The pearlite content increases proportional to the hardness values of the material. The proportion of pearlite also influences the magnetic properties of the material, which effects directly the form of the hysteresis loop, shown in figure. Casted iron with a high content of pearlite needs more energy to be magnetized than casted iron with a high content of ferrite

The course of the hysteresis loop is defined by different effects as e.g. reversible and irreversible dislocations of Blochwalls or rotary movements of elementary magnets out of their crystallographicaly preferred direction. In principle the Blochwalls need low energy levels to shift through an ideal crystal lattice, but inside a real crystal lattice there are different kinds of obstacles, depending on the material composition, which make the movement of the Blochwalls more difficult and as a matter of this finally influence the form of the hysteresis loop

Dear Dr. K. Prashanthi,

thank you so much for your answer to my question. I was actually asking about the phenomenon that is observed in the attached figure. Is it due to local magnitization happened in ferrite ceramic powder investigated?

Dear Prof. Sathishkumar Gangatharan,

thank you very much for your comprehensive answer to my question. Really helpful! I was actually asking about the phenomenon that is observed in the formerly attached figure . Can your answer also be suitable for ferrite ceramic powders? for example, barium hexaferrite?

Is this phenomenon observed when components with soft and hard magnetic properties are present at the same time in the powder? 

Dr. K. Prashanthi, thank you for your answer. These pieces of information are so helpful. 

As was indicated before, different mechanisms may give rise to similarly looking shapes of M(H) cycles. In order to determine whether a narrowing is real or apparent I find it useful to compute the difference of the two curves measured with the field sweeping upwards and downwards, respectively. It helps visualizing the hysteretic behavior.

In your specific case it appears that not only the sample is not saturated at your maximum field but also that the loop is not really a major loop (the two branches immediately open right at the end points). You therefore have to expect that loops measured with higher max. field will display altered curves. If possible, try to measure loops with max. field reaching into the purely reversible region (no more hysteresis).

If you need to find out about the mechanisms determining the shape of your M(H) curves then there are a number of recipes/strategies described in the literature for doing that. In any case, this involves multiple (partial) M(H) loops. One of the key issues is to discriminate reversible and irreversible magnetization changes along the M(H) curves. One of the earlier authors is J. Hesse (Braunschweig, Germany, now retired) others have developed further strategies.

Dear Amin Hodaei,

This paper might be useful to you

Article Magnetic M-H loops family characteristics in the microstruct...

Dear Dr. Kai Fauth, 

I have really benefited from your provided answer. I will definitely read articles authored by J. Hesse related to this field. thank you so much again.

Dear Idza Riati Ibrahim,

thank you very much for advising me reading this article.

I could download and read it. Thank you so much for your support. 

First you should check if your sample is a single-phase. Multiphase samples could exhibit strange-looking hysteresis loops.

Dear Prof. Sami Mahmood,

according to the XRD patterns of the investigated sample the main phase present in the sample is α-Fe2O3; However, it is possible that other phases be present in low quantities or in amorphous state too.

Can you please explain the magnetic behavior of your system? A single-phase magnetite sample should exhibit normal hysteresis with low coercivity in the bulk state, and with zero coercivity in the superparamgnetic state (Fine particle system). If your statement "narrow at the middle" means low coercivity, this is expected for a soft ferrite sample. If the coercivity approaches zero, then you may have small-size single domain particles exhibiting superparamgnetism at room temperature. Superparamgnetic behavior could be checked by performing low-temperature magnetization (or Mossbauer) studies, where below a particular (blocking) temperature the sample behaves like ferrite in the normal state.

oops, α-Fe2O3 is actually hematite, which is an antiferromagnet below ~260K. The Néel temperature is above 900K, though, and there is only a very weak "ferromagnetic" moment in between these temperatures (I guess this is due to canting). Pick your moment at max. field, determine the weight of your sample and calculate (by nominal stoichiometry) the average moment per Fe atom.  How does this fit with known props of bulk  α-Fe2O3 ? Maybe your moments are "just" given from off-stoichiometric fractions of the specimen (e.g. particle surfaces). This of course is not an answer to the question about the mechanism of narrowing but I agree with Sami that you should first check the obvious about what your sample is or isn't...

Yes I agree with K. Fauth. Please accept my apologies for giving an answer related to magnetite. Apparently my answer was based on Amin's original question regarding "ferrits' hysteresis", and in our common language we refer to Fe-oxide as ferrite when it is Fe3O4 (not Fe2O3). Can you Amin clarify which phase do you have, hematite or magnetite (ferrite)?

Well, gamma-Fe2O3 (maghemite) would still be a cubic spinel type Fe oxide and is ferrimagnetic as is Fe3O4. The stoichiometry is not sooo different between the two and especially at the nanoscale (i) any intermediate stoichiometry is possible [E. Pellegrin et al., pssb (1999)] and (ii) they are hardly distinguished by XRD at all!

Correct. However, the gamma phase incorporates oxygen vacancies in its structure. The low-Z of oxygen could be the reason behind the similarity in the XRD patterns of the two phases. But do you (K. Fauth) recall listing the gamma-Fe2 O3 phase under the category of "ferrites"?

Sami, I actually can't tell whether maghemite is usually considered a ferrite.

The difficulty with XRD in nanoparticulate matter is that already in the bulk the differences are minor and become hardly distinguishable due to finite size broadening (let alone off-stoichiometries etc.).

Dear Prof. Kai Fauth and Prof. Sami Mahmood,

I would like to thank you so much for detailed explanations through your answers to my question. As I said, the phase which is in the best agreement with peaks of the so called sample XRD pattern is α-Fe2O3 (Hematite). The other probable phases should be either amorphous or in low quantities (less the 5-10%). Is this shape of histeresis loop only seen in samples containing more than one phase? And if so, those phases should certainly have different magnetic behaviors?