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He, J. J.; Murphy, A. St. J.

doi:10.1103/physrevc.75.068801

Cited by 23 publications

(31 citation statements)

References 15 publications

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“…Hence, T B is expected further reduced from 0.48 K accordingly. At T > T B , the Ni nanocluster is expected to show SPM behavior [27]. The experimentally observed weak ferromagnetism at 300 K by the FC-ZFC and M(H) measurements is therefore inconsistent with this picture.…”

Section: C) Thermoremanent Magnetization Measurementscontrasting

confidence: 36%

“…The experimentally observed weak ferromagnetism at 300 K by the FC-ZFC and M(H) measurements is therefore inconsistent with this picture. On the other hand, for a Ni nanoparticle or a nanocluster embedded inside the Ni 3 C particle to exhibit ferromagnetism at T > 300 K, the diameter is calculated to be at least 21 nm by assuming ΔN = 0.1 with the finite size effect [29] and the temperature dependent shape anisotropy effect of Ni accounted for [27]. If the possibly incomplete reaction process leaves the unreacted Ni in the form of a large particle with the diameter D > 21 nm, then, it is difficult to interpret the appearance of the dip showing up in H C (T) around the freezing temperature by a simple magnetic core-shell structure of the Ni nanoparticles.…”

Section: C) Thermoremanent Magnetization Measurementsmentioning

confidence: 99%

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Weak ferromagnetism and spin-glass state with nanosized nickel carbide

Chen

Leng

2009

Journal of Applied Physics

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Section: C) Thermoremanent Magnetization Measurementscontrasting

confidence: 36%

Section: C) Thermoremanent Magnetization Measurementsmentioning

confidence: 99%

Weak ferromagnetism and spin-glass state with nanosized nickel carbide

Chen

Leng

2009

Journal of Applied Physics

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“…The lacking of the magnetic field dependence excludes both blocking temperature of fine ferromagnetic particle and freezing temperature of spinglass as the origin of the peaks. These characteristic temperatures decrease with increasing magnetic field [27][28][29]. The observed features in our experiment are suggestive of the AFM phase transitions [23].…”

Section: Figsupporting

confidence: 59%

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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“…With increasing temperature, both the coercivity and remanent magnetization decrease, as shown in the inset of Figure 5b, due to the thermal activation effect. 31 The coercivity and remanent magnetization are 390 Oe and 15 emu/g at 100 K, respectively. They become 217 Oe and 10.5…”

mentioning

confidence: 99%

Ni/Ni₃C Core–Shell Nanochains and Its Magnetic Properties: One-Step Synthesis at Low Temperature

et al. 2008

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One-dimensional Ni/Ni 3 C core-shell nanoball chains with an average diameter by around 30 nm were synthesized by means of a mild chemical solution method using a soft template of trioctylphosphineoxide (TOPO). It was revealed that the uniform Ni nanochains were capped with Ni 3 C thin shells by about 1~4 nm in thickness and each Ni core consists of polygrains. The coercivity of the core-shell nanochains is much enhanced (600 Oe at 5 K) and comparable with single Ni nanowires due 2 to the one-dimensional shape anisotropy. Deriving from the distinctive structure of Ni core and Ni 3 C shell, this architecture may possess a possible bi-functionality. This unique architecture is also useful for the study on the magnetization reversal mechanism of one-dimensional magnetic nanostructure.

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RevisedV45(p,γ)

Cited by 23 publications

References 15 publications

Weak ferromagnetism and spin-glass state with nanosized nickel carbide

Weak ferromagnetism and spin-glass state with nanosized nickel carbide

Anomalous magnetic properties of 7 nm single-crystal Co3O4 nanowires

Ni/Ni₃C Core–Shell Nanochains and Its Magnetic Properties: One-Step Synthesis at Low Temperature

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RevisedV45(p,γ)

Cited by 23 publications

References 15 publications

Weak ferromagnetism and spin-glass state with nanosized nickel carbide

Weak ferromagnetism and spin-glass state with nanosized nickel carbide

Anomalous magnetic properties of 7 nm single-crystal Co3O4 nanowires

Ni/Ni3C Core–Shell Nanochains and Its Magnetic Properties: One-Step Synthesis at Low Temperature

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Ni/Ni₃C Core–Shell Nanochains and Its Magnetic Properties: One-Step Synthesis at Low Temperature