# What kinds of behavioural anomalies can a zero-field-cooled (ZFC) / field-cooled (FC) split indicate?

If a material shows a spiltting in the ZFC and FC curves, is it necessarily superparamagnetic, or could there be any other reason for the irreversibility?

I have heard spin glasses also show ZFC-FC split; but whatever magnetisation measurements I have observed till now (from potential superconductors, to low dimensional magnets, to optically active materials, to thermoelectrics, to multiferroics, to rare earth - transition metal pyrochlores, to molecular magnets, and some strongly correlated systems - I just wish to clarify the range of systems I have seen measurements of so that there shouldn't be any bias in the category of materials) have always shown a split between the ZFC and FC curves. Would this imply that ALL these materials have a tendency to show superparamagnetism? (Because it has been confirmed that not all of them show spin glass behaviour).

Also a superparamagnetic material would not show a straight line M-H behaviour at temperatures like 2 and 10 K, from whatever I understand of the system. But most of these do. So what other kind of systems show ZFC FC split?

P.S. - I have also seen materials which show a superparamagnetic - like M-H curve at 2K (not a straight line, and no area inside of the hysteresis like curve) but no FC-ZFC split. What properties can lead to such a measurement?

• I guess what I am trying to ask is what sort of sample properties can a split in ZFC and FC imply? Several sources say that hysteresis is what gives rise to the split, but I have seen several samples showing non-hysteretic M-H curves but still showing ZFC-FC split... – Gamora Feb 28 '15 at 6:45

## 1 Answer

A zero-field-cooled/field-cooled split in the magnetic susceptibility vs. temperature doesn't have to be superparamagnetism. In the case of superconductors, if we apply a field to the material and cool past T$_c$, some flux can be trapped inside, but if we cool first and then apply field, that flux will be shielded away, resulting in greater diamagnetism.