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Grain size-dependent magnetic and electric properties in nanosized YMnO3 multiferroic ceramics.

Han TC, Hsu WL, Lee WD - Nanoscale Res Lett (2011)

Bottom Line: The magnetic characterization indicates that with increasing grain size, the antiferromagnetic (AFM) transition temperature increases from 52 to 74 K.Further analysis suggests that the rising of AFM transition temperature with increasing grain size should be from the structural origin, in which the strength of AFM interaction as well as the electrical polarization is dependent on the in-plane lattice parameters.Furthermore, among all samples, the sample with grain size of 95 nm is found to have the smallest leakage current density (< 1 μA/cm2).PACS: 75.50.Tt, 75.50.Ee, 75.85.+t, 77.84.-s.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan. tchan@nuk.edu.tw.

ABSTRACT
Magnetic and electric properties are investigated for the nanosized YMnO3 samples with different grain sizes (25 nm to 200 nm) synthesized by a modified Pechini method. It shows that magnetic and electric properties are strongly dependent on the grain size. The magnetic characterization indicates that with increasing grain size, the antiferromagnetic (AFM) transition temperature increases from 52 to 74 K. A corresponding shift of the dielectric anomaly is observed, indicating a strong correlation between the electric polarization and the magnetic ordering. Further analysis suggests that the rising of AFM transition temperature with increasing grain size should be from the structural origin, in which the strength of AFM interaction as well as the electrical polarization is dependent on the in-plane lattice parameters. Furthermore, among all samples, the sample with grain size of 95 nm is found to have the smallest leakage current density (< 1 μA/cm2).PACS: 75.50.Tt, 75.50.Ee, 75.85.+t, 77.84.-s.

No MeSH data available.


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Magnetic hysteresis loops at 5 K for the YMnO3 samples with different grain sizes. Inset: magnetic hysteresis curve at 55 K for the sample with grain size of 25 nm.
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Figure 5: Magnetic hysteresis loops at 5 K for the YMnO3 samples with different grain sizes. Inset: magnetic hysteresis curve at 55 K for the sample with grain size of 25 nm.

Mentions: The temperature-dependent magnetization curves M(T) were measured in a magnetic field of 500 Oe under the conditions of zero-field-cooled (ZFC) and field-cooled (FC). Figure 4 displays the temperature dependence of magnetization for the powders with different grain sizes. Open symbols are the data with the ZFC mode, while the solid ones with FC mode. As can be seen, typical AFM to paramagnetic (PM) phase transition is observed for the sample with grain size of 200 nm, and the Néel temperature (TN) is about 74 K. As the grain size decreases, the value of TN shifts to the lower temperatures and is equal to 52 K for the sample with grain size of 25 nm. This size-dependent TN is similar to the observation in the BiFeO3 nanoparticles [15], where the increase in TN with increasing size has been discussed both in terms of phenomenological scaling relations and possible correlations with the decreasing electrical polarization. To further explore the magnetic properties of the samples, magnetic hysteresis loops for the YMnO3 samples with different grain sizes have been measured at 5 K, as presented in Figure 5. For the samples with grain size of 25 and 45 nm, weak ferromagnetic (FM) behavior is observed with corresponding coercivity (Hc) about 395 and 260 Oe, respectively. The inset in Figure 5 shows the magnetic hysteresis curve for the sample with grain size of 25 nm has been measure at 55 K. It indicates the PM behavior which confirms that the FM component disappears above TN. Therefore, the weak FM component does not come from FM impurity phase. As the grain size increases, the weak FM behavior transforms into paramagnetism. Similar effect of grain size on magnetism was also reported in nanosized YMn2O5 [16] and BiFeO3 particles [17]. In fact, weak surface FM component is a universal feature for nanosized AFM systems, which is attributed to the deviation of the AFM arrangement to the disordered surface spin due to the lattice strain [17,18]. Based on the above consideration, the magnetic structure of the nanosized YMnO3 can be considered as a core/shell system, where the inner part of the particle is AFM phase and the surface is FM component.


Grain size-dependent magnetic and electric properties in nanosized YMnO3 multiferroic ceramics.

Han TC, Hsu WL, Lee WD - Nanoscale Res Lett (2011)

Magnetic hysteresis loops at 5 K for the YMnO3 samples with different grain sizes. Inset: magnetic hysteresis curve at 55 K for the sample with grain size of 25 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211257&req=5

Figure 5: Magnetic hysteresis loops at 5 K for the YMnO3 samples with different grain sizes. Inset: magnetic hysteresis curve at 55 K for the sample with grain size of 25 nm.
Mentions: The temperature-dependent magnetization curves M(T) were measured in a magnetic field of 500 Oe under the conditions of zero-field-cooled (ZFC) and field-cooled (FC). Figure 4 displays the temperature dependence of magnetization for the powders with different grain sizes. Open symbols are the data with the ZFC mode, while the solid ones with FC mode. As can be seen, typical AFM to paramagnetic (PM) phase transition is observed for the sample with grain size of 200 nm, and the Néel temperature (TN) is about 74 K. As the grain size decreases, the value of TN shifts to the lower temperatures and is equal to 52 K for the sample with grain size of 25 nm. This size-dependent TN is similar to the observation in the BiFeO3 nanoparticles [15], where the increase in TN with increasing size has been discussed both in terms of phenomenological scaling relations and possible correlations with the decreasing electrical polarization. To further explore the magnetic properties of the samples, magnetic hysteresis loops for the YMnO3 samples with different grain sizes have been measured at 5 K, as presented in Figure 5. For the samples with grain size of 25 and 45 nm, weak ferromagnetic (FM) behavior is observed with corresponding coercivity (Hc) about 395 and 260 Oe, respectively. The inset in Figure 5 shows the magnetic hysteresis curve for the sample with grain size of 25 nm has been measure at 55 K. It indicates the PM behavior which confirms that the FM component disappears above TN. Therefore, the weak FM component does not come from FM impurity phase. As the grain size increases, the weak FM behavior transforms into paramagnetism. Similar effect of grain size on magnetism was also reported in nanosized YMn2O5 [16] and BiFeO3 particles [17]. In fact, weak surface FM component is a universal feature for nanosized AFM systems, which is attributed to the deviation of the AFM arrangement to the disordered surface spin due to the lattice strain [17,18]. Based on the above consideration, the magnetic structure of the nanosized YMnO3 can be considered as a core/shell system, where the inner part of the particle is AFM phase and the surface is FM component.

Bottom Line: The magnetic characterization indicates that with increasing grain size, the antiferromagnetic (AFM) transition temperature increases from 52 to 74 K.Further analysis suggests that the rising of AFM transition temperature with increasing grain size should be from the structural origin, in which the strength of AFM interaction as well as the electrical polarization is dependent on the in-plane lattice parameters.Furthermore, among all samples, the sample with grain size of 95 nm is found to have the smallest leakage current density (< 1 μA/cm2).PACS: 75.50.Tt, 75.50.Ee, 75.85.+t, 77.84.-s.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan. tchan@nuk.edu.tw.

ABSTRACT
Magnetic and electric properties are investigated for the nanosized YMnO3 samples with different grain sizes (25 nm to 200 nm) synthesized by a modified Pechini method. It shows that magnetic and electric properties are strongly dependent on the grain size. The magnetic characterization indicates that with increasing grain size, the antiferromagnetic (AFM) transition temperature increases from 52 to 74 K. A corresponding shift of the dielectric anomaly is observed, indicating a strong correlation between the electric polarization and the magnetic ordering. Further analysis suggests that the rising of AFM transition temperature with increasing grain size should be from the structural origin, in which the strength of AFM interaction as well as the electrical polarization is dependent on the in-plane lattice parameters. Furthermore, among all samples, the sample with grain size of 95 nm is found to have the smallest leakage current density (< 1 μA/cm2).PACS: 75.50.Tt, 75.50.Ee, 75.85.+t, 77.84.-s.

No MeSH data available.


Related in: MedlinePlus