| The delafossite ABO2 and the rare-earth chromites AB1-xB'xO3 are the typical strongly correlated electron systems. The materials exhibit magnetic phase transition, magnetoelectric effcect, magnetostriction and magnetodielectric effect due to the interplay between spin, charges and orbital. Temperature, magnetic field and the ion substituted can directly affect the interaction between the spin, charge and lattice, and then change the physical behavior of the material. Therefore, we can study magnetoelectric properties of this compound by doping and external high magnetic field. We select CuFeO2 and YFe0.5Cr0.5O3 as the research object, detailed discuss the magnetic and electrical properties of doping hexagonal and orthogonal compounds. The primary contents are as follows,1. We birifly introduce the magnetism frustration and spin-lattice coupling of CuFeO2 multiferroic materials. We introduce the magnetic and electric properties of CuFeO2 through the research background, the crystal structure, magnetic structure, specific heat and the research status. The research status of several kinds of rare-earth chromium oxide is introduced.2. The single crystals of CuFeO2 and B-site doping samples with high quality are grown by float-zone technique using an image furnace. The polycrystalline samples of YFeo.5Cro.5O3 and A-site dopant with orthorhombic structure are prepared by the sol-gel reaction method. We constructed the magnetic and magnetoelectric measurement system based on the pulse magnetic field.3. The magnetic property of triangular lattice antiferromagnetic CuFeO2 is detailed studied in the steady and pulsed high magnetic field. We obtain the complete magnetic phase diagram of the CuFeO2 single crystal. The research results show that the sample is magnetocrystalline anisotropy. The field-induced multi-step magnetization transition is observed in CuFeO2. Above 72.8 T, the frustration is destroyed and transfers to a saturated FM state. In the dielectric polarization, the field-induced dielectric polarization with hysteresis is only observed in the incommensurate-noncollinear phase. Experimental results show that the dielectric polarization is related to the temperature and field sweep rate. The change of strain of CuFeO2 induced by the spin-lattice coupling is observed.4. We investigate the magnetic property and magneoelectric effect of B-site doping CuFe1-xGaxO2 single crystals. Experimental results reveal that the field-induced multi-step magnetization transition is observed in the samples with x?0.05, and the magnetic phase transitions become smooth with increase in temperature. The substitution leads to the change of exchange interactions and spin-lattice coupling of the samples and decreases the spin frustration of the system. The magnetization transition and magnetocrystalline anisotropy are disappeared when the doping content is above 0.08. The spontaneous dielectric polarization induced by the noncollinear incommensurate spin structure is enchanced by lower Ga-concentration (x?0.02).5. The anomalous magnetic properties and low-temperature dielectric response of YFeo.5Cro.5O3 are investigated. Experimental results reveal that a zero magnetization at a compensation temperature (Tcomp) of 244 K is observed, below which the value of magnetization becomes negative. The dielectric relaxation and magnetodielectric of YFeo.5Cr0.5O3 are observed, which is related to the spin reorientation and Maxwell-Wagner effect.6. We investigate the A-site doping effect of YFeo.5Cro.5O3 of magnetic and dielectric properties. The magnetization reversal is observed in 239 K and 48 K when Ho doping content x=0.05, which is related to Fe-O-Cr and Ho-O-Fe/Cr antiferromagnetic interaction. The magnetization reversal is disappeared when the doping content is above 0.3. The negative magnetization phenomenon is observed in the Y1-xEuxFeo.5Cro.5O3 (x? 0.5) samples. The compensation temperatures decrease with the doping content increasing. The decrease of dielectric relaxation of Yo.9Hoo.1Feo.5Cro.5O3 sample indicates that the dielectric response in this system is related to the spin reorientation. |
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