English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We investigate the coupling factor $\phi_\mu$ that quantifies the magneticflux $\Phi$ per magnetic moment $\mu$ of a point-like magnetic dipole thatcouples to a superconducting quantum interference device (SQUID). Representingthe dipole by a current-carrying loop, the reciprocity of mutual inductances ofSQUID and loop provides a way of calculating $\phi_\mu(\vec{r}, \vec{e}_\mu)$vs.~position $\vec{r}$ and orientation $\vec{e}_\mu$ of the dipole anywhere inspace from the magnetic field $B(\vec{r})$ produced by a supercurrentcirculating in the SQUID loop. We use numerical simulations based on London andGinzburg-Landau theory to calculate $\phi_\mu$ from the supercurrent densitydistributions in various SQUID geometries. We treat the far-field regime($r\gtrsim a=$ inner size of the SQUID loop) with the dipole placed on thesymmetry axis of circular or square shaped loops. We compare expressions for$\phi_\mu$ from filamentary loop models with simulation results for loops withfinite width $w$ (outer size $A>a$), thickness $d$ and London penetration depth$\lambda_L$ and show that for thin ($d\ll a$) and narrow ($w < a$) loops theintroduction of an effective loop size $a_{\rm eff}$ in the filamentaryloop-model expressions results in agreement with simulations. For a dipoleplaced in the center of the loop, simulations provide an expression$\phi_\mu(a,A,d,\lambda_L)$ that covers a wide parameter range. In thenear-field regime (dipole centered at small distance $z$ above one SQUID arm)only coupling to a single strip representing the SQUID arm has to beconsidered. Here, we compare simulations with an analytical expression derivedfor a homogeneous current density distribution, which yields excellentagreement for $\lambda_L>w,d$. Moreover, we analyze $\phi_\mu$ provided by theintroduction of a constriction in the SQUID arm below the magnetic dipole.

On the coupling of magnetic moments to superconducting quantum interference devices