Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites

Abstract

We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

Electronic properties of ultra-thin YCrO3 films

“…Specifically, since Cr 3+ can be further oxidized to higher valence states, oxygen-rich secondary phases can emerge [10]. Moreover, the choice of substrate is important to eliminate the formation of polycrystalline films [11,12]. To date, layer-by-layer growth of high-quality epitaxial YCO films has not been demonstrated.…”

A comprehensive review on the ferroelectric orthochromates: Synthesis, property, and application

“…In amorphous YCrO 3 thin films deposited by the pulsed laser, Araujo et al observed a FM order above room temperature [121]. The reported order-from-disorder phenomenon was accompanied by a phase transition from an insulating to a metal state, which was attributed to the wide distribution of bond angles (Cr-O-Cr) and the resultant metallization via free carriers [121]. X-ray absorption spectroscopy shows the formation of Cr 4+ oxidation state in the YCrO 3 thin film (see Fig.…”

“…A hysteresis of polarization-electric (P-E) loop of the polarization curve presents at 300, 325, and 350 K [72]. Previous studies of YCrO 3 compound focused mainly on polycrystals [74,98,[100][101][102][103][104][105][106][107][108], nanocrystals [109][110][111][112][113][114][115], and thin films [72,83,86,[116][117][118][119][120][121][122][123][124][125][126][127][128][129]. The lack of high-quality and large-scale single-crystalline samples has been a long-standing issue for realizing potential applications to some extent and studying their intrinsic physical properties [130][131][132][133][134][135][136][137].…”