A Comment on the Letter by D. Haskel et al., Phys. Rev. Lett. 95, 217207 (2005)PRLTAO0031-900710.... more A Comment on the Letter by D. Haskel et al., Phys. Rev. Lett. 95, 217207 (2005)PRLTAO0031-900710.1103/PhysRevLett.95.217207. The authors of the Letter offer a Reply.
The electronic structure and magnetism of Ir 5d5 states in nonmetallic, weakly ferromagnetic BaIr... more The electronic structure and magnetism of Ir 5d5 states in nonmetallic, weakly ferromagnetic BaIrO3 are probed with x-ray absorption techniques. Contrary to expectation, the Ir 5d orbital moment is found to be ˜1.5 times larger than the spin moment. This unusual, atomiclike nature of the 5d moment is driven by a strong spin-orbit interaction in heavy Ir ions, as confirmed by the nonstatistical large branching ratio at Ir L2,3 absorption edges. As a consequence, orbital interactions cannot be neglected when addressing the nature of magnetic ordering in BaIrO3. The local moment behavior persists even as the metallic-paramagnetic phase boundary is approached with Sr doping or applied pressure.
The strong local-moment magnetism in divalent Eu metal (4f^7) suppresses superconductivity. At ex... more The strong local-moment magnetism in divalent Eu metal (4f^7) suppresses superconductivity. At extreme pressure Eu is expected to become trivalent and nonmagnetic (4f^6). Recently, superconductivity in Eu was discovered by Debessai et al. for pressures above 80 GPa [1]. However, Eu's transition temperature lies near 2 K, nearly an order of magnitude lower than for comparable trivalent d-electron metals, possibly because Eu is not fully trivalent but rather mixed valent. Here we report recent experimental results on Eu's valence and magnetic state to Mbar pressures through synchrotron x-ray absorption near edge structure (XANES), synchrotron x-ray magnetic circular dichroism (XMCD), and synchrotron M"ossbauer spectroscopy (SMS).[4pt] [1] M. Debessai, T. Matsuoka, J. J. Hamlin, J. S. Schilling, and K. Shimizu, Phys. Rev. Lett. 102, 197002 (2009).
Iron in concentrations as small as 4 at. % (where the distance between Fe atoms is more than thre... more Iron in concentrations as small as 4 at. % (where the distance between Fe atoms is more than three lattice spacings) produces ferromagnetic behavior at temperatures up to 50 K above the Gd Curie temperature TC in Gd100-xFex nanostructures. X-ray diffraction and XAFS show that Gd100-xFex nanostructures made by inert-gas-condensation and melt-spinning have nanoscale hcp Gd grains with Gd-Fe grain
Using element-specific x-ray resonance techniques, we have investigated the interfacial magnetic ... more Using element-specific x-ray resonance techniques, we have investigated the interfacial magnetic coupling in SrRuO3/SrMnO3 superlattices. A strong out-of-plane SRO anisotropy coupled with AFM Ru-Mn interactions result in a canted Mn structure with a significant induced net Mn moment that reduces to zero under a strong magnetic field. At T > TC SRO, the SRO anisotropy is removed and the planar
ABSTRACT The appearance of magnetism in otherwise non-magnetic materials has recently been report... more ABSTRACT The appearance of magnetism in otherwise non-magnetic materials has recently been reported for a number of nanoscale materials. Coupled with the size-dependent optical and electronic properties of the nanocrystalline materials, this magnetic behavior opens the possibility for an extended range of technological applications. As such, identifying the origin of the magnetism is an extremely important goal, yet this remains the subject of some controversy in the literature. We report evidence that paramagnetism in CdSe QDs can be induced via manipulation of the particle size and surface ligands. Using SQUID magnetometry and x-ray absorption spectroscopy, we demonstrate that the paramagnetic behavior of the CdSe QDs can be varied by changing the ligand endgroup functionality of the passivating layer. Contrary to previous reports, no evidence for ferromagnetism was observed.
We combine x-ray magnetic circular dichroism spectroscopy at Fe L{sub 2,3} edges, at Eu M{sub 4,5... more We combine x-ray magnetic circular dichroism spectroscopy at Fe L{sub 2,3} edges, at Eu M{sub 4,5} edges, x-ray absorption spectroscopy (XAS) investigation of Eu valence, and local spin density calculations, to show that the filled skutterudite Eu{sub 0.95}FeSb is a ferrimagnet in which the Fe 3d moment and the Eu{sup 2+} 4f moment are magnetically ordered with dominant antiferromagnetic coupling. From Eu L edge XAS, we find that about 13% of the Eu have a formal valence of 3{sup +}. We ascribe the origin of ferrimagnetism at a relatively high transition temperature T{sub c} of 85 K in Eu{sub 0.95}FeSb to f-electron interaction with the nearly ferromagnetic [FeSb]{sup 2.2-} host lattice.
Codoping with Co has been shown to promote successful dilution of magnetic dopants of Mn and Fe i... more Codoping with Co has been shown to promote successful dilution of magnetic dopants of Mn and Fe into Ge up to a combined doping level of 15 at. %. Local structure, magnetic moment, and spin-dependant states of these diluted magnetic semiconductors (DMS) have been probed as a function of composition using X-ray and tunneling spectroscopy techniques. Extended X-ray Absorption Fine Structure (EXAFS) measurements reveal an increased level of substitution for each dopant species with respect to traditional single dopant DMS materials. A codoped environment results in 70% of Mn and 90% of Co successfully incorporating substitutionally into the Ge lattice. The remaining dopants are seen to form interstitial dimmers and trimers rather than metallic precipitates. Tunneling spectroscopy measurements on these systems through Al2O3 barriers using both Nb and Fe as spin detectors will be discussed in their correlation with the structural results.
A Comment on the Letter by D. Haskel et al., Phys. Rev. Lett. 95, 217207 (2005)PRLTAO0031-900710.... more A Comment on the Letter by D. Haskel et al., Phys. Rev. Lett. 95, 217207 (2005)PRLTAO0031-900710.1103/PhysRevLett.95.217207. The authors of the Letter offer a Reply.
The electronic structure and magnetism of Ir 5d5 states in nonmetallic, weakly ferromagnetic BaIr... more The electronic structure and magnetism of Ir 5d5 states in nonmetallic, weakly ferromagnetic BaIrO3 are probed with x-ray absorption techniques. Contrary to expectation, the Ir 5d orbital moment is found to be ˜1.5 times larger than the spin moment. This unusual, atomiclike nature of the 5d moment is driven by a strong spin-orbit interaction in heavy Ir ions, as confirmed by the nonstatistical large branching ratio at Ir L2,3 absorption edges. As a consequence, orbital interactions cannot be neglected when addressing the nature of magnetic ordering in BaIrO3. The local moment behavior persists even as the metallic-paramagnetic phase boundary is approached with Sr doping or applied pressure.
The strong local-moment magnetism in divalent Eu metal (4f^7) suppresses superconductivity. At ex... more The strong local-moment magnetism in divalent Eu metal (4f^7) suppresses superconductivity. At extreme pressure Eu is expected to become trivalent and nonmagnetic (4f^6). Recently, superconductivity in Eu was discovered by Debessai et al. for pressures above 80 GPa [1]. However, Eu's transition temperature lies near 2 K, nearly an order of magnitude lower than for comparable trivalent d-electron metals, possibly because Eu is not fully trivalent but rather mixed valent. Here we report recent experimental results on Eu's valence and magnetic state to Mbar pressures through synchrotron x-ray absorption near edge structure (XANES), synchrotron x-ray magnetic circular dichroism (XMCD), and synchrotron M"ossbauer spectroscopy (SMS).[4pt] [1] M. Debessai, T. Matsuoka, J. J. Hamlin, J. S. Schilling, and K. Shimizu, Phys. Rev. Lett. 102, 197002 (2009).
Iron in concentrations as small as 4 at. % (where the distance between Fe atoms is more than thre... more Iron in concentrations as small as 4 at. % (where the distance between Fe atoms is more than three lattice spacings) produces ferromagnetic behavior at temperatures up to 50 K above the Gd Curie temperature TC in Gd100-xFex nanostructures. X-ray diffraction and XAFS show that Gd100-xFex nanostructures made by inert-gas-condensation and melt-spinning have nanoscale hcp Gd grains with Gd-Fe grain
Using element-specific x-ray resonance techniques, we have investigated the interfacial magnetic ... more Using element-specific x-ray resonance techniques, we have investigated the interfacial magnetic coupling in SrRuO3/SrMnO3 superlattices. A strong out-of-plane SRO anisotropy coupled with AFM Ru-Mn interactions result in a canted Mn structure with a significant induced net Mn moment that reduces to zero under a strong magnetic field. At T > TC SRO, the SRO anisotropy is removed and the planar
ABSTRACT The appearance of magnetism in otherwise non-magnetic materials has recently been report... more ABSTRACT The appearance of magnetism in otherwise non-magnetic materials has recently been reported for a number of nanoscale materials. Coupled with the size-dependent optical and electronic properties of the nanocrystalline materials, this magnetic behavior opens the possibility for an extended range of technological applications. As such, identifying the origin of the magnetism is an extremely important goal, yet this remains the subject of some controversy in the literature. We report evidence that paramagnetism in CdSe QDs can be induced via manipulation of the particle size and surface ligands. Using SQUID magnetometry and x-ray absorption spectroscopy, we demonstrate that the paramagnetic behavior of the CdSe QDs can be varied by changing the ligand endgroup functionality of the passivating layer. Contrary to previous reports, no evidence for ferromagnetism was observed.
We combine x-ray magnetic circular dichroism spectroscopy at Fe L{sub 2,3} edges, at Eu M{sub 4,5... more We combine x-ray magnetic circular dichroism spectroscopy at Fe L{sub 2,3} edges, at Eu M{sub 4,5} edges, x-ray absorption spectroscopy (XAS) investigation of Eu valence, and local spin density calculations, to show that the filled skutterudite Eu{sub 0.95}FeSb is a ferrimagnet in which the Fe 3d moment and the Eu{sup 2+} 4f moment are magnetically ordered with dominant antiferromagnetic coupling. From Eu L edge XAS, we find that about 13% of the Eu have a formal valence of 3{sup +}. We ascribe the origin of ferrimagnetism at a relatively high transition temperature T{sub c} of 85 K in Eu{sub 0.95}FeSb to f-electron interaction with the nearly ferromagnetic [FeSb]{sup 2.2-} host lattice.
Codoping with Co has been shown to promote successful dilution of magnetic dopants of Mn and Fe i... more Codoping with Co has been shown to promote successful dilution of magnetic dopants of Mn and Fe into Ge up to a combined doping level of 15 at. %. Local structure, magnetic moment, and spin-dependant states of these diluted magnetic semiconductors (DMS) have been probed as a function of composition using X-ray and tunneling spectroscopy techniques. Extended X-ray Absorption Fine Structure (EXAFS) measurements reveal an increased level of substitution for each dopant species with respect to traditional single dopant DMS materials. A codoped environment results in 70% of Mn and 90% of Co successfully incorporating substitutionally into the Ge lattice. The remaining dopants are seen to form interstitial dimmers and trimers rather than metallic precipitates. Tunneling spectroscopy measurements on these systems through Al2O3 barriers using both Nb and Fe as spin detectors will be discussed in their correlation with the structural results.
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