The secondary battery industry is rapidly emerging as a new industry growth group to realize global eco-friendly policies and carbon neutrality. In particular, the cathode material, one of the main materials of secondary batteries, is a core material for the mobile, energy storage system (ESS), and electric vehicle industries. Therefore, the concept of cathode materials and oxidation/reduction reactions were introduced, and the magnetic properties of cathode materials were reviewed using Mössbauer spectroscopy. The charge/discharge mechanism is explained through the change of iron ions in the cathode material according to the charge/discharge process, the changes in the spectrum according to charge/discharge were also investigated through Mössbauer spectroscopy at low temperature. In addition to equipment for measuring electrochemical properties, the fusion of secondary batteries with equipment for measuring magnetic properties such as Mössbauer spectroscopy is expected to bring about the development of new cathode materials and secondary battery industries.

A study on the application of Mössbauer spectroscopy to Korean cultural properties, has been conducted for interpretation of ironcontaining mineral compositions, coloring factors, manufacturing technique, and provenance; such as Ulleungdo seokganju (natural red pigment), obsidian (Neolithic tool), Goryeo celadon, and black pottery. As reported, Mössbauer spectroscopic data provides newer and various information on the iron-containing cultural properties, further studies need to be applied to more various type of archaeological objects; such as earthen artifacts (additional ceramic wares by type and color, roof tiles, coffins, bricks and clay dolls), stone artifacts (royal seals, accessories in ornamental wares, glass beads), iron artifacts and objects (sword, tools, ore fragments, slags), and painted pigment (on the murals, painting, dancheong). In addition, it is expected that innovative research will be possible for more diverse cultural properties, via the application of the improved analyzing system, such as portable Mössbauer spectrometer.

Emergent materials that exhibit two or more complex properties are attracting attention as new functional materials and are being studied with the interest of many scholars. In particular, in multiferroic materials where ferroelectricity and magnetism coexist, it is very important to understand the interaction such as the reversible flipping of polarization (magnetization) actuated by magnetic (electric) field as well as the change of dielectric constant by applied magnetic field. The causes of physical properties resulting from the interaction of two or more order functions cannot be observed with conventional macroscopic magnetometry equipment. Thus, from the point of view of an atom that can measure electronic structure and energy level, quantum mechanical experiments that satisfy the uncertainty principle are essential. Here, I would like to introduce some examples of emergent materials researched through the Mösbauer spectroscopy experiment, a quantum mechanical experimental tool.

Mn-substituted M-type Sr-hexaferrites, SrFe_12-xMn_xO₁₉ (x = 0, 2, 4, 6, 8, 10, 12) were prepared using the sol-gel and post-annealing processes. XRD analysis on x = 0 sample revealed that the crystalline M-type hexaferrite phase can be formed at the post-annealing temperature, T_ann ≥ 700 ℃. The sol-gel processed powders of SrFe_12-xMn_xO₁₉ (x = 0, 2, 4, 6, 8, 10, 12) annealed at 900 ℃ were ground, pressed into pellets, and sintered in air at 1100 and 1200 ℃ for 4 h, respectively. Single M-type hexaferrite phase is formed in samples of x ≤ 8 sintered at 1100 ℃, while it is found in the samples of x ≤ 6 sintered at 1200 ℃. Scanning electron microscope (SEM) was used for the study of microstructure. For the samples sintered at 1100 ℃, as increase of x from 0 to 6, the resistivity significantly decreases from 1.8 × 10⁸ Ω‧cm to 5.5 × 10³ Ω‧cm, the saturation magnetization value decreases and the coercivity increases. Complex permittivity and permeability were measured on the toroidal shaped samples of SrFe_12-xMn_xO₁₉ (x = 0, 2, 4, 6, 8)-epoxy (10 wt%) composites. The effects of Mn substitution on the electrical and magnetic, and high frequency properties of the M-type Sr-hexaferrites are discussed.

As the performance of sensors embedded in mobile smart phones has improved, many studies using data collected from sensors are being conducted. In this study, using the data obtained from the 3-axis magnetic sensor mounted on the smartphone, a study on the recognition of four human activities was performed using machine learning. From the total data of the 3-axis magnetic sensor, the data was bundled into frames for 2 seconds, divided into several frames, and then supervised learning was carried out using it as an input to the convolutional neural network. The operation of the magnetic sensor depending on the direction was confirmed, and the human activity recognition for standing, sitting, walking, and jogging was verified.