During the VSM measurement, the data I measured shows hysteresis curve appearing only on the positive side of magnetic field what could be the possible reasons for that ?
Hai Surajkumar Duvey
Possible reasons for hysteresis curves appearing only on the positive side of magnetic fields could be due to magnetization losses, anisotropy or non-uniformity in the material, or incorrect direction of the applied magnetic field.
Other possible reasons for the hysteresis curve's appearance could be due to non-uniform heating of the sample, weak or inhomogeneous interactions between magnetization and applied field, or an inhomogeneous distribution of magnetic moments in the sample.
Additionally, there could be a lack of minor corrections needed to ensure that the measurement is accurate, or that the sample has not been magnetized by a prior measurement.
I think you are observing an example of the so called exchange bias.
Probably, you were cooling down the sample, which is a mixture of ferromagnetic and antiferromagnetic materials in the presence of a magnetic field:
W.H. Meiklejohn, C.P. Bean New Magnetic Anisotropy // Phys.Rev.Letters 102(5), 1413 (1956), ibid. Phys.Rev. 105 (3), 904 (1957)
Hysteresis curves appearing only in the positive values of the external magnetic fields can be explained by the existence of magnetization losses, anisotropy or non-uniformity of the material studied, or a bad choice of the direction of the external magnetic field applied.
Из рисунка видно,что намагниченность находится во внешнем магнитном поле, которое меняется по величине и направлению, и поле однонаправленной анизотропии. Если это нескомпенсированный монокристалл (а похоже на субмикронную пленку), то следует выяснить природу этой анизотропии, например отжечь образец или воздействовать сильным отрицательным полем и т.д.
Since the y-axis title is missing in the graph, I think it possibly represents magnetization. From the graph it is seen that, for zero field there is magnetization. This probably indicates a fault in the calibration of applied magnetic field in the VSM measurement.
What makes me think about exchange bias? The figure presents more than one hysteresis loop and we see traces of what is called training of hysteresis loop.
Yes, I completely agree with Marek Gutowski. The effect of the exchange bias of hysteresis loops - aka the Meiklejohn-Bean effect, was discovered in 1956 in the article to which I gave a quote. The effect continues to be actively studied to this day. Hundreds of articles are published every year. In particular, the effect of exchange bias training is also being studied in a variety of materials that are inhomogeneous in terms of magnetic ordering. It can manifest itself not only in magnetic but also in electronic transport properties as well, as magnetoresistance hysteresis loops may also be biassed by the same magnetic interaction.
Exchange bias effect refers to the shift of the hysteresis loop of a ferromagnet in direct contact with an antiferromagnet. This effect in ferro/antiferromagnetic heterostructures is also a recent interest in the literature.
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