Unconventional magnetostructural transition in CoCr2O4 at high magnetic fields

Area of Science:

• Condensed Matter Physics
• Materials Science
• Magnetism

Background:

• Single-crystalline CoCr(2)O(4) is a spinel compound exhibiting complex magnetic ordering.
• Understanding the interplay between magnetic order and lattice properties is crucial for developing advanced magnetic materials.

Purpose of the Study:

• To investigate the magnetic-field and temperature dependencies of ultrasound propagation and magnetization in CoCr(2)O(4).
• To identify and characterize magnetic phase transitions and their impact on material properties.

Main Methods:

• Measurements of ultrasound velocity and attenuation in static and pulsed magnetic fields (up to 62 T).
• Magnetization measurements as a function of temperature and magnetic field.
• Analysis of spin-lattice coupling effects.

Main Results:

• Observed distinct anomalies in sound velocity and attenuation at the onset of incommensurate-spiral-spin order (T(s)=27 K) and the transition to commensurate states (T(l)=14 K).
• Identified a new magnetostructural state between 6.2 and 16.5 K at high magnetic fields, evidenced by steplike changes in ultrasound.
• Demonstrated strong spin-lattice coupling and a metastable high-symmetry phase with ordered longitudinal magnetization.

Conclusions:

• The study reveals significant spin-lattice coupling in CoCr(2)O(4).
• A novel magnetostructural state, potentially a metastable high-symmetry phase, exists under specific magnetic field and temperature conditions.
• Ultrasound propagation serves as a sensitive probe for detecting complex magnetic transitions and associated structural changes.