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RFeO3 is an ideal candidate for the fabrication of spintronic devices, and its rare earth site doping is an important means to regulate and produce many unique spin behaviors. In this work, we report a high-quality Dy0.5Tb0.5FeO3 single crystal grown by optical floating zone method and its magnetic properties are studied explicitly. A type Ⅱ spin switching effect and suppressed spin reorientation transition are found in the Magnetization vs Temperature curves in Dy0.5Tb0.5FeO3. In the temperature region of spin reorientation transition, the transition of Fe3+ magnetic sublattice configuration becomes very complicated by the influence of competitive interaction with magnetic Dy3+/Tb3+ ions. Interestingly, a field tunable double-hysteresis loop is observed near the antiferromagnetic transition temperature of rare earth ions sublattice, which has never been reported in RFeO3 family compounds. By studying the dependence of double-hysteresis loop at different temperatures, the magnetic phase transition and spin reorientation transition induced by the applied magnetic field is inferred. This novel physical phenomenon helps us understand the mechanism of spin configuration transition better at low temperatures.

The magnetic behavior of rare-earth orthoferrite ErFeO3 single crystal can be controlled by low magnetic fields from a few to hundreds of Oe. Here we investigated high-quality ErFeO3 single crystal at the temperature range of 5 K-120 K, with two types of spin switching in the field-cooled-cooling (FCC) and field-cooled-warming (FCW) processes below the temperature of spin reorientation (SR) transition from Г4 to Г2 at 98 K-88 K. The magnitude of the applied magnetic fields could regulate two types of spin switching along a-axis of ErFeO3 single crystal but does not affect the type and temperature range of the SR transition. An interesting 'multi-step' type-II spin switching is observed in FCW under low magnetic fields (H ＜18 Oe) just below the SR transition temperature, which is associated with the interaction and the change of magnetic configurations from rare-earth and iron magnetic sublattices. When the magnetic field is lower than 15 Oe, the type-II spin switching in FCW process gradually changes to a continuous magnetic transition along the a-axis of the ErFeO3 single crystal. As the magnetic field is reduced to be less than 17 Oe, the type-I spin switching in the FCW process also transforms into a continuous magnetic transition. Understanding the magnetic reversal effects will help us explore the potential applications of these magnetic materials for future information devices.

Y-type hexaferrites with non-collinear conical magnetic structures, which induce electric polarization (P), are prospective single-phase multiferroics with broad applications, such as magnetic sensors, energy convertors, and memory devices, among others. Y-type hexaferrites have attracted considerable attention. In this study, we investigated the magnetoelectric properties of Ba0.7Sr1.3CoZnFe11AlO22 single crystals with Y-type hexaferrite structures by replacing half of Zn2+ ions with Co2+ ions. A transition from a screw order to the ferromagnetic is observed at TN2 = 356 K in Ba0.7Sr1.3CoZnFe11AlO22 single crystals. The electric polarization (P) and magnetoelectric coupling coefficient ( α ) reach a maximum of 130 μC/m2 and 16667 ps/m at T = 30 K and E = 880 kV/m, respectively. Most importantly, the in-plane Hab induced P can be fully reversed by applying in-plane Hab and it maintains a non-zero value even when the applied magnetic field is zero. Since the P does not decay and repeats many times under a fluctuating low magnetic field, it is important for potential applications in new types of non-volatile memory devices.

High quality Fe4Nb2O9 single crystal was grown by optical floating zone method. The magnetization-temperature(M-T) curves, isothermal magnetization curves(M-H) and pyroelectric current-temperature curves of the single crystal along different crystallographic directions were measured. The results of magnetization measurements which shows the Neel temperature TN of around 90 K and the in-plane magnetic structure of Fe4Nb2O9 are very consistent with the reported magnetic structure obtained by neutron diffraction. The isothermal magnetization curves along [210] direction show spin flop phase transition and a local ferromagnetic loop under 50 K. The critical field HC of spin flop phase transition is found to be 94 kOe. Pyroelectric current-temperature curves show ferroelectric polarization below about 90 K under zero magnetic field, which has not been reported before in single crystal Fe4Nb2O9. At the same time, Fe4Nb2O9 shows magnetoelectric coupling effect. With the increase of magnetic field, the polarization increases to over 300 μC/m2 along a axis under applied magnetic field of 70 kOe.

Field-tuning mechanisms of spin switching and spin reorientation (SR) transition were investigated in a series of high-quality single crystal samples of Pr

We report a single crystal of Dy0.75Nd0.25FeO3 by optical floating zone method. This well-grown single crystal displays threefold spin reorientation transition from Γ4 (GxAyFz) to a mix state of Γ4 and Γ2 (FxCyGz), then to Γ1 (AxGyCz), finally to Γ2 (FxCyGz) below 30 K. The phenomenon of threefold spin reorientation transition has not reported in rare earth orthoferrites, even barely in other compounds with spin reorientation transition. Besides, this bulk single crystal also displays a field induced spin switching transition. These distinguished responses in the single crystal present an opportunity to future application in magnetic devices of the emerging field of spintronics.

We report the interesting magnetic phase transitions of the rare earth doped single crystal Nd0.7Sm0.3FeO3. Temperature and magnetic field dependences of magnetizations are studied in detail, type Ⅰ spin switching under zero field cooling (ZFC) process at a temperature of 137 K and spin reorientation (SR) transition in the temperature region of 260 K–307 K are observed. Significantly, even though the undoped NdFeO3 and SmFeO3 only exhibit type Ⅰ spin switching, by field cooled and measured while warming (FCW) process, a rare earth doping induced type Ⅱ spin switching under very low field in this Nd0.7Sm0.3FeO3 single crystal was observed, which can be manipulated by magnetic field and even occur near room temperature at 273 K. Interestingly, at 4 K the M-H relationship shows a two-step magnetization process, it shows two different ferromagnetic magnetization processes, with an interval of antiferromagnetic process. This suggests the field induced magnetic configuration transition before and after the antiferromagnetic spin configuration interval, indicating intriguing magnetic transition and deep 3d-4f interaction information in the rare earth orthoferrites. The near room temperature type II spin switching coexist with its spin reorientation transition, and the field induced spin switching with very low triggering filed, may have future potential applications in magnetic devices.

In this research, we have successfully synthesized Lu1-xCaxMnO3 (x = 0.1, 0.3, and 0.5) single crystal samples with space group P63cm, and studied their magnetic properties with multiple methods. On the basis of AC susceptibility and magnetic relaxation rate, we can reveal the evolution of spin-glass (SG) behavior, which occurs in Ca doping with x = 0.1 and x = 0.3 and disappears at x = 0.5. Such SG behavior is induced by the competition between super-exchange and double-exchange interactions among Mn ions and the magnetic transition occurs at about 100 K. This study would be helpful to study the magnetism in RMnO3 compounds and the SG behavior in multi-valence doping.

The magnetic behavior of a rare-earth orthoferrite ErFeO

We have successfully synthesized La x Ca 3- x Mn 2 O 7 ( x = 0, 0.3, 0.5, 0.7, 0.9) samples with Ruddlesden-Popper (RP) structure in Cmcm space group. Meanwhile, X-ray photoelectron spectroscopy (XPS) results indicate that the concentrations of Mn 3+ and oxygen vacancy defects V O are enhanced with increasing doping. As a result, the magnetic and electrical transport properties can be tuned accordingly. With increasing doping, the antiferromagnetic (AFM) interaction was gradually weakened along with the enhancement of ferromagnetic (FM) interaction, and eventually the magnetic structure evolves from G-type to C-type. Our comprehensive experimental studies all propose that these manganates tend to intrinsically separate into AFM matrix state, spin glass regions, and FM cluster regions at lower temperature, which results from the competition between FM (Mn 3+ -O 2- -Mn 4+ ) and AFM (Mn 3+ -O 2- -Mn 3+ or/and Mn 4+ -O 2- -Mn 4+ ) domains. Especially, this behavior can be modulated by La doping, i.e. the spin glass regions and FM cluster regions tend to be enhanced with increasing La doping. According to molecular field theory, it indicates that the stronger Dzyaloshinskii-Moriya (DM) interaction effect and canted antiferromagnetism (CAFM) only present in C-type structure. The electrical transport properties can be also modulated by La doping, attributed to the changes of the local states around the mobility edge. Those results are quite essential for understanding the evolution of the complicated magnetoelectric properties in the RP La x Ca 3-x Mn 2 O 7 ceramics.

The Z-type hexaferrites Ba3(Zn1−xCox)2Fe24O41 (x = 0.2, 0.4, 0.6, 0.8, defined as Z1–Z4) were synthesized by a sol–gel method. With increasing cobalt concentration, the origin of magnetoelectric (ME) coupling and the effects of crystal parameters, occupation of ions, and magnetocrystalline anisotropy (MCA) on ME current were studied systematically. The mechanism of magnetic phase transition, revealing the evolution of the magnetic order in the temperature range of 10–400 K, was discussed in detail. Our results suggest that the ferroelectricity of Z1–Z4 originates from both inverse Dzyaloshinskii Moriya (DM) interaction and p–d hybridization mechanism. In particular the ME coupling property is only dominated by p–d hybridization with spin–orbit coupling. This study provides an effective way to improve the ME coupling property of hexaferrites, which have potential applications in the design of new electronic devices.

The structure, phase transitions, magnetocaloric effect, and exchange bias effect in Mn49Ni42-xCoxSn9 (x = 0, 1, 3 and 5) ferromagnetic shape memory alloys have been systematically investigated. X-ray diffraction results measured at room temperature reveal that Mn49Ni42-xCoxSn9 alloys with x = 0, 1 present martensite structure, and Mn49Ni42-xCoxSn9 alloys with x = 3, 5 exhibit mixture phases of both martensite and austenite. The martensitic transformation and exchange bias field (HEB) are very sensitive to the Co content. In addition, large positive magnetic entropy changes were observed in these alloys due to the magnetic-field-induced transition from the paramagnetic martensitic phase to the ferromagnetic austenitic phase, and a large effective refrigeration capacity of 230.8 J/kg was obtained under the magnetic field change of 70 kOe in Mn49Ni37Co5Sn9 alloy. We realized a continuous tuning of the HEB from 534.7 Oe to 1113.0 Oe after field cooling in presence of 10 kOe.

Interesting magnetic behaviors, including negative magnetization, zero field fooled and field cooled exchange bias effects, have been observed in Eu0.9Pr0.1CrO3. The negative magnetization at low temperature results from the antiparallel coupling between the Pr3+ moment and the canted moment of Cr3+ sublattice. Left shift of zero field cooled M-H loops, and right shift of field cooled M-H loops have been observed, due to the growth and competition of two types of magnetic structures with GxFz (EuCrO3) and GzFx (PrCrO3) orderings under magnetic field. When the cooling field is high enough, the Pr3+ moment is frozen antiparallel with the applied field during the cooling process, giving rise to a positive exchange bias (right shift of M-H). However, when the cooling field is near zero, magnetic clusters with GxFz (EuCrO3) or GzFx (PrCrO3) orderings are formed and distribute randomly during the cooling process, and the net Pr3+ moment get aligned along the applied field during the initial magnetization process to lower the Zeeman energy, and then negative exchange bias (left shift of M-H) appears.

Multiferroic Y-type hexaferrites are single-phase compounds in which the electric polarization (P) is induced by a low magnetic field (H). In this study, Y-type hexaferrite Ba0.5Sr1.5Mg1.6Co0.4Fe12O22 single crystal was synthesized using Na2CO3-Fe2O3 flux. Their structural, magnetic, and magnetoelectric properties were investigated. The different transition temperatures between the H ⊥ c and H//c configurations showed that the direction of the applied H was important for the spin configurations. The M-H loops exhibited that the field-induced transitions could occur at room temperature (RT). A first-order magnetic phase transition around 250 K was unveiled from the Arrott plots. The P was non-zero at zero H below 50 K. By studying the magnetic field dependence of the dielectric properties at selected temperatures, a magnetoelectric phase diagram exhibiting the evolution of the spin-induced ferroelectric order with the Hab and temperature (T) was revealed. The magnetoelectric phase diagram showed that the polarization was reversed by the magnetic fields below 150 K where the H-induced ferroelectric order was maintained in a zero magnetic field.

We have systematically investigated the exchange bias (EB) effect and low-temperature magnetic state transition in Mn42Cu6Ni42Sn10 Heusler alloy by means of AC and DC magnetization measurements. Experimental results suggest that the martensitic phase is in the state of superparamagnetic (SPM), following that the particles turn into the ferromagnetic (FM) state at the martensitic Curie temperature, and the moments are frozen as the temperature is below 150 K. In addition, EB effect was observed in the phase separated martensitic state, which can achieves about 536 Oe under the field of 500 Oe after field-cooled (FC) to 10 K. First-principle investigations indicate that such a small value is originated from nonmagnetic Cu atoms substitution. The appearance of EB effect can be ascribed to the competition between the FM martensitic phase and spin glass (SG) phase due to the impact of Mn atoms, whereas the nonmagnetic Cu atoms doping would hinder the magnetic aggregation, resulting the small EB value eventually.

We report the synthesis of a single-phase rare-earth perovskite ErFe0.75Cr0.25O3 polycrystalline and its magnetic properties. A transition occurs at temperature T N = 120 K below which we observe a weak magnetic moment from the canted antiferromagnetism. Interestingly, ErFe0.75Cr0.25O3 reveals the compensation-like behavior at T comp−like = 27 K, where the net magnetic moments of transition-metal ions are antiparallel and equal to the induced net moment of Er3+ ions, and the paramagnetic contribution of Er3+ moment presenting a nonzero magnetization. The temperature-dependent magnetization measurement shows a spin reorientation transition from Γ4 to Γ1 at 6 K. Furthermore, it is also observed that there is a spin-flop transition at low temperature induced by external magnetic field in Γ1 state (antiferromagnetic state). The interaction between (Fe/Cr)-3d and Er-4f electrons drives an extremely interesting spin reorientation transition which is highly sensitive to magnetic field and temperature.

The Z-type hexaferrites Ba3(Zn1-xCox)2Fe24O41 (x = 0.2, 0.4, 0.6, 0.8, defined as Z1-Z4) were synthesized by a sol-gel method. With increasing cobalt concentration, the origin of magnetoelectric (ME) coupling and the effects of crystal parameters, occupation of ions, and magnetocrystalline anisotropy (MCA) on ME current were studied systematically. The mechanism of magnetic phase transition, revealing the evolution of the magnetic order in the temperature range of 10-400 K, was discussed in detail. Our results suggest that the ferroelectricity of Z1-Z4 originates from both inverse Dzyaloshinskii Moriya (DM) interaction and p-d hybridization mechanism. In particular the ME coupling property is only dominated by p-d hybridization with spin-orbit coupling. This study provides an effective way to improve the ME coupling property of hexaferrites, which have potential applications in the design of new electronic devices.

A large single crystal Dy0.5Er0.5FeO3 of 5.2 mm in diameter and 55 mm in length is prepared using the optical floating zone furnace system. The good quality of the single crystal without impurities is confirmed by powder and Laue X-ray diffraction experiments. Magnetic measurements are conducted using 1~2 millimeter cubic sample of Dy0.5Er0.5FeO3 single crystal, which experiences spin switching in two measurement modes of zero-field-cooling (ZFC) and field-cooling (FC) magnetization vs temperature (M-T) curves under magnetic fields less than 48 Oe. The co-occurrence of spin switching (i.e. magnetization drop in FC mode and magnetization jump in ZFC mode) has not been reported in the parent materials of DyFeO3 and ErFeO3 single crystals. More interestingly this kind of spin switching can be easily tailored by using low fields in a large temperature range from below 50 K to nearly 400 K. Spin reorientation transition occurs near 35.9-48 K, where the spin configuration of the iron sublattice changes from Γ4 and Γ2. The magnetic interaction between (Dy, Er)-4f and Fe-3d electrons in the two different sublattices of Dy0.5Er0.5FeO3 single crystal which governs the spin reorientation transition and spin switching under different temperature and magnetic field are discussed.

We report the spin reorientation transition and spin switching transition in perovskite structure YbFeO3 single crystal. A spin reorientation transition of type Г4→Г2 occurs in the temperature range of 6 ∼ 8 K, and a type-Ⅱ spin switching along c-axis is found at temperature about 20 K under an applied magnetic field of 100 Oe. In field-cooled-cooling (FCC) process, due to the spin reversal of Yb3+ magnetic moments, the magnetic moments coupling of Yb3+ and Fe3+ change from parallel to antiparallel, which leads to a significant drop in magnetization at the transition temperature. Interestingly, the Magnetization vs. magnetic field curves at various temperatures above 8 K–200 K show magnetic field induced spin switching, for which the magnetization switches from negative/positive value to positive/negative value but without change of magnitude at a magnetic field induced spin switching point. The intriguing interaction between the two magnetic sublattices of rare earth (Yb3+) and iron (Fe3+) ions is controllable by the applied magnetic field to regulate the spin switching transition temperature in YbFeO3 single crystal and make it possible as one of low field potential materials for future application in spin devices.

We investigate the detailed analysis of the magnetic properties in a series of Pr1–x Sm x FeO3 single crystals from x = 0 to 1 with an interval of 0.1. Doping controlled spin reorientation transition temperature T SR Γ4 (G x , A y , F z ) to Γ2 (F x , C y , G z ) covers a wide temperature range including room temperature. A ‘butterfly’-shape type-I spin switching with 180° magnetization reversal occurs below and above the magnetization compensation points in x = 0.4 to 0.8 compounds. Interestingly, in Pr0.6Sm0.4FeO3 single crystal, we find an inadequate spin reorientation transition accompanied by uncompleted type-I spin switching in the temperature region from 138 to 174 K. Furthermore, a type-II spin switching appears at 23 K, as evidenced from the magnetization curve in field-cooled-cooling (FCC) mode initially bifurcate from zero-field-cooled (ZFC) magnetization curve at 40 K and finally drops back to coincide the ZFC magnetization value at 23 K. Our current research reveals a strong and complex competition between Pr3+–Fe3+ and Sm3+–Fe3+ exchange interactions and more importantly renders a window to design spintronic device materials for future potential applications.

We report the inhomogeneous magnetic state with the characteristics of spin-glass like behavior in KFeO2 from the low temperature magnetization and magnetization relaxation of zero field cooled measurements. The results reveal a possible spin glass state below the typical glass transition temperature (Tg). The low temperature isothermal hysteresis loops reveal a spin configuration consisting of a small ferromagnetic component within an antiferromagnetic ground state. The observation of spin-glass state in KFeO2 may be attribute to the competition between ferromagnetic and antiferromagnetic component. And the ferromagnetic component might origin from the frustration effect or nonstoichiometric caused mixed valence state of Fe ions in KFeO2. Hence, we expect that a similar phenomenon would exist in related AFeO2 (A: alkali metal) family with strong super-exchange interactions.

In this paper, we have systematically prepared a serials of polycrystalline Mn48−xCuxNi42Sn10 alloys (x=0, 1, 3, 5, 6, 8, 10 and 12) and investigated the influence of the Cu doping on martensitic transition (MT) as well as magnetic properties. Experimental results indicate that the MT temperature and the martensite Curie temperature (TcM) shift to high temperature with increasing the substitution of Cu (from Mn rich alloy to Ni rich alloy), while the austenite Curie temperature (TcA) is almost unchanged. It was found that the structures undergo L21 and 4O with the increasing of Cu concentration near room temperature. Therefore, the magnetostructural transition can be tuned by appropriate Cu doping in these alloys. Moreover, we mainly studied the multiple functional properties for inverse magnetocaloric effect and shape memory characteristics associated with the martensitic transition. A large positive isothermal entropy change of Mn48Ni42Sn10 was obtained, and the maximum transition entropy change achieves about 48 J/kg K as x=8. In addition, a considerable temperature-induced spontaneous strain with the value of 0.16% was obtained for Mn48Ni42Sn10 alloys.

A series of DyFe1-xInxO3 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1) polycrystalline samples have been prepared by the conventional solid reaction methods. The crystal structures, refined by the Fullprof, are found to be orthorhombic for 0 ≤ x ≤ 0.6 and hexagonal in the case of 0.7 ≤ x ≤ 1. The lattice constants are changed by the In ions doping, and a huge distortion of the magnetic sublattice was induced. The magnetization versus temperature curves are obtained for all the samples, at the temperature between 3 K and 300 K. The pure DyFeO3 sample undergoes a spin reorientation transition at around 50 K, whereas the doped In3+ ions significantly modify the phase transition. We reveal that such substitution retained the spin reorientation transition effect for x ≤ 0.8. We develop a formalism based on the molecular theory, giving explanation of the changes in the spin-reorientation temperature induced by the In-doping. Then, by performing density functional theory (DFT) calculation, we analyzed the magnetic phases for the hexagonal compounds. Furthermore, our findings indicate a type of Γ′4 - Γ′2 transition exists in the hexagonal Fe-In magnetic systems which directly point to a quasi-2 dimensional magnetic order.

We report temperature-induced spin reorientation and magnetization jump effects in the rare earth (RE) orthoferrite Ho 0.5 Pr 0.5 FeO 3 single crystal. The single crystal of about 6 mm in diameter and 50 mm in length was successfully grown by optical floating zone method. Both X-ray diffraction and Laue photograph confirmed the homogeneity and high quality of the crystal. Magnetic properties of Ho 0.5 Pr 0.5 FeO 3 single crystal are studied over a wide temperature range from 2 to 300 K. Spin reorientation transition from Γ 2 to Γ 4 phase is observed in the temperature range of 75–90 K. At lower temperature, the Ho 0.5 Pr 0.5 FeO 3 shows an abrupt jump of magnetization along the a -axis, which occurs only in the field-cooling process, and is sensitive to external applied magnetic field. By analyzing the jump temperature and magnitude of the magnetization, we conclude that it is caused by the spin reversal of the rare earth ions. The isothermal magnetization versus field hysteresis loop measurements along a axis explain the spin configuration variation from 3 K to 60 K.

The crystal structure and magnetic properties of hexagonal Y0.3Lu0.7MnO3 single crystal have been systematically investigated. The refinement results of X-ray diffraction pattern reveal that pure sample with single phase exhibits hexagonal structure with P63cm space group. Upon cooling, it undergoes multiple magnetic phase transitions, including antiferromagnetic, weak ferromagnetic, and spin-glass transitions. The spin glass at low temperature is not conventional but has a re-entrant character. We propose that the re-entrant spin-glass behavior comes from the competition between the ferromagnetic and antiferromagnetic interactions, and the disorder induced by Lu dopant, which are two characteristics of spin glass. Our study on Y0.3Lu0.7MnO3 single crystal would help people better understand the physical properties of the doped manganite compounds R1-xAxMnO3.

A temperature-induced spin reorientation transition between Γ4 (Gx, Ay, Fz) and Γ2 (Fx, Cy, Gz) has been studied in the family of Er1-xYxFeO3 (x = 0, 0.25, 0.5, 0.75, 1) single crystals. By doping nonmagnetic Y3+, we tuned the spin reorientation temperature to low temperature with increasing x. Moreover, the typical compensation point and spin flip transition of ErFeO3 also decreases with doping, and disappears above x = 0:75. We also report the Rietveld refinements and Raman spectroscopy of Er1-xYxFeO3, where some Raman peaks are shifted to low frequency with increasing doping. Our results shed light on the understanding of the interaction between two magnetic sub-lattices of rare earth (R3+) and iron (Fe3+) ions, and will also contribute to the materials design and potential applications.

We report experimental studies on enhancing the magnetoelectric (ME) coupling of Co4Nb2O9 by substituting the non-magnetic metal Mg for Co. A series of single crystal Co4–xMgxNb2O9 (x = 0, 1, 2, 3) with a single-phase corundum-type structure are synthesized using the optical floating zone method, and the good quality and crystallographic orientations of the synthesized samples are confirmed by the Laue spots and sharp XRD peaks. Although the Neel temperatures (TN) of the Mg substituted crystals decrease slightly from 27 K for pure Co4Nb2O9 to 19 K and 11 K for Co3MgNb2O9 and Co2Mg2Nb2O9, respectively, the ME coupling is doubly enhanced by Mg substitution when x = 1. The ME coefficient αME of Co3MgNb2O9 required for the magnetic field (electric field) control of electric polarization (magnetization) is measured to be 12.8 ps/m (13.7 ps/m). These results indicate that the Mg substituted Co4–xMgxNb2O9 (x = 1) could serve as a potential candidate material for applications in future logic spintronics and logic devices.

The effects of Ni doping on the physical properties of the newly discovered layered superconductor Bi_4O_4S_3 are studied. X-ray diffraction data indicates that the lattice constants a and c decrease with the increasing Ni doping. From resistivity-temperature curves, the superconducting transition temperature (T_c^(onset) is suppressed by only 0.5 K with the increase of Ni doping from 0.075 to 0.15; the T_c^(zero) is almost the same constant at different Ni ions’ doping level. The magnetic susceptibility results suggest the coexistence of superconductivity and ferromagnetism in this system. A possible superconductivity transition is observed around ˜14 K from M-T (FC) curves in x = 0.125, 0.15 samples, which may result from the doped magnetic Ni ions.

The rare-earth chromites have attracted increasing interests in recent years, as a member of a few single-phase multiferroic materials. We studied the structure and magnetic property of a series of Ca-doped EuCrO 3 samples by using X-ray powder diffraction and Physical Property Measurement System. Phase separation, rotation of magnetization in M ( T ) curve and exchange bias effect have been identified. The Eu 0.7 Ca 0.3 CrO 3 polycrystalline sample may be intrinsically phase-separated, with Cr 3+ -rich, Cr 4+ -rich canted antiferromagnetic regions surrounded by spin glass-like frustrated phase, resulting in several magnetic features including: (1) a broad and slow increase of M ( T ) curve with the decrease of temperature; (2) rotation of magnetization with increasing cooling field; (3) exchange bias and glassy magnetism. The rotation of magnetization is ascribed to the rotation of the moment of Cr 4+ -rich regions, arising from the competition between exchange coupling energy and magnetostatic energy. The exchange bias effect suggests the formation of weak ferromagnetic unidirectional anisotropy during field cooling, due to the exchange coupling among weak ferromagnetic domains and surrounding spin glass-like regions. This result helps understanding the interaction among different magnetic domains and phases in a complex system.

We have investigated the martensitic transformation, exchange bias, magnetoresistance (MR) and strain in Ni 50− x Fe x Mn 36 Sn 14 ( x =1, 2, 3, 4) Heusler alloys. With the increase of Fe content, the austenite phase could be stabilized with L 2 1 structure and hence the martensitic transition shifts to a lower temperature and finally disappears. This behavior can be understood by the weakening of Ni–Mn hybridization to suppress AFM interactions and enhancement of Fe–Fe ferromagnetic exchange interactions. The same reason can account for the slight decrease of exchange bias field ( H EB ) with the increase of the Fe content from x =1 to 2 and the disappearance of H EB for x =3. We observed MR effect for x =3, and a maximum MR value of −52% was achieved, which can be explained by the change in the electronic structure during martensitic transformation induced by the magnetic field. In addition, a large strain of 0.207% in Ni 49 Fe 1 Mn 36 Sn 14 was observed due to the changes of lattice parameters during the martensitic transformation induced by temperature.

A single crystal of Co4Nb2O9 about 7 mm in diameter and 55 mm in length was successfully grown by an optical floating zone method. X-ray powder diffraction (XRD) indicates that it has a single phase corundum-type structure. Clear Laue spots and sharp XRD peaks confirm the good quality and crystallographic orientations. Below TN, magnetization of Co4Nb2O9 along a axis shows dramatically different behaviors between H=1 kOe and 20 kOe, suggesting a spin flop occurs along a axis. Ma(H) curve at 5 K shows a change of slope at a critical magnetic field of 7.5 kOe for triggering the spin flip.

The spin reorientation transition in single crystal NdFeO3 is studied using AC magnetic susceptibility, hysteresis loops, and polarized terahertz (THz) time domain spectroscopy measurements. Different frequency dependence behaviors of AC susceptibility reflect that the dynamic response of magnetization inside the spin reorientation region differs from the phase outside the transition region. The magnetization hysteresis loops at different temperatures reveal that domains formed during the spin reorientation process, which coincides with the abrupt increase of AC magnetic susceptibility during the transition. In addition, temperature dependent THz wave excitation of quasi-antiferromagnetic mode indicates the process of spin reorientation as a continuous rotation of Fe3+ spins rather than a mixed phase of Γ4 and Γ2.

We report the structural, magnetoelectric (ME), magnetic and electric control of magnetic properties in Co4Nb2O9 (CNO) single crystal. A detailed ME measurement reveals a nonlinear ME effect instead of a linear ME effect in CNO single crystal. By fitting the magnetization-electric field (M-E) curve, it can be found that the linear ($${\alpha }_{e}$$ α e ) and quadratic (γ) coefficients equal to ~8.27 ps/m and ~−6.46 ps/MV for upper branch, as well as ~8.38 ps/m and ~6.75 ps/MV for the lower branch. More importantly, a pronounced response was observed under a small cooling magnetic field, which cannot even cause the spin flop. This suggests a magnetoelectric effect can occur at paraelectric state for CNO single crystal. Furthermore, we also found that the magnetization of every axis responds to electric field applied along a-axis, but fails to do so when the electric field is applied c-axis. Such findings supply a direct evidence to the magnetic structure and ME coupling mechanism indirectly reflected by our neutron experiment.

We report the structural, magnetoelectric (ME), magnetic and electric control of magnetic properties in Co4Nb2O9 (CNO) single crystal. A detailed ME measurement reveals a nonlinear ME effect instead of a linear ME effect in CNO single crystal. By fitting the magnetization-electric field (M-E) curve, it can be found that the linear (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\alpha }_{e}$$\end{document}αe) and quadratic (γ) coefficients equal to ~8.27 ps/m and ~−6.46 ps/MV for upper branch, as well as ~8.38 ps/m and ~6.75 ps/MV for the lower branch. More importantly, a pronounced response was observed under a small cooling magnetic field, which cannot even cause the spin flop. This suggests a magnetoelectric effect can occur at paraelectric state for CNO single crystal. Furthermore, we also found that the magnetization of every axis responds to electric field applied along a-axis, but fails to do so when the electric field is applied c-axis. Such findings supply a direct evidence to the magnetic structure and ME coupling mechanism indirectly reflected by our neutron experiment.

We report the anisotropic superconducting properties of nominal K0.8Fe1.97Mn0.03Se2 single crystal. The phase separation is characterized by X-ray diffraction and scanning electron microscopy techniques. The experimental crystal has three superconducting transitions at T c 1 mag = 31.9 K for the first, T c 2 mag = 36.8 K for second, T c 3 mag = 42.5 K for third superconducting phase as seen from magnetic susceptibility measurements. We can discriminate the anisotropic upper critical fields between the second and third superconducting phase by magnetotransport measurements. The upper critical field at T = 0 K are estimated to be μ 0 H c 2 ∥ ab ( 0 ) = 137.4 T and μ 0 H c 2 ∥ c ( 0 ) = 51.8 T for the second, μ 0 H c 2 ∥ ab ( 0 ) = 178.4 T and μ 0 H c 2 ∥ c ( 0 ) = 52.6 T for third superconducting phase, respectively. We also discuss the vortex pinning in framework of thermally activated flux flow model, by which the pinning potential U0 of the second superconducting phase is derived to be U 0 ∥ c = 5.1 × 10 3 K and U 0 ∥ ab = 6.1 × 10 3 K at μ0H = 0.25 T, respectively. Finally, we will evaluate the total critical current density, which shows moderate values Jc(0) ∼ 103 − 104 A/cm2 at T = 3 K.

Magnetic properties of Yb1−xCaxCrO3 with x = 0.0−0.30 have been investigated in a temperature range of 3–300 K. The evidence of the existence of small trapped field (TF) resulting from trapped magnetic flux inside the superconducting material of physical property measurement system (PPMS) has been found during zero-field cooling mode. By using two measuring approaches, we have demonstrated that YbCrO3 has a strong dependence on the cooling field for the first time. Experimental results indicated that the magnetization configuration of YbCrO3 can memorizes the initial magnetic state induced by the cooling field and behaves according to it. Also, due to the strong anisotropic exchange interaction between Cr3+ and Yb3+, magnetic reversal and negative magnetization have been observed in YbCrO3.To investigate the interaction between Cr3+ and Yb3+, Ca-doped YbCrO3, which has been chosen as the studying object, were systematically investigated. X-ray diffraction patterns show that all the samples are in pure phase which can be indexed in orthorhombic structure belonging to space group Pbnm. DC magnetization measurements show that all compounds exhibit an antiferromagnetic transition at Neel temperature T N . Ca doping leads to a reduction of Cr3+–O2−–Cr3+ interactions due to the transformation of Cr3+ to higher oxidized state Cr4+. In addition, other interactions between Cr3+, Cr4+, and Yb3+ would appear in Ca-doped YbCrO3, which would also dilute the interactions of Cr3+–O2−–Cr3+.

采用固相反应法制备了Ho0.5Pr0.5FeO3多晶样品, 对其磁性和磁介电特性进行了系统研究。在T=4.5 K附近存在Ho离子的反铁磁相变, 在T= 59 -80K可观测到Fe离子的自旋重取向转变, 磁滞回线表明样品呈现弱铁磁性。在T= 270 K, 介电常数可达-103, 研究表明该介电常数与270 K附近的电阻变化相关联, 该处电阻变小, 介质损耗减小, 导致介电值变大。尤其重要的是, 该样品在室温下表现出磁场诱导的巨磁介电效应, 在频率 kHz、外加磁场为1.6×106 A/m下, 其值可达5500%, 该巨磁介电效应可能来源于磁电阻效应。

We report the low field spin switching and spin reorientation transition in rare earth orthoferrite PrFeO3 single crystal grown by optical floating zone method. Applied magnetic fields can regulate the spin switching in a quite wide range of temperatures. The effective magnetic moments of Fe3+ and Pr3+ sublattices undergo parallel to antiparallel configurations in field-cooled-cooling processes, which produce an abrupt drop in magnetization at low temperatures. The reverse spin switching show a magnetization recovering jump at a rather higher temperature in the field-cooled-warming regime, even above 300 K under very low fields. These intriguing magnetic phase transitions are due to the intrinsic 3d-4f electron interactions between Fe3+ and R3+ sublattices, which dominate the interesting magnetic behaviors in RFeO3. In particular, PrFeO3 shows a great sensitivity to weak field even at room temperature, which makes it a controllable candidate for potential application in spintronic devices by using very low field. Finally, we summarize the spin configuration diagram of the RFeO3 family.