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

Question

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?

This post imported from StackExchange Physics at 2016-01-06 09:14 (UTC), posted by SE-user Gamora

Comments

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...

This post imported from StackExchange Physics at 2016-01-06 09:14 (UTC), posted by SE-user Gamora

Answer 1

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.

This post imported from StackExchange Physics at 2016-01-06 09:14 (UTC), posted by SE-user user1704042

Answer 2

I came across this opinion that whenever there is an instance of inhomogenous magnetisation, there is a split in ZFC and FC. In case there is a uniform long range ordering present, the ZFC will fall perfectly on the FC. Does any one have any insights on this view?

This post imported from StackExchange Physics at 2016-01-06 09:14 (UTC), posted by SE-user Gamora