arXiv subjects

R. M. L. McFadden

Publications and source records attributed to R. M. L. McFadden.

4 recordsLinked to original sources

arXiv2021

Evolution of the metallic state of LaNiO$_3$/LaAlO$_3$ superlattices measured by $^8$Li $β$-detected NMR

Using ion-implanted $^8$Li $β$-detected NMR, we study the evolution of the correlated metallic state of LaNiO$_3$ in a series of LaNiO$_3$/LaAlO$_3$ superlattices as a function of bilayer thickness. Spin-lattice relaxation measurements in an applied field of 6.55 T reveal two equal amplitude components: one with metallic ($T$-linear) $1/T_{1}$, and a second with a more complex $T$-dependence. The metallic character of the slow relaxing component is only weakly affected by the LaNiO$_3$ thickness, while the fast component is much more sensitive, exhibiting the opposite temperature dependence (increasing towards low $T$) in the thinnest, most magnetic samples. The origin of this bipartite relaxation is discussed.

cond-mat.str-el↗

arXiv2019

Observation of a charge-neutral muon-polaron complex in antiferromagnetic Cr$_2$O$_3$

We report a comprehensive muon spin rotation ($μ$SR) study of the prototypical magnetoelectric antiferromagnet Cr$_2$O$_3$. We find the positively charged muon ($μ^+$) occupies several distinct interstitial sites, and displays a rich dynamic behavior involving local hopping, thermally activated site transitions and the formation of a charge-neutral complex composed of a muon and an electron polaron. The discovery of such a complex has implications for the interpretation of $μ$SR spectra in a wide range of magnetic oxides, and opens a route to study the dopant characteristics of interstitial hydrogen impurities in such materials. We address implications arising from implanting a $μ^+$ into a linear magnetoelectric, and discuss the challenges of observing a local magnetoelectric effect generated by the charge of the muon.

cond-mat.mtrl-sci↗

arXiv2019

Bi-Arrhenius diffusion and surface trapping of $^{8}$Li$^{+}$ in rutile TiO$_2$

We report measurements of the diffusion rate of isolated ion-implanted $^{8}$Li$^{+}$ within $\sim$120 nm of the surface of oriented single-crystal rutile TiO$_2$ using a radiotracer technique. The $α$-particles from the $^{8}$Li decay provide a sensitive monitor of the distance from the surface and how the depth profile of $^{8}$Li evolves with time. The main findings are that the implanted Li$^{+}$ diffuses and traps at the (001) surface. The T-dependence of the diffusivity is described by a bi-Arrhenius expression with activation energies of 0.3341(21) eV above 200 K, whereas at lower temperatures it has a much smaller barrier of 0.0313(15) eV. We consider possible origins for the surface trapping, as well the nature of the low-T barrier.

cond-mat.mtrl-sci↗

arXiv2017

Determination of the nature of fluctuations using $^8Li$ and $^9Li$ $β$-NMR and spin-lattice relaxation

We report a comparison of the $1/T_1$ spin lattice relaxation rates (SLR) for $^9Li$ and $^8Li$ in Pt and SrTiO$_{3}$, in order to differentiate between magnetic and electric quadrupolar relaxation mechanisms. In Pt, the ratio of the $1/T_{1}$ spin relaxation rates $R_{Pt}$ was found to be 6.82(29), which is close to but less than the theoretical limit of $\sim7.68$ for pure magnetic relaxation. In SrTiO$_{3}$ this ratio was found to be 2.7(3), which is close but larger than the theoretical limit of $\sim2.14$ expected for pure electric quadrupolar relaxation. These results bring new insight into the nature of the fluctuations in the local environment of implanted $^8Li$ observed by $β$-NMR.

cond-mat.mtrl-sci↗