Abstract
The steadfast rule of a ferromagnetic hysteresis loop claims its saturation positioned within the first and third quadrants, whereas its saturation positioned in the second and fourth quadrants (named as self-reversed magnetic hysteresis) is usually taken as an experimental artifact and is always intentionally ignored. In this report, a new insight in this unique hysteresis phenomenon and its modulation were discussed in depth. Different iron oxides (magnetite, maghemite and hematite) with varying dimensions were soaked in FeCl3 aqueous solution and absorbed Fe3+ cations due to their negative enough surface zeta potentials. These iron oxides@Fe3+ core-shell products exhibit well pronounced self-reversed magnetic hysteresis which concurrently have typical diamagnetic characteristics and essential ferromagnetic features. The presence of pre-magnetized Fe3+ shell and its negatively magnetic exchange coupling with post-magnetized iron-oxide core is the root cause for the observed phenomena. More strikingly, this self-reversed magnetic hysteresis can be readily modulated by changing the core size or by simply controlling Fe3+ concentration in aqueous solution. It is anticipated that this work will shed new light on the development of spintronics, magnetic recording and other magnetically-relevant fields.
Highlights
The steadfast rule of a ferromagnetic hysteresis loop claims its saturation positioned within the first and third quadrants, whereas its saturation positioned in the second and fourth quadrants is usually taken as an experimental artifact and is always intentionally ignored
It has often been taken that the “negative” area of the hysteresis loop violates the thermo-mechanical second law, so that Self-reversed magnetic hysteresis (SRMH) is seen as an experimental artifact probably arising from inappropriate or asymmetric sample positioning and the misinterpretation of experimental data[1]
We propose a facile and versatile method to scalable synthesis of SRMH iron oxides
Summary
The steadfast rule of a ferromagnetic hysteresis loop claims its saturation positioned within the first and third quadrants, whereas its saturation positioned in the second and fourth quadrants (named as selfreversed magnetic hysteresis) is usually taken as an experimental artifact and is always intentionally ignored. The possible mechanism of SRMH can be described by experimental evidence that the preformed metastable “x phase” becomes weakly and normally magnetized in the presence of an applied magnetic field during cooling process This “x phase” is negatively exchange-coupled with a subsequently-formed stable phase at a lower temperature. Based on careful investigations of myriad rocks all over the world, geologists have found thermoremanent-magnetization direction of some rocks or minerals is totally opposite to the present geomagnetic direction, and they believe the Earth’s magnetic field has reversed its polarity many times throughout the earth history Such discredit geological speculations may well misconstrue the reality if the SRMH phenomenon is really relevant[8]. The two-dimensional (2-D) pine-like and three-dimensional (3-D) flower-like α-Fe2O3 architectures further confirm the applicability and effectiveness of this way to yield tailorable SRMH behaviors
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