Field-dependent low-field enhancement in effective paramagnetic moment with nanoscaled Co3O4

Chen, Weimeng; Chen, Chinping; Guo, Lin

doi:10.1063/1.3475249

Cited by 20 publications

(21 citation statements)

References 37 publications

(64 reference statements)

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“…In Co 3 O 4 , on the other hand, the weak tetrahedral-tetrahedral ( T-T ) AFM interactions between the Co 2+ tet cations lead to antiferromagnetism9 with a low ordering temperature T N of ~20–40 K. Consequently, a ferromagnetic order with a high Curie temperature can be stabilized at the interface if magnetic moments are present at both the octahedral and the tetrahedral sites. Such a scenario was previously explained by a transition from a normal to inverse spinel in Co 3 O 4 nanoparticles by Chen et al 32. and by Serrano et al 16 at the surfaces of nanoparticles on TiO 2 .…”

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confidence: 70%

Electrostatic doping as a source for robust ferromagnetism at the interface between antiferromagnetic cobalt oxides

Fontaíña-Troitiño

Kovács

et al. 2015

Sci Rep

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Polar oxide interfaces are an important focus of research due to their novel functionality which is not available in the bulk constituents. So far, research has focused mainly on heterointerfaces derived from the perovskite structure. It is important to extend our understanding of electronic reconstruction phenomena to a broader class of materials and structure types. Here we report from high-resolution transmission electron microscopy and quantitative magnetometry a robust – above room temperature (Curie temperature TC ≫ 300 K) – environmentally stable- ferromagnetically coupled interface layer between the antiferromagnetic rocksalt CoO core and a 2–4 nm thick antiferromagnetic spinel Co3O4 surface layer in octahedron-shaped nanocrystals. Density functional theory calculations with an on-site Coulomb repulsion parameter identify the origin of the experimentally observed ferromagnetic phase as a charge transfer process (partial reduction) of Co3+ to Co2+ at the CoO/Co3O4 interface, with Co2+ being in the low spin state, unlike the high spin state of its counterpart in CoO. This finding may serve as a guideline for designing new functional nanomagnets based on oxidation resistant antiferromagnetic transition metal oxides.

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confidence: 70%

Electrostatic doping as a source for robust ferromagnetism at the interface between antiferromagnetic cobalt oxides

Fontaíña-Troitiño

Kovács

et al. 2015

Sci Rep

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“…The effective moment is slightly higher than the bulk value, 4.14 m B . 5,6 It indicates that a fraction of the spinel structure of Co 3 O 4 might have undergone a transition from the spinel to the inverse spinel structure in an applied field due to electron transfer from the A-site Co +2 to the B-site Co +3 ions. 6 The FC curve does not even show any structure at the Neel point.…”

Section: Magnetic Propertymentioning

confidence: 99%

“…5,6 It indicates that a fraction of the spinel structure of Co 3 O 4 might have undergone a transition from the spinel to the inverse spinel structure in an applied field due to electron transfer from the A-site Co +2 to the B-site Co +3 ions. 6 The FC curve does not even show any structure at the Neel point. Obviously, there is a large part of the Co 3 O 4 does not undergo the AFM transition.…”

Section: Magnetic Propertymentioning

confidence: 99%

“…[1][2][3][4] Bulk Co 3 O 4 material exhibits antiferromagnetic (AFM) properties with a Neel temperature (T N ) of about 40 K. 5 In the nanoscale, the Neel temperature is suppressed mainly due to the finite size effect 5 and the lattice phase transition from spinel to inverse spinel structure can be initiated under low applied field. 6 Recently, the relationship between the magnetic core-shell structure and the relevant magnetic properties of Co 3 O 4 has been investigated for its potential applications. 7,8 It was found that not only its magnetic properties attract much attention for the development of the magnetic devices, but also it can be used as catalysts, 9 electrode materials [10][11][12] and chemical sensors 13,14 due to its multifunctionality.…”

Section: Introductionmentioning

confidence: 99%

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Phase formations, magnetic and catalytic properties of Co3O4 hexagonal micro-boxes with one-dimensional nanotubes

et al. 2013

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One-dimensional Co 3 O 4 nanotubes were grown in alignment on the surface of micron-sized Co 3 O 4 hexagonal-box via a mild template-free wet chemical method. The nanotubes are y250 nm in diameter with several micrometers in length. The growth mechanism and phase formation for the vertically grown nanotubes on the surface of the boxes have also been investigated. The intermediates of a-Co(OH) 2 and b-Co(OH) 2 towards the final products of Co 3 O 4 are also characterized. The magnetization, M(T), measurements for the micro-boxes with nanotubes reveals that the Neel temperature is suppressed from the bulk value of 40 K down to 22 K, possibly due to finite size effect. The Curie-Weiss analysis on the paramagnetic behavior above the Neel temperature gives the average effective moment of 4.4 m B per formula unit, slightly higher than 4.14 m B of its bulk counterparts. The electrocatalytic experiments for the oxidation of methanol reveal that the final product exhibits better catalytic performance compared with the intermediate product due to its higher specific surface area.

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“…It is a semiconductor with the band-gap of 1.5 eV [19] [22][23][24][25][26]. With decreasing the size of Co 3 O 4 , the ratio of surface-to-bulk increases and more Co 3+ cations with breaking of octahedral symmetry locate at the surface.…”

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confidence: 99%

Anomalous magnetic properties of 7 nm single-crystal Co3O4 nanowires

Lv¹,

Zhang²,

Xu³

et al. 2012

Journal of Applied Physics

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We present a study of magnetic properties of single-crystal Co 3 O 4 nanowires with diameter about 7 nm. The nanowires expose (111) planes composed of plenty of Co 3+ cations and exhibit two Néel temperatures at 56 K (T N of wire cores) and 73 K (T N of wire shells), which are far above T N = 40 K of bulk Co 3 O 4 . This novel bahavior is attributed to symmetry breaking of surface Co 3+ cations and magnetic proximity effect. The nanowire shells show macroscopic residual magnetic moments. Cooling in a magnetic field, a fraction of the residual moments are tightly pinned to the antiferromagnetic lattice, which results in an obvious horizontal and vertical shift of hysteresis loop. Our experiment demonstrates that the exchange bias field H E and the pinned magnetic moments M pin follow a simple expression H E = aM pin with a a constant.The studies of the exchange bias was starting with the pioneering work of Meiklejohn and Bean in 1956 when studying Co particles embedded in their native antiferromagnetic oxide [1,2]. Since that time, there has been a continuously growing interest in both the fundamental physics and applications of this effect [3][4][5]. Several decades later, new phenomena, such as positive exchange bias and exchange bias in nanoscale antiferromagnetic (AFM) system, are still being uncovered in this subject [6][7][8][9][10][11][12][13][14][15][16][17].In this letter, we present a study of magnetic properties of single-crystal AFM Co 3 O 4 nanowires with diameter about 7 nm. The nanowires are selectively exposing four (111) planes composed of plenty of Co 3+ cations according to scanning tunnelling microscopy (STM) studies [18][19][20]. Remarkably, the nanowires show two characteristic order temperatures at 56 K and 73 K, which are far above the AFM order temperature of bulk Co 3 O 4 ~ 40 K. The temperature 73 K is attributed to the Néel temperature of the nanowire shell with symmetry breaking of surface Co 3+ cations. The enhancement of T N of AFM core from about 40 K to 56 K is tentatively attributed to core-shell exchange interactions, i.e., the so-called magnetic proximity effect proposed in Ref. [15,17]. The Co 3 O 4 nanowire shell shows macroscopic residual magnetic moments below 35 K. Cooling the nanowires in a magnetic field larger than 20 kOe, up to 16% of the residual moments is tightly pinned to the antiferromagnetic lattice and does not rotate in an external magnetic field, which results in an obvious horizontal (exchange bias field H E ) and vertical shift of hysteresis loop. We show that the exchange bias field H E and the size of the pinned magnetic moments M pin follow a simple expression H E = aM pin with a a constant.The bulk Co 3 O 4 has a cubic spinel structure with lattice constant of 0.8065 nm. It is a semiconductor with the band-gap of 1.5 eV [19] [22][23][24][25][26]. With decreasing the size of Co 3 O 4 , the ratio of surface-to-bulk increases and more Co 3+ cations with breaking of octahedral symmetry locate at the surface. As a result, it is expected that nanoscale Co 3 O ...

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Field-dependent low-field enhancement in effective paramagnetic moment with nanoscaled Co3O4

Cited by 20 publications

References 37 publications

Electrostatic doping as a source for robust ferromagnetism at the interface between antiferromagnetic cobalt oxides

Electrostatic doping as a source for robust ferromagnetism at the interface between antiferromagnetic cobalt oxides

Phase formations, magnetic and catalytic properties of Co3O4 hexagonal micro-boxes with one-dimensional nanotubes

Anomalous magnetic properties of 7 nm single-crystal Co3O4 nanowires

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