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?