We report on muon spin rotation/relaxation and $^{119}$Sn nuclear magnetic resonance (NMR) measurements to study the microscopic superconducting and magnetic properties of the Heusler compound with the highest superconducting transition temperature, ypd ($T_c=5.4$ K). Measurements in the vortex state provide the temperature dependence of the effective magnetic penetration depth $lambda(T)$ and the field dependence of the superconducting gap $Delta(0)$. The results are consistent with a very dirty s-wave BCS superconductor with a gap $Delta(0)=0.85(3)$ meV, $lambda(0)= 212(1)$ nm, and a Ginzburg-Landau coherence length $xi_{mathrm{GL}}(0)cong 23$ nm. In spite of its very dirty character, the effective density of condensed charge carriers is high compared to the normal state. The mSR data in a broad range of applied fields are well reproduced by taking into account a field-related reduction of the effective superconducting gap. Zero-field mSR measurements, sensitive to the possible presence of very small magnetic moments, do not show any indications of magnetism in this compound.
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