Oscillation of coercivity between positive and negative in Mn_xGe_1−x:H ferromagnetic semiconductor films

Abstract

Amorphous MnxGe1−x:H ferromagnetic semiconductor films prepared in mixed Ar with 20% H2 by magnetron co-sputtering show global ferromagnetism with positive coercivity at low temperatures. With increasing temperature, the coercivity of MnxGe1−x:H films first changes from positive to negative, and then back to positive again, which was not found in the corresponding MnxGe1−x and other ferromagnetic semiconductors before. For Mn0.4Ge0.6:H film, the inverted Hall loop is also observed at 30 K, which is consistent with the negative coercivity. The negative coercivity is explained by the antiferromagnetic exchange coupling between the H-rich ferromagnetic regions separated by the H-poor non-ferromagnetic spacers. Hydrogenation is a useful method to tune the magnetic properties of MnxGe1−x films for the application in spintronics.

Strain induced exchange-spring magnetic behavior in amorphous (TbDy)Fe2 thin films

“…22 Since both TbDy-rich and Fe-rich layers are amorphous without magnetocrystalline anisotropy, the TbDy-rich produces greater changes in the elastically induced magnetic anisotropy when a mechanical strain is applied. Specifically, one can approximate the magnetic anisotropy as K ¼ 3 2 k s Ee where E is the Young's modulus and e is the uniaxial strain applied. Since the TbDy rich region has an order of magnitude larger saturation magnetostriction than the Fe-rich layers, the K increases more rapidly as the strain increases for the TbDy rich layers.…”

“…Nanocomposites of antiferromagnetically coupled hard and soft magnetic materials exhibiting an exchange-spring phenomenon have received considerable attention due to their potential applications in spintronics, magnetic data storage, and tunnel junction memory devices. [1][2][3] In an exchangespring magnetic system, the soft magnetic phase exhibits magnetization reversal prior to the magnetization reversal in the hard magnetic phase due to a strong magnetic exchange coupling. 4 A large number of exchange-spring systems studied are multilayers of RE-Fe 2 /(R*Fe 2 or TM), where RE ¼ rare earth elements, R* ¼ Y, and TM ¼ Fe and Co. [5][6][7][8][9][10][11][12][13][14] In these layered systems, the film's thickness ratio (t S /t H ) and/or the materials anisotropy is used to modify the coercivity/remanence values and cannot be modified once manufactured.…”