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.



Keywords and Phrases

Correlated disorder; Correlated electron materials; Ferromagnetic phase; Ionic radius; Itinerant magnets; Low temperatures; Magnetic phase diagrams; Magneto-optical; Microscopic models; Quantum fluctuation; Quantum magnets; Quantum phase transitions; Random disorders; Randomly distributed; Strong disorders; Theoretical study; Ultracold atomic gas; Zero temperatures; Calcium; Ferromagnetic materials; Paramagnetism; Ruthenium alloys

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