Characterization of the magnetic interactions of multiphase magnetocaloric materials using first-order reversal curve analysis

In order to understand the magnetocaloric response of materials, it is important to analyze the interactions between the different phases present in them. Recent models have analyzed the influence of these interactions on the magnetocaloric response of composites, providing an estimate value of the interaction field that is consistent with experimental results. This paper analyzes to which extent magnetization first-order reversal curve (FORC) method can be used to calculate these interactions. It is shown that the different field ranges that are explored using these techniques (inside the hysteretic region for FORC; close to magnetic saturation for magnetocaloric effect) produce interaction field values that differ in order of magnitude, with FORC being sensitive to the lower values of the interaction field and magnetocaloric analysis accounting for the larger interactions

Magnetic domain size tuning in asymmetric Pd/Co/W/Pd multilayers with perpendicular magnetic anisotropy

CAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOMagnetic multilayers presenting perpendicular magnetic anisotropy (PMA) have great potential for technological applications. On the path to develop further magnetic devices, one can adjust the physical properties of multilayered thin films by modifying their interfaces, thus determining the magnetic domain type, chirality, and size. Here, we demonstrate the tailoring of the domain pattern by tuning the perpendicular anisotropy, the saturation magnetization, and the interfacial Dzyaloshinskii-Moriya interaction (iDMI) in Pd/Co/Pd multilayers with the insertion of an ultrathin tungsten layer at the top interface. The average domain size decreases around 60% when a 0.2 nm thick W layer is added to the Co/Pd interface. Magnetic force microscopy images and micromagnetic simulations were contrasted to elucidate the mechanisms that determine the domain textures and sizes. Our results indicate that both iDMI and PMA can be tuned by carefully changing the interfaces of originally symmetric multilayers, leading to magnetic domain patterns promising for high density magnetic memories.1151816CAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO0012012/51198-22017/10581-1309354/2015-3302950/2017-6436573/2018-

Microscopic reversal magnetization mechanisms in CoCrPt thin films with perpendicular magnetic anisotropy: Fractal structure versus labyrinth stripe domains

The magnetization reversal of CoCrPt thin films has been examined as a function of thickness using magneto-optical Kerr effect (MOKE) microscopy and first-order reversal curves (FORC) techniques. MOKE images show differentiated magnetization reversal regimes for different film thicknesses: while the magnetic domains in 10-nm-thick CoCrPt film resemble a fractal structure, a labyrinth stripe domain configuration is observed for 20-nm-thick films. Although FORC distributions for both cases show two main features related to irreversible processes (propagation and annihilation fields) separated by a mostly flat region, this method can nonetheless distinguish which magnetization reversal process is active according to the horizontal profile of the first FORC peak, or propagation field. A single-peak FORC profile corresponds to the fractal magnetization reversal, whereas a flat-peak FORC profile corresponds to the labyrinth magnetization reversal

Microscopic reversal magnetization mechanisms in CoCrPt thin films with perpendicular magnetic anisotropy: fractal structure versus labyrinth stripe domains

Sem informaçãoThe magnetization reversal of CoCrPt thin films has been examined as a function of thickness using magneto-optical Kerr effect (MOKE) microscopy and first-order reversal curves (FORC) techniques. MOKE images show differentiated magnetization reversal regimes for different film thicknesses: while the magnetic domains in 10-nm-thick CoCrPt film resemble a fractal structure, a labyrinth stripe domain configuration is observed for 20-nm-thick films. Although FORC distributions for both cases show two main features related to irreversible processes (propagation and annihilation fields) separated by a mostly flat region, this method can nonetheless distinguish which magnetization reversal process is active according to the horizontal profile of the first FORC peak, or propagation field. A single-peak FORC profile corresponds to the fractal magnetization reversal, whereas a flat-peak FORC profile corresponds to the labyrinth magnetization reversal.961815Sem informaçãoSem informaçãoSem informaçãoThis work was supported by Spanish Grants No. AEI FIS2013-45469 and No. AEI FIS2016-76058, and UE FEDER “Una manera de hacer Europa”, the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No. 734801. D.N. thanks Fundaçao para a Ciência e Tecnologia (Contract No. IF/01191/2013) for financial support

Magnetization reversal and exchange bias effects in hard/soft ferromagnetic bilayers with orthogonal anisotropies

21 p.The magnetization reversal processes are discussed for exchange-coupled ferromagnetic hard/soft bilayers made from Co0.66Cr0.22Pt0.12 (10 and 20 nm)/Ni (from 0 to 40 nm) films with out-of-plane and in-plane magnetic easy axes respectively, based on room temperature hysteresis loops and first-order reversal curve analysis. On increasing the Ni layer thicknesses, the easy axis of the bilayer reorients from out-of-plane to in-plane. An exchange bias effect, consisting of a shift of the in-plane minor hysteresis loops along the field axis, was observed at room temperature after in-plane saturation. This effect was associated with specific ferromagnetic domain configurations experimentally determined by polarized neutron reflectivity. On the other hand, perpendicular exchange bias effect was revealed from the out-of-plane hysteresis loops and it was attributed to residual domains in the magnetically hard layer.CAR and DN gratefully acknowledge the support of the National Science Foundation and the MIT-Spain/La Cambra de Barcelona Seed Fund. CR and DN thank the Ministerio de Economia y Competitividad for financial support (MAT2010-20798-C05-02)

Dimensionality tuning of the electronic structure in Fe3Ga4 magnetic materials

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOThis work reports on the dimensionality effects on the magnetic behavior of Fe3Ga4 compounds by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. Our results show that reducing the Fe3Ga4 dimensionality, via nanowire shape, intriguingly modifies its electronic structure. In particular, the bulk system exhibits two transitions, a ferromagnetic (FM) transition temperature at T-1 = 50 K and an antiferromagnetic (AFM) one at T-2 = 390 K. On the other hand, nanowires shift these transition temperatures, towards higher and lower temperature for T-1 and T-2, respectively. Moreover, the dimensionality reduction seems to also modify the microscopic nature of the T-1 transition. Instead of a FM to AFM transition, as observed in the 3D system, a transition from FM to ferrimagnetic (FERRI) or to coexistence of FM and AFM phases is found for the nanowires. Our results allowed us to propose the magnetic field-temperature phase diagram for Fe3Ga4 in both bulk and nanostructured forms. The interesting microscopic tuning of the magnetic interactions induced by dimensionality in Fe3Ga4 opens a new route to optimize the use of such materials in nanostructured devices.This work reports on the dimensionality effects on the magnetic behavior of Fe3Ga4 compounds by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. Our results show that reducing the Fe3Ga4 dimensionality, via nanowire shape, intriguingly modifies its electronic structure. In particular, the bulk system exhibits two transitions, a ferromagnetic (FM) transition temperature at T-1 = 50 K and an antiferromagnetic (AFM) one at T-2 = 390 K. On the other hand, nanowires shift these transition temperatures, towards higher and lower temperature for T-1 and T-2, respectively. Moreover, the dimensionality reduction seems to also modify the microscopic nature of the T-1 transition. Instead of a FM to AFM transition, as observed in the 3D system, a transition from FM to ferrimagnetic (FERRI) or to coexistence of FM and AFM phases is found for the nanowires. Our results allowed us to propose the magnetic field-temperature phase diagram for Fe3Ga4 in both bulk and nanostructured forms. The interesting microscopic tuning of the magnetic interactions induced by dimensionality in Fe3Ga4 opens a new route to optimize the use of such materials in nanostructured devices.619FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOSem informaçãoSem informaçãoThis work was supported by Brazilian funding agencies Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). The authors would like to acknowledge the Brazilian Nanotechnology National Laboratory (LNNANO) for providing the equipment and technical support for the experiments involving scanning electron microscopy and the Brazilian Synchrotron Light Laboratory (LNLS) for the beamtime (XRD1 16980) and the staff of the XDS Beamline for providing assistance during the experiment. We thank Anna Paula Sotero Levinsky, Junior Cintra Mauricio and Santiago J.A. Figueroa (LNLS) for help in the XAS measurements and data manipulation/analysis

Zinātniskā komunisma jautājumi

CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOIn order to understand the magnetocaloric response of materials, it is important to analyze the interactions between the different phases present in them. Recent models have analyzed the influence of these interactions on the magnetocaloric response of composites, providing an estimate value of the interaction field that is consistent with experimental results. This paper analyzes to which extent magnetization first-order reversal curve (FORC) method can be used to calculate these interactions. It is shown that the different field ranges that are explored using these techniques (inside the hysteretic region for FORC; close to magnetic saturation for magnetocaloric effect) produce interaction field values that differ in order of magnitude, with FORC being sensitive to the lower values of the interaction field and magnetocaloric analysis accounting for the larger interactions. (C) 2015 AIP Publishing LLC.In order to understand the magnetocaloric response of materials, it is important to analyze the interactions between the different phases present in them. Recent models have analyzed the influence of these interactions on the magnetocaloric response of composites, providing an estimate value of the interaction field that is consistent with experimental results. This paper analyzes to which extent magnetization first-order reversal curve (FORC) method can be used to calculate these interactions. It is shown that the different field ranges that are explored using these techniques (inside the hysteretic region for FORCclose to magnetic saturation for magnetocaloric effect) produce interaction field values that differ in order of magnitude, with FORC being sensitive to the lower values of the interaction field and magnetocaloric analysis accounting for the larger interactions.1171714CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO401921/2013-1This work was supported by the Science Without Borders Program of the Brazilian funding agency CNPq (#401921/2013‐1), the Spanish MINECO and EU FEDER (Project No. MAT 2013-45165-P) and the PAI of the Regional Government of Andalucía (Project No. P10-FQM-6462)

Applications in energy and environment of nanocolumnar films

Resumen del trabajo presentado en el CMD30-FisMat 2023 celebrado en Milán (Italia), del 4 al 8 de septiembre de 2023Glancing Angle Deposition (GLAD) with magnetron sputtering (MS) is an easy and versatile route to fabricate nanocolumnar films in large areas (several cm2 and above) in a single-step process, in clear contrast to other techniques in the nanoscale range such as e-beam lithography and ion-beam lithography. The morphology of the nanocolumns can be controlled depending on several parameters such as the gas pressure, the angle of inclination of the substrate and its possible rotation, the electromagnetic power, the deposition time, and the optional use of collimating masks [1-4]. Moreover, as GLAD with MS it is usually carried out at RT and does not involve chemical products (thus, without associated recycling issues), this technique is environmentally friendly. In this talk, I will start explaining the fundamentals of GLAD with MS and then I will present some recent examples of nanocolumnar films that are of interest in the field of energy and environment: Gold nanocolumnar templates for effective chemical sensing by surface-enhanced Raman scattering [5], Iron nanocolumnar films with tailored magnetic behavior [6], and Titanium oxide nanocolumnar films that exhibit photo‐induced self‐cleaning properties [7]. It will be finally shown that this latter effect can be enhanced when the nanocolumns are decorated with gold nanoparticles using a gas aggregation source that is also based on MS. References:[1] R. Alvarez et al., Nanotechnology 24, 045604 (2013). [2] R. Alvarez et al., J. Phys. D: Appl. Phys. 49, 045303 (2016). [3] A. Vitrey et al., Beilstein J. Nanotechnol. 8, 434 (2017).[4] G. Troncoso et al., Appl. Surf. Sci. 526, 146699 (2020).[5] G. Barbillon et al., Nanomaterials 12, 4157 (2022).[6] E. Navarro et al., Nanomaterials 12, 1186 (2022).[7] F. Fresno et al., Adv. Sustainable Syst. 5, 2100071 (2021)