We describe a compact capacitive dilatometer for measuring thermal expansion and magnetostriction below 1 K using a home-made capacitance bridge with long-term stability of ΔC/C ∼ 1.6 × 10−7. We measured the thermal expansion and magnetostriction of a heavy-Fermion compound CeRu2Si2 and those of a standard copper sample to clarify the dilatometer cell effect. The temperature-dependent cell effect of our dilatometer, ΔL/L, was less than 10−8 below 0.2 K. The magnetic-field-dependent cell effect was not observed below 52.6 mT at 85 mK, and was less than −2 × 10−9 up to 10 T at 4.2 K. Our dilatometer provides precise thermal expansion and magnetostriction measurements at millikelvin temperatures.
