Development of nano-structured permanent hard magnetic thin films

Chowdhury, P and Barshilia, Harish C and Rajam, KS (2010) Development of nano-structured permanent hard magnetic thin films. Project Report. NAL.

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In exchange coupled nano-composite magnets, the length scale of the soft phase is limited to twice the domain wall thickness of the hard phase. To maximize the energy product of exchange-spring permanent magnets, we investigate the sputtered deposited Sm/Co multilayered structures with varying thickness of both Sm and Co layers. On deposition at elevated temperatures ( ~ 450 oC) and subsequent annealing at temperatures between 450 to 650 oC, the multilayered structures of hard/soft structure forms. Retaining of multilayer structures after the annealing was confirmed through characterization using transmission electron microscopy. X-ray diffraction indicates the formation of polycrystalline SmCo5 hard phase. Magnetic hysteresis measurements shows single phase like behavior, which indicates the soft layer (Co) is well exchange coupled with the neighboring hard phase of SmCo5. Maximum energy product of 19.29 MGOe has been obtained for sample with following processing parameters: as deposited multilayer structure Cr(10nm)/ [Sm(1.6nm)/Co(5.7nm)]25\Cr(20nm)/Si, substrate temperature, Ts, = 450 oC , annealing temperature, Ta = 450 oC and annealing duration, tanneal = 1 hr. With increasing the annealing temperature to 600 oC, though there is an enhancement of coercive field from 0.5 T to 1.25 T, reduction of (BH)max to 3.73 MGOe was observed. This might be due to the enhancement of thermal diffusion of Co layer into Sm and subsequently decrease of soft layer thickness. These observations are similar to those predicted by micromagnetic simulations.

Item Type: Monograph (Project Report)
Subjects: PHYSICS > Physics(General)
Depositing User: Mr N Selvakumar
Date Deposited: 24 Aug 2011 07:58
Last Modified: 24 Aug 2011 07:58

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