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Using magnetic force microscopy operating at sub-Kelvin temperatures, we characterize the heavy fermion superconductor CeCoIn5. We pinpoint the absolute London penetration depth of λ (0) = 435 ± 20 nm and report its temperature dependence, which is closely linked to the symmetry of the superconducting gap. In addition, we directly measure the pinning force of individual Abrikosov vortices and estimate the critical current density of j c = 9 × 10 4 A/cm2. In contrast to the related, well-established tunnel diode oscillator technique, our method is capable of resolving inhomogeneities locally on the micrometer scale at ultra-low temperature. [ABSTRACT FROM AUTHOR]

We constructed a 3He magnetic force microscope operating at the base temperature of 300 mK under a vector magnetic field of 2-2-9 T in the x-y-z direction. Fiber optic interferometry as a detection scheme is employed in which two home-built fiber walkers are used for the alignment between the cantilever and the optical fiber. The noise level of the laser interferometer is close to its thermodynamic limit. The capabilities of the sub-Kelvin and vector field are demonstrated by imaging the coexistence of magnetism and superconductivity in a ferromagnetic superconductor (ErNi2B2C) at T = 500 mK and by probing a dipole shape of a single Abrikosov vortex with an in-plane tip magnetization. [ABSTRACT FROM AUTHOR]