Before we start magnetic characterization by using SQUID, we need to locate the center of sample through either DC mode, VSM mode, or even mannually enter a position. In the automatic DC or VSM mode, the sample center can be located, which corresponds to the extremum in M-P (P for position) curve. Normally, this M-P curve is symmetric around the extremum.

However, we recently found that the M-P curve is always antisymmetric for straw background, while symmetric for quarts and standard sample. As a result, the M-H data on base of straw holder is not precise, and even changing at same temperature while measured at different time.

I wish to ask for some advice to solve this problem. Is this a technical problem of machine, which was brand new and installed in last month, or an artifical problem during sample loading? Thanks a lot!