Emergent ultra-high temperature ferromagnetism in La_(2)CoO_(4±x) thin films

Searching for novel ferromagnetic oxides with high Curie temperature(TC)has been one of the main goals for oxide spintronics.The well-known perovskite cobaltate LaCoO_(3) is a classical ferromagnet in its thin-film form;however,it suffers from a low TC(~85 K).Here we report a new type of ferromagnetic La-Co-O films with an ultrahigh TC of~820 K.They are fabricated by pulsed laser deposition from a LaCoO_(3) target at low oxygen partial pressures.Detailed structural analysis indicates that they crystallize in terms of the Ruddlesden–Popper phase of La_(2)CoO_(4±x).In sharp contrast to the antiferromagnetism of bulk La_(2)CoO_(4),the strong ferromagnetism in the La_(2)CoO_(4±x) thin films is firmly demonstrated by magnetometry measurements,X-ray magnetic circular dichroism characterization,and magnetotransport experiments.More importantly,density functional theory calculations indicate that the nonstoichiometric oxygen induces an antiferromagnetic-to-ferromagnetic phase transition,accompanied by the orbital reconstruction of Co 3d electrons.Thus,our study provides an attractive strategy for designing or synthesizing exotic magnetic oxides with high ordering temperatures.

反铁磁自旋电子学:迈向超高密度和超快响应的信息技术

Spintronics is a field focusing on the quantum spin degree of freedom of electrons in condensed matter physics and information technology.One of the major tasks in this field is to explore and utilize exotic magnetoelectronic effects,which are electrical outputs yielded by the variation of spin vectors or vice versa.For example,the anisotropic magnetoresistance effect is a prototypical magnetoelectronic effect,as the rotation of the magnetic vector of a magnetic material can yield a change in its resistivity.This effect is based on the resulting anisotropic density of states relative to the orientation of the magnetic vector due to the relativistic spin–orbit coupling and the potential distribution of defects.