181 research outputs found
The multiferroic phase of DyFeO:an ab--initio study
By performing accurate ab-initio density functional theory calculations, we
study the role of electrons in stabilizing the magnetic-field-induced
ferroelectric state of DyFeO. We confirm that the ferroelectric
polarization is driven by an exchange-strictive mechanism, working between
adjacent spin-polarized Fe and Dy layers, as suggested by Y. Tokunaga [Phys.
Rev. Lett, \textbf{101}, 097205 (2008)]. A careful electronic structure
analysis suggests that coupling between Dy and Fe spin sublattices is mediated
by Dy- and O- hybridization. Our results are robust with respect to the
different computational schemes used for and localized states, such as
the DFT+ method, the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional and the
GW approach. Our findings indicate that the interaction between the and
sublattice might be used to tailor ferroelectric and magnetic properties of
multiferroic compounds.Comment: 6 pages, 4 figures-Revised versio
Exchange bias and interface electronic structure in Ni/Co3O4(011)
A detailed study of the exchange bias effect and the interfacial electronic
structure in Ni/Co3O4(011) is reported. Large exchange anisotropies are
observed at low temperatures, and the exchange bias effect persists to
temperatures well above the Neel temperature of bulk Co3O4, of about 40 K: to
~80 K for Ni films deposited on well ordered oxide surfaces, and ~150 K for Ni
films deposited on rougher Co3O4 surfaces. Photoelectron spectroscopy
measurements as a function of Ni thickness show that Co reduction and Ni
oxidation occur over an extended interfacial region. We conclude that the
exchange bias observed in Ni/Co3O4, and in similar ferromagnetic metallic/Co3O4
systems, is not intrinsic to Co3O4 but rather due to the formation of CoO at
the interface.Comment: 8 pages, 6 figures. Accepted for publication in Physical Review B
Magnetic entropy changes in nanogranular Fe:Ni\u3csub\u3e61\u3c/sub\u3eCu\u3csub\u3e39\u3c/sub\u3e
Artificial environment-friendly Gd-free magnetic nanostructures for magnetic cooling are investigated by temperature-dependent magnetic measurements. We consider two-phase nanocomposites where nanoclusters (Fe) are embedded in a Ni61Cu39 matrix. Several composite films are produced by cluster deposition. The average Fe cluster size depends on the deposition conditions and can be tuned by varying the deposition conditions. The quasiequilibrium Curie temperature of the Fe particles is high, but slightly lower than that of bulk Fe due to finite-size effects. Our experiments have focused on ensembles of 7.7 nm Fe clusters in a matrix with a composition close to Ni61Cu39, which has a TC of 180 K. The materials are magnetically soft, with coercivities of order 16 Oe even at relatively low temperature of 100 K. The entropy changes are modest, –ΔS = 0.05 J/kg K in a field change of 1 T and 0.30 J/kg K in a field change of 7 T at a temperature of 180 K, which should improve if the cluster size is reduced
Magnetic entropy changes in nanogranular Fe:Ni\u3csub\u3e61\u3c/sub\u3eCu\u3csub\u3e39\u3c/sub\u3e
Artificial environment-friendly Gd-free magnetic nanostructures for magnetic cooling are investigated by temperature-dependent magnetic measurements. We consider two-phase nanocomposites where nanoclusters (Fe) are embedded in a Ni61Cu39 matrix. Several composite films are produced by cluster deposition. The average Fe cluster size depends on the deposition conditions and can be tuned by varying the deposition conditions. The quasiequilibrium Curie temperature of the Fe particles is high, but slightly lower than that of bulk Fe due to finite-size effects. Our experiments have focused on ensembles of 7.7 nm Fe clusters in a matrix with a composition close to Ni61Cu39, which has a TC of 180 K. The materials are magnetically soft, with coercivities of order 16 Oe even at relatively low temperature of 100 K. The entropy changes are modest, –ΔS = 0.05 J/kg K in a field change of 1 T and 0.30 J/kg K in a field change of 7 T at a temperature of 180 K, which should improve if the cluster size is reduced
Follow-up Study to Evaluate the Long-term Safety and Efficacy of Darvadstrocel (Mesenchymal Stem Cell Treatment) in Patients With Perianal Fistulizing Crohn’s Disease: ADMIRE-CD phase 3 randomized controlled trial
BACKGROUND: Darvadstrocel is an expanded allogeneic adipose-derived mesenchymal stem cell therapy for the treatment of complex perianal fistulas in patients with Crohn’s disease. Safety and efficacy outcomes from the clinical trial known as “Adipose derived mesenchymal stem cells for induction of remission in perianal fistulizing Crohn’s disease,” or ADMIRE-CD (NCT01541579), from up to 52 weeks posttreatment were previously reported. Here, the outcomes from an extended 104-week follow-up are reported. OBJECTIVE: The goal of this study was to assess the long-term safety and efficacy of darvadstrocel at 2 years post-treatment in patients with Crohn’s disease and complex perianal fistulas. DESIGN: This was a phase 3 double-blind randomized controlled study (ADMIRE-CD) in patients with perianal fistulizing Crohn’s disease. SETTINGS: This study extension was conducted in multiple hospitals across 7 European countries and Israel. PATIENTS: Forty patients entered the extended follow-up period: 25 patients in the darvadstrocel treatment group and 15 in the control group. INTERVENTIONS: Darvadstrocel or saline solution (control group) was administered once, locally, after fistula tract curettage and internal opening closure (with previous seton placement). All patients were permitted to continue ongoing medical treatments for fistulas. MAIN OUTCOME MEASURES: Treatment-emergent serious adverse events were recorded through week 104. Clinical remission, defined as closure of all treated external openings that were draining at baseline despite gentle finger compression, was assessed at week 104. RESULTS: Of 40 patients, 37 completed the extended follow-up. Through week 104, 7 treatment-emergent serious adverse events were reported, of which 4 occurred between weeks 52 and 104. At week 104, clinical remission was reported in 14/25 (56%) patients in the darvadstrocel group and 6/15 (40%) patients in the control group. LIMITATIONS: Limitations include the small number of patients who entered the extended follow-up period, and no imaging examinations were performed at the 104-week time point. CONCLUSIONS: Darvadstrocel was well tolerated and clinical remission after treatment with darvadstrocel may be sustained for up to 104 weeks in patients with perianal fistulizing Crohn’s disease
Electric field effects on magnetotransport properties of multiferroic Py/YMnO3/Pt heterostructures
We report on the exchange bias between antiferromagnetic and ferroelectric
hexagonal YMnO3 epitaxial thin films sandwiched between a metallic electrode
(Pt) and a soft ferromagnetic layer (Py). Anisotropic magnetoresistance
measurements are performed to monitor the presence of an exchange bias field.
When the heteroestructure is biased by an electric field, it turns out that the
exchange bias field is suppressed. We discuss the dependence of the observed
effect on the amplitude and polarity of the electric field. Particular
attention is devoted to the role of current leakage across the ferroelectric
layer.Comment: Accepted for publication in Philosophical Magazine Letters (Special
issue on multiferroics
Robust isothermal electric switching of interface magnetization: A route to voltage-controlled spintronics
Roughness-insensitive and electrically controllable magnetization at the
(0001) surface of antiferromagnetic chromia is observed using magnetometry and
spin-resolved photoemission measurements and explained by the interplay of
surface termination and magnetic ordering. Further, this surface in placed in
proximity with a ferromagnetic Co/Pd multilayer film. Exchange coupling across
the interface between chromia and Co/Pd induces an electrically controllable
exchange bias in the Co/Pd film, which enables a reversible isothermal (at room
temperature) shift of the global magnetic hysteresis loop of the Co/Pd film
along the magnetic field axis between negative and positive values. These
results reveal the potential of magnetoelectric chromia for spintronic
applications requiring non-volatile electric control of magnetization.Comment: Single PDF file: 27 pages, 6 figures; version of 12/30/09; submitted
to Nature Material
Large Orbital Magnetic Moment and Coulomb Correlation effects in FeBr2
We have performed an all-electron fully relativistic density functional
calculation to study the magnetic properties of FeBr2. We show for the first
time that the correlation effect enhances the contribution from orbital degrees
of freedom of electrons to the total magnetic moment on Fe as
opposed to common notion of nearly total quenching of the orbital moment on
Fe site. The insulating nature of the system is correctly predicted when
the Hubbard parameter U is included. Energy bands around the gap are very
narrow in width and originate from the localized Fe-3 orbitals, which
indicates that FeBr2 is a typical example of the Mott insulator.Comment: 4 pages, 3 figures, revtex4, PRB accepte
Quantum Spin Glasses
Ising spin glasses in a transverse field exhibit a zero temperature quantum
phase transition, which is driven by quantum rather than thermal fluctuations.
They constitute a universality class that is significantly different from the
classical, thermal phase transitions. Most interestingly close to the
transition in finite dimensions a quantum Griffiths phase leads to drastic
consequences for various physical quantities: for instance diverging magnetic
susceptibilities are observable over a whole range of transverse field values
in the disordered phase.Comment: 10 pages LaTeX (Springer Lecture Notes style file included), 1
eps-figure; Review article for XIV Sitges Conference: Complex Behavior of
Glassy System
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