Disorder promotes ferromagnetism: Rounding of the quantum phase transition in Sr_{1-x}Ca_xRuO_3

• Main Authors: Demko, L, Bordacs, S, Vojta, T, Nozadze, D, Hrahsheh, F, Svoboda, C, Dora, B, Yamada, H, Kawasaki, M, Tokura, Y, Kezsmarki, I
• Format: Journal Article
• Language: English
• Published: 16-02-2012
• Subjects: Physics - Disordered Systems and Neural Networks; Physics - Materials Science
• DOI: 10.48550/arxiv.1202.3810

Physical Review Letters 108, 185701 (2012) The subtle interplay of randomness and quantum fluctuations at low
temperatures gives rise to a plethora of unconventional phenomena in systems
ranging from quantum magnets and correlated electron materials to ultracold
atomic gases. Particularly strong disorder effects have been predicted to occur
at zero-temperature quantum phase transitions. Here, we demonstrate that the
composition-driven ferromagnetic-to-paramagnetic quantum phase transition in
Sr1-xCaxRuO3 is completely destroyed by the disorder introduced via the
different ionic radii of the randomly distributed Sr and Ca ions. Using a
magneto-optical technique, we map the magnetic phase diagram in the
composition-temperature space. We find that the ferromagnetic phase is
significantly extended by the disorder and develops a pronounced tail over a
broad range of the composition x. These findings are explained by a microscopic
model of smeared quantum phase transitions in itinerant magnets. Moreover, our
theoretical study implies that correlated disorder is even more powerful in
promoting ferromagnetism than random disorder.