Tuning hyper-Rayleigh scattering amplitude on magnetic colloids by means of an external magnetic field

Author(s)

Goncalves, E. S. ^[1] ; Fonseca, R. D. ^{[2, 3]} ; De Boni, L. ^[2] ; Figueiredo Neto, A. M. ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Fis, Sao Paulo, SP - Brazil

^[2] Univ Sao Paulo, Inst Fis Sao Carlos, Sao Carlos, SP - Brazil

^[3] Univ Popular Cesar, Campus Univ, Valledupar - Colombia

• Document type: Journal article
• Source: JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS; v. 35, n. 11, p. 2681-2689, NOV 1 2018.
• Web of Science Citations: 1

Abstract

The first-order hyperpolarizability beta of magnetite nanoparticles in colloidal dispersion was measured in the presence and absence of an external magnetic field of magnitude H = 800 G, applied with permanent neodymium magnets. For that, the (linear) attenuation spectrum was measured, and the nonlinear properties were obtained through the hyper-Rayleigh scattering technique. The attenuation spectrum is the same regardless of the external magnetic field, indicating that large aggregates of nanoparticles were not formed on our system. The first hyperpolarizability, on the other hand, increased when the incident beam polarization was parallel to the magnetic field lines and decreased when the directions were orthogonal, due to the alignment of crystallographic planes of the material when nanoparticles rotate in order to align their individual magnetic momentum, with respect to the external field. In the absence of a magnetic field, the hyperpolarizability beta(H=0) = 8.5(1) x 10(-28) cm(5)/esu. For the parallel case, beta(||) = 9.8(2) x 10(-28) cm(5)/esu, while for the perpendicular configuration, beta((sic)) = 8.1(1) x 10(-28) cm(5)/esu. Defining the x axis of the particle reference frame parallel to the < 111 > crystallographic direction, which corresponds to the direction of easy magnetization, beta(||) = beta(xxx), and beta(sic) corresponds to an average from beta(yyy) and beta(zzz). When there is no external field applied, the nanoparticles are randomly oriented, and the measured hyperpolarizability corresponds to an average over the three orthogonal directions; that is, <beta(H)> = 1/3(beta(||) + 2 beta((sic))) = 8.6(1) x 10(-28) cm(5)/esu, which is compatible with the measured value for the system without a magnetic field beta(H=0). (c) 2018 Optical Society of America. (AU)

• FAPESP's process: 08/57685-7 - NICT of Complex Fluids (IFCx)
• Grantee: Antonio Martins Figueiredo Neto
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 11/13616-4 - Optical and structural properties of elastomers and complex fluids of biological interest
• Grantee: Antonio Martins Figueiredo Neto
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 15/20555-2 - Second harmonic generation by centrossymetric nanoparticles in magnetic colloids
• Grantee: Eduardo Sell Gonçalves
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 16/20886-1 - Ultrafast nonlinear optical spectroscopy: Transient Absorption and optical Kerr Gate with polarization control
• Grantee: Leonardo de Boni
• Support Opportunities: Regular Research Grants