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Magnetic properties of bulk polycrystalline Mn-doped SrRu 1− x Mn x O 3 perovskite, at doping range 0.2≤ x ≤0.3, were studied by both magnetization and ac-susceptibility measurements. It was found that the exchange bias (EB) effect emerges with increasing Mn doping in SrRu 1− x Mn x O 3 at x ≈0.25, following the ferromagnetic (FM) to antiferromagnetic (AFM) phase transition. This transition is accompanied with the change in structure symmetry and then the EB field, H EB , increases significantly in doping range 0.25 x ≤0.3. The EB effect was verified by both cooling magnetic field, H cool , dependence of the H EB and training effect. A markedly nonmonotonic H EB vs. H cool dependence with maximum at around 40 kOe was found, resembling the behavior of phase-separated EB systems. Moreover, a clear analogy with behavior of classic EB system of Pr 1/3 Ca 2/3 MnO 3 was noticed, strongly suggesting that the EB effect in SrRu 1− x Mn x O 3 originates from exchange interactions at the interface of nanoscale FM clusters (size of ~1.6 nm at x =0.3) coe x isting together with dominant AFM phase at the boundary of the first-order FM/AFM transition. The training effect observed is well understandable within the spin-configuration relaxation model and indicates important contribution to the EB behavior from the AFM domains rearrangement at the interface.

Non-equilibrium magnetic properties of the near half-doped Sm 0.43 Ca 0.57 MnO 3 nanoparticles with an average size as small as 15 nm have been investigated by measuring temperature dependence of zero field cooled (ZFC) magnetization, ac-susceptibility, time dependence of ZFC magnetization, relaxation of the remanent magnetization, and memory effects in ZFC magnetization. For the studied particles, charge ordering, characteristic for the bulk, is gradually suppressed with decreasing particle size and fully disappears in 15 nm particles, while the Neel temperature decreases slightly from 73 K for 60 nm to 58 K for 15 nm particles. It was found that dipolar interaction between 15 nm nanoparticles is enough to leads to the formation of a superspin glass state. Characteristic features of superspin glass state, such as aging and memory effects have been observed in 15 nm samples. In a difference to atomic spin glasses, no strong rejuvenation of magnetization has been observed at low temperatures.

Magnetic properties of nanocrystalline LaMnO 3 + δ manganites with particle sizes of 20 (LMO20), 25 (LMO25), and 30 nm (LMO30), prepared by the citrate method, have been investigated. All nanoparticles exhibit paramagnetic to ferromagnetic transition (PFT) at T C > 200 K . It was found that the relative volume of the ferromagnetic phase increases with increasing particle size and approaches a value of about 93% for LMO30. Ac susceptibility of LMO20 sample exhibits strong frequency dependence below T C , whereas for LMO30 sample only weak frequency dependence was observed. The magnetization of LMO30 sample exhibits a PFT of second order. It was found that an applied pressure enhances T C of LaMnO 3 + δ particles with a pressure coefficient of d T C / d P ≈ 1.4 – 1.9 K / kbar for all samples. Peculiar magnetic memory and negative magnetization effects observed for LMO20 sample are discussed.

The appearance of superconductivity and the relaxation of T c to the equilibrium value T c ≈30 K in a period of five days were observed in the tetragonal ceramic NdBa2Cu3O6.67 under a pressure of 1 GPa. The superconducting phase vanishes 1.3 h after the pressure is released. This behavior is explained by the charge redistribution occurring as a result of pressure-induced ordering of oxygen in the CuOx planes.

Magnetic properties of compacted Sm0.1Ca0.9MnO3 particles with 25 and 60 nm average sizes have been investigated. Particular attention has been paid to Griffiths-like features at temperatures above magnetic transition temperature TC and to the system glassiness at low temperatures. Griffiths-like features in inverse magnetic susceptibility of Sm0.1Ca0.9MnO3 nanoparticles have been linked to the presence of short range ferromagnetically correlated spin clusters above TC. Glassy behavior has been revealed in temperature and frequency dependence of ac-susceptibility, temperature and field dependence of thermoremanent and isothermoremanent magnetization, and time decay of the remanent magnetization. Experiments revealed the major impact of the glassy component on magnetic properties of investigated nanoparticles. The magnetic relaxation associated with glassy features was found to be much more pronounced in smaller particles, where a formation of collective state in an ensemble of phase separated nanoparticle...

Pressure effect on magnetic state of Ru-doped charge-ordered manganite Bi0.4Ca0.6Mn1 − xRuxO3 (x = 0.1, 0.2) was investigated by magnetization measurements in the temperature range of 5−315 K and under pressure up to ∼10 kbar. It was found that the x = 0.2 composition is basically ferromagnetic (FM) while the low-doped (x = 0.1) one exhibits a FM cluster glass behavior and exchange bias (EB) effect at low temperatures. Bi0.4Ca0.6Mn0.9Ru0.1O3 demonstrates a substantial pressure-enhanced ferromagnetism, evidenced by ∼70% increase in spontaneous magnetization at 10 K under 10.3 kbar. It appears that an applied pressure strongly increases the FM to antiferromagnetic (AFM) phase ratio in the sample, leading to a notable decrease in both coercive field HC and EB field HE (HC and HE at 10 K decrease under pressure of ∼10 kbar by about 40% and 50%, respectively). The pressure-induced changes are qualitatively described within the simple model for FM size-variable clusters embedded in an AFM matrix. It is argued t...

Magnetic properties of compacted Sm0.1Ca0.9MnO3 nanoparticles with average particle size of 25 and 60 nm have been investigated. It was found that the relative volume of the ferromagnetic phase decreases with decreasing particle size. Magnetization curves measured in field cooled and zero field cooled mode separate near the transition temperature TC and remain different even in magnetic field of 15 kOe. AC-susceptibility is strongly frequency dependent below TC, although the temperature of the maximum depends on frequency only slightly. Magnetization hysteresis loops exhibit horizontal and vertical shifts, relatively small in 60 nm and much larger in 25 nm particles, due to size-dependent exchange bias effect. The exchange bias field and the coercive field depend in a non-monotonic way on cooling magnetic field, while the asymmetry of remanence magnetization and magnetic coercivity increase monotonously with the increase of cooling field. Applied pressure enhances Curie temperature TC of nanoparticles wit...

Strong enhancement of exchange bias (EB) effect in phase-separated CaMn0.9Ru0.1O3 manganite with ferromagnetic phase heavily suppressed under pressure was observed in the measurements of field-cooled magnetization hysteresis loop. It was found that both EB field HE and normalized remanence asymmetry pronouncedly increase with increasing pressure P, enlarging by one order of magnitude at P = 10 kbar. In contrast, the coercive field HC shows a non-monotonic variation with pressure, reaching a maximum value at around 5 kbar. Such unusual HC(P) dependence may be explained by transformation from multi-domain to single-domain state in a system of ferromagnetic (FM) size-variable particles. Comparison of HE(P) with HC(P) data indicates remarkable enhancement of EB with decrease in HC in the pressure range between 5 and 10 kbar. It is argued that a strong increase of HE under pressure is attributed to the suppression of FM phase, i.e., to the decrease in size of FM clusters embedded in antiferromagnetic matrix. P...

The temperature of the superconducting transition of Ru1−xSr2RECu2+xO8−d (RE=Gd, Eu) compounds was raised up to 72 K (for x=0.4; compare to TC=45 K observed for RuSr2GdCu2O8) by changing the ratio between Ru and Cu. Magnetization experiments performed under external pressure for RE=Gd: x=0.1, 0.2, 0.3, and 0.4, and RE=Eu: x=0.4 samples reveal that TC increases at a rate of 5–6 K/GPa. The hole doping achieved along the series has been probed in Hall effect, thermopower, and XANES experiments and is found to increase with x. Muon spin rotation spectroscopy experiments reveal the presence of a low temperature magnetic transition for Ru0.6Sr2EuCu2.4O8−d (Tm≈5 K), similar to that recently observed in the Ru1−xSr2GdCu2+xO8−d system [P. W. Klamut, et al., Physica C 364, 313 (2001)]. Low temperature magnetization data suggest the constrained dimensionality of the superconducting phase in both RE=Gd and Eu based compounds.