  Multi-layered materials provide fascinating platforms to realize various
functional properties, possibly leading to future electronic devices controlled
by external fields. In particular, layered magnets coupled with conducting
layers have been extensively studied recently for possible control of their
transport properties via the spin structure. Successful control of
quantum-transport properties in the materials with antiferromagnetic (AFM)
layers, so-called natural spin-valve structure, has been reported for the Dirac
Fermion and topological/axion materials. However, a bulk crystal in which
magnetic and superconducting layers are alternately stacked has not been
realized until now, and the search for functional properties in it is an
interesting yet unexplored field in material science. Here, we discover
superconductivity providing such an ideal platform in EuSn2As2 with the van der
Waals stacking of magnetic Eu layers and superconducting Sn-As layers, and
present the first demonstration of a natural spin-valve effect on the
superconducting current. Below the superconducting transition temperature (Tc),
the electrical resistivity becomes zero in the in-plane direction. In contrast,
it, surprisingly, remains finite down to the lowest temperature in the
out-of-plane direction, mostly due to the structure of intrinsic magnetic
Josephson junctions in EuSn2As2. The magnetic order of the Eu layers (or
natural spin-valve) is observed to be extremely soft, allowing one to easy
control of the out-of-plane to in-plane resistivities ratio from 1 to infinity
by weak external magnetic fields. The concept of multi-functional materials
with stacked magnetic-superconducting layers will open a new pathway to develop
novel spintronic devices with magnetically controllable superconductivity.
