Yantao Su

Temperature- and magnetic-field-induced magnetization reversal in perovskite YFe0.5Cr0.5O3

Perovskite YFe0.5Cr0.5O3 exhibits magnetization reversal at low applied fields due to the competition between the single ion magnetic anisotropy and the antisymmetric Dzyaloshinsky–Moriya interaction. Below a compensation temperature (Tcomp), a tunable bipolar switching of magnetization is demonstrated by changing the magnitude of the field while keeping it in the same direction. The present compound also displays both normal and inverse magnetocaloric effects above and below 260 K, respectively. These phenomena coexisting in a single magnetic system can be tuned in a predictable manner and have potential applications in electromagnetic devices.

Ferromagnetic antiphase domain boundary in Mn-doped hexagonal BaTiO3 multiferroics

The magnetic properties of hexagonal Ba(Ti1−xMnx)O3 (x = 1/9, 1/6) samples specifically treated under different thermal conditions are investigated. A magnetic transformation from paramagnetism of as-grown samples to weak ferromagnetism of post-annealed samples is observed at room temperature. Associated with the structural modulation characteristics and dielectric behaviors, our experimental results reveal that the high-temperature ferromagnetism in Mn-doped hexagonal BaTiO3 derives from RIII types of antiphase domain boundaries. Spin glass transitions are observed at Tsg = 48 K and 44 K in the densely doped as-grown and post-annealed samples, respectively, but the transitions are not intrinsic properties of the hexagonal phases.

Producing well aligned in situ composites in peritectic systems by directional solidification

Recently, it was found that cellular peritectic coupled growth (CPCG) can be a candidate method to grow well aligned in situ composites in peritectic alloys. In this letter, we experimentally show that there is a narrow growth region in which CPCG can be stable to avoid the influences of peritectic reaction around the trijunctions and the sidebranching instability to produce well aligned in situ composites. A simplified model was developed to predict the growth region of stable CPCG. Good agreement was obtained between the theoretical predictions and the experimental observations.

Large reversible magnetocaloric effect in HoTiO3 single crystal

Large magnetocaloric effect has been observed in perovskite-type HoTiO3 single crystal accompanied by a second-order magnetic phase transition at TC ≈ 53 K. The values of maximum magnetic entropy change are about 5.96 and 11.56 J kg−1 K−1 under the magnetic field change of 2 and 5 T, respectively, without any detectable thermal and magnetic hysteresis loss. The large magnetic entropy change is attributed to the sharp magnetization jump, related to anomalies of the lattice parameters just at the Curie temperature. Such a large reversible magnetocaloric effect makes the perovskite HoTiO3 attractive for pursuing new materials for magnetic refrigeration.

Evidence of two distinct dynamical freezing processes in single-layered perovskite La0.7Sr1.3CoO4

The static and dynamic features of magnetization have been investigated in terms of dc magnetization, ac susceptibility, and memory effects on single-layered perovskite La(0.7)Sr(1.3)CoO(4). The results indicate that short-range ferromagnetic clusters coexist with the glassy magnetic state, i.e., a cluster-glass phase between T(f) and T(G) and a spin-glass-like phase below T(f). The clear evidence of memory effects in the dc magnetization is also observed below T(f) and T(G), respectively. These two glassy states with cooperative relaxation processes may derive from the different interaction processes among nanoscale ferromagnetic clusters mediated by the matrix, which is influenced by changing the spin state of Co(3+) ions in spontaneously phase-separated cobaltite.

Polaron response dominated multiferroic property in 12R-type hexagonal Ba(Ti{sub 1/3}Mn{sub 2/3})O{sub 3-δ} ceramics

We report the multiferroic properties of 12R-type hexagonal Ba(Ti1/3Mn2/3)O3-δ found in Mn-doped BaTiO3 series samples. Hysteresis measurements reveal the coexistence of weak ferromagnetism and ferroelectricity at room temperature. Furthermore, frequency-driven dynamic ferroelectric phase transition is disclosed around a critical frequency of 220 Hz. Analyses on the dielectric relaxation, leakage current, crystal structure, and magnetic susceptibility lead us to conclude that the response of polarons dominates the observed physical properties, and the dynamic phase transition may ascribe to the response mode changes of the localized electrons. More importantly, we figure out the crucial factors leading to difference of the ferroelectric and magnetic properties of the 12R-type Ba(Ti1/3Mn2/3)O3-δ samples from that of the 6H-type Ba(Ti1-xMx)O3-δ (M = Fe, Mn) samples.

Polaron response dominated multiferroic property in 12R-type hexagonal Ba(Ti1/3Mn2/3)O3-δ ceramics

We report the multiferroic properties of 12R-type hexagonal Ba(Ti1/3Mn2/3)O3-δ found in Mn-doped BaTiO3 series samples. Hysteresis measurements reveal the coexistence of weak ferromagnetism and ferroelectricity at room temperature. Furthermore, frequency-driven dynamic ferroelectric phase transition is disclosed around a critical frequency of 220 Hz. Analyses on the dielectric relaxation, leakage current, crystal structure, and magnetic susceptibility lead us to conclude that the response of polarons dominates the observed physical properties, and the dynamic phase transition may ascribe to the response mode changes of the localized electrons. More importantly, we figure out the crucial factors leading to difference of the ferroelectric and magnetic properties of the 12R-type Ba(Ti1/3Mn2/3)O3-δ samples from that of the 6H-type Ba(Ti1-xMx)O3-δ (M = Fe, Mn) samples.

Magnetocaloric properties of single crystalline YbTiO3 with second order phase transition

Magnetic entropy change and refrigerant capacity in applied magnetic fields up to 5 T have been investigated for the single crystalline YbTiO3. The maximal magnetic entropy changes at the second order magnetic phase transition temperature TC (42 K) are about 2.47 and 5.25 J kg?1 K?1 under 1.5 and 5 T, respectively. The magnetic entropy change is attributed to the sharp magnetization jump, related with anomalies of the lattice parameters just at the Curie temperature. The magnetic entropy change for YbTiO3 can be well described by a phenomenological universal curve behavior. The field dependence of the magnetic entropy change and the relative cooling power was also studied. From the analysis of the relationship between the local exponent n and the critical exponents, we conclude that the critical behavior of YbTiO3 belongs to the three-dimensional Heisenberg class, which was also confirmed by the heat capacity measurement.

Large reversible magnetocaloric effect in TmTiO3 single crystal

The magnetic properties and magnetocaloric effect (MCE) of TmTiO3 single crystal were studied by magnetization and heat capacity measurements. A large reversible MCE was observed at the Curie temperature T-C of 65 K, which is related to a second-order magnetic transition from paramagnetic to ferrimagnetic state. The values of maximum magnetic entropy change can reach 7.2 and 13.5 J kg(-1) K-1 for a field change of 2 and 5 T, respectively, with no obvious hysteresis loss in the vicinity of the Curie temperature. The corresponding maximum adiabatic temperature changes are found to be 3.5 and 6.8 K. The magnetic transition and the origin of large MCE in TmTiO3 single crystal are discussed