Origin of Transitions Inversion in Rare-Earth Vanadates.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid-State Chemistry

Background:

• In most transition-metal oxides, orbital ordering (OO) typically precedes magnetic ordering (MO), with transition temperatures satisfying T_{N} < T_{OO}.
• The rare earth vanadate (RVO3) series presents an anomaly, exhibiting an inversion where magnetic ordering precedes orbital ordering (T_{N} > T_{OO}) as the rare earth ionic radius (R_{I}) increases.
• The underlying physical mechanism driving this inversion in vanadates has remained unexplained.

Purpose of the Study:

• To elucidate the fundamental reason behind the inverted ordering temperatures (T_{N} > T_{OO}) observed in the RVO3 series.
• To identify the specific interplay of interactions that leads to this rare phenomenon.
• To establish criteria for discovering similar inverted ordering phenomena in other material systems.

Main Methods:

• Analysis based on the decomposition of the order parameter into irreducible tensors.
• Investigating the competition between lattice effects and spin-spin interactions.
• Examining the influence of rare earth ionic radius (R_{I}) on the relative strengths of these interactions.

Main Results:

• In RVO3, increasing R_{I} weakens lattice effects, diminishing their influence on orbital physics.
• Concurrently, orbital-independent dipolar spin-spin interactions become dominant for antiferromagnetic spin order.
• This balance leads to the observed inversion, where magnetic ordering precedes orbital ordering (T_{N} > T_{OO}).

Conclusions:

• The T_{N} > T_{OO} inversion in RVO3 is driven by the ineffectiveness of lattice effects and the dominance of spin-spin interactions as R_{I} increases.
• This mechanism explains the rarity of this phenomenon and provides guidelines for identifying it in other materials.
• These vanadate systems serve as ideal platforms for studying unconventional orbital phases due to the unique balance of interactions.