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تسجيل مستخدم جديدEnhanced Magnetism & Time - Stable Remanence at the Interface of Hematite and Carbon Nanotubes
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The interface of two dissimilar materials is well known for surprises in condensed matter, and provides avenues for rich physics as well as seeds for future technological advancements. We present some exciting magnetization (M) and remnant magnetization ($mu$) results, which conclusively arise at the interface of two highly functional materials, namely the graphitic shells of a carbon nanotube (CNT) and $alpha$-Fe$_2$O$_3$, a Dzyaloshinskii-Moriya Interaction (DMI) driven weak ferromagnet (WFM) and piezomagnet (PzM). We show that the encapsulation inside CNT leads to a very significant enhancement in M and correspondingly in $mu$, a time- stable part of the remanence, exclusive to the WFM phase. Up to 70% of in-field magnetization is retained in the form of $mu$ at the room temperature. Lattice parameter of CNT around the Morin transition of the encapsulate exhibits a clear anomaly, confirming the novel interface effects. Control experiments on bare $alpha$-Fe$_2$O$_3$ nanowires bring into fore that the weak ferromagnets such as $alpha$-Fe$_2$O$_3$ as are not as weak, as far as their remanence and its stability with time is concerned, and encapsulation inside CNT leads to a substantial enhancement in these functionalities.
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We have recently established that a number of Dzyaloshinskii-Moriya interaction driven canted antiferromagnets or weak ferrromagnets (WFM) including hematite exhibit an ultra-slow magnetization relaxation phenomenon, leading to the observation of a t
ime-stable remanence (Phys. Rev. B 96, 104422 (2017)). In this work, our endeavor is to optimize the magnitude of this time-stable remanence for the hematite crystallites, as a function of shape size and morphology. A substantial enhancement in the magnitude of this unique remanence is observed in porous hematite, consisting of ultra-small nano particles, as compared to crystallites grown in regular morphology, such as cuboids or hexagonal plates. This time-stable remanence exhibits a peak-like pattern with magnetic field, which is significantly sharper in porous sample. The extent and the magnitude of the spin canting associated with the WFM phase can be best gauged by the presence of this remanence and its unusual magnetic field dependence. Temperature variation of lattice parameters bring out correlations between strain effects that alter the bond length and bond angle associated with primary super exchange paths, which in-turn systematically alter the magnitude of the time-stable remanence. This study provides insights regarding a long standing problems of anomalies in the magnitude of magnetization on repeated cooling in case of hematite. Our data caps on these anomalies, which we argue, arise due to spontaneous spin canting associated with WFM phase. Our results also elucidate on why thermal cycling protocols during bulk magnetization measurements are even more crucial for hematite which exhibits both canted as well as pure antiferromgnetic phase.
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