Doctoral Dissertations
Date of Award
12-2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Physics
Major Professor
Jian Liu
Committee Members
Cristian Batista, David Mandrus, Haidong Zhou
Abstract
Complex metal oxides are a curious class of materials with diverse states of matter, such as magnetism, superconductivity, multiferroics, and topological phases. In heavy materials like 5d Iridates, the spin and orbit components are mixed, yielding pseudospins and giving rise to effects like pseudospin lattice coupling, which connects lattice distortion in the system with pseudospins. In the bigger picture, such effects can be attributed to magnetoelastic couplings, and we probe the lattice by applying strain to the system to study its effect on magnetic ordering. We implemented uniaxial and epitaxial strains, creating a lattice mismatch between films and substrates. When an in-situ uniaxial strain of $B_{2g}$ symmetry is applied to single crystal Sr$_2$IrO$_4$, we observed a “new state” below the Néel Temperature $(T_N)$ that breaks the translational symmetry of a crystal lattice, evidenced by the observation of $\left(1\ 0\ L = 2n\pm\frac{1}{3}\right)$ satellite peaks in XRMS measurements and an unusual long-extended tail in the Magnetoresistance. We investigated the minimal free energy model of the metamagnetic transition to identify the fundamental interactions responsible for this new state. The proposed model simulates the $B_{2g}$ strain effect and the emergent state very well by including a nontrivial quartic interaction of two-fold rotational symmetry that is in-situ tuned by strain and different from the rotation invariant quartic interactions. In addition, we observed a strain-induced highly tunable incommensurate (IC) magnetic order just below the $(T_N)$, with no spontaneous incommensurate instability. By applying strains of different symmetry channels and signs, i.e., tensile and compressive, we unveiled that the IC order is induced when the strain-induced anisotropy competes against the spontaneous anisotropy in an orthogonal symmetry channel. On the other hand, we used Pulsed Laser Deposition (PLD), one of the remarkable techniques to deposit high-quality thin films of a wide range of materials, inducing epitaxial strain on thin film like SrIrO$_3$ grown on substrates like STO and TSO along (001) and (110). We observed anomalous Hall Effects on SrIrO$_3$ films grown on TSO(001) and Sn-doped SrIrO$_3$ films grown on TSO(001) substrates. The X-ray diffraction, reflectivity, electric, and magnetotransport results from these measurements are also presented.
Recommended Citation
Pandey, Shashi, "Anisotropic Strain Effects On Complex Metal Oxides. " PhD diss., University of Tennessee, 2024.
https://trace.tennessee.edu/utk_graddiss/11380