Influence Of Low Doses Ga~+ Irradiation And Temperature On The Magnetic Properties And Stability Of Spin Valves

Spin valve with a low saturation field and high sensitivity has become the research hotspot due to its valuable application in magnetic record reading heads, magnetic random access memories. Among the preparation methods of spin-valve magnetic electronic devices, focused ion beam (FIB) is considered to be a convenient way to prepare electronic devices and modify magnetic properties of magnetic thin film materials. However, during the preparation process of electronic devices with FIB, low doses of radiation of the ion beam end will affect the reliability of magnetic electronic devices. In addition, spin-valve electronic devices are usually annealed at a certain temperature for couple of hours during preparation process, and temperature rising happens in the practical application of them due to the role of current. As a result, diffusion may occur between the layers, destroying interlayer coupling of the ferromagnetic/antiferromagnetic layers, which affects the exchange bias and the reliability of magnetic electronic devices.This paper focuses on the problems caused during the preparation of nano-magnetic spin-valve electronic devices by FIB and the influence of annealing temperature on spin-valve multilayers. X-ray diffractometer, atomic force microscope, transmission electron microscope and vibrating sample magnetometer have been used to examine the stability of magnetic properties of spin-valve multilayers and ferromagnetic/antiferromagnetic bilayers with different annealing temperatures and doses of Ga⁺ ion irradiation. The investigation on the influence of annealing temperature and low-dose ion radiation on the microstructure, magnetization reversal and thermal stability of spin-valve multilayers and ferromagnetic/antiferromagnetic bilayers can provide some technical guidance and theoretical basis on preparing nano-magnetic electronic devices by FIB and application of spin valves in electronic devices.The study on the influence of low-dose Ga⁺ ion irradiation on CoFe/Cu/CoFe/IrMn spin-valve multilayers shows that low-dose Ga⁺ ion irradiation reduces the texture of IrMn(111) orientation in spin-valve multilayers and increases the mixing of interfacial atoms, which give rise to the decrease of the exchange bias field, coercivity of pinned layers and magnetoresistance. After 3×10¹⁴ion·cm^-2 dose of Ga⁺ ion irradiation, the exchange bias field turns into 99 Oe from 234 Oe, the coercivity values of pinned layer and free layer turns into 175 Oe from 195 Oe and into 126 Oe from 59 Oe, respectively. The decrease of texture, stress relaxation and the increase of the mixing of interfacial atoms induced by low-dose Ga⁺ ion irradiation increase the energy barrier for the reversal of the magnetization of antiferromagnetic layer. Consequently, the thermal magnetic stability of spin-valve multilayer enhances after low-dose Ga⁺ ion irradiation.The study on the influence of low-dose Ga⁺ ion irradiation on CoFe/IrMn bilayers shows that low-dose Ga⁺ ions on the CoFe/IrMn bilayers has little effect on the texture of IrMn (111) direction, but decreases the CoFe/IrMn bilayer interface roughness. Low-dose Ga⁺ ion irradiation reduces the exchange bias field and the coercivity of the CoFe/IrMn bilayers. After 1×10¹⁴ion·cm^-2 dose of Ga⁺ ion irradiation, the exchange bias field decreases from 324 Oe to 280 Oe, the coercivity increases from 111 Oe to 175 Oe. The decrease of energy barrier for the reversal of the magnetization of antiferromagnetic layer induced by low-dose Ga⁺ ion irradiation is responsible for the decrease of thermal stability of CoFe/IrMn bilayers.The study on temperature dependence of structure and magnetic property of CoFe/Cu/CoFe/ IrMn spin-valve multilayers indicates that the texture of IrMn (111) weakens after annealing. Annealing reduces the exchange bias field and the coercivity of pinning layer, but increases the coercivity of free layer. Different temperatures make the decline of the exchange bias field of spin valves, which results from the reduction of texture and the increase of the mixing of interfacial atoms. Continuously heating reduces the texture IrMn (111) orientation in CoFe/Cu/CoFe/IrMn spin-valve multilayers resulting in the decrease of exchange bias field and coercivity of pinned layer.The study on temperature dependence of structure and magnetic property of CoFe/IrMn bilayers indicates that annealing reduces the texture of IrMn (111) orientation and the exchange bias field, while increases the roughness. Different heating temperatures have little influence on the IrMn (111) texture, but the exchange bias field has declined.Studies on thermal stability of CoFe/IrMn bilayers and CoFe/Cu/CoFe/IrMn spin-valve multilayers indicate that annealing reduces the thermal stability of CoFe/IrMn bilayers, but enhances the thermal stability of CoFe/Cu/CoFe/IrMn spin valve multilayers. Different heating temperatures reduce the thermal stability of both the CoFe/IrMn bilayers and the CoFe/Cu/CoFe/IrMn spin valve multilayers.