Tuning the magnetic properties of ${\mathrm{V}}_2{\mathrm{O}}_3/\mathrm{CoFeB}$ heterostructures across the ${\mathrm{V}}_2{\mathrm{O}}_3$ structural transition

In this work, we investigate the effects of the ${\mathrm{V}}_2{\mathrm{O}}_3$ structural phase transition on the magnetic properties of an amorphous magnetic thin film of CoFeB in contact with it. ${\mathrm{V}}_2{\mathrm{O}}_3$ thin films are deposited epitaxially on sapphire substrates, reaching bulklike properties after few nm of growth. By means of temperature dependent Kerr effect characterizations, we prove that crossing the ${\mathrm{V}}_2{\mathrm{O}}_3$ structural phase transition induces reproducible and reversible changes to CoFeB magnetic properties, especially to its coercive field. By decreasing the oxide layer thickness, its effects on the magnetic layer decreases, while reducing the magnetic layer thickness maximizes it, with a maximum of 330% coercive field variation found between the two ${\mathrm{V}}_2{\mathrm{O}}_3$ structural phases. By simply tuning the temperature, this systematic study shows that the engineering of ${\mathrm{V}}_2{\mathrm{O}}_3$ structural transition induces large interfacial strain and thus strong magnetic property variations to an amorphous thin film, opening wide possibilities in implementing strain-driven control of the magnetic behavior without strict requirements on epitaxial coherence at the interface.

Figure 1

(a) θ-2θ scans recorded on ${\mathrm{Al}}_2{\mathrm{O}}_3\text{/}{\mathrm{V}}_2{\mathrm{O}}_3\left(t\right)\text{/}\mathrm{CoFeB}\left(30\mathrm{nm}\right)\text{/}\mathrm{MgO}$ for different oxide thicknesses: 0 nm (green), 5 nm (blue), 25 nm (black), and 80 nm (red). Diamonds indicate the spurious diffraction peaks coming from the nonmonochromatic source. For the 25-nm-thick ${\mathrm{V}}_2{\mathrm{O}}_3$ (b), φ scans are shown on the (0 2 −2 10) reflection of the substrate (black) and the oxide (grey) as well as (c) normalized 2D reciprocal space map around this reflection. In (a) and (c), the bulk values of ${\mathrm{V}}_2{\mathrm{O}}_3$ are pointed out by a dashed line.

Figure 2

Transport measurements collected between LT and RT for two different thickness of ${\mathrm{V}}_2{\mathrm{O}}_3$ thin films, 25 nm (black) and 80 nm (red). On both curves, the left branch corresponds to the cooling one and the right branch to the heating one.

Figure 3

(a) Hysteresis loops measured along 270° in-plane angle at two relevant temperatures, i.e., RT (black and green) and LT (red and blue), and for two different CoFeB thicknesses, i.e., 3 (black and red) and 30 nm (green and blue), deposited on 25-nm-thick ${\mathrm{V}}_2{\mathrm{O}}_3$. (b) Polar plot of the magnetic coercive field $H_C$ measured for the same conditions. The two black arrows represent the in-plane crystallographic directions of both the substrate and ${\mathrm{V}}_2{\mathrm{O}}_3$. (c) Hysteresis loops of ${\mathrm{V}}_2{\mathrm{O}}_3$(25 nm)/CoFeB(3 nm) along the same angle are recorded at LT after ZFC (red) and FC (pink).

Figure 4

(a) Half hysteresis loops of ${\mathrm{V}}_2{\mathrm{O}}_3$(25 nm)/CoFeB(6 nm) heterostructure along the easy between LT and RT. (b) $H_C$ ($T$) curves for both the same (black) and the reference (green) samples.

Figure 5

$H_C$ ($T$) curves of the ${\mathrm{V}}_2{\mathrm{O}}_3$(80 nm)/CoFeB(3 nm) heterostructure for both heating (red) and cooling (blue) branches.

Figure 6

(a) $H_C$ ($T$) curves of the 80-nm-thick ${\mathrm{V}}_2{\mathrm{O}}_3$ for different CoFeB thicknesses: 3 nm (red), 6 nm (pink), 15 nm (light orange), and 30 nm (orange). (b) $H_C$ ($T$) curves of the 3-nm-thick CoFeB for different ${\mathrm{V}}_2{\mathrm{O}}_3$ thicknesses, 0 nm (green), 5 nm (blue), 25 nm (black), and 80 nm (red). (c) Percentage variation of the coercive field measured between LT and RT for different thicknesses of ${\mathrm{V}}_2{\mathrm{O}}_3$ and CoFeB.