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Submitted on 1 Jan 1980
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LOW-TEMPERATURE TRANSITION
METAL-SEMICONDUCTOR IN CdCr2Se4 SINGLE CRYSTALS DOPED WITH INDIUM AND GALLIUM
T. Aminov, K. Below, V. Kalinnikov, L. Koroleva, L. Tovmasjan
To cite this version:
T. Aminov, K. Below, V. Kalinnikov, L. Koroleva, L. Tovmasjan. LOW-TEMPERATURE TRANSITION METAL-SEMICONDUCTOR IN CdCr2Se4 SINGLE CRYSTALS DOPED WITH INDIUM AND GALLIUM. Journal de Physique Colloques, 1980, 41 (C5), pp.C5-155-C5-156.
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JOURNAL DE PHYSIQUE Coilogue CS, suppldment au n o 6 , Tome 41, juin 1980, page C5-155
LOW-TEMPERATURE TRANSITION METAL-SEWICONDUCTOR IN CdCr2Se4 SINGLE CRYSTALS DOPED WITH INDIUM AND GALLIUR,
*
T.G. Aminov, K.P. Below, V.T. Kalinnikov, L.I. Koroleva , L.N. Tomasjan
N.S. Kurnakov I n s t i t u t e of General and Inorganic Chemistry oJ t h e Academy of Sciences of t h e U. S. S . R., Department o f Physics, Moscow S t a t e University, Moscow, U. S. S. R.
We have investigated the electroresis- tivity p of single crystals of Cdl-xInxCr 2 Se4 (X = 0.012; 0.013; 0.017 and 0.051) and Cd Ga Cr2Se4 (y = 0.017; 0.019; 0.037;
1-Y Y
0.043) in wlde temperature range from 2 to 200 K and in magnetic fields up to 50 kOe.
Samples and production of the ohmic contacts to them as well as measuring procedure were described in our articles / 1 1 2 /
We have observed three characteristic types of the curves p(T) shown in figures 1 , 2. Figure 1 shows the temperature dependene of the electroresistivity p(T) of the sample with x = 0.012 in the different magnetic
fields : 1 - 0 kOe; 2 - 10 kOe; 3 - 30 kOe:
4 - 50 kOe. The samples with x s 0.017 and y 4 0.037 have similar dependence.
Figure 2 shows the curves p (T) a) f o r the sample with y = 0.043; b) for the sample with x = 0.051 in the same magnetic fields as in figure 1. The temperature of the maximum negative magnetoresistance
( P N M R ) is marked by the dotted line. E.s one
notes from figurss 1, 2, the temperature behaviour of the electroresistivity in the Curie point Tc region is very similar for all of the investigated samples. Above the Tc the maximum on the curves p(T) is obser-.
ved, its value and position being affected strongly by a magnetic field. MNMR is on 10-15' below the maximum on the curve p ( ~ ) and amounts to gigantic value : for instance for the sample with x = 0.013 the magnetic field of 50 kOe decreases p by 214 times.
*Special materials. L.I. Koroleva, Moscow State University, Dept Physics, Moscow 117234, USSR.
Fig. 2
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980526
JOURNAL DE PHYSIQUE
Below 50 K the temperature dependence P(T) is essentially different for the sam.~le with x ,<. 0.017 and y ,< 0.037 on the one hand and with x = 0.051 and y = 0.043 on the other hand. The minimum in the 40- 60 K range on the curve p(T) and sudden increase of electroresistivity p with fur- ther temperature decrease is observed for weakly doped samples.
For the samples with x = 0.051 and y = 0.043 below 12 K p suffers a sudden decrease with T reduction; for instance, for the first sample - by 4.5 orders rea- ching 7, 9 loh2 om sm value at T = 2 K. Here transition metal-semiconductor is observed.
It is distinguished from all the others known transitions of such type by the fact that low-temperature phase is cond.ucting in this case and high-temperature one is iso- lating. Material EuO with deficiency of oxygen was so far the only ferromagnetic semiconductor in which the transition metal- semiconductor was found 13/. The transition in CdCr2Se4 discovered by us occurs at a certain concentration of single-charged donors and is likely to be connected with the formation of cooperative ferron state above the transition point 14/.
References
/1/ Belov, K.P., Koroleva, L.I., Batorova, S.D., Zh. Eksp. Teor. Fiz., 70 (1976)
141.
/2/ Kalinnikov, V.T., Aminov, T.G., Vigileva, E.D., Shapsheva, N.P., PTE
(USSR) 1 (1975) 227.
/3/ Oliver, M.R., Dimmock, J.O., Reed, T.B., IBM J. Res. Develop., 14 (1970) 276.
/4/ Nagaev, E.L., Soviet Phys. Uspekhi, 117 (1975) 437.
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