The gravitational field is the negative differential of the gravitational potential. Now the gravitational potential due to a particle at a distance $r$ is $-Gm/r$ where $m$ is the mass of the particle. If I take the negative differential of this potential I get $-Gm/r^2$, which should be the magnitude of the gravitational field due to that particle at a distance $r$.
My question is, why is it coming out to be negative? I know that at a distance $r$ due to a particle the gravitational field is $Gm/r^2$ and it is not negative, so why am I getting a negative sign when I take the differential of the gravitational potential?