INFLUENCE OF STRESS AND SIZE OVER THE MAGNETIC RESPONSE OF NICKEL NANOWIRES Román López-Ruiz*, Fernando Luis and Juan Bartolomé Instituto de Ciencia de Materiales de Aragón, CSIC - Universidad de Zaragoza. Departamento de Física de la Materia Condensada C/ Pedro Cerbuna 12, 50009 Zaragoza, Spain Aluminium 1st anodization

%

SYNTHESIS : AN ELECTROCHEMICAL ROUTE

It is possible to independently control the size and the aspect ratio of the nanowires.

Electrolyte V t1

A template-assisted method Alumina removal

K2Cr2O7 in H3PO4 10%

The film growth: Current control

1.1 μm

A. TOP

50 ºC 30 min

2nd anodization

The TC (D= infinite) shows a decrease of about 3 K with respect the bulk value. Stresses also modify TC.

Electrolyte V t2 Al2O3

Alumina (PAM) B. SIDE

Voltage reduction

850 nm

Barrier Layer

To 18 V Al

Metal Solution Room T

Porous Alumina Membrane: Hoenycomb structure

tplate

V controls pore diameter (D)

t2 controls pore length

The shape anisotropy role

The influence of T-induced stress NanoSpain 2008: NanoIberian Conference, Braga (Portugal) April 14-18, 2008

tplate controls wire length (L)

• L. Sun, P. C. Searson and C. L. Chien, Physical Review B 61 (2000) R6463. • D. P. Landau, Physical Review B, 14 (1976) 255. • L. Patrick, Physical Review, 93 (1954) 384.

ν

Nanowires (NW)

Easy axis

Shape easy axis

H

H

H

H Magnetoelastic easy axis

Kshape + Kstress

Kshape

Size influence on TC

300 K 5K

100 K

No sustaining aluminium

Stress origin is due to the different thermal contraction between ALUMINIUM and nickel. Experimental evidence ends a controversial question about the origin of this effect.

200 K

ROOM 400 K TEMPERATURE

Sustaining aluminium

600 K FM

Hysteresis loops does not reveal superparamagnetic blocking. Important in data storage applications.

Aluminium expansion produces a tensile stress that is the responsible of a coercive field maximum at room temperature.

• P. M. Paulus, F. Luis, M. Kroll, G. Schmid and L. J. de Jongh, Journal of Magnetism and Magnetic Materials, 224 (2001) 180. • A. Kumar, S. Fahler, H. Schlorb, K. Leistner and L. Schultz, Physical Review B, 73 (2006) 064421 • M. Vazquez, K. Pirota, J. Torrejon, D. Navas and M. Hernandez-Velez, Journal of Magnetism and Magnetic Materials, 14 (2005) 715.

500 K

627 K Nickel bulk TC PM

Size influence in spin reversal

• I. S. Jacobs and C. P. Bean, PhysicalReview 100 (1955) 1060 • E. H. Frei, S. Shtrikman and D. Treves, PhysicalReview 106 (1957) 446.

VAC

• H. He and N. J. Nongjian, Encyclopedia of Nanoscience and nanotechnology, X (2003) 1

Electroplating

The coercive field shows an agreement with “FANNING” reversal mode for diameters lower than 43 nm. For larger diameters, the “CURLING” reversal mode is in qualitatively agreement with our experimental data. *[email protected]

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superparamagnetic blocking. Important in data storage applications. The coercive field shows an agreement with. “FANNING” reversal mode for diameters lower.
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