Probing of micromagnetic configuration in manganite channels by transport measurements

Abstract

We explore the possibility of tracking magnetization orientation in artificial structures patterned in ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ epitaxial films by magnetotransport measurements, exploiting the anisotropic magnetoresistance effect. We perform resistance measurements as a function of temperature, magnetic field, and angle between the applied in-plane magnetic field and the channel or crystalline axes in micrometric channels of different widths. We analyze quantitatively our results and extract information about magnetization easy axes, crystalline anisotropy, domain wall resistance, anisotropic magnetoresistance, energy of magnetic domain pinning, and magnetic reversal mechanisms. For channel widths larger than a few micrometers, the magnetization direction at low field $(\ensuremath{\leqslant}200\phantom{\rule{0.3em}{0ex}}\mathrm{Oe})$ is determined by magnetocrystalline easy axes, whereas for channel widths of $\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ or smaller, the shape anisotropy forces the magnetization to align along the channel axis. This gives a precise indication on how artificial patterning can be used to force the magnetization direction in manganite based spintronic devices. Values of magnetocrystalline constant up to $8000\phantom{\rule{0.3em}{0ex}}\mathrm{J}∕{\mathrm{m}}^{3}$ and anisotropic magnetoresistance values between 0.1% and 0.6% are found. Our data also indicate that, in the low field $(\ensuremath{\leqslant}200\phantom{\rule{0.3em}{0ex}}\mathrm{Oe})$ hysteretic regime, magnetization reversal occurs by thermal activated hopping of domain walls, with a characteristic hopping distance of $4--5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$.