Introduction: Exchange Bias(EB) originates from the interfacial interaction between a ferromagnetic (FM) and an Antiferromagnetic (AFM) material, after cooling the sample in a magnetic field below the Neel temperature (TN) of the AFM [1]. The main feature of EB is training effect which is a gradual reduction of EB field when hysteresis loop (n) measured many times at constant temperature. The training effect is inversely dependence on FM layer thickness and interface structure, etc [2]. We have carried out the Kerr microscopy measurements to get direct information about magnetization irreversible of FM layers along with hysteresis loops. Experimental details: Thin films of Al(10nm)/Fe(30nm)/Fe57(10nm)/Fe(30nm)/Si substrate were deposited using Ion-beam sputtering technique. The films were implanted with 35 keV Fluorine ions. With this ion energy, the maximum energy has been deposited only at the centre of the Fe film to obtain FeF2 at the center, which is an antiferromagnet and its Neel temperature is 78 K. For magnetic characterization, the measurements were done using in-plane Magneto-optic Kerr effect microscope (MOKE) at 50 K after field cooling from room temperature. Results and discussions Fig. 1(a) shows the hysteresis loop as function of number of loops. It clearly shows the exchange bias and it becomes quite constant. Similar observation has also been showed for the sample irradiated with 5×1016 F-ions/cm2. Magnetic domain evolution during the magnetization irreversible and the training effect have been studied after F-ion implantation at 50 K. Kerr microscopy measurements were carried out at different temperatures after the field-cooling across the Neel temperature of the antiferromagnetic (AFM) FeF2 layer. It is observed that with the increasing anti-ferromagnetic (AFM) FeF2 layer thickness, the exchange bias increase and the training effect becomes weaker. Analysis of the temperature variation of the exchange bias field indicates the disorder decreases at the FM-AFM interface with the increasing F-Ion fluences. Higher fluence specimen indicates a behavior that is changing from non-equilibrium state to equilibrium state and behavior of training effect is suggesting step-like. For 1×1017 ions/cm2 sample, change in the exchange bias field after measuring the 6th cycle is 4.42% while in case of 5×1016ions/cm2 27.32%. Remarkably, for the largest fluences, the relative training becomes smaller than the one for the lower fluence. It indicates higher ion fluence EB system is suitable for device application.

**References:**

 [1] W. H. Meiklejohn and C. P. Bean, Phys. Rev. 102, 1413(1956). [2] M. Gruyters and D. Riegel, Phys. Rev. B 63, 052401 (2000).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/a97c3e88eac11173ccbf237d54b463aa.jpg)
Figure 1: (a) The hysteresis loops as a function of number of loops (n) for the specimen 1×1017 ions/cm2 (b) Value of Exchange bias for both the films implanted with ion fluences 5×1016 ions/cm2 and 1×1017 ions/cm2 at 50 K.

 Observation of training effect in Fe thin film implanted with F+ ions

*Session Chair: Aidan Hindmarch, University of Durham*

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Observation of training effect in Fe thin film implanted with F+ ions

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