Magnetic coupling in Mn₃O₄-coated γ-MnOOH nanowires Available to Purchase

Mn₃O₄-coated γ-MnOOH nanowires were synthesized by using the hydrothermal method. X-ray diffraction and transmission electron microscopy studies reveal that the nanowires have a core (γ-MnOOH)–shell (Mn₃O₄) structure. The magnetic transition temperature of Mn₃O₄ is slightly lower than the previously reported value because of the increased thermal disturbance for nanomaterials and the influence of the helical magnetism of γ-MnOOH. The hysteresis loop at 50 K keeps the same shape as was measured below the Néel temperature of Mn₃O₄ because of the short-range order of γ-MnOOH above the transition temperature. The short-range ordering is responsible for the deviation of the hysteresis loop at 300 K from the linear behavior of a normal paramagnetic phase. The magnetic coupling behavior between Mn₃O₄ and γ-MnOOH also induces an exchange bias effect in the system. The hysteresis loop shifts to the positive direction with increasing measurement temperature. A lower barrier energy is requested for the reversal of magnetic moments on the interface to generate the exchange bias behavior because of the asymmetric magnetic natures of Mn₃O₄ and γ-MnOOH, which should possess shorter responsive time compared with the traditional antiferromagnetic-ferromagnetic coupling induced exchange bias systems.