Journal of Mignetism and F&guetic Materials 14.0-144 (1995) so3-
Magnetoresistance in Ni-Pt multilayers with and in-plane magnetization
B. Ahneida a, LB. Sousa ay * , R. Krishnan b, pi. Lassri b, A%. Porte b,
a IFIiUUP and CFUP, FaculaMe Cihcias, Uniuersialadk Porte, Pr. Gumes Teireira, 4&W Porto, Pormgd b Laboratoire Magne~dsne et Mat. Magdqw, CNRS 921195, Me&ion, France
Abstract
High resolution magnetoresistance (Ap/p) measurements were made on have shown the dominance of perpendicular spontaneous magnetization (Y) in-plane) our Ap/p results show the usual Smitt anisotropy with respect t while for thin Ni-layer (M petpendicuiar) Ap/p is always negative. In mechanisms leads to an anomalous minimum in Ap/p at Iow gelds, when Wll I.
It is known that systems like Co-Pt [l] and Fe-p1 [2]
can develop a perpendicular magnetic anisotropy, which makes them interesting for magneto-optical storage appli- cations. Previous studies on Ni,Pt,, A multilayers de- posited on silicon substrates at 200°C have shown [3] that Z-P! multilayers also exhi!it perpendicular anisotropy, for thin Ni-layers (X I 17 A!, whereas for large n the spontaneous magnetization M, is in-plane.
To investigate this problem further we performed high resoIution magnetoresistance (Ap/p) measurements onoa set of Ni,-Ptz, A samples, with x = 9, 16, 19.5 and 39 A.
The number of Ni/Pt bilayer repetitions was 20, 12, 15 and 8, respectively. They were prepared 131 by sequential evaporation in ultrahigh vacuum, with a base pressure of 5 X lCt-’ Torr. Their thickness was monitored by an in-situ quartz oscillator, calibrated with a profiometer. The sam- ples were deposited on a silicon zubstrate at 2tWC, having a 100 A Pt buffer and a 30 A Pt top layer, with the exception of the Ni,,, @, A and Ni,, &,, A which had no buffer. The magnetoresistance measurements were made from 20-300 K with the magnetic field (HI applied in the plane of the films, either parallel or perpendicular to the electrical current (I).
Our samples can be divided in three main groups:
Ni 39 APt, A with in-plane magnetization, Ni, bPt, A and Ni r6 opt, ji with perpendicular anisotropy (the second one at Iow temperatures only) and Ni ,9,5 opt, A as a transition case [3].
In the sample with thick Ni layers (X = 39 A> Ap/p is positive for H I] I and negative for H II, as shown in Fig. 1. In aII cases, magnetic saturation is easily reached
l
Corresponding author. Fax: +351-Z-319267.
with &r = loo0 Oe. This hehaviour is to observed in buM Ni, and attributed to the Smitt [4]. In this mechanism the resi
6 between the current I a,td the ma magnetoresistance A p/p = A dependence has been confirmed in
giving A = -3.92 x 10-3 and B = 10.6x 1W3, as shown in Fig. 2 for T = 1757 K.
-0.OO6 ’ i- 1
Hrl0304-8853/95/.$09.50 8 19!J5 Elsevier Science B.V. All rights reserved
SW 0304-8853(94)01540-6
’ ’ * ’ ’
0 0.2 0.4
0.6cm’8 0.3 I
v&es of (Apjp),, 1755 K tic energy. This could enhance the
r tbis model we could under-
get much larger. As a aI .q&disorder scattering de-
a mametoresistive behaviour
ximately zero [3] (near balance in-pkme M6 orientation), the iwr gets rncwe ~m~Iex hecause this sample
rvgd in the temperature derivatives sides of the transition point
e tbe normal Smitt with ~Ip/p> 0 for This suggests that in
-0.002 : I I-
HHI
-a.004 \. :
. .
296.7K-
-0.001 -1
27.3K -
