= Transport and magnetic tests of superconducting ceramics
<Four-terminal sensing> tests a conducting connection between the voltage contacts. A <magnetometer> instead tests the sample's magnetic response. These measurements provide complementary constraints: the first is sensitive to a continuous path, while the second also depends on screening geometry and preparation history.
\Image[/superconducting-ceramic-transport-and-magnetic-probes.png]
{title=Separate transport and magnetic questions for a superconducting ceramic}
{description=Original functional comparison, not a reconstruction of historical apparatus. Separate drive and sense contacts measure <electrical resistance>; a calibrated magnetic readout tests <magnetization>. The two preparation histories distinguish shielding after applying a <magnetic field> from expulsion during cooling in an existing <magnetic field>.}
For transport, define $V_{ab}$ between the inner contacts and use the reversed-<electric current> estimator from <four-terminal sensing>. Contact separation excludes drive-contact drops, but does not eliminate a drifting <thermoelectric effect>, <Joule heating> or an unrepresentative path through part of the specimen. Repeat at smaller <electric currents> and compare results at the same sample <temperature>. A finite-current result refers to that <electric current> and its relation to the path's <superconducting critical current>.
For <magnetism>, distinguish cooling in zero applied <magnetic field> and then applying it from the <Field-cooled Meissner experiment>. Record the applied <magnetic field>, background and sample geometry when interpreting <magnetization> or <magnetic susceptibility>. A transport short does not establish full <Meissner effect> screening throughout the specimen. Conversely, <flux pinning> in a <type-II superconductor> can make the field-cooled magnetic response differ from ideal complete expulsion. Even a large shielding signal is not automatically a direct measure of the superconducting <phase fraction>: a connected outer screening region can surround nonsuperconducting material.
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