Effect of The Orientation of The Magnetic Field on The Giant Magnetoresistance of Fe/Cr Superlattices
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V.V. USTINOV, V.I. MININ, L.N. ROMASHEV, AB. SEMERIKOV AND A.R. DEL Institute of Metal Physics, GSP-170, Ekaterinburg, 620219, Russia
ABSTRACT
We study the magnetoresistance of [Fe/Cr]3o/MgO superlattices grown by molecular beam epitaxy at a various magnetic field directions. The theory of the orientation dependence of the effect is developed. It is shown that the magnetic field strength dependence of magnetoresistance can be calculated for arbitrary orientation of magnetic field if this dependence is known for in-plane and perpendicular-to-plane magnetic fields. It is noted that the magnetization curve can be obtained by making use of the results of the magnetoresistance measurements.
INTRODUCTION
Since discovering the giant magnetoresistance (MR) effect in metallic superlattice 1,2 the MR measurement is a standard procedure for every new multilayer. The magnetoresistance r(H) is usually defined by the relation
411) =(RH -Ro) /Ro
(1)
where RH is a resistance of a sample placed in a magnetic field H, Ro is a resistance at H=0. As a rule the electric current j flows in the sample plane. Three types of MR can be distinguished depending on the direction of H with respect to j: longitudinal MR (r II ) with in-plane H and 1V[j, transverse MR ( rr ) with in-plane H and Hlj, and perpendicular MR ( r±) with H perpendicular to the film plane. The magnetic field dependence of r11 and rL in Fe/Cr superlattice turns out to be different '-3. It has been supposed that this difference is caused by the magnetic anisotropy, but a detailed analysis has not been made. To our opinion, two problems have to be solved. First it is not clear how the magnetic field dependence of MR changes if the angle 0 between H and the film plane changes from 00 to 900. Further it is interesting to know whether one can calculate r(H-,dO) for arbitrary angle provided that the functions rI(H) and r.(H) are known. If the orientation dependence of MR really correlates with that of magnetization, one could obtain the magnetization curves by making use of the MR measurements. 317 Mat. Res. Soc. Symp. Proc. Vol. 384 01995 Materials Research Society
EXPERIMENTAL RESULTS
We studied Fe/Cr multilayers grown by molecular beam epitaxy method on MgO (100) substrates. The resistance was measured by standard four-probe method. The temperature was 290K and 77K. The longitudinal and transverse MR are practically identical. Shown in Fig. I is r (H) and r±(H)curves for the epitaxial superlattice [Fe(23A)/Cr(8A)] 30 .
q= 00, T--290K D=-90P, T= 290K A 0= OP,TI-- 77K 0
H*
0-10
"C-15 0
-20 S-25 -200
-30
-20
0
-10
H(Oe200
0
10
20
Magnetic field H (KOe) Figure 1
One can see that the longitudinal MR decreases linearly with growing magnetic field at low H and is practically constant if H exceeds the saturation field H,/. The perpendicular MR practically does not change if the field is less than /* =8 kOe (we define /-* as non-zero value of magnetic field vanishing rL, i.e. r±( -*)=.0, see Fig 1); moreover, at the range from 0 to 6 kOe the resistance slight
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