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Oscar MOZE

Professore Associato presso: Dipartimento di Scienze Fisiche, Informatiche e Matematiche sede ex-Fisica

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2020 - Coupling Nanostructured CsNiCr Prussian Blue Analogue to Resonant Microwave Fields [Articolo su rivista]
Ghirri, Alberto; Herrero, Christian; Mazérat, Sandra; Mallah, Talal; Moze, Oscar; Affronte, Marco

Collective spin excitations in magnetically ordered materials are exploited for advanced applications in magnonics and spintronics. In these contexts, conditions for minimizing dissipative effects are sought in order to obtain long living excitations that can be coherently manipulated. Organic and coordination magnetic materials may offer alternative options for their flexibility and low spin-orbit effects. Likewise, ferromagnetic nanostructures provide a versatile platform for hybrid architectures, yet downsizing affects the dynamics of magnetic excitations and needs to be controlled. Here we report a systematic investigation on insulating CsNiCr Prussian blue analogue with different degree of nanostructuring. Combining complementary microwave spectroscopic techniques, we performed magnetic resonance in a wide temperature range across the bulk ferromagnetic transition occurring at TC=90 K. This allows us to monitor key parameters of the spin dynamics through different types of nanostructured samples. We found that, below TC, the Gilbert damping parameter of 10 nm nanoparticles compares well (10-3) with values reported for prototypical inorganic analogues (YIG). Strong coupling with the microwave field of a planar microstrip resonator is then observed for bulk CsNiCr as well as for mutually interacting NPs. These results clarify conditions for the coherent manipulation of collective spin degrees of freedom in nanostructured coordination materials.

2008 - From single-molecule magnetism to long-range ferromagnetism in Hpyr [Fe17 O16 (OH) 12 (py) 12 Br4] Br4 [Articolo su rivista]
Vecchini, C.; Ryan, D. H.; Cranswick, L. M. D.; Evangelisti, M.; Kockelmann, W.; Radaelli, P. G.; Candini, A.; Affronte, M.; Gass, I. A.; Brechin, E. K.; Moze, O.

The molecular magnet Hpyr [Fe17 O16 (OH) 12 (py) 12 Br4] Br4 (" Fe17 ") has a well-defined cluster spin ground state of S=35/2 at low temperatures and an axial molecular anisotropy of only D-0.02K. Dipolar interactions between the molecular spins induce long-range magnetic order below 1.1 K. We report here the magnetic structure of Fe17, as determined by unpolarized neutron diffraction experiments performed on a polycrystalline sample of deuterated Fe17 in zero applied magnetic field. In addition, we report bulk susceptibility, magnetization, and specific heat data. The temperature dependence of the long-range magnetic order has been tracked and is well accounted for within mean-field theory. Ferromagnetic order along the crystallographic c axis of the molecular spins, as determined by the neutron diffraction experiments, is in agreement with ground-state dipolar energy calculations. © 2008 The American Physical Society.

2006 - Dipolar correlations in a nanocomposite: A neutron scattering study of Nanoperm Fe89Zr7B3Cu [Articolo su rivista]
Michels, A; Vecchini, C; Moze, Oscar; Suzuki, K; Pranzas, Pk; Kohlbrecher, J; Weissmuller, J.

We present results for the magnetic-field, temperature, and neutron-polarization dependence of the small-angle neutron scattering intensity in the soft magnetic iron-based nanocomposite Nanoperm (Fe89Zr7B3Cu). An unusual clover-leaf-shaped intensity distribution on the detector is attributed to the dipolar stray fields around the nanosized iron particles, which are embedded in an amorphous magnetic matrix of lesser saturation magnetization. The dipole field induces spin disorder, correlating the spin misalignment of neighboring particles and matrix over several particle spacings. The clover-leaf-shaped anisotropy is observed over a wide range of applied magnetic field and momentum transfer. It persists up to several hundred degrees Kelvin above the Curie temperature of the matrix phase, indicating that some degree of magnetic coupling persists even when the matrix is paramagnetic.

2005 - Dipole-field-induced spin disorder in a nanocomposite soft magnet [Articolo su rivista]
Michels, A; Vecchini, C; Moze, Oscar; Suzuki, K; Cadogan, Jm; Pranzas, Pk; Weissmuller, J.

We report on a study of a magnetic nanocomposite of the Nanoperm type (Fe89Zr7B3Cu1) by magnetic small-angle neutron scattering (SANS). The understanding of the magnetic microstructure of these materials leaves much to be desired since we lack techniques capable of resolving the spin structure in the bulk with nanoscale resolution. Here, we present an analysis of the SANS signal by which one cannot only characterise the nanoscale structure of the spin system, but which allows to identify origin and structure of the perturbing field. In Nanoperm, an unusual angular anisotropy of the scattering suggests that the local spin misalignment decorates, as the most important perturbing field, dipole stray fields around the crystalline phase of the composite.

2005 - Neutron scattering and modeling of dipole-field-induced spin disorder in Nanoperm [Articolo su rivista]
Vecchini, C; Moze, Oscar; Suzuki, K; Pranzas, Pk; Weissmuller, J; Michels, A.

We present magnetic-field-dependent small-angle neutron scattering data for the ferromagnetic nanocomposite Nanoperm (Fe89Zr7B3Cu1). The spin-misalignment scattering in the approach-to-saturation regime unexpectedly reveals pronounced lobes of high intensity at angles +/- 30-40 degrees relative to the magnetic-field axis. Based on numerical calculations, the four-fold angular symmetry of the scattering pattern can be explained in terms of local spin misalignment, which originates from dipolar stray fields due to the mismatch of the saturation-magnetization values between the bcc Fe particles and the amorphous magnetic matrix.