Magnetic Nature of a Ni Dopant in La1.85Sr0.15CuO4: Spin-Glass Behavior

A. Malinowski, V.L. Bezusyy, R. Minikayev, W. Paszkowicz, P. Dziawa, Y. Syryanyy and M. Sawicki Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warsaw, Poland

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The magnetic properties of La1.85Sr0.15CuO4 doped with Ni was investigated in the field up to 5 T and in the temperature range from 2 K to 400 K using both dc and ac techniques. For Ni content larger than 0.05 the system exhibits irreversibility of low-field susceptibility χ(T) below a certain temperature depending on y and a cusp at Tg in χ(T) measured after zero-field cooling. The decay of remnant magnetization below Tg with time is described by a stretched-exponential function. In accordance with scaling theory, all the χ(T) data for y = 0.50 sample taken in the vicinity of Tg at different fields collapse onto two separate curves when plotted as q|t|-β vs. B2 |t|-β - γ, where q is the spin-glass order parameter, t = (T - Tg)/Tg, and β and γ are the critical exponents. All these features taken together reveal existence of spin-glass phase below Tg. Variation of Tg with y is linear below y = 0.25 and Tg extrapolates to 0 K for y → 0 what strongly suggests that spin-glass phase extends into superconducting region of the phase diagram.

DOI: 10.12693/APhysPolA.118.244 PACS numbers: 74.62.Dh, 75.40.Cx, 75.40.Gb, 75.50.Lk