Invited Paper TF2-ThM3
Composition and Finite Size Effects in Thin Magnetic Films for Data Storage Applications: Magnetic and Transport Properties

Thursday, November 3, 2011, 8:40 am, Room 110

Scaling of magneto-resistance (MR) and resistance area product (RA) with thickness is one of a critical materials specific properties of hard disk drive sensors. We consider fundamental aspects of MR-RA scaling with two planar FM/NM/FM hetero-structures: (i) Fe/MgO/Fe tunneling junctions and (ii) all Heusler alloy giant-magneto-resistance (GMR) spin valves [1-3]. In both cases we focus on the electronic structure contributions to RA(MR). Third example motivated by rapidly decreasing grain size of data storage media where material specific finite size effects originate from magnetic interactions of 3d-5d(4d) elements [4,5]. First, we show that calculated within the QSGW theory [6] decay constant controlling thickness dependence of RA are consistent with experiment [7]. We also present results of direct spin dependent electronic transport simulations for two types of GMR structures (i) non-magnetic Heusler alloy spacers [1,2] and (ii) Ag spacer [3]. The (110) textured Co₂MnGe (CMG) and Rh₂CuSn (RCS) [1] have been used to build test hard disk drive reader and yielded MR of about 7 % and DRA of about 4.0 mW­-mm² [2]. The (001) textured FM Co₂Fe(Ge-Ga) with Ag spacer yielded MR values in excess of 45 % and DRA of 9.5 mW­-mm² [3]. Ab-initio electronic structure methods used to account for composition effects are shown to reproduce experimentally observed trends [1-3]. Finally we investigate finite size effects in the recording media granular films using model of magnetic interactions proposed to explain temperature dependence of magnetic anisotropy energy (MAE) observed in highly order L1₀ FePt thin films [4]. We discuss measurements protocol to quantify single vs. two ion contributions to MAE responsible for particular contributions to finite size effects in of 3d-5d(4d) thin films.

References:

[1]. T. Ambrose and O. Mryasov, US Patent 6, 876, 522 (April 5. 2005) .

[2]. K. Nikolaev, P. Kolbo, T. Pokhil, X. Peng, Y. Chen, T. Ambrose and O. Mryasov, APL., v.94, p. 222501 (2009).

[3]. Y. K. Takahashi, A. Srinivasan, B. Varaprasad, A. Rajanikanth, N. Hase, T.M. Nakatani, S. Kasaki, T. Furubayashi and K. Hono, Appl. Phys. Lett. 98, 152501 (2011).

[4]. O. N. Mryasov , U. Nowak, K. Guslienko, R.W. Chantrell , EuroPhysics Letters, v. 69(5), 805 (2005).

[5]. U. Nowak, O. N. Mryasov, R. Weiser, K. Guslienko, R.W. Chantrell , Phys. Rev. B, v. 72 p.172410, (2005).

[6]. S. Faleev, O. Mryasov and T. Mattsson, Phys. Rev. B., v.81, p. 205436 (2010) and references therein