A carbon-nanotube based nano-furnace for in-situ restructuring of a magnetoelectric oxide

Bajpai, Abhishek; Aslam, Zabeada; Hampel, Silke; Klingeler, R.; Grobert, Nicole

doi:10.1016/j.carbon.2016.12.008

Cited by 5 publications

(16 citation statements)

References 36 publications

(100 reference statements)

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“…[21,33,34] If this enhancement in M was arising only due to the nano scaling of α-Fe2O3 or if it was morphology related (aligned forest), the effect should have persisted in the template. Though, both the size effects & morphology certainly have a role to play as far as WFM is concerned, [21,28] , data in Figure 1h&1i suggest that the significant enhancement in M is related to the interface effects.…”

Section: Enhanced Magnetization: Magnetization As a Function Of Tempementioning

confidence: 99%

“…Weak Ferromagnetism & Time-stable μ : As we have recently shown, manifestation of canting appears in the form of time-stable μ with a functional form, evidently different from other physical mechanisms. [21,28] From the measurements conducted on single crystal α-Fe2O3, we found that this time-stable μ appears in WFM region and vanishes in pure AFM region and the effect is also significantly tunable by nano scaling [21] . More importantly, while M increases with increasing H, the corresponding μ exhibits a peak like behavior with increasing H [21] .…”

Section: Weak Ferromagnetism and Unusual Magnetization Dynamicsmentioning

confidence: 99%

“…candidates for novel interface effects. [25][26][27][28] In this work, we present experimental results that indicate that encapsulation of α-Fe2O3 inside CNT is the most efficient way to enhance the magnitude of the DMI driven WFM and consequently PzM.…”

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Enhanced magnetism andtime-stableremanence at the interface of hematite and carbon nanotubes

et al. 2019

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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 (µ) results, which conclusively arise at the interface of two highly functional materials, namely the graphitic shells of a carbon nanotube (CNT) and α-Fe2O3, 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 µ, 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 µ 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 α-Fe2O3 nanowires bring into fore that the weak ferromagnets such as α-Fe2O3 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.Hematite (or α-Fe2O3) is an earth abundant and environment-friendly oxide, generally considered as a menace, for its appearance as common rust over elemental Fe, but technologically, it is well known for a very diverse range of applications. [1] However, the observation of WFM [2,3] nearly six decades ago in hematite and its connection to spin orbit coupling (SOC) has had profound implications in the field of spintronics. A variety of nontrivial topological spin structures in chiral magnets stabilizing through DMI/SOC have triggered new research areas such as antiferromagnetic spintronics and spin orbitronics [4,9] .Generation of WFM in α-Fe2O3 is due to a slight canting of its inherent AFM sublattice [2,3] which persists from 950 K (TN) down to 265 K, well-known Morin Transition temperature (TM). Below TM, the spins turn from "a" axis to "c" axis (rhombohedral unit cell in hex setting) and the canting vanishes for hematite. Many of such canted AFM, either DMI driven or systems in which canting takes place due to other mechanism, are also known to exhibit the phenomenon of piezomagnetism. [10,14] Here, PzM implies that magnetization can be tuned by stress alone.Another important point is the occurrence of WFM which is concurrent with PzM as theoretically predicted [10] and experimentally observed [11,14] . Dzyaloshinskii also showed that the spin canting effect is larger for compounds with smaller TN [2] . Thus, WFM / PzM is seen to be the weakest in α-Fe2O3 with TN ~950 K as compared to MnCO3 or NiCO3 (TN below 50 K).This work centers around remanence µ, which, in general, is an important parameter for any magnetic material for a variety of practical applications related to permanent magnets, soft or hard, relate to this quantity [15,17] . In addition, it is an important tool for probing fundamental magnetic interactions in conventional lon...

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Section: Enhanced Magnetization: Magnetization As a Function Of Tempementioning

confidence: 99%

Section: Weak Ferromagnetism and Unusual Magnetization Dynamicsmentioning

confidence: 99%

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Enhanced magnetism andtime-stableremanence at the interface of hematite and carbon nanotubes

et al. 2019

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“…We also find that the magnitude of the time-stable remanence is small in hematite, as compared to MnCO 3 , which has relatively smaller T N ∼ 30 K. It is known to be a stronger WFM as compared to hematite, for which the T N ∼ 960 K. Thus comparing the magnitude of µ in different systems provides insights about the magnitude of spin canting, a non trivial parameter to estimate. Nano scaling significantly tunes the magnitude of this peculiar remanence [26][27][28]. Considering that the spin canting and associated WFM and PzM effects exist in hematite near the room temperature, it is more suitable for practical applications.…”

Section: Introductionmentioning

confidence: 99%

Weak ferromagnetism andtime-stable remanencein hematite: effect of shape, size and morphology

Pattanayak

Bhattacharyya

Chakravarty

et al. 2019

J. Phys.: Condens. Matter

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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 time-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. arXiv:1811.05231v1 [cond-mat.str-el]

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“…For instance, α-Fe2O3 is an AFM insulator and a piezomagnet [10], whereas Fe3O4 is an FM (half) metal that possesses spin polarization larger than Fe metal. The oxides of other transition metals, such as chrome oxides can be half metals or magneto electric in their bulk state and exhibit remarkable emergent properties upon nano-scaling [11][12][13][14][15][16][17][18][19][20]. These metals and oxides, when confined and protected within CNT, can thus provide huge tunability in their functional properties as well as give rise to new emergent phenomena that are possible at the interface of these hybrids [9,[13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

3d transition metals and oxides within carbon nanotubes by co-pyrolysis of metallocene & camphor: High filling efficiency and self-organized structures

Kapoor

Singh

Dey

et al. 2018

Carbon

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We demonstrate that a single zone furnace with a modified synthesis chamber design is sufficient to obtain metal (Fe, Co or Ni) filled carbon nanotubes (CNT) with high filling efficiency and controlled morphology. Samples are formed by pyrolysis of metallocenes, a synthesis technique that otherwise requires a dual zone furnace. Respective metallocene in all three cases are sublimed in powder form, a crucial factor for obtaining high filling efficiency.While Fe@CNT is routinely produced using this technique, well-formed Ni@CNT orCo@CNT samples are reported for the first time. This is achieved by sublimation of nickelocene (or cobaltocene) in combination with 'camphor'. These samples exhibit some of the highest saturation magnetization (Ms) values, at least an order of magnitude higher than that reported for Ni or Co@CNT, by aerosol assisted pyrolysis. The results also elucidate on why Ni or Co@CNT are relatively difficult to obtain by pyrolyzing powder metallocene 2 alone. Overall, a systematic variation of synthesis parameters provides insights for obtaining narrow length and diameter distribution and reduced residue particles outside filled CNTfactors which are important for device related applications. Finally, the utility of this technique is demonstrated by obtaining highly aligned forest of Fe2O3@CNT, wherein Fe2O3 is a functional magnetic oxide relevant to spintronics and battery applications.

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A carbon-nanotube based nano-furnace for in-situ restructuring of a magnetoelectric oxide

Cited by 5 publications

References 36 publications

Enhanced magnetism andtime-stableremanence at the interface of hematite and carbon nanotubes

Enhanced magnetism andtime-stableremanence at the interface of hematite and carbon nanotubes

Weak ferromagnetism andtime-stable remanencein hematite: effect of shape, size and morphology

3d transition metals and oxides within carbon nanotubes by co-pyrolysis of metallocene & camphor: High filling efficiency and self-organized structures

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