We report the generation of a stable continuous-wave low-frequency squeezed vacuum field with a squeezing level of $7.4\pm 0.1\mathrm{dB}$ at $1064\mathrm{nm}$ , the wavelength at which laser-interferometric gravitational wave (GW) detectors operate, using periodically poled $\mathrm{K}\mathrm{Ti}\mathrm{O}\mathrm{P}{\mathrm{O}}_4$ (PPKTP) in a subthreshold optical parametric oscillator. The squeezing was observed in a broad band of frequencies above $700\mathrm{Hz}$ where the sensitivity of the currently operational GW detectors is limited by shot noise. PPKTP has the advantages of higher nonlinearity, smaller pump-induced seed absorption, and wider temperature tuning range than alternative nonlinear materials such as MgO-doped or periodically poled $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_3$ , and is, therefore, an excellent material for generation of squeezed vacuum fields for application to laser interferometers for GW detection.