  Adjusting chemical pressure through doping is a highly effective method for
customizing the chemical and physical properties of materials, along with their
respective phase diagrams, thereby uncovering novel quantum phenomena. Here, we
successfully synthesized Sr-doped Eu$_{1-x}$Sr$_x$AgP $(x = 0.0-0.6)$ and
conducted a comprehensive investigation involving crystallography,
magnetization, heat capacity, and magnetoresistance. Utilizing X-ray
diffraction and PPMS DynaCool measurements, we studied Eu$_{1-x}$Sr$_x$AgP in
detail. The hexagonal structure of parent EuAgP at room temperature, with the
$P6_3/mmc$ space group, remains unaltered, while the lattice constants expand.
The magnetic phase transition from paramagnetism to ferromagnetism, as
temperature decreases, is suppressed through the gradual introduction of
strontium doping. Heat capacity measurements reveal a shift from
magnon-dominated to predominantly phonon and electron contributions near the
ferromagnetic phase with increasing doping levels. The resistivity-temperature
relationship displays distinct characteristics, emphasizing the impact of Sr
doping on modifying charge transport. Magnetoresistance measurements uncover
novel phenomena, illustrating the adjustability of magnetoresistance through Sr
doping. Notably, Sr doping results in both positive magnetoresistance (up to
20\%) and negative magnetoresistance (approximately -60\%). The resistivity and
magnetic phase diagram were established for the first time, revealing the
pronounced feasibility of Sr doping in modulating EuAgP's resistivity. This
study has provided valuable insights into the intricate interplay between
structural modifications and diverse physical properties. The potential for
technological advancements and the exploration of novel quantum states make
Sr-doped Eu$_{1-x}$Sr$_x$AgP a compelling subject for continued research in the
field of applied physics.
