co-rich or Ni-rich regions. A first-principles calculation pertaining to the L12-Mn3Ir/FM (FM = Ni4-nCon, Co4-nFen, Fe4-nNin; n = 0, 1, 2, 3) bilayer system was carried out to characterize the UC-Mn moments near the interface. It was found that the UC-Mn moments originate from the reorientation of the magnetic moments of Mn and other ferromagnetic atoms near the AF/FM interface. The calculated result for the compositional dependence of the UC-Mn moment is in good agreement with the obtained experimental data. As a result, the dependence of the UC-Mn moment on the composition of the FM layer can be explained qualitatively based on the model that the band filling fraction modifies the direction and the magnitude of exchange coupling between AF and FM atoms, depending on the crystal structure and the composition of the FM layer. [ABSTRACT FROM AUTHOR]

The tetragonally distorted antiperovskite Mn3CuN exhibits large magnetostriction of up to 2000 ppm, due to the ferromagnetic shape memory effect. Magnetocrystalline anisotropy, which is deeply involved in the magnetostriction, is investigated for Mn3CuN via quantitative evaluation of spin and orbital magnetic moments using soft x ray magnetic circular dichroism. Although Cu and Mn have finite magnetic contributions, the Cu contribution may be too small to dominate the magnetism of Mn3CuN. The orbital magnetic moment of Mn is found to be negligibly small, suggesting small magnetocrystalline anisotropy. Even with small magnetocrystalline anisotropy, the system exhibits ferromagnetic shape memory effects, presumably because the simultaneously small crystallographic anisotropy enhances the magnetic shear stress acting across the twinning plane. [ABSTRACT FROM AUTHOR]

The electronic structure of Cu-doped ZnO thin films, synthesized with a nominal composition of Zn1-xCuxO (x=0.03, 0.05, 0.07, and 0.10) by using spray pyrolysis method, has been investigated using near-edge x-ray absorption fine structure (NEXAFS) experiments at the O K- and the Cu L3,2-edges and resonant inelastic x-ray scattering (RIXS) measurements at Cu L3,2 edge. The Zn1-xCuxO thin films showed single phase wurtzite-hexagonal like crystal structure and ferromagnetic behavior at room temperature (RT). The intensity of the pre-edge spectral feature at the O K-edge increases with the Cu concentration, which clearly reveals that there is strong hybridization of O 2p–Cu 3d orbitals in the ZnO matrix. Spectral features of the Cu L3,2-edge NEXAFS exhibit multiple absorption peaks and appreciable x-ray magnetic circular dichroism signal that persists even at RT. These results demonstrate that Cu is in mixed valence state of Cu2+,3+/Cu1+, substituting at the Zn site and Cu2+/3+ ions are magnetically polarized. RIXS experiments at Cu L3 edge show strong d-d excitations due to localized nature of Cu ions in the ZnO matrix. [ABSTRACT FROM AUTHOR]

We have measured x-ray magnetic circular dichroism spectra at the Co and Pt L2,3-edges in Co80Pt20 perpendicular magnetization films, wherein the uniaxial magnetic anisotropy constant, Ku, significantly increases with decreasing film thickness, δ, and reaches 1.7×107 erg/cm3 for δ=3 nm. The anisotropy of the orbital magnetic moment (AOM) was estimated as a function of δ, and the relationship between AOM and Ku is discussed. When the thickness was reduced, the AOM for Pt 5d was nearly constant, whereas a weak increase was observed for Co 3d. Both AOMs are small in contrast to the large Ku, and any proportionality between AOM and Ku was hardly recognized. This result indicates that a large AOM is not always a necessary and sufficient condition for the appearance of perpendicular magnetization. [ABSTRACT FROM AUTHOR]

Through the full potential linearized augmented plane wave method, we have explored the vacancy defect induced magnetism in wurtize ZnO. It has been found that the Zn vacancy defect brings a spin polarized state in the nearest neighbor oxygen atoms, whereas the oxygen vacancy defect has no influence on the magnetism. However, it is found that the lattice distortion is a crucial factor for the Zn vacancy induced ferromagnetism because the ferromagnetic ground state cannot be achieved if there is no lattice distortion due to Zn vacancy defect. The magnetic moment of oxygen atom in the nearest neighbor from the Zn vacancy site is ranged from 0.10 to 0.19 μB and the spin polarized oxygen atoms have metallic feature in both spin states. These results are quite different from those found in other calculation [Q. Wang et al., Phys. Rev. B 77, 205411 (2008)]. In addition, we have found that the ferromagnetic exchange interaction among oxygen atoms is mediated by Zn 3d state. Along with these, the theoretically calculated x-ray absorption spectroscopy and x-ray magnetic circular dichroism are presented. [ABSTRACT FROM AUTHOR]

We present the structural and element specific magnetic properties of Co2MnSn and Co2MnSb thin films grown on GaAs (100) substrates using pulsed laser deposition. X-ray magnetic circular dichroism (XMCD) spectra were measured for 400 Å thick films at the L2,3 edges of Co and Mn. Element specific moments for Co and Mn in Co2MnSn were calculated from the x-ray absorption and XMCD spectra using the XMCD sum rules. The ratios of orbital to spin magnetic moments for Co and Mn were calculated for Co2MnSn and Co2MnSb. [ABSTRACT FROM AUTHOR]

We report studies by x-ray diffraction, ferromagnetic resonance (FMR), and x-ray magnetic circular dichroism (XMCD) in Co/Ru superlattices grown by magnetron sputtering. We studied the [Co(50 Å)/Ru(tRu)]20 samples, which were deposited at room temperature on Si substrates with the Ru thicknesses, tRu, varying between 9 and 33 Å. The main and secondary uniform absorption modes, observed in the FMR spectra, are associated with the Co/Ru interfaces and the bulk Co regions, respectively. The main mode becomes more intense than the secondary one for increasing tRu. This is attributed to the roughness and/or atomic interdiffusion, which leads, with increasing tRu, to an increasing volume of Co/Ru interfacial regions and a decreasing volume of pure Co regions. The XMCD measurements provide Co spin magnetic moments lower than the bulk Co value, confirming the presence of a Co magnetic region with a lower local effective magnetization attributed to the Co/Ru interfaces. [ABSTRACT FROM AUTHOR]

We report magnetic behavior of a dilute ferromagnetic alloy Ni1-xMnx, 0

Surface and interface magnetisms in oxide thin films and heterostructures have been a recurrent topic during the past years due to their relevance in the implementation of magnetoelectronic devices. Magneto-optical techniques, such as x-ray magnetic circular dichroism, turn out to be a very efficient tool to study surface magnetism due to their sensitivity to magnetic and chemical variations across the sample depth. Nevertheless, the application of the sum rules for the determination of the spin magnetic moment might lead to uncertainties as large as 40%. To overcome this problem we present an alternative approach consisting in using x-ray magnetic circular dichroism in reflection geometry. Data analysis by using a computer code based on a 4×4 matrix formalism indicates that surface and interface roughnessas are of major relevance for a proper description of the experimental data and a correct interpretation of the results. By using such an approach, we discuss the presence of a narrow surface region with strongly depressed magnetic properties in La2/3Ca1/3MnO3 thin films. [ABSTRACT FROM AUTHOR]

We demonstrate that a standing-wave/wedge (swedge) method for probing buried solid-solid interfaces can be carried out using soft x-ray emission spectroscopy (XES) and resonant inelastic x-ray scattering (RIXS). For the particular case of an Al2O3/Fe/Cr structure of relevance to giant magnetoresistance, measurements of Fe L and Cr L total intensities and Fe L magnetic circular dichroism are used to derive for both the top and bottom Fe interfaces the depth profile of composition and the depth dependence of the atom-specific Fe contribution to magnetization. Using XES and RIXS in this method, as compared to photoelectron spectroscopy in prior work, permits studying more deeply buried interfaces, and suggests future applications to a wide variety of magnetic and nonmagnetic nanostructures. [ABSTRACT FROM AUTHOR]

Systematic investigations were performed concerning the crystal structure and excitonic-related transitions of Zn1-xCoxO layers. The substitution of Co atoms for Zn sites was initially identified from the intra-emissions originating from the 3d levels of the Co2+ ions. Microresonant Raman scattering (μ-RRS) revealed that the local crystal structure of the host was disordered even at Co concentrations of a few percent, as determined by monitoring the A1(LO) mode and also supported by the ω-rocking curves obtained from x-ray diffraction. A critical point (Γ-edge) derived from magnetic circular dichroism systematically shifted to higher energy with increasing x, representing clear evidence for a widening of the band gap, and that the photoluminescent peaks correlated closely with absorption peaks related to excitonic transitions. The obvious excitonic structures gradually became diffuse with the appearance of photoexcited charge-transfer levels of Co2+ ions when x exceeded 2%. This allowed for observations of excitonic luminescence of samples with a Co content not exceeding 0.8%. The excitonic luminescence for all Co-doped ZnO layers was superimposed distinctly with Stokes and anti-Stokes LO phonons. This was attributed to outgoing multiphonon resonance Raman scattering due to a Fröhlich interaction based on strong coupling between photoexcited carriers and LO phonons, and further supported by the results of μ-RRS. [ABSTRACT FROM AUTHOR]

Fe8 high-spin molecules exhibit quantum spin tunneling at very low temperatures. Eight Fe3+ ions are sixfold coordinated and magnetically coupled through oxygen bridges. The net magnetization (MS=20 μB per molecule) results from competing antiferromagnetic interactions between the various Fe3+ ions (S=5/2). Because of the structural anisotropy of these molecules, the magnetization curve presents a hysteresis loop with staircases below 2 K. The staircases of the hysteresis loop are due to the quantum spin tunneling, which is temperature dependent for 400 mK

We have studied the influence of an inserted nano-oxide layer (NOL) on the interfacial magnetism in spin-valve systems showing the giant magnetoresistance effect. Specifically, we performed a magnetic depth profile of these structures with and without a NOL, using the x-ray magnetic circular dichroism technique. We found that insertion of a NOL into the spin-valve structure is correlated with a stronger reduction of the magnetic moments at the ferromagnetic (FM)/NOL/FM interface in comparison with a spin valve without NOL. [ABSTRACT FROM AUTHOR]

We present measurements of element- and time-resolved ferromagnetic resonance (FMR) in magnetic thin films at gigahertz frequencies via an implementation of time-resolved x-ray magnetic circular dichroism (TR-XMCD). By combining TR-XMCD and FMR, using a rf excitation that is phase locked to the photon bunch clock, the dynamic response of individual layers or precession of individual elements in an alloy can be measured. The technique also provides extremely accurate measurements of the precession cone angle (to 0.1°) and the phase of oscillation (to 2°, or ∼5 ps at 2.3 GHz). TR-XMCD combined with FMR can be used to study the origins of precessional damping by measuring the relative phase of dissimilar precessing magnetic moments. We have used the technique to measure the response of specific elements and separate layers in several alloys and structures, including a single Ni81Fe19 layer, a pseudo-spin-valve structure (Ni81Fe19/Cu/Co93Zr7), magnetic bilayers consisting of low damping (Co93Zr7) and high damping (Tb-doped Ni81Fe19) layers joined across a common interface, and elemental moments in Tb-doped Ni81Fe19. [ABSTRACT FROM AUTHOR]

The electronic structure and x-ray magnetic circular dichroism (XMCD) spectra of the Heusler alloy Co2MnGe were investigated theoretically from first principles, using the fully relativistic Dirac linear muffin-tin orbital band structure method. Densities of valence states, orbital and spin magnetic moments, as well as polarization of the electronic states at the Fermi level are analyzed and discussed. The origin of the XMCD spectra in the Co2MnGe compound is examined. The calculated results are compared with available experimental data. [ABSTRACT FROM AUTHOR]

We studied the electronic states and magnetic moments of a bcc-Co(001) monatomic layer facing an amorphous Al–O tunneling barrier using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at the L2,3 core edges of Co. Both the XAS and XMCD measurements revealed that 1 monolayer (ML) Co is not oxidized. The magnetic moment of 1 ML bcc Co(001) facing the amorphous Al–O was observed to be almost the same as that of bulk Co. In contrast, the total magnetic moment of 1 ML bcc Co(001) facing a metallic Al layer was reduced by the effect of the proximity to Al atoms. [ABSTRACT FROM AUTHOR]