Temperature dependence of magnetic anisotropy and domain wall tuning in BaTiO₃(111)/CoFeB multiferroics

Artificial multiferroics consist of two types of ferroic materials, typically a ferroelectric and a ferromagnet, often coupled interfacially by magnetostriction induced by the lattice elongations in the ferroelectric. In BaTiO3, the magnitude of strain induced by these elongations is heavily temperature dependent, varying greatly between each of the polar crystal phases and exerting a huge influence over the properties of a coupled magnetic film. Here, we demonstrate that temperature and, thus, strain are effective means of controlling the magnetic anisotropy in BaTiO3(111)/CoFeB heterostructures. We investigate the three polar phases of BaTiO3: tetragonal (T) at room temperature, orthorhombic (O) below 280 K, and rhombohedral (R) below 190 K across a total range of 77–420 K. We find two distinct responses: a step-like change in the anisotropy across the low-temperature phase transitions and a sharp high-temperature reduction around the ferroelectric Curie temperature, measured from hard axis hysteresis loops. Using our measurements of this anisotropy strength, we are then able to show by micromagnetic simulation the behavior of all possible magnetic domain wall states and determine their scaling as a function of temperature. The most significant changes occur in the head-to-head domain wall states, with a maximum change of 210 nm predicted across the entire range, effectively doubling the size of the domain wall as compared to room temperature. Notably, similar changes are seen for both high and low temperatures, which suggests different routes for potential control of magnetic anisotropy and elastically pinned magnetic domain walls

Temperature Dependence of Magnetic Anisotropy and Domain Wall Width Tuning in a BaTiO₃(111)/CoFeB Heterostructure

Composite multiferroics consist of two types of ferroic materials, typically a ferroelectric and ferromagnet, often coupled interfacially by strain induced by the lattice elongations in the ferroelectric. In BaTiO3 (BTO) substrates the magnitude of the strain is strongly temperature dependent, varying greatly between each of the polar crystal phases and exerting a huge influence over the properties of a coupled magnetic film. In this work we determine the temperature dependence of the strain-induced magnetoelastic anisotropy within ferromagnetic domains in a CoFeB film coupled to the ferroelectric domains from a BTO(111) substrate. Using our measurements of this anisotropy strength we then micromagnetically determine the scaling of magnetic domain wall widths as a function of temperature, demonstrating an increase of 100% across the entire range with the most significant changes occurring around the BTO phase transitions