## 3 Results and Discussion
### Thermal Stability Characteristics  
To investigate the thermal stability characteristics of CoFeB thin films with Ta and W buffer and capping layers, we extracted \(M_{\text{s}}\) and \(H_{\text{k}}\) data and calculated \(K_{\text{u}}\) and \(\Delta\) values. The values were analyzed along with the fitted data derived through interpolation based on the experimentally obtained data. The value of \(K_{\text{u}}\) is calculated using Equation (4) [71]:  
\[K_{\text{u}}=\frac{M_{\text{s}}H_{\text{k}}}{2} \tag{4}\]  
Figure 6: (**a**) Gilbert damping constant of Ta buffer and capping layers sample and W buffer and capping layers sample as a function of temperature. (**b**) Symbols show magnetic anisotropy field measured by FMR between 306 and 443 K for Ta buffer and capping layers sample and W buffer and capping layers sample. Solid lines represent linear fits of experimental data. A linear approximation was applied for interpolation to estimate the \(H_{\text{k}}\) values at measurable temperatures using FMR spectroscopy. The \(M_{\text{s}}\) values were calculated using the \(T^{1/3}\) power law. Figure 7a shows the temperature dependence of \(K_{\text{u}}\) for both the prepared samples, where the data points represent values determined through experimentally measured data for \(M_{\text{s}}\) and \(H_{\text{k}}\), and the solid lines are computed based on the temperature changes in \(M_{\text{s}}\) and \(H_{\text{k}}\). As the temperature increased from 293 to 550 K, the \(K_{\text{u}}\) values for the samples with Ta and W buffer and capping layers decreased from 1.32 \(\times\) 10\({}^{5}\) to 0.64 \(\times\) 10\({}^{5}\) erg/cc and from 0.76 \(\times\) 10\({}^{5}\) to 0.43 \(\times\) 10\({}^{5}\) erg/cc, respectively. In particular, at 400, 500, and 550 K, the \(K_{\text{u}}\) values for the sample with Ta buffer and capping layers decreased by 22.1, 41.6, and 51.7%, respectively, compared with those at room temperature. Furthermore, those for the samples with W buffer and capping layers decreased by 18.1, 34.1, and 42.8%, respectively, compared with those at room temperature. These results demonstrated that the sample with Ta buffer and capping layers exhibited a higher \(K_{\text{u}}\) value than the sample with W buffer and capping layers. Furthermore, the absolute \(K_{\text{u}}\) value of the W buffer and capping layers sample was smaller than that of the Ta buffer and capping layers sample, but the relative thermal stability of \(K_{\text{u}}\) for the sample with W buffer and capping layers was higher than that for the sample with Ta buffer and capping layers at high temperatures. Notably, the magnetic anisotropy characteristics of magnetic thin film samples show less dependence on temperature. This is advantageous for the temperature dependence of data read-write operations in memory devices, such as STT-MRAM and SOT-MRAM. Simultaneously, the temperature dependence on the external magnetic field must remain stable with minimal changes. Therefore, it is imperative to analyze the relative temperature dependence of the thermal stability factor. The thermal stability factor is calculated as [72; 73]:  
\[\Delta=\frac{K_{\text{u}}V}{k_{B}T} \tag{5}\]  
where \(V\) and \(T\) represent the volume of the magnetic film layer and absolute temperature, respectively. To compare the relative changes in the thermal stability factor between the Ta buffer and capping layers and W buffer and capping layers at various temperatures, these values were normalized at 293 K. Figure 7b shows the temperature dependence of \(\Delta\) for both the prepared samples, where the data points denote values determined from experimentally measured data for \(M_{\text{s}}\) and \(H_{\text{k}}\), and the solid lines are computed based on  
Figure 7: Magnetic properties of Ta buffer and capping layers sample and W buffer and capping layers sample as a function of temperature: (**a**) in-plane uniaxial magnetic anisotropy energy.