• Kühne, Philipp
• Ivády, Viktor
• Knight, Sean
• Schubert, Mathias
• Bulancea-Lindvall, Oscar
• Van De Walle, Chris
• Richter, Steffen
• Rindert, Viktor
• Darakchieva, Vanya
• Ruder, Alexander
• Abrikosov, Igor

Abstract

<jats:p>We demonstrate detection and measurement of electron paramagnetic spin resonances (EPR) of iron defects in <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mi>β</a:mi><a:mtext>−</a:mtext><a:msub><a:mi>Ga</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi mathvariant="normal">O</a:mi><a:mn>3</a:mn></a:msub></a:mrow></a:math> utilizing generalized ellipsometry at frequencies between 110 and 170 GHz. The experiments are performed on an Fe-doped single crystal in a free-beam configuration in reflection at <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:msup><c:mn>45</c:mn><c:mo>∘</c:mo></c:msup></c:math> and magnetic fields between 3 and 7 T. In contrast with low-field, low-frequency EPR measurements, we observe all five transitions of the <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:mi>s</d:mi><d:mo>=</d:mo><d:mn>5</d:mn><d:mo>/</d:mo><d:mn>2</d:mn></d:mrow></d:math> high-spin state <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:msup><e:mrow><e:mi>Fe</e:mi></e:mrow><e:mrow><e:mn>3</e:mn><e:mo>+</e:mo></e:mrow></e:msup></e:math> simultaneously. We confirm that ferric <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:msup><f:mrow><f:mi>Fe</f:mi></f:mrow><f:mrow><f:mn>3</f:mn><f:mo>+</f:mo></f:mrow></f:msup></f:math> is predominantly found at octahedrally coordinated Ga sites. We obtain the full set of fourth-order monoclinic zero-field splitting parameters for both octahedrally and tetrahedrally coordinated sites by employing measurements at multiple sample azimuth rotations. The capability of high-field EPR allows us to demonstrate that simplified second-order orthorhombic spin Hamiltonians are insufficient, and fourth-order terms as well as consideration of the monoclinic symmetry are needed. These findings are supported by computational approaches based on density-functional theory for second-order and on ligand-field theory for fourth-order parameters of the spin Hamiltonian. Terahertz ellipsometry is a way to measure spin resonances in a cavity-free setup. Its possibility of varying the probe frequency arbitrarily without otherwise changing the experimental setup offers unique means of truly disentangling different components of highly anisotropic spin Hamiltonians.</jats:p><jats:sec><jats:title/><jats:supplementary-material><jats:permissions><jats:copyright-statement>Published by the American Physical Society</jats:copyright-statement><jats:copyright-year>2024</jats:copyright-year></jats:permissions></jats:supplementary-material></jats:sec>

Topics

• density
• impedance spectroscopy
• single crystal
• theory
• experiment
• anisotropic
• defect
• ellipsometry
• iron
• electron spin resonance spectroscopy
• size-exclusion chromatography