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Magneto-optical information storage has been a hot research subject for several years. FePt exhibits abundant physical properties and has received much attention as a candidate material. Its alloy film with perpendicular anisotropy and small grain size has important applications in magnetic recordings due to the large intrinsic magnetic anisotropy which ensures long-time thermal stability of nanometer sized bits. However, the large coercive field of FePt is a significant factor that hinders its application. As is well known, the magnetic anisotropy in FePt alloy can be precisely modulated by carbon-doping, and as a result, the coercive field of FePt film can be modified effectively with the carbon dopant. On the other hand, the microscopic mechanism of magnetic storage relies on the motion of spin system. Ultrashort femtosecond laser has been demonstrated to be a very effective tool to investigate the dynamical coupling among different degrees of freedom, such as electron, spin and lattice in a ferromagnetic film. The research on spin dynamics has become a new frontier of condensed matter physics, which is crucial for ultrafast magnetic recording materials. In this work, by using the time-resolved magneto-optical Kerr effect spectroscopy, we study the ultrafast spin dynamics of two FePt alloy films with different carbon dopants under the applied magnetic field along the film surface. The FePt alloy films with different carbon dopants are fabricated on silicon substrates by the sputtering method. The main experimental findings in this work are as follows. (i) The transient Kerr signal is linearly proportional to the magnetization with the magnetic field up to 0.8 T, while the transient reflectivity of the film is independent of the applied magnetic field. (ii) For FePt alloy films with different coercive fields, it is found that the demagnetization time of the film with smaller coercive field is significantly faster than that of the larger counterpart: the former shows 0.8 ps demagnetization time, and the latter has a magnitude of 1.2 ps. The demagnetization times for both soft and hard magnetic films are independent of the applied magnetic field. (iii) With ultrafast laser pulse radiation, we observe the propagation of acoustic phonon with a resonance frequency of ～ 49 GHz, and the frequency of the acoustic phonon is independent of the applied magnetic field. From the above, the spin dynamics of the samples shows strong correlation with carbon-doping. Our experimental findings are desired for basic research as well as for the design and development of novel magneto-optical devices.
[1] Becher J, Mosendz O, Weller D, Kirilyuk A, Maan J C, Chrstanen P C M, Rasing Th, Kimel A 2014 Appl. Phys. Lett. 104 152412
[2] Li Z H, Li X 2014 Acta Phys. Sin. 63 167504 (in Chinese) [李正华, 李翔 2014 63 167504]
[3] Wu J B, Zhou M J, Wang X M, Wang Y Y, Xiong Z W, Cheng X L, Casanove M J, Gatel C, Wu W D 2014 Acta Phys. Sin. 63 166801 (in Chinese) [吴建邦, 周民杰, 王雪敏, 王瑜英, 熊政伟, 程新路, Marie-Jos Casannove, Christophe Gatel, 吴卫东 2014 63 166801]
[4] Jin Z M, Guo F Y, Ma H, Wang L H, Ma G H, Chen J Z 2011 Acta Phys. Sin. 60 087803 (in Chinese) [金钻明, 郭飞云, 马红, 王丽华, 马国宏, 陈建中 2011 60 087803]
[5] Kimel A V, Kirilyuk A, Usachev P A, Pisarev R V, Balbashov A M, Rasing T 2005 Nature 435 655
[6] Beaurepaire E, Merle J C, Daunois A, Bigot J Y 1996 Phys. Rev. Lett. 76 4250
[7] Carva K, Battiato M, Oppeneer P M 2011 Phys. Rev. Lett. 107 207201
[8] Kampfrath T, Ulbrich R G, Leuenberger F, Munzenberg M, Sass B, Felsch W 2002 Phys. Rev. B 65 104429
[9] He P, Ma L, Shi Z, Guo G Y, Zheng J G, Xin Y, Zhou S M 2012 Phys. Rev. Lett. 109 066402
[10] Zhang Z Z, Cui B Y, Wang G Z, Ma B, Jin Q Y, Liu Y W 2010 Appl. Phys. Lett. 97 172508
[11] Ma X, He P, Ma L, Guo G Y, Zhao H B, Zhou S M, Lpke G 2014 Appl. Phys. Lett. 104 192402
[12] He P, Ma X, Zhang J W, Zhao H B, Lpke G, Shi Z, Zhou S M 2013 Phys. Rev. Lett. 110 077203
[13] Mendil J, Nieves P, Chubykalo-Fesenko O, Walowski J, Santos T, Pisana S, Mnzenberg M 2014 Sci. Rep. 4 3980
[14] Moisan N, Malinowski G, Mauchain J, Hehn M, Vodungbo B, Lning J, Mangin S, Fullerton E E, Thiaville A 2014 Sci. Rep. 4 4658
[15] Li X L, Xu X H, Wu H S 2005 Rare Metal Mater. Engi. 34 1509 (in Chinese) [李小丽, 许小红, 武海顺 2005 稀有金属材料与工程 34 1509]
[16] Pan Q F, Zhang Z Y, Jin Z M, Lin X, Ma G H, Shen H, Hong F, Cheng Z X 2015 Europhys. Lett. 109 47002
[17] Xu Y, Jin Z M, Zhang Z B, Zhang Z Y, Lin X, Ma G H, Cheng Z X 2014 Chin. Phys. B 23 044206
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[1] Becher J, Mosendz O, Weller D, Kirilyuk A, Maan J C, Chrstanen P C M, Rasing Th, Kimel A 2014 Appl. Phys. Lett. 104 152412
[2] Li Z H, Li X 2014 Acta Phys. Sin. 63 167504 (in Chinese) [李正华, 李翔 2014 63 167504]
[3] Wu J B, Zhou M J, Wang X M, Wang Y Y, Xiong Z W, Cheng X L, Casanove M J, Gatel C, Wu W D 2014 Acta Phys. Sin. 63 166801 (in Chinese) [吴建邦, 周民杰, 王雪敏, 王瑜英, 熊政伟, 程新路, Marie-Jos Casannove, Christophe Gatel, 吴卫东 2014 63 166801]
[4] Jin Z M, Guo F Y, Ma H, Wang L H, Ma G H, Chen J Z 2011 Acta Phys. Sin. 60 087803 (in Chinese) [金钻明, 郭飞云, 马红, 王丽华, 马国宏, 陈建中 2011 60 087803]
[5] Kimel A V, Kirilyuk A, Usachev P A, Pisarev R V, Balbashov A M, Rasing T 2005 Nature 435 655
[6] Beaurepaire E, Merle J C, Daunois A, Bigot J Y 1996 Phys. Rev. Lett. 76 4250
[7] Carva K, Battiato M, Oppeneer P M 2011 Phys. Rev. Lett. 107 207201
[8] Kampfrath T, Ulbrich R G, Leuenberger F, Munzenberg M, Sass B, Felsch W 2002 Phys. Rev. B 65 104429
[9] He P, Ma L, Shi Z, Guo G Y, Zheng J G, Xin Y, Zhou S M 2012 Phys. Rev. Lett. 109 066402
[10] Zhang Z Z, Cui B Y, Wang G Z, Ma B, Jin Q Y, Liu Y W 2010 Appl. Phys. Lett. 97 172508
[11] Ma X, He P, Ma L, Guo G Y, Zhao H B, Zhou S M, Lpke G 2014 Appl. Phys. Lett. 104 192402
[12] He P, Ma X, Zhang J W, Zhao H B, Lpke G, Shi Z, Zhou S M 2013 Phys. Rev. Lett. 110 077203
[13] Mendil J, Nieves P, Chubykalo-Fesenko O, Walowski J, Santos T, Pisana S, Mnzenberg M 2014 Sci. Rep. 4 3980
[14] Moisan N, Malinowski G, Mauchain J, Hehn M, Vodungbo B, Lning J, Mangin S, Fullerton E E, Thiaville A 2014 Sci. Rep. 4 4658
[15] Li X L, Xu X H, Wu H S 2005 Rare Metal Mater. Engi. 34 1509 (in Chinese) [李小丽, 许小红, 武海顺 2005 稀有金属材料与工程 34 1509]
[16] Pan Q F, Zhang Z Y, Jin Z M, Lin X, Ma G H, Shen H, Hong F, Cheng Z X 2015 Europhys. Lett. 109 47002
[17] Xu Y, Jin Z M, Zhang Z B, Zhang Z Y, Lin X, Ma G H, Cheng Z X 2014 Chin. Phys. B 23 044206
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