Doctor of Philosophy
Institute for Superconducting and Electronic Materials
The magnetic properties of several rare earth orthoferrites single crystal samples, RFeO3, were studied in this project. RFeO3 compounds show unique spin dynamics, such as reversal of spin (spin flip), spontaneous spin reorientation process and field-induced magnetic transitions. Understanding the exchange interactions behaviour of R-Fe ions through magnetic measurements improves our ability to manipulate spins, and that will be useful for emerging spintronic materials. The effect of R3+ ions on the magnetic moment of RFeO3 (NdFeO3, ErFeO3, YFeO3, HoFeO3) along b-axis (Mb) was studied in a wide temperature range. Mb was found to be non-zero generally below ~ 200 K with the highest Mb (~10–3 μB/f.u.) in the spin reorientation temperature region and below. This work refines previous measurements showing a very small but detectable non-zero Mb using magnetic measurements techniques. While neutron techniques do not have good enough sensitivity to detect this small Mb.
The magnetic properties of RFeO3 single crystal doped with another type of rare earth can give more details about the Fe-R and R-R magnetic interactions. New features can be obtained through that doping, such as the twofold spin reorientation and spin phase transition with applied high fields. Dy0.5Pr0.5FeO3 single crystal, a doped RFeO3 studied in this project, has two different types of R (Dy, Pr). The interaction R-R was found to be the strongest below their antiferromagnetic ordering temperatures of Dy3+ and Pr3+ (below 5 K). However, this interaction still happens even at higher temperatures (~15K). Below the ordering temperature of Dy3+ spins, the interaction between Dy3+ and Pr3+ spins has a significant effect on the magnetic moment of Dy0.5Pr0.5FeO3. Measuring these samples along the crystalline a- and b-axes at temperatures below ~10 K display a fast increasing in a magnetic moment with cooling in small magnetic fields. The symmetry considerations cannot agree with that increasing of magnetic moment for these systems; so, it cannot be a spontaneous property of these crystals. Only polarization of rare earth spins by an external magnetic field can explain that increasing in moment.
Mohammed, Mohanad Hazim, Magnetic properties of rare earth orthoferrites, Doctor of Philosophy thesis, Institute for Superconducting and Electronic Materials, University of Wollongong, 2020. https://ro.uow.edu.au/theses1/980
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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.