Study Of Local Structure And Ferromagnetism In Transition Metals Doped LiNbO₃

LiNbO₃is a well-known ferroelectric crystal with a variety of applications,especially in photorefractive devices, optical wave guide, and surface acoustic wavefilters. Previous works have found that both ferromagnetism and ferroelectricity couldbe obtained through doping magnetic ions into the LiNbO₃matrix. This triggered ourinterests whether more transition metal doped LiNbO₃could be explored and appliedas spin source in the field of spintronics or multiferrotics.In this paper, layered room temperature ferromagnetic V/Cr/Fe dopedand C/Co co-doped LiNbO₃with concentrations from1at.%to5at.%wereprepared by ion implantation. The doping concentration, recovery annealing,and doping elements were studied to reveal their influences on local structureand magnetic property of lithum niobate.The Atomic magnetism moments （AMMs） for V-doped samples were1.85,3.82,0.28,0.46and0.13μB/V corresponding to the doping contents.Simulations of XANES spectrum showed that V substituted principally in theNb position in the LiNbO₃lattice, and was distorted octahedral coordinatedwith oxygen. The formed VO₆unit worked as whole to induce theferromagnetism. Simulations also proved the existence of O vacancies, whichplayed an important role in the introduction and interaction of local magneticmoment.The AMMs for Cr-doped samples were0.60,1.70,0.18,1.30and0.25μB/Cr corresponding to the doping contents. XRD and XANES spectrumproved the existence of the Cr3O8cluster. After annealing, the clusterdispeared, and the ferromagnetism of the samples increased to an AMM ofμB/Cr.The AMMs for Fe-doped samples were3.33,0.87,0.30,0.96and0.35μB/Fe corresponding to the doping contents. Simulation of XANESspectrum showed that Fe substituted principally in the Li position. With the aid of electric structure calculation using LDA+U method, we found a strongd-d electron interaction between the doped Fe atom and its neighboring Nbatoms, which could work at long range through the whole crystalline cell.C and Co co-doped LiNbO₃was studied, and we found that the co-dopingof C could increase the magnetism of Co doped LiNbO₃.