Ryuji Hashimoto

Effect of Strain on Magnetic Properties of Nd-Fe-B Thin Film Magnets on BaTiO 3

The influence of strain in the Nd-Fe-B was investigated by using the structural phase transition of BaTiO3 in films consisting of a Mo top layer (10 nm), Nd-Fe-B (30 nm), and a Mo bottom layer (20 nm) deposited onto BaTiO3 (001) substrates by sputtering. As a result, it was found that the magnetization along the easy axis jumps up in magnitude by 3% at around 280 K. This significant effect is certainly due to the lattice strain accompanying the structural phase transition of BaTiO3 from orthorhombic to tetragonal. First-principles calculations were applied to simulate the relationship between magnetization, magnetocrystalline anisotropy and the strain in the Nd-Fe-B main phase. It was also found that the magnetization along the easy axis increases as the lattice constant of the a-axis expands, which shows mostly good agreement with the experimental results under some assumptions.

The temperature dependence of magnetic anisotropy of Nd-Fe-B thin films

The magnetic properties of Nd-Fe-B thin films with the three different compositions (#1: Nd12.6Fe81.5B5.9, #2: Nd14.6Fe78.1B7.4 and #3: Nd22.6Fe66.2B11.2) are discussed. With increasing Nd content, the c-axis orientation along the film normal is enhanced. It is found that sample #2 possesses the saturation magnetization Ms very close to that for Nd2Fe14B over a temperature range from 100 to about 300K. The magnetic anisotropy constant Ku2 for sample #2 is the highest among those samples, but smaller by about 20%, as compared to that for Nd2Fe14B. It is of interest to note that the temperature TR at which Ku1 changes its sign is lower by about 30K as compared to that previously reported for Nd2Fe14B. The reason for this discrepancy is not clear, but could be due to the presence of the minority phases of Nd-rich compounds and also a possible contribution of the magneto-elastic effect to the net magnetic anisotropy.