A new class of magnetoelastic gel that demonstrates drastic and reversible changes in storage modulus without using strong magnetic fields was obtained. The magnetic gel consists of carrageenan and carbonyl iron particles. The magnetic gel with a volume fraction of magnetic particles of 0.30 exhibited a reversible increase by a factor of 1400 of the storage modulus upon a magnetic field of 500 mT, which is the highest value in the past for magnetorheological soft materials. It is considered that the giant magnetoelastic behavior is caused by both high dispersibility and high mobility of magnetic particles in the carrageenan gel. The off-field storage modulus of the magnetic gel at volume fractions below 0.30 obeyed the Krieger-Dougherty equation, indicating random dispersion of magnetic particles. At 500 mT, the storage modulus was higher than 4.0 MPa, which is equal to that of magnetic fluids, indicating that the magnetic particles move and form a chain structure by magnetic fields. Morphological study revealed the evidence that the magnetic particles embedded in the gel were aligned in the direction of magnetic fields, accompanied by stretching of the gel network. We conclude that the giant magnetoelastic phenomenon originates from the chain structure consisting of magnetic particles similar to magnetic fluids.

We investigated the bubble-domain dynamics in TbFeCo wires with perpendicular magnetization under electric current flows. In TbFeCo wires with relatively low saturation magnetization (M s ), the current pulse caused the bubble domains to collapse without moving. In TbFeCo wires with relatively high M s , however, the bubble domains grew in the current direction. We explain these shape changes by assessing the M s -dependent forces caused by the exchange field and magnetostatic field. We also found that we could control the current-induced behaviors of the bubble domains by using an external magnetic field.

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