Synopsis

# Every single layer matters

Physics 2, s37
A critical thickness below which thin films of the metallic ferromagnet ${\text{SrRuO}}_{3}$ become insulating and lose their ferromagnetic properties has been determined.

$SrRuO3$ belongs to a class of complex perovskite oxides that display an interesting interplay of spin, charge, and orbital degrees of freedom, and may provide alternatives to conventional silicon-based electronics. While bulk $SrRuO3$ is a metallic ferromagnet at low temperatures, thin films of $SrRuO3$ undergo a metal-to-insulator transition and exhibit intriguing changes in the magnetic order as a function of thickness. A detailed understanding of how the thickness of the films affects the underlying physics is, however, absent.

In a Rapid Communication published in Physical Review B, Wolter Siemons and Gertjan Koster of the University of Twente in the Netherlands, and Jing Xia, Malcolm Beasley, and Aharon Kapitulnik of Stanford University study the transport and magnetic properties of thin films of $SrRuO3$ grown on a $SrTiO3$ substrate. They pin the critical thickness for the metal-insulator transition to four layers, observing eight orders of magnitude increase in resistance when the thickness decreases from four to three layers. In addition, they find that for two and three layers, the axis of the magnetic moment associated with ferromagnetism collapses to the plane of the films, compared to the bulk case where the alignment is close to perpendicular. The authors propose that reconstruction of the crystal lattice at the interface with the $SrTiO3$ substrate creates an antiferromagnetic layer and induces the insulating state in the two and three layer case. The implication is that a thickness of four layers is adequate to overcome the interface influence, resulting in a phase transition to the bulk properties of $SrRuO3$.– Alex Klironomos

Nanophysics

## Related Articles

Atomic and Molecular Physics

### Enhanced Emission for Improved Electron Spectroscopy

Researchers have demonstrated a new electron field emitter with unprecedented brightness and spectral purity, promising a breakthrough in electron microscope spectroscopy. Read More »

Condensed Matter Physics

### Frequency Combs from Just One Mode

Experiments disprove the general assumption that more than one wave mode is needed to produce a spectral pattern called a frequency comb. Read More »

Optics

### Optical Vortex Sizes Up Nanoparticles

A novel method for measuring nanoparticle size could have applications in industry and basic materials science research. Read More »