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The morphotropic phase boundary (MPB) has been recently extended from ferroelectrics to ferromagnets, especially for giant magnetostrictive materials. The giant magnetostrictive system in turn presents abundant research opportunities on MPB investigation. In this work, we demonstrate that a magnetic-ordering tricritical type MPB near room temperature can be constructed in the Tb xHo 1−x(Fe 0.9Co 0.1) 2 magnetostrictive system. An ultrahigh magnetostrictive sensitivity is obtained that achieves the performance of the commercial Tb 0.27Dy 0.73Fe 2 (Terfenol-D) polycrystal in the Tb 0.2Ho 0.8(Fe 0.9Co 0.1) 2 alloy. The detailed domain microstructures near the magnetic-ordering tricritical region are determined using phase-field simulations. Our results provide the underlying insights of magnetic-ordering tricritical MPB needed to guide the design of ultrasensitive magnetostrictive materials.

The amorphization of Ni‐Nb multilayered alloy films by xenon ion irradiation at room temperature and by high‐temperature solid‐state reaction was studied. The composition range favoring amorphization was carefully determined to be 20–85 at. % Ni by energy‐dispersive spectroscopy attached to the transmission electron microscope. A new metastable crystalline phase (MX) of hexagonal structure was formed in Ni75Nb25 and Ni70Nb30 multilayered films. Interestingly, in the Ni75Nb25 multilayered films, with increasing mixing dose an amorphous phase was first formed and then the MX‐phase was observed, while in the Ni70Nb30 multilayered films the MX phase was formed at relatively low doses and turned amorphous upon further mixing or 400 °C annealing for 2 h. Besides, annealing of the as‐deposited Ni70Nb30 multilayered films at 300 °C for half an hour also resulted in the formation of the MX phase. The thermal stability of the ion‐mixed amorphous alloys was also studied by subsequent annealing. To give semiquantitative interpretation to all the above observations, the Gibbs free‐energy diagram of the system, in which especially the free‐energy curve of the MX phase is added, was constructed on the basis of the model of Nissen et al. [CALPHAD 7, 51 (1981)] and the method proposed by Alonso and Simozar [Solid State Commun. 46, 765 (1983)]. The explanation based on this diagram is in good agreement with our experimental results.

We study the strain effects on magnetic domain stability and dynamics in nanoscale magnetic thin films using phase-field simulations. Numerous strain-stabilized single-/multi-domain states are discovered, including various magnetic vortices with circular in-plane domains. Furthermore, a strain-domain stability map was constructed, displaying the stable magnetic domain and domain wall structures as a function of biaxial isotropic and anisotropic in-plane strains at room temperature. The present work provides useful guidelines for a precise engineering and experimental observation of domain structures in nanoscale magnetic thin films and a promising scheme towards a low-power and local control over magnetic domain structures.

We show that, using phase-field simulations, large voltage-driven perpendicular magnetic domain switching can be realized in magnetic-ferroelectric nanoislands with relieved substrate constraint, which is difficult in continuous multiferroic layered thin films due to significant substrate clamping. The as-grown magnetic and ferroelectric domain structures in the heterostructured nanoislands can be tailored by engineering their respective geometric sizes and/or the underlying substrate strain. Influences of the lateral size of the island on the dynamic voltage-driven magnetic domain switching are addressed, whereby an optimum lateral size is identified for illustration. Thus, such three-dimensional multiferroic nanoislands should provide great flexibilities for designing novel high-density spintronic/microelectronic devices with purely voltage-driven means.