Metal–insulator transition induced by O16−O18 oxygen isotope exchange in colossal negative magnetoresistance manganites

Abstract

The effect of 16 O → 18 O isotope exchange on the electric resistivity was studied for (La1−yPry)0.7Ca0.3MnO3 ceramic samples. Depending on y, this mixed perovskite exhibited different types of low-temperature behavior ranging from ferromagnetic metal (FM) to charge ordered (CO) antiferromagnetic insulator. It was found that at y = 0.75, the substitution of 16 O by 18 O results in the reversible transition from a FM to a CO insulator at zero magnetic field. The applied magnetic field (H ≥ 2 T) transformed the sample with 18 O again to the metallic state and caused the increase in the FM transition temperature TC of the 16 O sample. As a result, the isotope shift of TC at H = 2 T was as high as 63 K. Such unique sensitivity of the system to oxygen isotope exchange, giving rise even to the metal-insulator transition, is discussed in terms of the isotope dependence of the effective electron bandwidth which shifts the balance between the CO and FM phases.

Phase diagram and isotope effect in(Pr1−yEuy)0.7Kalinov1, Gorbenko2, Талденков3 et al. 2010Phys. Rev. BSelf Cite154200View full textAdd to dashboardCite

“…The enrichment process is described in detail elsewhere. 40 The similarity of the oxygen isotope composition in the sample to that in the gas medium indicated that a thermodynamic equilibrium was achieved during annealing and, hence, the difference in the diffusion rates of the oxygen isotopes did not significantly affect the results of the investigation. It should also be noted that the mass of a sample annealed in 16 O 2 remained unchanged (within the experimental error) during the prolonged heat treatment.…”

“…Close to the LS -IS crossover even small changes in hopping t and bandwidth W ∼ 2zt (z is the number of nearest neighbors) lead to a pronounced shift of the phase equilibrium. 40 Indeed, we see that T SS is much higher for the samples with the heavier oxygen isotope. Note, however, that the isotope effect for T FM , being much weaker, is of the opposite sign.…”

“…The bandwidth changes with the oxygen isotope substitution but the resulting effect on T FM is relatively weak. 40 At the same time, the SST of the HD samples (in the right part of the phase diagram) is accompanied by a more drastic change of the electronic structure. Whereas in the insulating LS state the e g bands are practically empty, they are partially occupied in the high-temperature phase with the promotion of a part of the Co 3+ ions to the IS state.…”

Possible spin-glass state in SmSr-manganites as the origin of the magnetization jumps

“…The enrichment of the samples by 18 O was performed at T ¼ 950 1C and at a pressure p ¼ 1 bar for 200 h using the method reported in Ref. [9]. Magnetization was measured by a Quantum Design MPMS-7 SQUID magnetometer, by a vibrating sample magnetometer, and using Fitz's technique (for high-speed measurements).…”

Quenched-Disorder-Induced Magnetization Jumps in (Sm,Sr)MnO3

“…17 So, for this system the electronic and magnetic state can be tuned by the application of a magnetic field or by oxygen-isotope substitution. Sm 0.5 Sr 0.5 Mn 18 O 3 is an insulator in the low-temperature ground state, and undergoes an I-M transition after 18 O-to- 16 O substitution, after reduction of the doping level to x = 0.45, or under application of the magnetic field of the order of 1 T. 18 Our magnetization data (Fig. 1) show that there are two types of field-induced transition for 18 O samples: at low temperatures there appears an irreversible transition from an AFM to FM state, and at high temperatures T Ͼ T c -a reversible albeit slightly hysteretic PM-FM transition.…”