Investigation of the Stripe-Bubble Phase in La2-2xSr1+2xMn2O7(x=0.32) by Magnetic Force Microscopy

We constructed a home-built low temperature magnetic force microscope (LTMFM) with the fiber interferometer detection scheme: The base temperature is 4 K and magnetic field range is up to 6 T. The MFM system is applied to investigate unconventional magnetism of La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$(x=0.32) in a wide span of temperature and magnetic field. We imaged spin reorientation transition and found two types of bubble domains. The behavior of bubble domains shows the same upon field cycle, indicating a reversible magnetization property reported previously in the bulk magnetization measurement. The origin of the two types of the bubble domains will be discussed by comparing MFM and bulk magnetization data.