The transition-metal pnictide CrAs has recently attracted significant attention due to the emergence of superconductivity when the helimagnetic order is suppressed by hydrostatic pressure. However, the microscopic mechanism underlying the huge anisotropic spontaneous strain at the helimagnetic transition, which is incompatible with the spin structure, remains unresolved. Here, we have investigated this unconventional magnetoelastic coupling in CrAs through stress-strain relationship measurements and first-principles calculations. A superelasticlike nonlinear stress-strain curve emerges across the uniaxial stress-induced first-order helimagnetic-paramagnetic transition. Remarkably, uniaxial stress is found to have a substantially stronger influence on the helimagnetic transition than hydrostatic pressure. Theoretical calculations reveal that the observed drastic response against uniaxial stress originates from a strong entanglement between the anisotropic strain and orbital-dependent correlation. Our findings indicate that the spin-orbital coupling induced by local electron correlations plays a broadly important role in transition-metal pnictides, including iron pnictide superconductors.

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• Elasticity
• Magnetic phase transitions
• Phase diagrams
• Pressure effects
• Helimagnets
• Strongly correlated systems
• Superconductors
• First-principles calculations
• Pressure techniques