I discuss principal mechanisms of the effective exchange interaction between magnetic moments of transition element atoms in metals and compounds. The purpose is to present clear-cut physical pictures and well-defined terminology of the mechanisms on the basis of the electronic structures revealed by the first principles calculations. Discussion covers transition metals, alloys and compounds including Nd-Fe-B, magnetic semiconductors, and double perovskites. The mechanisms of the effective exchange interaction are categorized into the double exchange interaction, the p-d exchange interaction due to hybridization and the superexchange interaction. The naming and precise definitions are discussed in their historical context.

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The magnetic phase transition of [m ML Fe/12.5 ML Au] ₂₀ (m=0.7, 0.9, 1.1) multilayers was investigated. The quality of samples was well defined by RHEED observation and the 4 circle X-ray diffraction method. Perpendicular anisotropy was observed for samples thinner than 2ML Fe. The Curie temperature T_C and a critical exponent β were precisely determined by the new method to evaluate the spontaneous magnetization from the measured magnetization as a function of temperature. The Curie temperature T_C decreased with decreasing Fe thickness. The critical exponent β for an ultra-thin Fe layer of around 1 ML is similar to that for the Heisenberg model. The spacer layer of Au plays an important role in making the system's three-dimensional ferromagnetism.

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The saturation spin polarization of secondary electrons from a clean Ni (110) surface was quantitatively measured at 0.094 after careful calibration of a compact Mott detector installed in an Auger electron analyzer for strict inspection of the cleanness of the surface. The spin-dependent mean absorption length of Ni (110) was deduced to be about four layers of Ni (110), that is, λ₊= 1.016 nm and λ _{_}= 0.972 nm for the majority spin and minority spin electrons, respectively, from the primary electron energy dependence of the yield and the asymmetry of secondary electrons. The saturation spin polarization was reduced to 0.060, that is, 64% of that for the clean Ni (110) surface, after only 1 hour in a UHV chamber (2×10^-7Pa) following a cleaning procedure, for sub-mono-layer oxygen-chemisorbed Ni (110). A model of anti-ferromagnetic Ni spin moments resulting from 180-degree super-exchange through oxygen atoms in the first layer, based on reported STM observations of Ni-O atomic arrangement, is proposed for use in further investigations to explain this drastic reduction in the polarization, which must be very sensitive to the surface magnetic configuration.

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A peculiar phenomenon of a gradual decrease of the electric resistivity in the water triggered with a milli-gauss low-frequency pulsed magnetic field was found. A typical decrease ratio of the electric resistivity ρ is about 10% during 40 min., and 20-30% during 15 hours after applying a pulsed magnetic field of 1 milli gauss (mG) and 3 Hz with 1 % duty ratio through 1 s. While the non-magnetized water (Control) with ρ of 8-10 k Ω· m rather increased its resistivity through several hours and then showed almost constant through another several hours.
A mixed water of an, as-prepared water with ρ of 9.24 kΩ· m and a magnetized water of 4.50 k Ω· m also gradually decreased its resistivity after mixing through several hours and days. A higher stability of ρ against cooling (icing) and then warming temperature variations in the magnetized water.
These phenomena stably appear through cool seasons except hot summer season.

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