All ferromagnetic materials show deterioration of magnetism-related properties such as magnetization and magnetostriction with increasing temperature, as the result of gradual loss of magnetic order with approaching Curie temperature T_C. However, technologically, it is highly desired to find a magnetic material that can resist such magnetism deterioration and maintain stable magnetism up to its T_C, but this seems against the conventional wisdom about ferromagnetism. Here we show that a Fe–Ga alloy exhibits highly thermal-stable magnetization up to the vicinity of its T_C, 880 K. Also, the magnetostriction shows nearly no deterioration over a very wide temperature range. Such unusual behaviour stems from dual-magnetic-phase nature of this alloy, in which a gradual structural-magnetic transformation occurs between two magnetic phases so that the magnetism deterioration is compensated by the growth of the ferromagnetic phase with larger magnetization. Our finding may help to develop highly thermal-stable ferromagnetic and magnetostrictive materials.

Development of miniaturized magnetostriction-associated devices requires low-field-triggered large magnetostriction. In this study, we acquired a large magnetostriction (800 ppm) triggered by a low saturation field (0.8 kOe) in iron-palladium (Fe-Pd) alloys. Magnetostriction enhancement jumping from 340 to 800 ppm was obtained with a slight increase in Pd concentration from 31.3 to 32.3 at. %. Further analysis showed that such a slight increase led to suppression of the long-range ordered martensitic phase and resulted in a frozen short-range ordered strain glass state. This strain glass state possessed a two-phase nanostructure with nanosized frozen strain domains embedded in the austenite matrix, which was responsible for the unique magnetostriction behavior. Our study provides a way to design novel magnetostrictive materials with low-field-triggered large magnetostriction.

We employ transmission electron microscopy to explore the reason for large piezoelectricity (d₃₃≈400pC/N) in a Pb-free 0.96(K_0.5Na_0.5)_0.95Li_0.05Nb_0.93Sb_0.07O₃ −0.04BaZrO₃ ceramic from microstructure. The result shows that the high piezoelectricity corresponds to a miniaturized nanodomain configuration in a domain hierarchy. The nanodomains disappear on heating accompanied by a reduction in d₃₃ value. Further convergent beam electron diffraction study reveals a coexistence of tetragonal and orthorhombic phase, which indicates that large piezoelectricity of KNLNS_0.07-BZ may stem from easy polarization rotation due to low polarization anisotropy on the tetragonal-orthorhombic phase boundary.

Strain glass is a glassy state with frozen ferroelastic/martensitic nanodomains in shape memory alloys, yet its nature remains unclear. Here, we report a glassy feature in strain glass that was thought to be only present in structural glasses. An abnormal hump is observed in strain glass around 10 K upon normalizing the specific heat by cubed temperature, similar to the boson peak in metallic glass. The simulation studies show that this boson-peak-like anomaly is caused by the phonon softening of the non-transforming matrix surrounding martensitic domains, which occurs in a transverse acoustic branch not associated with the martensitic transformation displacements. Therefore, this anomaly neither is a relic of van Hove singularity nor can be explained by other theories relying on structural disorder, while it verifies a recent theoretical model without any assumptions of disorder. This work might provide fresh insights in understanding the nature of glassy states and associated vibrational properties.