Cryogen free spin polarized scanning tunneling microscopy and magnetic exchange force microscopy with extremely low noise.

Spin polarized scanning tunneling microscopy (SP-STM) and magnetic exchange force microscopy (MExFM) are powerful tools to characterize spin structure at the atomic scale. For low temperature measurements, liquid helium cooling is commonly used, which has the advantage of generating low noise but has the disadvantage of having difficulties in carrying out measurements with long durations at low temperatures and measurements with a wide temperature range. The situation is just reversed for cryogen-free STM, where the mechanical vibration of the refrigerator becomes a major challenge. In this work, we have successfully built a cryogen-free system with both SP-STM and MExFM capabilities, which can be operated under a 9 T magnetic field provided by a cryogen-free superconducting magnet and in a wide temperature range between 1.4 and 300 K. With the help of our specially designed vibration isolation system, the noise is reduced to an extremely low level of 0.7 pm. The Fe/Ir(111) magnetic skyrmion lattice is used to demonstrate the technical novelties of our cryogen-free system.

Pulsed laser deposition of large-sized superlattice films with high uniformity.

Oxide superlattices often exhibit emergent physical properties that are desirable for future information device applications. The most common growth technique for fabrication of oxide superlattices is pulsed laser deposition (PLD), which is convenient yet powerful for the growth of various oxide superlattices. However, the sample size prepared by PLD is rather small confined by the plasmon plume, which greatly limits its potential for device applications. Here, we design a PLD system that is capable of fabricating large-sized oxide superlattices with high uniformity. Specifically, during growth, the laser beam scans the target surface by combining the pitch and yaw angle rotation of the high reflective mirror and the linear motion of the focus lens. A SiC susceptor is placed in between the sample holder and the substrate to improve the large area infrared heating efficiency. Using such a system, droplet-free 10 × 10 mm2 [(LSMO)12/(PCMO)6]7 superlattices are epitaxially grown with the same period of superlattices across the whole sample areas. The high uniformity of the superlattices is further illustrated by near identical physical properties of all regions of the superlattice films. The present PLD system can be used to grow various kinds of oxide superlattices with the area size as large as 2 in., which is highly useful for device applications of oxides.