Spontaneous ferromagnetic spin ordering at the surface ofLa2CuO4

Abstract

Magnetic properties of high purity stoichiometric La2CuO4 nanoparticles are systematically investigated as a function of particle size. Ferromagnetic single-domain spin clusters are shown to spontaneously form at the surface of fine grains as well as paramagnetic defects. Hysteresis loops and thermomagnetic irreversibility are observed in a wide temperature range 5 − 350 K with the remnant moment and coercivity gradually decreasing with increasing temperature. Possible origins of the spontaneous surface ferromagnetic clusters and the relation of our data to the appearance of unusual magnetic phenomena and phase separation of doped cuprates are discussed.

Magnetic Properties of La2-xSrxCuO4Nanoparticles in Mesoporous Silica

“…The spin values of superparamagnetic moment due to the Cu 2+ ions with S = 1/2 were estimated to be about 470 and 860 at 30 K and 50 K, respectively. Both the temperature dependence of susceptibility and the magnetization curves for x = 0 were qualitatively similar to that observed for La 2 CuO 4 particles with diameter of 0.22−4.1 μm [5]. In contrast, the magnetization for x = 0.15 consistently increased in proportion to magnetic field without diamagnetic behavior.…”

“…The ferromagnetic behavior originates from formation of ferromagnetic anisotropic single domain cluster of the surface of particle. In contrast, the antiferromagnetic or the paramagnetic component is attributed to the Cu 2+ defects at surface [5]. The ferromagnetic component is corresponding to the ESR absorption line changed from Lorentzian line to Gaussian one above 77 K. For antiferromagnetic particles, the superparamagnetic moment is estimated as the moments composed of the uncompensated spins of two sublattices on surface.…”

“…For nanometer scale materials, the proportion of the surface and interface to total volume increases with decreasing the material size, resulting in influencing the physical properties. In the case of La 2 CuO 4 particles with grain size of 0.22−4.1 μm, ferromagnetic single-domain spin clusters are shown to spontaneously form at the surface of fine grains as well as paramagnetic defects [5]. In the present study, we are interested in the magnetic size effect on LSCO nanoparticles with particle size of a few nano-meters.…”

Detail Synthesis Route of Free-Standing Antiferromagnetic La2CuO4 Nanoparticles via Sol-gel Method

“…The suggestion about uncompensated spins at the surface was proposed leading to magnetism in other antiferromagnetic systems such as La2CuO4. The ferromagnetic component was observed in La2CuO4 at 20 K until 350 K when its particle size was reduced to 1.53 µm [7]. Both CuO nanoparticles and La2CuO4 microparticles were not encapsulated by other molecules, but the explanation on these systems is limited to the role of the surface effect only.…”

Coexistence of Superconductivity and Ferromagnetism in La2-xSrxCuO4 Nanoparticles

“…It is well-known that the substitution of nonmagnetic Zn 14 or magnetic Fe 15 ions for Cu in La 2-x Sr x CuO 4 considerably suppresses both the superconductivity and the antiferromagnetic correlation in the CuO 2 plane. 16 Recently, a weak ferromagnetism has been observed in nonsuperconducting CuO, 17 La 2 CuO 4 , 18 and superconducting YBa 2 Cu 3 O 7-δ 6−8 nanoparticles, and a large magnetization enhancement with decreasing particle size is also reported in nonsuperconducting La 2-x Sr x CuO 4-δ (x = 0.04). 19 In view that all these types of nanoparticles have CuO 2 planes similar to that in HTSCs, weak ferromagnetism may exist in superconducting La 2-x Sr x CuO 4-δ nanoparticles as well.…”