Out-of-plane polarization reversal and changes in in-plane ferroelectric and ferromagnetic domains of multiferroic BiFe0.9Co0.1O3 thin films by water printing

Abstract BiFe0.9Co0.1O3 is a promising material for an ultra-low-power-consumption nonvolatile magnetic memory device because local magnetization reversal is possible through application of an electric field. Here, changes in ferroelectric and ferromagnetic domain structures in a multiferroic BiFe0.9Co0.1O3 thin film induced by “water printing”, which is a polarization reversal method involving chemical bonding and charge accumulation at the interface between the liquid and the film, was investigated. Water printing using pure water with pH = 6.2 resulted in an out-of-plane polarization reversal from upward to downward. The in-plane domain structure remained unchanged after the water printing process, indicating that 71° switching was achieved in 88.4% of the observation area. However, magnetization reversal was observed in only 50.1% of the area, indicating a loss of correlation between the ferroelectric and magnetic domains because of the slow polarization reversal due to nucleation growth

Systematic charge distribution changes in Bi- and Pb-3d transition metal perovskites

鉛・ビスマス系と３ｄ遷移金属によるペロブスカイト酸化物について、その電荷状態と３ｄレベルの関係性を系統的に明らかにした。それによって、この系でしばしばみられる電荷移動型相転移の背景が明らかとなるとともに、この相転移を利用した負膨張材料開発に重要な指針を与えた

Optimized negative thermal expansion induced by gradual intermetallic charge transfer in Bi1-xSbxNiO3

Negative thermal expansion induced by intermetallic charge transfer between Bi^(5+) and Ni^(2+) was observed in perovskite-type Bi_(1−x)Sb_(x)NiO_(3) (x = 0.05 and 0.10). Bi^(3+) and Bi^(5+) had a long-range ordering in the low-temperature phase of Bi_(0.95)Sb_(0.05)NiO_(3) while the ordering was short-range in Bi_(0.9)Sb_(0.1)NiO_(3). The latter compound exhibited a continuous negative thermal expansion with a linear coefficient of thermal expansion of αL = −106 ppm K^(−1) without temperature hysteresis in a wide temperature range of 200–320 K