Causer Grace L, Zhu Hanliang, Ionescu Mihail, Mankey Gary J, Wang Xiaolin L, Klose Frank
Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, New South Wales 2500, Australia. Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales 2234, Australia.
J Phys Condens Matter. 2018 Aug 8;30(31):315804. doi: 10.1088/1361-648X/aad075. Epub 2018 Jul 2.
We report on artificial exchange bias created in a continuous epitaxial FePt film by introducing chemical disorder using a He beam, which features tailorable exchange bias strength through post-irradiation annealing. By design, the ferromagnetic (FM)/antiferromagnetic (AF) heterostructure exhibits stratified degrees of chemical order; however, the chemical composition and stoichiometry are invariant throughout the film volume. This uniquely allows for a consideration purely of the magnetic exchange across the FM/AF interface without the added hindrance of structural boundary parameters which inherently affect exchange bias quality. Annealing at 840 K results in the strongest exchange biased system, which displays a cross-sectional morphology of fine (<10 nm) domain structure composed of both of chemically ordered and chemically disordered domains. A magnetic model developed from fitting the characteristic polarised neutron reflectometry spectral features reveals that dual interactions can be attributed to the observed exchange bias: magnetic coupling at the FM/AF interface and also between neighbouring FM (chemically disordered) and AF (chemically ordered) domains within the nominally FM layer. Our results indicate that exchange bias is hindered at interfaces which are both chemically and magnetically perfect, while annealing can be used to balance the volume proportions of interfacial FM and AF domains to enhance the magnetic interface roughness for customisable exchange bias in mono-stoichiometric FM/AF heterostructures crafted by ion beams.
我们报道了通过使用氦束引入化学无序在连续外延FePt薄膜中产生的人工交换偏置，其特点是通过辐照后退火可定制交换偏置强度。通过设计，铁磁（FM）/反铁磁（AF）异质结构表现出分层的化学有序度；然而，整个薄膜体积内的化学成分和化学计量是不变的。这独特地允许纯粹考虑FM/AF界面上的磁交换，而没有结构边界参数的额外阻碍，这些参数会固有地影响交换偏置质量。在840 K退火会产生最强的交换偏置系统，其横截面形态为由化学有序和化学无序畴组成的精细（<10 nm）畴结构。通过拟合特征极化中子反射光谱特征建立的磁模型表明，双重相互作用可归因于观察到的交换偏置：FM/AF界面处的磁耦合以及名义上FM层内相邻FM（化学无序）和AF（化学有序）畴之间的磁耦合。我们的结果表明，在化学和磁学上都完美的界面处交换偏置受到阻碍，而退火可用于平衡界面FM和AF畴的体积比例，以增强磁界面粗糙度，从而在离子束制备的单化学计量FM/AF异质结构中实现可定制的交换偏置。
