L1 0 -FeNi ordered phase in AC electrodeposited iron-nickel biphasic nanowires

MENESES, FERNANDO; PEDERNERA, ANALÍA; BLANCO, CECILIA; BAJALES, NOELIA; URRETA, SILVIA E.; BERCOFF, PAULA G.

JOURNAL OF ALLOYS AND COMPOUNDS

ELSEVIER SCIENCE SA

Año: 2018

0925-8388

Nanowire arrays with nominal composition FexNi100-x(x = 0, 18, 53, 93, 100) have been synthesized by AC electrodeposition into thecylindrical pores of alumina templates. Except for the composition Fe53Ni47,nanowires are single-phase, consisting of small grains of the A1-FeNidisordered phase. Near the equiatomic nominal composition nanowires arebiphasic, consisting of grains of the A1-FeNi disordered phase (g-FeNiphase) as well as grains of the L10-FeNi ordered phase (g´´-FeNiphase). Even in nanowires with high Fe content the a-Febcc phase is absent. The coercivefield and reduced remanence dependences on composition are non monotonic but gothrough a local maximum near the equiatomic composition. Biphasic nanowiresbehave as a magnetic single phase, exhibiting a unique switching field for polarizationreversal in the entire range between 5 K and 300 K.  The linear dependence of thecoercive field on temperature and the dependence of the coercive field on theangle between the nanowire long axis and the applied field are consistent witha polarization reversal mechanism controlled by the nucleation by curling andexpansion of inverse domains, assisted by thermal fluctuations and the appliedfield. The effective uniaxial anisotropy resulting from these measurements suggeststhat the shape anisotropy makes a small contribution to the high coercive fieldobserved (170 mT). The effective uniaxial magnetocrystalline constant measuredat room temperature, 130 - 170 k Jm-3, may be explained byconsidering nucleation at favorable sites in an exchange-hardened g-FeNisoft phase.