The magneto-structural coupling of BiFeO3 (BFO)–CoFe2O4 (CFO)/LaAlO3 (LAO) heteroepitaxy with various lateral sizes of CFO pillars embedded in a BFO matrix was investigated.

YMnO3 (YMO) thin film is one of the highly studied multiferroic materials due to its tunable crystalline structure via misfit strain from the substrate. This tunability involves intriguing physical phenomena that encourage further explorations for fundamental research and practical applications. The configuration of the initial atomic layers during the growth of YMO thin films plays a key role in determining their physical properties. In the present research, the correlation between the substrate’s polarity and the misfit strain of the YMO films is studied comprehensively. The results showed that despite the YMO films grown on MgO (100) and MgO (111) being under the same growth conditions and having resulted in the same hexagonal crystal structure (h-YMO), the films do exhibit distinctly different microstructures, electronic structures, and magnetic properties. We suggest that the extent of charge accumulation induced by the surface polarity of the substrates may have resulted in a substantially different intermixing feature at the h-YMO/substrate interfaces, which, in turn, alters the structure and thus the physical properties of the films. Our results open up the possibility of manipulating the h-YMO thin film’s magnetic properties by interfacial engineering without significantly altering the structure of the films which could benefit the fabrication efficiency for various next-generation electronics.

This work reports molecular beam epitaxy (MBE) of two-dimensional (2D) GaSe1-xTex ternary alloys recently attracted numerous interesting physics for prospective electronics and optoelectronics even facing crucial challenges in their epitaxial...

The origin of insulating ferromagnetism in epitaxial LaCoO3 films under tensile strain remains elusive despite extensive research efforts are devoted. Surprisingly, the spin state of its Co ions, the main parameter of its ferromagnetism, is still to be determined. Here, the spin state in epitaxial LaCoO3 thin films is systematically investigated to clarify the mechanism of strain‐induced ferromagnetism using element‐specific X‐ray absorption spectroscopy and dichroism. Combining with the configuration interaction cluster calculations, it is unambiguously demonstrated that Co3+ in LaCoO3 films under compressive strain (on LaAlO3 substrate) is practically a low‐spin state, whereas Co3+ in LaCoO3 films under tensile strain (on SrTiO3 substrate) have mixed high‐spin and low‐spin states with a ratio close to 1:3. From the identification of this spin state ratio, it is inferred that the dark strips observed by high‐resolution scanning transmission electron microscopy indicate the position of Co3+ high‐spin state, i.e., an observation of a spin state disproportionation in tensile‐strained LaCoO3 films. This consequently explains the nature of ferromagnetism in LaCoO3 films. The study highlights the importance of spin state degrees of freedom, along with thin‐film strain engineering, in creating new physical properties that do not exist in bulk materials.