[S-EM15] 地磁気・古地磁気・岩石磁気

[SEM15-08] 樹木年輪中の磁性物質の走査型SQUID磁気顕微鏡による高感度・高分解能検出

*小田 啓邦¹ (1.産業技術総合研究所地質情報研究部門)

キーワード：アカマツ、走査型SQUID磁気顕微鏡、低温磁性

We conducted magnetic imaging on a red pine tree using scanning SQUID microscope. Thin sections were prepared with a thickness of about 1 mm from a tree trunk of a red pine containing the part close to the bark. Magnetic field values measured on thin sections were very weak typically less than about 0.2 nT. After exposing to a vertical magnetic field of 2T, surface magnetic fields of a few nT were observed as stripes parallel to the annual growth rings. Areas with strong magnetic field correspond to spring layers with high growth rate composed of less dense material. Spring layer has reddish brown spots, which shows dipole magnetic anomalies. These might be isolated magnetic mineral grains contained in the tree. Low temperature magnetometry conducted on a sample from the tree trunk suggest that there are two mineral phases with distinct magnetic phase transition temperatures of 65K and 105K. The higher transition temperature might be Verwey transition of magnetite with some impurities or non-stoichiometry. In the presentation, we discuss possible origins of the magnetic minerals based on magnetic microscopy and rock magnetism as well as element mapping using X-ray Fluorescense.