Bernat Bozzo

• PhD in Materials Science
• R&D Manager at Spanish National Research Council

We present a broadband ferromagnetic resonance study of the Gilbert damping enhancement (Δα) due to spin pumping in NiFe/Pt bilayers. The bilayers, which have negligible interfacial spin memory loss, are studied as a function of the Pt layer thickness (tPt) and temperature (100–293 K). Within the framework of diffusive spin pumping theory, we demon...

We present a broadband ferromagnetic resonance study of the Gilbert damping enhancement ($\Delta \alpha$) due to spin pumping in NiFe/Pt bilayers. The bilayers, which have negligible interfacial spin memory loss, are studied as a function of the Pt layer thickness ($t_{\text{Pt}}$) and temperature (100-293 K). Within the framework of diffusive spin...

The temperature dependence of the spin pumping process in Fe80Ni20 (Py)/Pt bilayers is analyzed for different Pt capping layer thickness. Samples have been grown by means of dc magnetron sputtering, at room temperature, on top of Si substrates. In order to get an optimized interface between the Py and the Pt layers, the Pt capping layers were depos...

In this work we report on the epitaxial growth of La2NiMnO6 double perovskite thin films on top of (001) oriented SrTiO3 substrates by RF magnetron sputtering. The influence of oxygen pressure (PO2) and growth temperature on the microstructure, stoichiometry of the films and magnetic and transport properties is thoroughly investigated. It is found...

Modulation of carrier concentration in strongly correlated oxides offers the unique opportunity to induce different phases in the same material which dramatically change their physical properties, providing novel concepts in oxide electronic devices with engineered functionalities. This work reports on the electric manipulation of the superconducti...

Multiple spin functionalities are probed on Pt/La2Co0.8Mn1.2O6/Nb:SrTiO3, a device composed by a ferromagnetic insulating barrier sandwiched between non-magnetic electrodes. Uniquely, La2Co0.8Mn1.2O6 thin films present strong perpendicular magnetic anisotropy of magnetocrystalline origin, property of major interest for spintronics. The junction has...

Cobalt-based oxides are attracting the interest as strongly coupled spin-lattice-charge systems due to the relevance of the cobalt spin state for their functional properties. In addition, different inorganic structures containing cobalt are being investigated as multiferroic systems or responsive magnetoelectric compounds. The relationship between...

X-ray absorption spectroscopy was used to determine the valence state in La$_2$Co$_{1-x}$Mn$_{1+x}$O$_6$ ($x\approx 0.23$) thin films. We found that in spite of the non-stoichiometry, Co is in a divalent state while Mn ions show a mixed valence state. The relation of this finding with the magnetic properties of the films is discussed. X-ray magneti...

X-ray absorption spectroscopy was used to determine the valence state in La$_2$Co$_{1-x}$Mn$_{1+x}$O$_6$ ($x\approx 0.23$) thin films. We found that in spite of the non-stoichiometry, Co is in a divalent state while Mn ions show a mixed valence state. The relation of this finding with the magnetic properties of the films is discussed. X-ray magneti...

The fabrication procedure of hollow iron oxide nanoparticles with a large surface to volume ratio by a single-step gas condensation process at ambient temperature is presented. Fe clusters formed during the sputtering process are progressively transformed into hollow cuboids with oxide shells by the Kirkendall mechanism at the expense of oxygen cap...

Antiferromagnetic spintronics is an emerging field; antiferromagnets can improve the functionalities of ferromagnets with higher response times, and having the information shielded against external magnetic field. Moreover, a large list of aniferromagnetic semiconductors and metals with N\'eel temperatures above room temperature exists. In the pres...

In half-doped Pr0.50A0.50CoO3 metallic perovskites, the spin-lattice coupling brings about distinct magnetostructural transitions for A=Ca and A=Sr at temperatures close to 100 K. However, the ground magnetic properties of Pr0.50Sr0.50CoO3 (PSCO) strongly differ from Pr0.50Ca0.50CoO3 ones, where a partial Pr3+ to Pr4+ valence shift and Co spin tran...

LnCrO3-xNx perovskites with Ln = La, Pr and Nd and nitrogen contents up to x = 0.59 have been synthesised through ammonolysis of LnCrO4 precursors. These new materials represent one of the few examples of chromium oxynitrides. Hole-doping through O2-/N3- anion substitution suppresses the magnetic transition far less drastically than Ln3+/M2+ (M = C...

Ferromagnetic insulating La$_2$CoMnO$_{6-\epsilon}$ (LCMO) epitaxial thin films grown on top of SrTiO$_3$ (001) substrates presents a strong magnetic anisotropy favoring the out of plane orientation of the magnetization with a strong anisotropy field ($\sim 70$ kOe for film thickness of about 15 nm) and with a coercive field of about 10 kOe. The an...

Ferromagnetic insulating La$_2$CoMnO$_{6-\epsilon}$ (LCMO) epitaxial thin films grown on top of SrTiO$_3$ (001) substrates presents a strong magnetic anisotropy favoring the out of plane orientation of the magnetization with a strong anisotropy field ($\sim 70$ kOe for film thickness of about 15 nm) and with a coercive field of about 10 kOe. The an...

We report on magnetotransport properties on La0.7Sr0.3MnO3/MgO/Fe tunnel junctions grown epitaxially on top of (001)-oriented SrTiO3 substrates by sputtering. It is shown that the magnetoresistive response depends critically on the MgO/Fe interfacial properties. The appearance of an FeOX layer by the interface destroys the �1 symmetry filtering eff...

A systematic study of the growth process of LaMnO3 (LMO) thin films, by pulsed laser deposition, on top of SrTiO3 substrates under different oxygen partial pressures (PO2) is reported. It is found that the accommodation of the orthorhombic LMO phase onto the cubic STO structure, i.e., the amount of structural strain, is controlled by the background...

Two successive magnetic transitions of Pr0.50Sr0.50CoO3 contrast with the single ferromagnetic transition in other Ln0.50Sr0.50CoO3 compounds.

The Pr0.50Sr0.50CoO3 perovskite exhibits unique magnetostructural properties among the rest of the ferromagnetic/metallic Ln0.50Sr0.50CoO3 compounds. Existing reports are largely controversial. We have determined and described its structural evolution, which follows the Pm3̅m → R3̅c → Imma → I4/mcm transformations. The structural changes have been...

In this work we report on a combined macro, micro and nanoscale investigation where electronic transport properties through La⅔Sr⅓MnO3 (LSMO) microfabricated bridges, in which nano-sized resistive states are induced by using a conducting scanning probe microscope (C-SPM), are analyzed. The strategy intentionally avoids the standard capacitor-like g...

We report on the magnetic and structural properties of ferromagnetic-insulating La$_2$CoMnO$_6$ thin films grown on top of (001) STO substrates by means of RF sputtering technique. Careful structural analysis, by using synchrotron X-ray diffraction, allows identifying two different crystallographic orientations that are closely related to oxygen st...

We present a comparative study of the magnetic transitions in metallic Pr0.50Sr0.50CoO3 (PSCO) perovskites prepared in polycrystalline and thin film forms. As the bulk system, the strained epitaxial PSCO (010) film grown on LAO (100) is metallic in all the temperature range, with a ferromagnetic transition at 225 K, close to Tc ̃ 235 K in the ceram...

A route to engineer the intrinsic colossal magnetoresistance (CMR) response in manganite thin films through an accurate control of the growth kinetics is presented. It is shown that under specific growth conditions, a particular strained state, substantially different from that of bulk-like materials and standard films, can be quenched up to film t...

Oxide-based resistive switching memories (RRAMs) or memristors based on metal oxides have been recently shown to have excellent properties in terms of switching speed, endurance and low programming energy. This chapter presents a numerical model for ion migration in bipolar resistive switching devices. Experimental data were collected on metal-insu...

Electroresistance phenomena have been investigated in La2/3Sr1/3MnO3 (LSMO) microbridges through the analysis of I-V characteristic curves. I-V curves are nonlinear in all the range of temperatures explored, but are almost reversible and exhibit origin symmetry which suggest the existence of Joule self-heating effects. However, comparing the resist...

The effect of Gd2Ba6Al4O15 powder addition on microstructure, field trapping capability and critical transition temperature, Tc, of GdBCO–Ag superconductors grown in air is reported. Single-grain GdBCO–Ag bulk superconductors with different amounts of Gd2Ba6Al4O15 powder were fabricated by the top seeded melt growth process. Addition of 0.3 wt% Gd2...

Transport properties of high quality La2/3Sr2/3MnO3 (LSMO) thin films are studied by using Conducting Scanning Force Microscopy (C-SFM) measurements. Current images were acquired in a non-invasive manner by using the contact operation mode at the lowest possible applied load needed. LSMO thin film surface consists of one unit cell steps separating...

The ac susceptibility and magnetization curves of a glued Dy(2)O(3) powder sample are measured by an ac susceptometer and a dc superconducting quantum interference device magnetometer, both of which have been calibrated previously. It is shown that the magnetic moment of the paramagnetic sample as a function of field and temperature may be accurate...

The mech. properties of melt-textured YBCO bulk boundaries are a topic of special interest esp. in the manufg. of superconductor devices for engineering applications. Instrumented indentation technique is a powerful tool widely employed to characterize the mech. properties of small vols. We presented results of the nanohardness (H) and Young's modu...

Superconducting welding of bulk YBCO is a key technology allowing the fabrication of large, complex-shaped pieces for applications such as levitation, bearings or large magnets. Ideally, the electrical and mechanical properties of welds should be comparable to that of the joint grains. In this paper, we have investigated the correlation between the...

Magnetic Hall probe microscopy in combination with an inverse problem solver was used to simultaneously determine the intragranular and intergranular critical current density dependences on the applied field of YBCO melt-textured welds with [001]-misorientation angles from 0° to 30°. This methodology enabled us to investigate the pinning mechanisms...

The microstructure of welds parallel to the {100} and the {110} crystal planes of the single-grain YBa2Cu3O7/Y2BaCuO5 (Y123/Y211) bulk superconductors welded by Ag foil has been studied. It is shown that a zone free of small Y211 particles is formed along the both sides of the welds. Formation of this zone is explained by higher Y content in the me...

A Bean model-based program (“Trazacorrientes”®) has been used to simulate the current distribution in the saturated remanent state of type-II superconducting bicrystal-like squared samples. The grain boundary was modeled by a set of periodically spaced holes geometrically defining the current transparency. Current simulations performed as a functio...

Three half-half jointed melt-textured YBCO rings have been prepared and their ac susceptibility X has been measured at 77 K as a function of field amplitude H and frequency f. All the half rings have their c-axis along the ring axis and there is a nonzero a(b)-axis misalignment angle phi between the two jointed halves. It is found that chi(H-m) is...

The oxygenation of TSMG YBCO bulk superconductor at 450degC was studied by thermogravimetry and optical microscopy. It is shown that the observed deviation from the parabolic dependence of the sample weight on time can be related to cracking induced during the first oxygenation of as grown tetragonal sample. The development of cracks along the {100...

Nondestructive testing of superconducting blocks and thin films is a worth point in their development and their industrial production. The most intrinsic characteristic to be tested is the critical current, so is the maximum current can be carried in the superconducting state. The measurement of the current flowing through the samples could be done...

The microstructural and magnetic properties of YBa2Cu3O7 (YBCO) welds with different crystallographic [001]-tilt misorientation, prepared by the Ag surface melting induced welding technique, have been studied. The inter- and intra-grain critical current densities have been simultaneously obtained by solving the Inverse Problem from the remanent loc...

We present the latest progress of our computation method for critical currents in bulk YBCO samples from magnetic field measurements with Hall probe, based on discretization of the magnetization M and resolution of the linearized inverse Biot-Savart problem by QR inversion. While computationally harder than other linear/FFT methods, it is more robu...

Magnetic Hall probe microscopy constitutes an excellent method for the investigation of the spatially distributed magnetic properties of superconducting materials. We have developed a Hall probe magnetic imaging system that can operate in varying fields up to 1 T (at 77 K), allowing to study the dynamics of the magnetization distribution with the f...

A method for determining simultaneously the inter- and intra-grain critical currents has been developed in welded YBa2Cu3O7 (YBCO) ceramics by solving the Inverse Problem for local maps of the magnetic field in the remanent state. From that current distribution, the current density flowing through the superconducting weld as well as the current den...

The direct observation of the magnetic field at the surface of SC samples when the field is applied or in the remanent state, allows the observation of the current distribution along the magnetization loop by using inverse problem solvers. Furthermore, the mean value of the field reflects well the magnetization of the sample obtaining the magnetiza...

The interface melting process of melt-textured Y Ba2Cu3O7 induced by Ag foils has been investigated in view of developing a large area welding technology. The influence of the processing methodology and the initial microstructure of the melt-textured ceramics has been considered. High temperature quench experiments have shown that the interface mol...