Composition Gradients and Magnetic Properties of 5-100 nm Thin CoNiFe Films Obtained by Electrodeposition

• Published in: Journal of the Electrochemical Society Vol. 159; no. 7; pp. D447 - D454
• Main Authors: Gong, Jie, Riemer, Steve, Morrone, Augusto, Venkatasamy, Venkatram, Kautzky, Michael, Tabakovic, Ibro
• Format: Journal Article
• Language: English
• Published: The Electrochemical Society 01.01.2012
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/2.082207jes

The composition gradient and properties of magnetic 5-100 nm thin CoNiFe films electrodeposited on Cu or Pt substrate were studied. It was found that the average elemental composition of CoNiFe, obtained by ICP analysis, changes during electrodeposition. The extent of anomalous co-deposition achieved at deposit thickness <100 nm was found to be several times larger than in thicker CoNiFe films. The partial current densities for all three metals (Co, Ni, Fe) increase during the time of electrodeposition and gives rise to stable value when the thickness reaches about 100 nm. The partial current density for hydrogen evolution decreases and becomes stable at the thickness >100 nm. The observations related to the experimental results could be explained through a modified Bockris-Drazic-Despic reduction mechanism. The time-dependent dynamics of roughening surface exhibits two characteristic regions, i.e. the first with fast roughening at the thickness <100 nm and the second with slow roughening at the thickness >100 nm. The stress evolution show typical compressive-tensile-compressive behavior in the thickness range 5-100 nm. The crystal structure of 20 nm CoNiFe films is mixed fcc + bcc crystallites with the larger grain size close to the substrate while thick films show fcc-rich structure. The mechanism of coercivity in CoNiFe films is governed by magnetoelastic anisotropy and follows Neel's thickness dependence relation, i.e. Hc = c t−n. The "volcano" type of Hc-t curve obtained at 5-50 nm was explained taking into account: change of composition, stress, crystal structure and roughness.