Magnetic nanogranular materials, viz. systems made of nanosized magnetic (M) particles dispersed in a non magnetic (NM) matrix, belong to a class of materials that show an enhanced magnetoresistive effect, the so called giant magnetoresistance (GMR). In particular, in nanogranular systems the M/NM interface area is high and so the spin-dependent scattering that originates GMR is promoted. GMR intensity and efficiency are related to the magnetic and structural properties of the granular samples, and in this paper we focus on this latter topic. More in detail we study how the structural features, the growth process and, along with that, interfacial roughness, are related to nanoparticle size. In this paper, we concentrate on samples produced combining the typical multilayer stacking with the presence of very thin M layers [1]. Actually, below a critical thickness a layer fragmentation process is induced and a granular arrangement of the magnetic species is obtained. We investigated Co/Cu fragmented multilayers, and we followed the structure and interfacial roughness evolution as the thickness of the Co layers is reduced, viz. changing M particles average size. This was possible as, thanks to the inner vertical periodicity of the samples, we used structural techniques such as X-Ray specular reflectivity and grazing incidence small angle X-Ray (GISAXS) scattering to probe the vertical arrangement of the nanograins and the self- and cross-correlation of M/NM interfaces. Due to the small difference between Co and Cu electronic density, the measurements were performed in anomalous conditions, i.e. tuning X-Ray energy in order to enhance the otherwise poor optical contrast. The nanocrystalline structure of the samples was investigated with diffraction measurements, performed both in grazing incidence as well as in the usual theta-2theta configuration; details about the way in which the growth process of the granular multilayers develops and influences samples structure were accessed, as well, since GISAXS patterns reflect the universality class which the growth process belongs to [2]. The findings deduced from the X-Ray analysis will be presented and compared with the magnetic and magnetoresistive properties of the granular samples. [1] G. Turilli, L. Pareti, and L. Castaldi, Superlattices and microstructures 25, 591 (1999). F. Casoli et al., J. Magn. Magn. Mat. 262/1, 69 (2003). [2] R. Paniago et al., Phys. Rev. B 56(20) 13442 (1997).
X-Ray structural investigation of Co/Cu granular multilayers with GMR
SPIZZO, Federico;RONCONI, Franco;
2009
Abstract
Magnetic nanogranular materials, viz. systems made of nanosized magnetic (M) particles dispersed in a non magnetic (NM) matrix, belong to a class of materials that show an enhanced magnetoresistive effect, the so called giant magnetoresistance (GMR). In particular, in nanogranular systems the M/NM interface area is high and so the spin-dependent scattering that originates GMR is promoted. GMR intensity and efficiency are related to the magnetic and structural properties of the granular samples, and in this paper we focus on this latter topic. More in detail we study how the structural features, the growth process and, along with that, interfacial roughness, are related to nanoparticle size. In this paper, we concentrate on samples produced combining the typical multilayer stacking with the presence of very thin M layers [1]. Actually, below a critical thickness a layer fragmentation process is induced and a granular arrangement of the magnetic species is obtained. We investigated Co/Cu fragmented multilayers, and we followed the structure and interfacial roughness evolution as the thickness of the Co layers is reduced, viz. changing M particles average size. This was possible as, thanks to the inner vertical periodicity of the samples, we used structural techniques such as X-Ray specular reflectivity and grazing incidence small angle X-Ray (GISAXS) scattering to probe the vertical arrangement of the nanograins and the self- and cross-correlation of M/NM interfaces. Due to the small difference between Co and Cu electronic density, the measurements were performed in anomalous conditions, i.e. tuning X-Ray energy in order to enhance the otherwise poor optical contrast. The nanocrystalline structure of the samples was investigated with diffraction measurements, performed both in grazing incidence as well as in the usual theta-2theta configuration; details about the way in which the growth process of the granular multilayers develops and influences samples structure were accessed, as well, since GISAXS patterns reflect the universality class which the growth process belongs to [2]. The findings deduced from the X-Ray analysis will be presented and compared with the magnetic and magnetoresistive properties of the granular samples. [1] G. Turilli, L. Pareti, and L. Castaldi, Superlattices and microstructures 25, 591 (1999). F. Casoli et al., J. Magn. Magn. Mat. 262/1, 69 (2003). [2] R. Paniago et al., Phys. Rev. B 56(20) 13442 (1997).I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
