In spite of its frustrated lattice, the multiferroicLu0.5Sc0.5FeO3 exhibits two consecutivemagnetic transitions at T N1 ≈ 175 K and T N2 ≈ 70 K determined from neutron diffraction. In the orderedstate, magnetic fluctuations are present, most likely arising from the in-planefrustrated interaction of the Fe hexagonal lattice. Furthermore, a crossover ofthe magnetic intensity is observed from elastic to inelastic upon warming,indicating that magnetic fluctuations persist well above T N1, a common feature in hexagonal multiferroics.

The multiferroic material Bi1-x SmxFeO3 shows ferroelectric and antiferromagnetic properties inthe ground state of the Bi-rich side. When the Sm content increases fromx = 0 in BiFeO3, the (ferroelectric-R3c→ paraelectric-Pnma) state change occurs around x= 0.14. According to the previous studies onBi1-x SmxFeO3, the state boundary between the R3c and Pnma states can beidentified as a morphotropic phase boundary (MPB), which is nearly parallel tothe temperature axis in the state diagram. The notable feature ofBi1-x SmxFeO3 is that a remarkable piezoelectric response was also foundnear the MPB. However, the origin of the remarkable response has not beenunderstood sufficiently. In this study, thus, the crystallographic features inthe vicinity of the MPB have been examined by x-ray powder diffraction andtransmission electron microscopy. It was confirmed that the R3c and Pnma stateswere present for 0 ≤ x ≤ 0.15 and for0.16 ≤ x ≤ 0.30, respectively. Inaddition to these states, there also existed the PbZrO3-type statearound x = 0.15, which was identified as a modulatedstructure. Based on the analysis of the modulated structure, furthermore, it wassuggested that the PbZrO3-type state could be regarded as a 2q state,which is characterized by two transverse modulation waves with k1= [1/2 0 0]o and k2 = [0 1/20]o in the orthorhombic-Pnma notation.

In the highly-correlated electronic system Ca1-x PrxMnO3 having the simple perovskite structure, it has beenreported that there exists the C-type orbital-ordered (COO) state accompanyingan antiferromagnetic ordering for 0.10 ≤ x≤ 0.25. According to the previous studies concerning orbital-orderedstates in simple perovskite manganites, the COO state was understood to becharacterized by a spatial array of (3z2-r2)-type orbitalsfor 3d electrons in Mn ions. The notable feature of the COO state inCa1-x PrxMnO3 is that the state with the monoclinic-P21/msymmetry appears as a result of the structural transition from the disorderedstate with the orthorhombic-Pnma symmetry. Compared with the COO-state formationfrom the cubic-Pm $\overline 3$m state, however, the formation from the disordered-Pnma statehas not been understood yet. We have thus examined the crystallographic featuresof the formation of the COO state in Ca1-x PrxMnO3, mainly by x-ray powder diffraction and transmissionelectron microscopy. In the case of x = 0.16, forinstance, the COO state was found to appear from the disordered-Pnma statearound 90 K on cooling. The notable feature of the formation is that, in thePnma state just before the COO-state formation, characteristic diffusescattering appeared around each reflection in electron diffraction patterns,together with the splitting of the 200c reflection in x-ray powder diffractionprofiles in the pseudo-cubic notation. Based on these experimental data, it isunderstood that the formation of the COO state in Ca1-x PrxMnO3 accompanies remarkable fluctuations of the C-type orbitalordering in the disordered-Pnma state.

Phase pure Pb[(Fe0.5-xScx)Nb0.5]O3 [x= 0 to 0.5] multiferroic relaxors have been synthesized to study theeffect of Sc on dielectric phase tansition. Rietveld refinement of x-raydiffraction patterns confirm that the structure transforms from monoclinic (Cm)to rhomobohedral (R3m) at x = 0.3. Absence of low frequency dielectricresponse in compositions with low Sc content attributed to interfacialpolarizabilty arising due to differences in conductivities of grain and grainboundary. Moreover, value of diffusivity parameter (γ) of high of Sccontent compositions is near to 2, confirms relaxor charactertistic of thesecompositions. However, an essential feature of relaxors i.e., frequencydependent dielectric permittivity as a function of temperature is observed onlyin x = 0.5 composition[Pb(Sc0.5Nb0.5)O3 (PSN)]. In addition,ferroelectric phase transition temperature (Tmax) increases initiallyat lower Sc content (upto x ≤ 0.25), and further drops beyond x≥ 0.3. Such behavior of Tmax in these compositions is due to theonset of B'-B" local cation ordering at x = 0.3. Hightemperature Raman spectra of Pb(Sc0.5Nb0.5)O3(x = 0.5) confirm the stability of cation ordering in compositions withhigh Sc content well above the phase transition temperature.

The multiferroic material YbMnO3 has been reported to exhibit bothferroelectric and antiferromagnetic orders in the ground state. Of these twoorders, the ferroelectric order is associated with theP63/mmc-to-P63cm structural transition, which occursaround 1270 K. The interesting feature of the ferroelectric state is that acloverleaf domain structure with a pseudo-six-fold symmetry is observed intransmission electron microscopy images with the beam incidence parallel to thehexagonal axis. To understand the origin of the formation of the cloverleafdomain structure, we have examined the crystallographic features of theferroelectric state in YbMnO3 by transmission electron microscopy. Inthis study, particularly, we adopted the experimental condition that electronbeam incidences are perpendicular to the hexagonal axis. It was, as a result,found that there existed various ferroelectric domain structures including thecloverleaf domain structure under the present condition. The notable feature ofdomain structures found in this study is that each domain structure basicallyconsists of six domains, whose domain boundaries are terminated at one point.Because this feature makes us reminiscent of a discommensurate structure in anincommensurate state, we took high-resolution electron micrographs of areasincluding domain boundaries. Their analysis indicated that a domain boundarycould be identified as a discommensuration with a phase slip of π/3.It is thus understood that the cloverleaf domain structure should be one ofdomain morphologies for a discommensurate structure, which is related to thebreak of the translational symmetry.

Transition metal oxide thin film heterostructures have garnered increasingresearch interest in the last decade due to their multifunctional properties,such as ferromagnetism and ferroelectricity, which may be utilized in nextgeneration device applications. Many previous works reported on the depositionof such structures on oxide substrates such as SrTiO3, which are notcompatible with CMOS applications where Si(100) is the mainstay substratematerial. BiFeO3 (BFO) is a room temperature insulating ferroelectricand antiferromagnet, a well-known multiferroic material. SrRuO3 (SRO)is a ferromagnetic metal with the Curie temperature (TC) of 165K.Unexpected properties emerge when these two dissimilar materials are conjoined.However, there has been no report on exploring the magnetic properties of BFOwhen it is in contact with SRO, and particularly when they are integrated withSi(100) substrates, which is the subject of present study. BFO/SRO thin filmshave been epitaxially grown on Si (100) substrates by introducing MgO/TiNepitaxial buffer layers using pulsed laser deposition. BFO thin films show roomtemperature ferroelectricity as observed from piezo force microscopy (PFM)measurements. The magnetic data collected from BFO thin films show typicalantiferromagnetic features as expected. The TC of SRO in all thesamples studied was found be ∼ 170K, close to the reported value of165K. Interestingly, we have noticed that the coercive field of SRO layerincreased from 4 kOe to 15 kOe (nearly fourfold) by reducing its thickness from180 to 23nm, while keeping the thickness of BFO layer constant at 100nm. Pinningof Ru ions by ferroelectric domain walls in BFO, strong interfacial exchangecoupling and SRO layer thickness could cause the observed enhancement incoercivity. Our near future work will address the precise underlying mechanismsin greater detail.

The presence of the C- and A-type orbital-ordered states has been reported in thehighly-correlated electronic systemSr1-xNdxMnO3 (SNMO). The interesting feature ofthe oxide system is that an increase in the Nd content leads to the (C-type→ A-type) state change across a temperature-independent morphotropicphase boundary (MPB). Although structural fluctuations can be expected near theMPB, the detailed features of the state change have not been understoodsufficiently. Thus, the crystallographic features of the state change in SNMOwith 0.35 ≤ x ≤ 0.49 have been investigated mainly at 300K, by x-ray powder diffraction and transmission electron microscopy. It wasfound that the C-type orbital-ordered state with the tetragonal-I4/mcm symmetryand the disordered orthorhombic-Imma state were present for 0.35 ≤ x≤ 0.43 and for 0.45 ≤ x ≤ 0.49 at 300 K,respectively. The notable feature of the state change is that disordered regionswith the cubic-Pm $\bar 3$ m symmetry were also found locally for x= 0.43, in addition to the C-type state. Because therotational-displacement pattern for oxygen octahedra involved in thedisordered-Imma state is the same as that in the A-type state, furthermore, theformer disordered state may be regarded as a precursor state to the A-typeorbital ordering.

YCrO3 (YCO) is known to be a multiferroic with orthorhombic,Pnma, structure with center of inversion. However, thelocal structural inhomogeneity in this compound is believed to give rise toferroelectric behavior. In this study we explore high temperature Ramaninvestigations of YCO and observed that one of its Raman mode B3g (3)(CrO6 Octahedral tilt mode) softens around the structural phasetransition which could be the origin of ferroelectric nature in YCO. Inaddition, we substitute bismuth (Bi) in YCO to understand the structuraldistortions that lead to local structural inhomogeneity. Besides B3g(3) mode softening with composition and high temperature studies inY1-xBixCrO3 the study reveals thestructural distortions and the structural tunability Bi offers in suchsystems.

The simple perovskite manganite Sr1-x SmxMnO3 (SSMO) has been reported to have a highly-correlatedelectronic system for e g-electrons in a Mn ion. According to the previous studies, the C-typeorbital-ordered (COO) state with the I4/mcm symmetry was found to be formed fromthe disordered-cubic (DC) state on cooling. The feature of the COO state is thatits crystal structure involves both the Jahn-Teller distortion to orbitalordering and the R 25-type rotational displacement of oxygen octahedra. Because of theinvolvement of both the distortion and the displacement, their competitionshould be expected in the formation of the COO state. However, the detailedfeatures of the competition have not been understood yet. Thus, thecrystallographic features of the COO state in SSMO have been examined by x-raypowder diffraction and transmission electron microscopy. It was found that, whenthe Sm content increased from x = 0 at roomtemperature, the DC state changed into the COO state with the tetragonalsymmetry around x = 0.13. The notable feature of theCOO state is that the state is characterized by a nanometer-scaled bandedstructure consisting of an alternating array of two tetragonal bands. Onetetragonal band consisted of the COO state involving both the Jahn-Tellerdistortion and the R 25-type rotational displacement. But, there was only the latter displacementin the other, the state of which could be identified as a disordered tetragonal(DT) state. Based on this, it is understood that the COO-state formation fromthe DC state should take place via the appearance of the DT state, which mayinvolve fluctuations of the C-type orbital ordering.