Study of transitions in intermetallic compounds metamagnéticas R6F14-xAlx (R = Nd, La)

Author(s)

Shintaro Jonen

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Física (IF/SBI)
• Defense date: 2002-03-14

Examining board members

Hercilio Rodolfo Rechenberg; Carlos Castilla Becerra; Paulo Henrique Porcheto Domingues; Alberto Passos Guimarães Filho; João Edgar Schmidt

• Advisor: Hercilio Rodolfo Rechenberg

Abstract

Rare earth-based intermetallic compounds R IND.6Fe IND.14-xAl IND.x with R=(Nd, La) are antiferromagnetic and undergo a metamagnetic transition at 2~3 T applied fields. In order to further characterize their magnetic behavior, polycrystalline samples were investigated with magnetometry, magneto resistance, magnetostriction and neutron diffraction. Samples have been prepared by arc melting under argon and annealed at 750°C for four weeks. The crystal structure is tetragonal of La IND.6Co IND.11Ga IND.3-type (space group 14/mcm). In contrast to La-based compounds, Nd IND.6Fe IND.14-xAl IND.x exhibits a large transition hysteresis and magnetic history effects at T<30 K, and antiferromagnetic ordering of Nd moments at 70 K. The T IND.N was determined by magnetic susceptibility measurements in the 150-310 K and 100-230 K range for the Nd and La compounds, respectively. The metamagnetic transition was observed for all samples and a ~3-5% resistivity drop was found to occur concomitantly, suggesting a magnetic multilayer-like structure. Unfortunately the magnetic structure of this compound could not be determined in this work by neutron diffraction. However, neutron diffraction measurements in the Nd IND.6Fe IND.10Al IND.4 compound revealed a change of space group from 14/mcm to P4 IND.2/mcm at 70 K, where the magnetic susceptibility exhibits a sharp peak. Mossbauer spectroscopy measured in the 4.2-100 K range has shown no evidence of Fe spin rotation, suggesting an isolated Nd phenomenon. Another result from neutron diffraction measurements was the presence of a magnetic (001) reflection that grows below 30 K, indicating the development of a spin component parallel to the basal plane. No such effect was observed with La-based samples. This increase is likely to be due to a canting of Nd moments towards the basal plane. The coincidence of this effect with the onset temperature for irreversible behavior in magnetic measurements is consistent with this interpretation. (AU)