Flexible magnetic devices, i.e., magnetic devices fabricated on flexible substrates, are very attractive in applications such as detection of magnetic field in an arbitrary surface, non-contact actuators, and microwave devices, due to their stretchable, biocompatible, light-weight, portable, and low cost properties. Flexible magnetic films are essential for the realization of various functionalities of flexible magnetic devices. To give a comprehensive understanding for flexible magnetic films and related devices, recent advances in the study of flexible magnetic films are reviewed, including fabrication methods, magnetic and transport properties of flexible magnetic films, and their applications in magnetic sensors, actuators, and microwave devices. Our aim is to foster a comprehensive understanding of these films and devices. Three typical methods have been introduced to prepare the flexible magnetic films, by deposition of magnetic films on flexible substrates, by a transfer and bonding approach or by including and then removing sacrificial layers. Stretching or bending the magnetic films is a good way to apply mechanical strain to them, so that magnetic anisotropy, exchange bias, coercivity, and magnetoresistance can be effectively manipulated. Finally, a series of examples is shown to demonstrate the great potential of flexible magnetic films for future applications.
We fabricated flexible spin valves on polyvinylidene fluoride（PVDF） membranes and investigated the influence of thermal deformation of substrates on the giant magnetoresistance（GMR） behaviors. The large magnetostrictive Fe_（81）Ga_（19）（Fe Ga） alloy and the low magnetostrictive Fe_（19）Ni_（81）（Fe Ni） alloy were selected as the free and pinned ferromagnetic layers.In addition, the exchange bias（EB） of the pinned layer was set along the different thermal deformation axes α_（31） or α_（32） of PVDF. The GMR ratio of the reference spin valves grown on Si intrinsically increases with lowering temperature due to an enhancement of spontaneous magnetization. For flexible spin valves, when decreasing temperature, the anisotropic thermal deformation of PVDF produces a uniaxial anisotropy along the α_（32） direction, which changes the distribution of magnetic domains. As a result, the GMR ratio at low temperature for spin valves with EB α_（32）becomes close to that on Si, but for spin valves with EB α_（31）is far away from that on Si. This thermal effect on GMR behaviors is more significant when using magnetostrictive Fe Ga as the free layer.
