Qian Zhan

Magnetic properties and microstructure of FePt/Au multilayers with high perpendicular magnetocrystalline anisotropy

FePt/Au multilayers were deposited on preheated 100 °C MgO (001) single crystal substrates by magnetron sputtering. Magnetic properties and microstructure of the films were studied. Results show that the film possesses high coercivity HC, excellent perpendicular magnetic anisotropy (PMA), and weak interparticle exchange coupling (IEC) after annealing. FePt and Au can grow epitaxially on MgO substrates along the [001] direction, leading to excellent PMA. Au atoms partly diffuse to the boundaries of FePt phases and function as grain refiners and particle isolators, which markedly decrease the FePt grain size and IEC. Moreover, the additional FePt/Au interface energy, the stress energy due to the mismatch between FePt and Au lattices, and the diffusion of Au atoms all promote the ordering process of FePt film. This leads to the decrease in ordering temperature by 150 °C and a considerable increase in HC.

Enhancement of the magnetic field sensitivity in Al2O3 encapsulated NiFe films with anisotropic magnetoresistance

The anisotropic magnetoresistance value (ΔR/R) and magnetic field sensitivity (Sv) of NiFe films can be remarkably enhanced by using Al2O3 encapsulation, and the Sv is comparable to that of a spin valve. For an ultrathin NiFe film with the structure of Ta/Al2O3/NiFe/Al2O3/Ta, the Al2O3 layers suppress the formation of the magnetic dead layers and the interdiffusions between the NiFe layer and Ta layers, and decrease the current shunting of the Ta layers. More importantly, the flatter Al2O3/NiFe and NiFe/Al2O3 interfaces can significantly enhance the specular reflection of conduction electrons and lead to a higher ΔR/R. In addition, the formations of the NiFe (111) texture and the columnar grains by annealing can also increase the ΔR/R.

Electromigration induced fast L10 ordering phase transition in perpendicular FePt films

Realizing fast L10 ordering phase transition (LOPT) in L10 structured magnetic materials without heat treatment is crucial for their applications in spintronic devices. This article reports on the electromigration controlled momentum transfer and rapid ordering of Fe and Pt atoms in the as-deposited FePt films. Lattice defects in the films provide enough diffusion pathways and allow the Fe and Pt atoms rearranging. Through the current driven atomic motion and rearrangement, fast LOPT can result in the establishment of perpendicular magnetic anisotropy of the FePt films at room temperature. This effect is expected to work with other L10 typed magnetic materials for spintronic devices development.

Perpendicular Anisotropic Magnetoresistance Induced by Surface Spin-Orbit Scattering in a MgO/Fe/Cu Heterostructure

A large perpendicular anisotropic magnetoresistance (AMR) is obtained in a MgO/Fe/Cu heterostructure, with a maximum AMR ratio of 0.59%. The perpendicular AMR is approximately inversely dependent on the thickness of the Fe layer above 2.5 nm. It can be increased by enhanced structural asymmetry, which implies an interface effect mainly derived from interfacial Rashba spin-orbit scattering in the MgO/Fe/Cu heterostructure. The perpendicular AMR is temperature dependent.

Current-Induced Fast-Ordering of L1

Current-induced fast-ordering method (CIFOM) was designed to achieve an ordered L10 -FePt film with small grain size under low energy consumption by applying direct current (DC) in the FePt film. The grain size (~ 8 nm) of the L10-FePt film prepared by CIFOM method is about one-third of that produced by the post-annealing method (PAM). The fast ordering of the L10-FePt film by CIFOM is probably attributed to the momentum exchange between the FePt atoms and the conductive electrons. The short ordering time by CIFOM contributes to the smaller grain size of FePt film.

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A micromagnetic simulation analysis is systematically carried out to explore the magnetization reversal mechanism, residual stress and exchange interaction in L10-FePt/Au nanocomposite films with perpendicular magnetic anisotropy. Results show that: (1) the domain-wall pinning mode is the main mechanism responsible for magnetization reversal in L10-FePt/Au films; (2) considering the magnetoelastic energy produced by lattice mismatches between Au and FePt, the simulated out-of-plane loop matches the experimental loop very well. The residual tensile stress in the films is quantitatively described by both experimental calculations and micromagnetic simulations; (3) the exchange interaction within FePt grains of the films is strong, which allows for the coherent switching of the magnetization moments of an FePt grain.

-FePt Films With Small Grain Size

with high perpendicular magnetocrystalline anisotropy” †Appl. Phys. Lett. 93, 152513 „2008...‡ Chun Feng, Qian Zhan, Baohe Li, Jiao Teng, Minghua Li, Yong Jiang, and Guanghua Yu Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China Received 11 November 2008; accepted 14 November 2008; published online 30 December 2008 DOI: 10.1063/1.3041635