Inhomogeneous alloying in FePt nanoparticles as a reason for reduced magnetic moments

The reduced magnetic moments of oxide-free FePt nanoparticles are discussed in terms of lattice expansion and local deviation from the averaged composition. By analyses of the extended x-ray absorption fine structure of FePt nanoparticles and bulk material measured both at the Fe K and Pt L(3) absorption edge, the composition within the single nanoparticles is found to be inhomogeneous, i.e. Pt is in a Pt-rich environment and, consequently, Fe is in an Fe-rich environment. The standard Fourier transformation-based analysis is complemented by a wavelet transformation method clearly visualizing the difference in the local composition. The dependence of the magnetic properties, i.e. the element-specific magnetic moments on the composition in chemically disordered Fe(x)Pt(1-x) alloys, is studied by fully relativistic SPR-KKR band structure calculations supported by experimental results determined from the x-ray magnetic circular dichroism of 50 nm thick films and bulk material.

Using magnetic circular dichroism for the study of the magnetization and the magnetic moments of atoms in Nd(3)Fe(27.5)Ti(1.5)

An element-specific study of the Nd(3)Fe(27.5)Ti(1.5) compound using the hard x-ray magnetic circular dichroism (XMCD) technique is presented. The Nd L(2) and L(3) edge XMCD, as well as the Fe K edge XMCD, were measured in a magnetically oriented sample, parallel and perpendicular to its alignment direction. The XMCD spectra were recorded at three different temperatures, above, below and in between the characteristic peaks that the specific compound presents in AC susceptibility measurements. By probing the Nd L edges and the Fe K edge XMCD, we found that the dipolar R(5d)-Fe(3d) exchange interaction behaves differently with temperature change than the Fe-Fe magnetic interaction. Those differences appear to be in the vicinity of the AC susceptibility characteristic peaks. An XMCD signal was recorded at the Ti K edge, revealing a small orbital polarization due to the hybridization with Fe atomic states. This demonstrates the existence of a small finite magnetic moment in Ti atoms.

Low temperature exchange bias in [DyFe(2)/YFe(2)] superlattices: effect of the thermo-magnetic preparation

The effect of the thermo-magnetic preparation on exchange bias is investigated in an exchange-coupled [3 nm DyFe(2)/12 nmYFe(2)](22) superlattice. X-ray magnetic circular dichroism (XMCD) experiments at low temperature reveal that exchange bias originates from the quenched DyFe(2) magnetization, biasing the unpinned YFe(2) reversal. This quenched configuration can be tailored by changing the cooling field or the magnetic preparation at 300 K before zero-field cooling. Changing the amplitude of the cooling field induces interface domain walls and tends to modify the orientation of the pinning moments at the interfaces. This results in the observation of single loops and in the continuous variation of the bias field as a function of the cooling field. A specific magnetic preparation (field cycling) at 300 K induces different remanent states with lateral domains in the pinning layer, which remain unchanged at low temperature after zero-field cooling and behave independently. This gives rise to combined loops, whose shape reflects the domain populations.

Evidence for room-temperature multiferroicity in a compound with a giant axial ratio

In the search for multiferroic materials magnetic compounds with a strongly elongated unit-cell (large axial ratio c/a) have been scrutinized intensely. However, none was hitherto proven to have a switchable polarization, an essential feature of ferroelectrics. Here, we provide evidence for the epitaxial stabilization of a monoclinic phase of BiFeO3 with a giant axial ratio (c/a=1.23) that is both ferroelectric and magnetic at room temperature. Surprisingly, and in contrast with previous theoretical predictions, the polarization does not increase dramatically with c/a. We discuss our results in terms of the competition between polar and antiferrodistortive instabilities and give perspectives for engineering multiferroic phases.

Long range spin ferromagnetic order with zero magnetization in (111)Sm(1-x)Gd(x)Al(2) films

Bulk Sm(1-x)Gd(x)Al(2) (0.01<x<0.035) compound exhibits an exciting magnetic property: its magnetization drops to zero at a compensation temperature T(comp) while it maintains a long range ferromagnetic order. We achieved recently the first epitaxial growth of (111)Sm(1-x)Gd(x)Al(2) films by molecular beam epitaxy. Macroscopic magnetization measurements confirmed the existence of a magnetic compensated state, occurring at a temperature that depends on the concentration of Gd. Specific features observed in the Sm(1-x)Gd(x)Al(2) films are a strong [111] perpendicular anisotropy and a very large coercivity. X-ray magnetic circular dichroism at Sm and Gd L(2,3) edges allows us to directly evidence the existence of a long range magnetic polarization of the Sm and Gd sublattices at T(comp), and a parallel coupling between the total magnetic moment of Sm(3+) and Gd(3+). Moreover, it is possible to tailor the magnetic behavior at T(comp) by changing the thermo-magnetic treatment.

Absence of intrinsic ferromagnetic interactions of isolated and paired Co dopant atoms in Zn1-xCoxO with high structural perfection

We report element specific structural and magnetic investigations on Zn(1-x)Co(x)O epitaxial films using synchrotron radiation. Co dopants exclusively occupy Zn sites as revealed by x-ray linear dichroism having an unprecedented degree of structural perfection. Comparative magnetic field dependent measurements by x-ray magnetic circular dichroism and conventional magnetometry consistently show purely paramagnetic behavior for isolated Co dopant atoms with a magnetic moment of 4.8 (mu B). However, the total magnetization is reduced by approximately 30%, demonstrating that Co-O-Co pairs are antiferromagnetically coupled. We find no sign of intrinsic ferromagnetic interactions for isolated or paired Co dopant atoms in Co:ZnO films.

Element-selective X-ray detected magnetic resonance: a novel application of synchrotron radiation

X-ray detected magnetic resonance (XDMR) is a new element-selective spectroscopy in which X-ray magnetic circular dichroism is used to probe the resonant precession of spin and orbital magnetization components when a strong microwave pump field is applied perpendicularly to the static bias field. Experimental configurations suitable for detecting the very weak XDMR signal are compared. XDMR signatures were measured in yttrium iron garnet and related thin films on exciting not only the iron K-edge but also the yttrium at diamagnetic sites. These measurements are shown to yield unique information regarding the wide-angle precession of induced magnetization components involving either orbital p-projected densities of states at the iron sites, or spin polarized d-projected densities of states at the yttrium sites. Extending XDMR measurements into the millimeter wave range would make it possible to study paramagnetic systems routinely and investigate optical modes as well as acoustic modes in ferrimagnetic/antiferromagnetic systems.

Enhanced orbital magnetism in Fe(50)Pt(50) nanoparticles

X-ray absorption and magnetic circular dichroism spectra at both the Fe and Pt L(3,2) edges were measured on wet-chemically synthesized monodisperse Fe(50)Pt(50) particles with a mean diameter of 6.3 nm before and after complete removal of the organic ligands and the oxide shell covering the particles by soft hydrogen plasma resulting in a pure metallic state. After thermal treatment of the metallic particles, the coercive field increased by a factor of 6, the orbital magnetic moment at the Fe site increased by 330% and is reduced at the Pt site by 30%, while the effective spin moments did not change. A decrease of the frequency of oscillations in the extended x-ray absorption fine structure at the Pt L(3,2) edges provides evidence for crystallographic changes towards the L1(0) phase.

Final results of a randomized study comparing two dosing regimens of epoetin alfa in patients with chemotherapy-induced anemia: 80,000 U every two weeks vs 40,000 U weekly

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Background: Epoetin alfa is typically administered weekly (QW) for the treatment of chemotherapy (CT)-induced anemia. Less frequent dosing can be more convenient for patients (pts) and healthcare providers. This is the first study to examine extended interval initial dosing with epoetin alfa 80,000 U every two weeks (Q2W) vs the standard 40,000 U QW regimen. Methods: This randomized, open-label, 13-week study enrolled pts with non-myeloid malignancies with baseline (BL) hemoglobin (Hb) ≤ 11 g/dL and CT planned for ≥ 12 weeks. Pts were assigned (1:1) to receive epoetin alfa 40,000 U QW or 80,000 U Q2W subcutaneously. Drug was held for Hb > 13 g/dL and dose was reduced for Hb > 12 g/dL or rate of rise > 1 g/dL in any 2-week period. For inadequate Hb response, 80,000 U Q2W pts were switched to 40,000 U QW and 40,000 U QW patients were increased to 60,000 U QW. The primary analysis was a comparison of the mean Hb change from BL to end of study (EOS). Results: 298 pts received ≥ 1 dose of drug (153 Q2W, 145 QW). BL characteristics were comparable between groups: 66% female, overall mean age 62 yrs, and BL Hb 10.0 g/dL. Most common tumor types were breast (25%), NSCLC (15%) and colorectal (14%). Efficacy was analyzed in 295 pts (151 Q2W, 144 QW) who had ≥ 1 post-BL Hb value. The mean Hb change from BL to EOS for Q2W was 1.27 ± 1.48 g/dL compared to 1.28 ± 1.60 g/dL for QW [difference 0, 1-sided 95% CI -0.25,–]. In the per protocol population, the difference in mean Hb change was similar. Mean Hb values over time were also similar between groups. Kaplan-Meier estimates of post-28 day transfusion rates were 11.2% in Q2W vs. 12.0% in QW. Fewer Q2W pts compared to QW pts required dose holds (21% vs 42%) or dose reductions (41% vs 59%). 13% of Q2W pts were switched to QW dosing and 37% of QW pts required a dose increase. The incidences of clinically relevant TVEs and deaths were similar in the Q2W vs QW groups (7.8% vs 7.6% and 6.5% vs 6.2%, respectively). Conclusions: Pts treated with epoetin alfa 80,000 U Q2W demonstrated similar Hb increases, transfusion rates, and safety outcomes compared to pts treated with 40,000 U QW. Epoetin alfa 80,000 U every other week is an effective regimen that may provide a more convenient dosing option for pts with CT-induced anemia.

[Table: see text]