  Photo-Thermoelectric (PTE) response is usually one of the main working
mechanisms for photodetectors. However, as another fast and easier way to
measure thermoelectric characteristics of materials, it can also reveal
important physics such as electric-phonon coupling, electron-electron
correlation, etc. Recently, the spin entropy related to magnetic order
transition which contributes to thermoelectric power is attracting more and
more attention. Here, we demonstrate the PTE response can be reshaped when
Ca3Ru2O7 undergoes meta-magnetic phase (MMP) transition driven by both
temperature and magnetic field. Firstly, a sign change is observed crossing TS
= 48 K and the linear polarization angle dependent PTE current maximizes along
a-axis above TS while maximizes along b-axis below TS, which indicates that the
antiferromagnetic spin order contributes to such spatial anisotropy. Secondly,
in the temperature range of around 40 ~ 50 K, the PTE current is found to be
sharply suppressed when external magnetic field is applied in plane along
a-axis but is only gradually suppressed when applied field is along b-axis
which gives out two critical fields. We attribute such suppression of PTE
current under magnetic field to the suppression of the spin entropy in the
phase transition between the antiferromagnetic state and the MMP state and the
H-T phase diagrams of Ca3Ru2O7 is redrawn accordingly. Compared to previously
work which trying to understand the magnetic phase transition in Ca3Ru2O7, such
as neutron scattering, specific heat, and other advanced transport
measurements, our work provides a more convenient yet efficient method, which
may also find applications in other correlated spin materials in general.
