arXiv subjects

Kasper S. Pedersen

Publications and source records attributed to Kasper S. Pedersen.

6 recordsLinked to original sources

arXiv2026

Lithography-free patterning of SrTiO$_3$-based two-dimensional electron gases using direct atomic layer processing

We present a scalable and lithography-free strategy for the realization of a two-dimensional electron gas (2DEG) in TiO$_2$-patterned SrTiO$_3$ (100) via Al deposition using magnetron sputtering. A 15 nm thick TiO$_2$ layer, deposited by direct atomic layer processing, is employed to spatially define the conducting regions, enabling direct transport measurements without post-growth microfabrication. Upon Al deposition, an insulating AlO$_x$ overlayer is formed, and the region lacking the TiO$_2$ pattern leads to the creation of oxygen vacancies in SrTiO$_3$. These oxygen vacancies act as electron donors, populating the Ti 3$d$ conduction bands and giving rise to a confined 2DEG at the interface. Magneto-transport measurements reveal a sheet carrier density on the order of $\approx5-7\times10^{13}$ cm$^{-2}$, comparable to values typically achieved in pulsed laser deposition-grown SrTiO$_3$-based heterostructures, along with effective electrostatic tunability. This work demonstrates a simple, cost-effective, and industry-compatible route for engineering oxide 2DEGs, providing a versatile platform for scalable device fabrication and interfacial transport studies.

cond-mat.mtrl-sci↗

arXiv2026

Magnetism and nonlinear charge transport in NiFe2O4/γ-Al2O3/SrTiO3 heterostructure: Toward Spintronic Applications

We present the synthesis and study of the magnetic and electronic properties of NiFe2O4/γ-Al2O3/SrTiO3 heterostructure. The γ-Al2O3/SrTiO3 interface hosts a high-mobility two-dimensional electron gas (2DEG) with large spin-orbit coupling, making it promising for spintronics applications if it can be coupled to a suitable source of spin currents. Here, we synthesize a ferrimagnetic insulating NiFe2O4(001) layer on γ-Al2O3(001)/SrTiO3(001) using a low-temperature reactive sputtering at 150 deg C without compromising the mobility and charge carrier density of the 2DEG at the γ-Al2O3(001)/SrTiO3(001) interface. The sheet resistance of both γ-Al2O3/SrTiO3 and NiFe2O4/γ-Al2O3/SrTiO3 exhibits metallic behavior down to cryogenic temperatures, with a low temperature upturn driven by the Kondo-like scattering. Most importantly, NiFe2O4/γ-Al2O3/SrTiO3 behaves as a magnetic diode at low temperatures, and its rectification performance increases significantly with increasing magnetic field strength giving rise to a robust magneto-electronic rectification effect at low temperatures, which provides a first step towards the development of all-oxide heterostructures capable of efficient spin-charge conversion.

cond-mat.mtrl-sci↗

arXiv2022

Tuning magnetoelectricity in a mixed-anisotropy antiferromagnet

Control of magnetization and electric polarization is attractive in relation to tailoring materials for data storage and devices such as sensors or antennae. In magnetoelectric materials, these degrees of freedom are closely coupled, allowing polarization to be controlled by a magnetic field, and magnetization by an electric field, but the magnitude of the effect remains a challenge in the case of single-phase magnetoelectrics for application. We demonstrate that the magnetoelectric properties of the mixed-anisotropy antiferromagnet LiNi$_{1-x}$Fe$_x$PO$_4$ are profoundly affected by replacing a fraction of the Ni$^{2+}$ ions with Fe$^{2+}$ on the transition metal site. This introduces random site-dependent single-ion anisotropy energies and causes a lowering of the magnetic symmetry of the system. In turn, magnetoelectric couplings that are symmetry-forbidden in the parent compounds, LiNiPO$_4$ and LiFePO$_4$, are unlocked and the dominant coupling is enhanced by two orders of magnitude. Our results demonstrate the potential of mixed-anisotropy magnets for tuning magnetoelectric properties.

cond-mat.str-el↗

arXiv2021

Emergent magnetic behaviour in the frustrated Yb$_3$Ga$_5$O$_{12}$ garnet

We report neutron scattering, magnetic susceptibility and Monte Carlo theoretical analysis to verify the short range nature of the magnetic structure and spin-spin correlations in a Yb$_3$Ga$_5$O$_{12}$ single crystal. The quantum spin state of Yb$^{3+}$ in Yb$_3$Ga$_5$O$_{12}$ is verified. The quantum spins organise into a short ranged emergent director state for T $<$ 0.4 K derived from anisotropy and near neighbour exchange. We derive the magnitude of the near neighbour exchange interactions $0.6\; {\rm K} < J_1 < 0.7\; {\rm K}, J_2 = 0.12$~K and the magnitude of the dipolar exchange interaction, $D$, in the range $0.18 < D < 0.21$ K. Certain aspects of the broad experimental dataset can be modelled using a $J_1D$ model with ferromagnetic near neighbour spin-spin correlations while other aspects of the data can be accurately reproduced using a $J_1J_2D$ model with antiferromagnetic near neighbour spin-spin correlation. As such, although we do not quantify all the relevant exchange interactions we nevertheless provide a strong basis for the understanding of the complex Hamiltonian required to fully describe the magnetic state of Yb$_3$Ga$_5$O$_{12}$.

cond-mat.str-el↗

arXiv2019

Coherent manipulation of a molecular Ln-based nuclear qudit coupled to an electron qubit

We demonstrate that the [Yb(trensal)] molecule is a prototypical coupled electronic qubit-nuclear qudit system. The combination of noise-resilient nuclear degrees of freedom and large reduction of nutation time induced by electron-nuclear mixing enables coherent manipulation of this qudit by radio-frequency pulses. Moreover, the multi-level structure of the qudit is exploited to encode and operate a qubit with embedded basic quantum error correction.

cond-mat.mes-hall↗

arXiv2017

A Co(II)-based Molecular Magnet with a 6 T Coercive Field

Hard magnets with high coercivity, such as Nd2Fe14B and SmCo5 alloys, can maintain magnetisation under a high reverse external magnetic field and have therefore become irreplaceable parts in many practical applications. Molecular magnets are promising alternatives, owing to their precise and designable chemical structures, tuneable functionalities and controllable synthetic methods. Here, we demonstrate that an unusually large coercive field can be achieved in a single-chain magnet. Systematic characterisations, including magnetic susceptibility, heat capacity and neutron diffraction measurements, show that the observed giant coercive field originates from the spin dynamics along the one-dimensional chain of the compound because of the strong exchange coupling between Co(II) centres and radicals.

physics.chem-ph↗