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Positive temperature coefficient of magnetic anisotropy in polyvinylidene fluoride (PVDF)-based magnetic composites.

Liu Y, Wang B, Zhan Q, Tang Z, Yang H, Liu G, Zuo Z, Zhang X, Xie Y, Zhu X, Chen B, Wang J, Li RW - Sci Rep (2014)

Bottom Line: We ascribe the enhanced magnetic anisotropy of the magnetic film at elevated temperature to the strain-induced anisotropy resulting from the anisotropic thermal expansion of the β-phase PVDF.The simulation based on modified Stoner-Wohlfarth model and the ferromagnetic resonance measurements confirms our results.The present results may help to design magnetic devices with improved thermal stability and enhanced performance.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Magnetic Materials and Devices &Zhejiang Province Key Laboratory of Magnetic Materials and Application Technology, Ningbo Institute of Materials Technology and Engineering (NIMTE), Chinese Academy of Sciences (CAS), Ningbo 315201, People's Republic of China.

ABSTRACT
The magnetic anisotropy is decreased with increasing temperature in normal magnetic materials, which is harmful to the thermal stability of magnetic devices. Here, we report the realization of positive temperature coefficient of magnetic anisotropy in a novel composite combining β-phase polyvinylidene fluoride (PVDF) with magnetostrictive materials (magnetostrictive film/PVDF bilayer structure). We ascribe the enhanced magnetic anisotropy of the magnetic film at elevated temperature to the strain-induced anisotropy resulting from the anisotropic thermal expansion of the β-phase PVDF. The simulation based on modified Stoner-Wohlfarth model and the ferromagnetic resonance measurements confirms our results. The positive temperature coefficient of magnetic anisotropy is estimated to be 1.1 × 10(2) J m(-3) K(-1). Preparing the composite at low temperature can enlarge the temperature range where it shows the positive temperature coefficient of magnetic anisotropy. The present results may help to design magnetic devices with improved thermal stability and enhanced performance.

No MeSH data available.


Related in: MedlinePlus

Temperature dependence of magnetic properties of CoFeB/PVDF.(a) In-plane magnetic hysteresis loops measured along x direction at various temperatures (b) In-plane magnetic hysteresis loops measured along y direction at various temperatures. (c) Temperature dependence of the remanent magnetization with H along x and y directions. The inset: angular dependence of Mr/Ms at 290 and 310 K. (d) Temperature dependence of the remanent magnetization with H along x and y directions for the samples prepared at different temperatures.
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f2: Temperature dependence of magnetic properties of CoFeB/PVDF.(a) In-plane magnetic hysteresis loops measured along x direction at various temperatures (b) In-plane magnetic hysteresis loops measured along y direction at various temperatures. (c) Temperature dependence of the remanent magnetization with H along x and y directions. The inset: angular dependence of Mr/Ms at 290 and 310 K. (d) Temperature dependence of the remanent magnetization with H along x and y directions for the samples prepared at different temperatures.

Mentions: In order to study the temperature coefficient of magnetic anisotropy in the CoFeB/PVDF composite, we measured the magnetic hysteresis loops along the easy (x direction) and hard axis (y direction) at different temperatures. Figure 2a shows the in-plane magnetic hysteresis loops measured with H along x direction (φ = 0°). It is quite surprising to observe that the loop becomes squarer as the temperature is increased. On the other hand, the hard axis magnetic hysteresis loop along y direction (φ = 90°) becomes more slanted (Figure 2b). Figure 2c shows the Mr/Ms versus temperature for H along x and y directions, respectively. With temperature increasing from 250 to 350 K, the Mr/Ms increases from 0.32 to 0.86 and decreases from 0.68 to 0.16 for H along x and y directions, respectively (Figure S1). The crossover occurs at about 298 K, which means that the sample is magnetically isotropic at around 298 K. When the temperature decreases from above 298 K to below 298 K, the easy axis is switched from x to y direction. When the temperature is higher than 298 K, the Mr/Ms difference between the easy and hard axes is increased with increasing temperature. That is, the easy axis becomes easier while the hard axis becomes harder, indicating an abnormal enhanced magnetic anisotropy with increasing temperature. Thus, we can conclude that the CoFeB/PVDF composite possesses a positive temperature coefficient of magnetic anisotropy. The behavior of composites with CoFeB of different thickness (10 nm, 100 nm, and 200 nm) was also studied (Figure S2). All of them show similar temperature dependence of magnetic anisotropy as CoFeB (60 nm)/PVDF. However, when the thickness of CoFeB is too large (i.e. 200 nm), the temperature tunability of Mr/Ms decreases (Figure S2). Figure 2d shows the temperature dependence of Mr/Ms for the samples prepared at 298, 333 and 363 K. The results show that the temperature at which isotropic magnetic behavior is observed to increase with increasing deposition temperature (the small discrepancy is likely due to the difference between the actual sample temperature and the thermal couple reading, which is located behind the heater). After this point, all the samples exhibit an increase of magnetic anisotropy with temperature.


Positive temperature coefficient of magnetic anisotropy in polyvinylidene fluoride (PVDF)-based magnetic composites.

Liu Y, Wang B, Zhan Q, Tang Z, Yang H, Liu G, Zuo Z, Zhang X, Xie Y, Zhu X, Chen B, Wang J, Li RW - Sci Rep (2014)

Temperature dependence of magnetic properties of CoFeB/PVDF.(a) In-plane magnetic hysteresis loops measured along x direction at various temperatures (b) In-plane magnetic hysteresis loops measured along y direction at various temperatures. (c) Temperature dependence of the remanent magnetization with H along x and y directions. The inset: angular dependence of Mr/Ms at 290 and 310 K. (d) Temperature dependence of the remanent magnetization with H along x and y directions for the samples prepared at different temperatures.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4196102&req=5

f2: Temperature dependence of magnetic properties of CoFeB/PVDF.(a) In-plane magnetic hysteresis loops measured along x direction at various temperatures (b) In-plane magnetic hysteresis loops measured along y direction at various temperatures. (c) Temperature dependence of the remanent magnetization with H along x and y directions. The inset: angular dependence of Mr/Ms at 290 and 310 K. (d) Temperature dependence of the remanent magnetization with H along x and y directions for the samples prepared at different temperatures.
Mentions: In order to study the temperature coefficient of magnetic anisotropy in the CoFeB/PVDF composite, we measured the magnetic hysteresis loops along the easy (x direction) and hard axis (y direction) at different temperatures. Figure 2a shows the in-plane magnetic hysteresis loops measured with H along x direction (φ = 0°). It is quite surprising to observe that the loop becomes squarer as the temperature is increased. On the other hand, the hard axis magnetic hysteresis loop along y direction (φ = 90°) becomes more slanted (Figure 2b). Figure 2c shows the Mr/Ms versus temperature for H along x and y directions, respectively. With temperature increasing from 250 to 350 K, the Mr/Ms increases from 0.32 to 0.86 and decreases from 0.68 to 0.16 for H along x and y directions, respectively (Figure S1). The crossover occurs at about 298 K, which means that the sample is magnetically isotropic at around 298 K. When the temperature decreases from above 298 K to below 298 K, the easy axis is switched from x to y direction. When the temperature is higher than 298 K, the Mr/Ms difference between the easy and hard axes is increased with increasing temperature. That is, the easy axis becomes easier while the hard axis becomes harder, indicating an abnormal enhanced magnetic anisotropy with increasing temperature. Thus, we can conclude that the CoFeB/PVDF composite possesses a positive temperature coefficient of magnetic anisotropy. The behavior of composites with CoFeB of different thickness (10 nm, 100 nm, and 200 nm) was also studied (Figure S2). All of them show similar temperature dependence of magnetic anisotropy as CoFeB (60 nm)/PVDF. However, when the thickness of CoFeB is too large (i.e. 200 nm), the temperature tunability of Mr/Ms decreases (Figure S2). Figure 2d shows the temperature dependence of Mr/Ms for the samples prepared at 298, 333 and 363 K. The results show that the temperature at which isotropic magnetic behavior is observed to increase with increasing deposition temperature (the small discrepancy is likely due to the difference between the actual sample temperature and the thermal couple reading, which is located behind the heater). After this point, all the samples exhibit an increase of magnetic anisotropy with temperature.

Bottom Line: We ascribe the enhanced magnetic anisotropy of the magnetic film at elevated temperature to the strain-induced anisotropy resulting from the anisotropic thermal expansion of the β-phase PVDF.The simulation based on modified Stoner-Wohlfarth model and the ferromagnetic resonance measurements confirms our results.The present results may help to design magnetic devices with improved thermal stability and enhanced performance.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Magnetic Materials and Devices &Zhejiang Province Key Laboratory of Magnetic Materials and Application Technology, Ningbo Institute of Materials Technology and Engineering (NIMTE), Chinese Academy of Sciences (CAS), Ningbo 315201, People's Republic of China.

ABSTRACT
The magnetic anisotropy is decreased with increasing temperature in normal magnetic materials, which is harmful to the thermal stability of magnetic devices. Here, we report the realization of positive temperature coefficient of magnetic anisotropy in a novel composite combining β-phase polyvinylidene fluoride (PVDF) with magnetostrictive materials (magnetostrictive film/PVDF bilayer structure). We ascribe the enhanced magnetic anisotropy of the magnetic film at elevated temperature to the strain-induced anisotropy resulting from the anisotropic thermal expansion of the β-phase PVDF. The simulation based on modified Stoner-Wohlfarth model and the ferromagnetic resonance measurements confirms our results. The positive temperature coefficient of magnetic anisotropy is estimated to be 1.1 × 10(2) J m(-3) K(-1). Preparing the composite at low temperature can enlarge the temperature range where it shows the positive temperature coefficient of magnetic anisotropy. The present results may help to design magnetic devices with improved thermal stability and enhanced performance.

No MeSH data available.


Related in: MedlinePlus