C. Sanchez-Hanke

Mutual ferromagnetic-ferroelectric coupling in multiferroic copper-doped ZnO.

A mutual ferromagnetic and ferroelectric coupling (multiferroic behavior) in Cu‐doped ZnO is demonstrated via deterministic control of Cu doping and defect engineering. The coexistence of multivalence Cu ions and oxygen vacancies is important to multiferroic behaviors in ZnO:Cu. The samples show clear ferroelectric and ferromagnetic domain patterns. These domain structures may be written reversibly via electric and magnetic bias.

Fabrication of Films by Sputtering Process and Experimental Investigation of Origin of Giant Saturation Magnetization in

We present a systematic study to address a longstanding mystery in magnetic materials and magnetism, whether there is giant saturation magnetization in Fe16N2 and why. Experimental results based on sputtered thin film samples are presented. The magnetism of Fe16N2 is discussed systematically from the aspects of material processing, magnetic characterization and theoretical investigation. It is observed that thin films with Fe16N2+Fe8N mixture phases and high degree of N ordering, exhibit a saturation magnetization up to 2.68T at room temperature, which substantially exceeds the ferromagnetism limit based on the traditional band magnetism understanding. From X-ray magnetic circular Dichorism (XMCD) experiment, transport measurement and first-principle calculation based on LDA+U method, it is both experimentally and theoretically justified that the origin of giant saturation magnetization is correlated with the formation of highly localized 3d electron states in this Fe-N system. A large magnetocrystalline anisotropy for such a material is also discussed. Our proposed “cluster+atom” theory provides promising directions on designing novel magnetic materials with unique performances.

Structural ordering effects in Fe nanoparticle two- and three-dimensional arrays

Two- and three-dimensional arrays were prepared by self-assembly of iron nanoparticles with similar magnetic moments and interparticle separations, and characterized both magnetically and structurally. The rapid magnetization decay in the three-dimensional (3D) arrays suggests a relaxation mechanism than has been previously reported, perhaps associated with the existence of domain walls within large structurally ordered regions. Small angle x-ray scattering indicates the presence of such regions in the 3D arrays.

A soft x-ray beamline capable of canceling the performance impairment due to power absorbed on its optical elements

We present an entrance slitless beamline design capable of maintaining its very high performance in terms of energy resolution (>10(4)) and spot size (4x4 microm2) at the sample position despite being exposed to more than 2.15 kW of undulator radiation and a maximum power density on the optics of more than 0.9 W/mm2. Ray tracing simulations of this beamline under the worst-case thermal deformations of the optical element surfaces verify that appropriate focusing corrections are able to cancel the deleterious effects of these deformations. One of the necessary conditions for this cancellation is to illuminate the optical elements with a larger solid angle than the undulators central cone, which contains the usable photons but is considerably smaller than the angular power distribution.

Magnetic force microscopy and x-ray scattering study of 70×550 nm2 pseudo-spin-valve nanomagnets

The room-temperature magnetic properties of large area arrays of 70×550 nm2 nanoelements made from a NiFe 6 nm/ Cu 3 nm/ Co 4 nm multilayer stack have been investigated using magnetic force microscopy (MFM), alternating gradient magnetometry (AGM), and scattering experiments using synchrotron radiation. MFM measurements on individual elements show square major and minor loops, while the collective magnetization reversal, measured from both AGM and elementally specific hysteresis loops obtained from synchrotron scattering experiments, show a wide distribution of switching fields and interaction fields, due to the variability between the elements.

An element-sensitive hysteresis loop study of an exchange-biased Co/NiO bilayer

Abstract An exchange-biased Co/NiO bilayer was studied by measuring element specific hysteresis loops. A phase-sensitive detection scheme based on fast switching of the polarization of the X-rays was developed for this measurement. Uncompensated Ni 2+ spins at the Co/NiO interface were observed for the first time. In addition, part of the Ni 2+ spins were found to switch with the Co layer.

Fabrication of Fe16N2 Films by Sputtering Process and Experimental Investigation of Origin of Giant Saturation Magnetization in Fe16N2

We present a systematic study to address a longstanding mystery in magnetic materials and magnetism, whether there is giant saturation magnetization in Fe16N2 and why. Experimental results based on sputtered thin film samples are presented. The magnetism of Fe16N2 is discussed systematically from the aspects of material processing, magnetic characterization and theoretical investigation. It is observed that thin films with Fe16N2+Fe8N mixture phases and high degree of N ordering, exhibit a saturation magnetization up to 2.68T at room temperature, which substantially exceeds the ferromagnetism limit based on the traditional band magnetism understanding. From X-ray magnetic circular Dichorism (XMCD) experiment, transport measurement and first-principle calculation based on LDA+U method, it is both experimentally and theoretically justified that the origin of giant saturation magnetization is correlated with the formation of highly localized 3d electron states in this Fe-N system. A large magnetocrystalline anisotropy for such a material is also discussed. Our proposed “cluster+atom” theory provides promising directions on designing novel magnetic materials with unique performances.

A Direct Observation of Room-Temperature Stable Magnetism in LaAlO3/SrTiO3 Heterostructures

Along with an unexpected conducting interface between nonmagnetic insulating perovskites LaAlO3 and SrTiO3 (LaAlO3/SrTiO3), striking interfacial magnetisms have been observed in LaAlO3/SrTiO3 heterostructures. Interestingly, the strength of the interfacial magnetic moment is found to be dependent on oxygen partial pressures during the growth process. This raises an important, fundamental question on the origin of these remarkable interfacial magnetic orderings. Here, we report a direct evidence of room-temperature stable magnetism in a LaAlO3/SrTiO3 heterostructure prepared at high oxygen partial pressure by using element-specific soft X-ray magnetic circular dichroism at both Ti L3,2 and O K edges. By combining X-ray absorption spectroscopy at both Ti L3,2 and O K edges and first-principles calculations, we qualitatively ascribe that this strong magnetic ordering with dominant interfacial Ti3+ character is due to the coexistence of LaAlO3 surface oxygen vacancies and interfacial (TiAl-AlTi) antisite defects. On the basis of this new understanding, we revisit the origin of the weak magnetism in LaAlO3/SrTiO3 heterostructures prepared at low oxygen partial pressures. Our calculations show that LaAlO3 surface oxygen vacancies are responsible for the weak magnetism at the interface. Our result provides direct evidence on the presence of room-temperature stable magnetism and a novel perspective to understand magnetic and electronic reconstructions at such strategic oxide interfaces.

Optimization of the Coherent Intensity from Multi‐Segment Undulators by Phase Matching

The use of inline insertion devices at third‐generation synchrotron radiation sources can result in destructive interference effects if the relative phase between the devices is not properly adjusted. The destructive interference can strongly affect the emission spectrum and coherent wavefront of a compound insertion device. We simulate the photon source generated by a dual‐inline elliptically polarizing undulator (EPU) situated in a low‐β straight section of the planned NSLS‐II storage ring and show that a magnetic chicane with adjustable field integral can be used to phase‐match the devices. Furthermore, we show that the maximum coherent intensity is delivered by a focusing x‐ray beamline if the chicane is adjusted to phase‐match the off‐axis and red‐shifted radiation. Such a system will be installed at the coherent soft x‐ray (CSX) beamline of the NSLS‐II in order to provide the highest possible coherent flux for coherent soft x‐ray scattering experiments.

Magnetic leverage effects in amorphous SmCo/CoAlZr heterostructures

Although magnetic heterostructures are the basis of many magnetic technologies, the mechanisms involved in magnetization reversals in such structures are not fully understood, especially in amorphous multilayers. Here, we report on the SmCo/CoAlZr system and exploit resonant magnetic x-ray scattering to probe the element specific magnetization reversals. When combined into a tri-layer structure, two different switching fields and reversal mechanisms are observed for the Sm and Co sub-lattices. We argue that the decoupling of the sub-lattices arises from the local distribution of atomic species within the amorphous matrix leading to a strong magnetic leverage effect and exchange pinning. The decoupling arises due to strong interactions between regions of high Co density which span the interface. The relatively sparse interactions between Sm and Co induce a localized pinning of the Co-rich areas, resulting in an exchange bias in minor loops and an enhanced coercivity.