Weak ferromagnetism and spin-glass state with nanosized nickel carbide

Chen, Chinping; Leng, Yonghua; Li, Xingguo

doi:10.1063/1.3155997

Cited by 25 publications

(31 citation statements)

References 31 publications

(39 reference statements)

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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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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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“…12 The value of ϕ represents the strength of exchange interaction and it falls within the range of 0.004 to 0.018 for spin-glass, whereas for a superparamagnetic phase 0.05 < ϕ < 0.13. 2,6,9,12 In our studies, the ϕ values calculated for Ni 3 C 1.5 nanoparticles is ∼0.015, which is in the range of spin-glass systems. Fig.…”

Section: H/∆jmentioning

confidence: 90%

“…In case of superparamagnetic nanoparticles, this type of magnetic cooling effect has been seen when the effective anisotropy energy is equivalent to the thermal energy. 6,12 It is worthwhile to mention that the ZFC peak position remains within the range 12 to 17 K for all the Ni carbide nanoparticles. The magnetic cooling effect could also be possible due to the spin-glass freezing of localized spins.…”

Section: Methodsmentioning

confidence: 99%

“…5 However, the Ni 3 C NPs synthesized by both the physical and chemical methods always have carbon defects, which yield formation of Ni-rich regions. 2,3,6 Further, depending on the exchange coupling among the spins in the Ni-rich regions, different magnetic behavior: superparamagnetic, weak ferromagnetic and spin-glass have been noticed. 4,[6][7][8] Moreover, in nanoparticles the surface spins also dominate the magnetization due to their lower coordination and uncompensated exchange couplings.…”

Section: Introductionmentioning

confidence: 99%

“…demonstrated a weak ferromagnetism and surface spin-glass like state in hexagonal phase Ni 3 C nanoparticles. 6 According to your knowledge, these magnetic behaviors have not been studied with variation of carbon content in the nickel carbide NPs. In this study, we first time report the effect of carbon content on the low temperature magnetic properties of rhombohedral nickel carbide nanoparticles.…”

Section: Introductionmentioning

confidence: 99%

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Magnetic properties of nickel carbide nanoparticles with enhanced coercivity

et al. 2017

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Rhombohedral nickel carbide (Ni3Cx, x=0.7, 1.2 and 1.5) nanoparticles (∼ 110 nm) with enhanced magnetic coercivity (HC up to 1.3 kOe) at temperature below the spin-glass freezing (Tf) have been demonstrated. The presence of spin-glass state, which is seen at ∼17 K, is evident by the field dependence of the freezing temperature following the de Almeida–Thouless (AT) relationship and frequency dependence of Tf. Moreover, the spin-glass state is irreversible to the sweeping applied field and results in high HC at 10 K. With increases of the carbon content, we have found a gradual increasing trend in the saturation magnetization (MS: 6.6 to 9.2 emu/g) and coercivity (350 Oe to 1.3kOe) at 10 K. This is attributed to the increase of spin-glass contribution and the weak ferromagnetic phase.

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