Magnetic properties of MnO nanocrystals dispersed in a silica matrix

S. Mukherjee, H. D. Yang, A. K. Pal, S. Majumdar

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

Magnetic nanocrystalline MnO particles have been synthesized in a silica glass matrix by the sol–gel method at calcination temperatures up to 1000 °C. EPR spectra of 0.1 mol% MnO doped silica gel and glasses studied in the temperature range 10–290 K show with the exception of those samples calcined at 900 and 1000 °C 6-line characteristic Mn(II) hyperfine (HF) lines. Additionally five spin-forbidden doublets have been observed at 100 K and below. Small spreads in spin Hamiltonian parameters (D and E) imply that the ligand field environments of Mn(II) ions embedded in the silica glass are nearly uniform. Monotonous decrease in HF linewidth in going from 120 °C gel to 800 °C calcined glass has been interpreted as the continuous decrease in population of isolated Mn2+ ions in silica glass matrix resulting in the decrease of magnetic dipolar interactions leading to the observed decrease in HF linewidth. XRD and TEM of sample calcined at 1000 °C shows the presence of nanocrystals of MnO having orthorhombic crystalline phase and sizes about 10 nm. The thermal behavior of magnetization (zero-field-cooled and field-cooled) and magnetic hysteresis of MnO nanocrystals in the 5–300 K temperature interval have demonstrated that the MnO nanocrystals display superparamagnetic–ferromagnetic transition at low temperatures. X-band EPR linewidth data plotted versus inverse of temperature (1/T) for samples calcined at 900 and 1000 °C (EPR recorded in the vicinity of 0.35 T applied field) depict similar transitions.
Original languageEnglish
Pages (from-to)1690-1697
JournalJournal of Magnetism and Magnetic Materials
Volume324
Issue number9
DOIs
Publication statusPublished - 2012
MoE publication typeA1 Journal article-refereed

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silica glass
Silicon Dioxide
Nanocrystals
Fused silica
Magnetic properties
nanocrystals
Silica
silicon dioxide
magnetic properties
Linewidth
Paramagnetic resonance
matrices
Temperature
temperature
Ions
silica gel
Hamiltonians
Magnetic hysteresis
superhigh frequencies
roasting

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Mukherjee, S. ; Yang, H. D. ; Pal, A. K. ; Majumdar, S. / Magnetic properties of MnO nanocrystals dispersed in a silica matrix. In: Journal of Magnetism and Magnetic Materials. 2012 ; Vol. 324, No. 9. pp. 1690-1697.
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abstract = "Magnetic nanocrystalline MnO particles have been synthesized in a silica glass matrix by the sol–gel method at calcination temperatures up to 1000 °C. EPR spectra of 0.1 mol{\%} MnO doped silica gel and glasses studied in the temperature range 10–290 K show with the exception of those samples calcined at 900 and 1000 °C 6-line characteristic Mn(II) hyperfine (HF) lines. Additionally five spin-forbidden doublets have been observed at 100 K and below. Small spreads in spin Hamiltonian parameters (D and E) imply that the ligand field environments of Mn(II) ions embedded in the silica glass are nearly uniform. Monotonous decrease in HF linewidth in going from 120 °C gel to 800 °C calcined glass has been interpreted as the continuous decrease in population of isolated Mn2+ ions in silica glass matrix resulting in the decrease of magnetic dipolar interactions leading to the observed decrease in HF linewidth. XRD and TEM of sample calcined at 1000 °C shows the presence of nanocrystals of MnO having orthorhombic crystalline phase and sizes about 10 nm. The thermal behavior of magnetization (zero-field-cooled and field-cooled) and magnetic hysteresis of MnO nanocrystals in the 5–300 K temperature interval have demonstrated that the MnO nanocrystals display superparamagnetic–ferromagnetic transition at low temperatures. X-band EPR linewidth data plotted versus inverse of temperature (1/T) for samples calcined at 900 and 1000 °C (EPR recorded in the vicinity of 0.35 T applied field) depict similar transitions.",
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Magnetic properties of MnO nanocrystals dispersed in a silica matrix. / Mukherjee, S.; Yang, H. D.; Pal, A. K.; Majumdar, S.

In: Journal of Magnetism and Magnetic Materials, Vol. 324, No. 9, 2012, p. 1690-1697.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

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AU - Pal, A. K.

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N2 - Magnetic nanocrystalline MnO particles have been synthesized in a silica glass matrix by the sol–gel method at calcination temperatures up to 1000 °C. EPR spectra of 0.1 mol% MnO doped silica gel and glasses studied in the temperature range 10–290 K show with the exception of those samples calcined at 900 and 1000 °C 6-line characteristic Mn(II) hyperfine (HF) lines. Additionally five spin-forbidden doublets have been observed at 100 K and below. Small spreads in spin Hamiltonian parameters (D and E) imply that the ligand field environments of Mn(II) ions embedded in the silica glass are nearly uniform. Monotonous decrease in HF linewidth in going from 120 °C gel to 800 °C calcined glass has been interpreted as the continuous decrease in population of isolated Mn2+ ions in silica glass matrix resulting in the decrease of magnetic dipolar interactions leading to the observed decrease in HF linewidth. XRD and TEM of sample calcined at 1000 °C shows the presence of nanocrystals of MnO having orthorhombic crystalline phase and sizes about 10 nm. The thermal behavior of magnetization (zero-field-cooled and field-cooled) and magnetic hysteresis of MnO nanocrystals in the 5–300 K temperature interval have demonstrated that the MnO nanocrystals display superparamagnetic–ferromagnetic transition at low temperatures. X-band EPR linewidth data plotted versus inverse of temperature (1/T) for samples calcined at 900 and 1000 °C (EPR recorded in the vicinity of 0.35 T applied field) depict similar transitions.

AB - Magnetic nanocrystalline MnO particles have been synthesized in a silica glass matrix by the sol–gel method at calcination temperatures up to 1000 °C. EPR spectra of 0.1 mol% MnO doped silica gel and glasses studied in the temperature range 10–290 K show with the exception of those samples calcined at 900 and 1000 °C 6-line characteristic Mn(II) hyperfine (HF) lines. Additionally five spin-forbidden doublets have been observed at 100 K and below. Small spreads in spin Hamiltonian parameters (D and E) imply that the ligand field environments of Mn(II) ions embedded in the silica glass are nearly uniform. Monotonous decrease in HF linewidth in going from 120 °C gel to 800 °C calcined glass has been interpreted as the continuous decrease in population of isolated Mn2+ ions in silica glass matrix resulting in the decrease of magnetic dipolar interactions leading to the observed decrease in HF linewidth. XRD and TEM of sample calcined at 1000 °C shows the presence of nanocrystals of MnO having orthorhombic crystalline phase and sizes about 10 nm. The thermal behavior of magnetization (zero-field-cooled and field-cooled) and magnetic hysteresis of MnO nanocrystals in the 5–300 K temperature interval have demonstrated that the MnO nanocrystals display superparamagnetic–ferromagnetic transition at low temperatures. X-band EPR linewidth data plotted versus inverse of temperature (1/T) for samples calcined at 900 and 1000 °C (EPR recorded in the vicinity of 0.35 T applied field) depict similar transitions.

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