Advanced Ceramics and Nanocomposites of Half-metallic Ferromagnetic CrO2 for Magnetic, GMR and Optical Sensors

Ram, S.; Biswas, Sajib; J-Fecht, H.

doi:10.1007/978-0-387-48805-9_1

Cited by 2 publications

(7 citation statements)

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“…Freshly prepared aqueous solutions of AgNO 3 (0.5 M in 50 ml) and CrO 3 (0.5 M in 50 ml) were added dropwise to an aqueous solution (150 ml) of PVA (4.0 g) and sucrose (20 g) at 65-70 1C under continuous magnetic stirring in the dark. As reported elsewhere, 28,40,41 the PVA molecular chains encapsulate the cations and induce a controlled reaction in dispersed micelles in the solution. As a consequence, the reaction progressed slowly in steps with a regular change in average color from pale yellowish/light orange to maroon reddish and finally to a dark reddish/blackish red color.…”

Section: Synthesis Of Ag-coated Multiphasic Chromium Oxide Nanocompos...mentioning

confidence: 65%

“…The formation of a discontinuous Ag layer on the nanocomposite particles can be ascribed to the prevailing thermodynamics during the reaction involving a simultaneous mixing of AgNO 3 and CrO 3 in the PVA-sucrose solution at 65-70 1C. In our previous work, 41,52 encapsulation of the Cr 6+ ions in the micellar reactors of PVA molecules in the hot solution and the subsequent formation of a stable Cr 4+ -PVA complex chelate structure was reported. The derived complex chelates were further treated with AgNO 3 to obtain Ag-coated anisotropic CrO 2 nanorods and fibrils.…”

Section: Structure and Morphologymentioning

confidence: 95%

“…Pristine CrO 2 nanocrystallites grow in a bit different intensity pattern showing the maximum intensity of the (101) peak when no foreign additives are used in the wet chemical method. 41 The Rietveld analysis (details are given in the ESI †) of the t-CrO 2 phase in the as-synthesized nanocomposites reveals the usual rutile type crystal structure with significantly larger lattice parameters a = 0.4424 nm and c = 0.3009 nm (lattice volume V 0 = 0.0589 nm 3 and density d = 4.74 g cm À3 ) in comparison to bulk CrO 2 of a = 0.4419 nm and c = 0.2915 nm (V 0 = 0.0569 nm 3 and d = 4.90 g cm À3 ). 49 In terms of thermodynamics, the difference lies in the high-energy structure of small t-CrO 2 crystallites.…”

Section: Structure and Morphologymentioning

confidence: 99%

“…The PVA solution used in this work served the dual purpose of a controlled reducer as well as a template for nucleation and controlled growth of the complex diluted magnetic nanocomposites. 28,40,41,52 Such types of magnetic nanocomposites retain the SDT effects at RT and show significant RTMR for smart applications.…”

Section: Structure and Morphologymentioning

confidence: 99%

“…31,32 CrO 2 has been tailored in various forms to improve its electrical and magnetotransport properties, which depend on several factors including shape anisotropy, particle size, and grain boundaries. 27,28,30,[33][34][35][36][37][38] In this regard, diluted CrO 2 composites, e.g., CrO 2 -Cr 2 O 3 , 34,39 CrO 2 -TiO 2 , 18,37 Ag-coated CrO 2 , 28 or CrO 2 -polymer, 38,40,41 have spurred much attention. Such a binary composite is technologically smart in tuning the functional properties of CrO 2 in the presence of a nonmagnetic phase.…”

Section: Introductionmentioning

confidence: 99%

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Enhanced room-temperature magnetoresistance in self-assembled Ag-coated multiphasic chromium oxide nanocomposites

Dwivedi

Biswas

2016

Phys. Chem. Chem. Phys.

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Self-assembled Ag-coated multiphasic diluted magnetic chromium oxide nanocomposites were developed by a facile chemical synthesis route involving a reaction of CrO3 in the presence of Ag(+) ions in an aqueous solution of poly-vinyl alcohol (PVA) and sucrose. The tiny ferromagnetic single domains of tetragonal and orthorhombic CrO2 (t-CrO2 and o-CrO2) embedded in a dominantly insulating matrix of antiferromagnetic Cr2O3 and Cr3O8, and paramagnetic CrO3 and Cr2O, with a correlated diamagnetic thin and discontinuous shell layer of Ag efficiently tailor useful magnetic and room-temperature magnetoresistance (RTMR) properties. The t-CrO2, o-CrO2, possible canted ferromagnetism due to spin disorder in the matrix components, and the associated exchange interactions are the elements responsible for the observed ferromagnetism in the composite structure. The chain of ferromagnetic centers embedded in the composite matrix constitutes a type of magnetic tunnel junction through which spin-polarized electrons can effectively move without significant local interruptions. Electrical transport measurements showed that the spin-dependent tunneling (SDT) mechanism in the engineered microstructure of the nanocomposites exists even at room temperature (RT). A typical sample unveils a markedly enhanced RTMR-value, e.g., -80% at an applied field (H) of 3 kOe, compared to the reported values for compacted CrO2 powders or composites. The enhanced RTMR-value observed in the Coulomb blockade regime appears not only due to the considerably suppressed spin flipping at RT but primarily due to a highly effective SDT mechanism through an interlinked structure of Ag-coated multiphasic chromium oxide nanocomposites.

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Section: Synthesis Of Ag-coated Multiphasic Chromium Oxide Nanocompos...mentioning

confidence: 65%

Section: Structure and Morphologymentioning

confidence: 95%

Section: Structure and Morphologymentioning

confidence: 99%

Section: Structure and Morphologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Enhanced room-temperature magnetoresistance in self-assembled Ag-coated multiphasic chromium oxide nanocomposites

Dwivedi

Biswas

2016

Phys. Chem. Chem. Phys.

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Magnetism in a Spintronic Compound Zr0.8Cr0.2O2 of Small Crystallites

Sengupta

Misra

Ram

2014

JNanoR

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A transition metal ion Cr4+(3d2 spins) doped ZrO2 of small crystallites presents tailored magnetic, electrical and optical properties useful for magnetodielectric and spintronic applications. A liquid polymer precursor gel (Cr4+ and Zr4+ complex with glycerol) when heated in an autoclave at a small pressure 0.6-0.7 atm at 420–470 K results in a compound Zr0.8Cr0.2O2 with an average 5 nm crystallite size of a stabilized cubic (c)-ZrO2-type phase (after 2 h annealing at 773 K in air). A broad Raman band is observed at ~300 cm-1 in acoustic and transverse optic phonons characteristic of the c-ZrO2-type structure, with a prominent O–Cr–O stretching band at 878 cm-1 in a ferromagnetic order. A CrO2/Cr2O3 surface layer exhibits two weak bands at ~1011 cm-1 and 1032 cm-1. The sample exhibits an ‘S’-shaped ferromagnetic hysteresis loop (does not saturate below 60 kOe fields) at 5 K, with a magnetization M = 85.79 emu/g (in the CrO2 part) at 60 kOe and coercivity Hc = 100 Oe. With warming above 5 K, the loop converges progressively with only a weak ferromagnetism at room temperature, M = 9.08 emu/g and Hc = 54.2 Oe. As a pinning barrier, the uncompensated spins in the surface layer supports coercivity at low temperature. A model magnetic structure describes the magnetic properties in correlation to the microstructure.

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Advanced Ceramics and Nanocomposites of Half-metallic Ferromagnetic CrO2 for Magnetic, GMR and Optical Sensors

Cited by 2 publications

References 184 publications

Enhanced room-temperature magnetoresistance in self-assembled Ag-coated multiphasic chromium oxide nanocomposites

Enhanced room-temperature magnetoresistance in self-assembled Ag-coated multiphasic chromium oxide nanocomposites

Magnetism in a Spintronic Compound Zr<sub>0.8</sub>Cr<sub>0.2</sub>O<sub>2</sub> of Small Crystallites

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