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We report the observation of unidirectional magnetoresistance (UMR) in the ferrimagnetic insulator CoFe2O4(CFO)/Pt heterostructures, which stem from the giant interfacial Rashba–Edelstein effect. Furthermore, UMR has been found to show sign reversal and amplitude enhancement characteristics with decrease in temperature. We have ascribed it to the modulated distortion of Fermi contours due to pronounced spin canting at low temperatures. The presence of spin canting induced interfacial magnetic state has also been demonstrated by spin Hall magnetoresistance in CFO/Pt/Co/Al2O3 films. Our work reveals the interfacial magnetic state modulated UMR in CFO/Pt bilayers, thereby paving the way for extending its applications in ferrimagnet-based spintronic devices. [ABSTRACT FROM AUTHOR]

In this work, we have prepared an antiferromagnetic insulated α-Fe2O3 film with a large out-of-plane magnetic component and studied the spin Hall magnetoresistance (SMR) in α-Fe2O3/Pt bilayers. Both angular-dependent magnetoresistance and field-dependent magnetoresistance have featured a sign change characteristic with varying temperature, which is ascribed to the competition between a modulated interface magnetic state and an antiferromagnetic bulk state of the α-Fe2O3 film. According to a generalized theoretical model, which takes the effective spin conductance into consideration, the spin transport can be mathematically expressed as the change of field dependent average spin operators with varying temperature. The critical temperature also depends on the α-Fe2O3 film thickness and the magnetic field, which are ascribed to the magnons transport and long-range order of non-collinear spin textures, respectively. Furthermore, we have given a phenomenological form to fit the SMR curves in the critical temperature interval, which further reveals the origin of SMR with complex magnetic structures. [ABSTRACT FROM AUTHOR]

We have investigated the spin Hall magnetoresistance (SMR) in CoFe2O4/Pt heterostructures deposited on (001) MgO and (001) MgAl2O4 substrates, respectively. It is found that the interface non-collinear magnetic configurations should exist in both of the two films in the whole temperature range from 5 to 300 K but mainly dominate the spin transport properties at low temperature. Furthermore, the spin transport has featured epitaxial-strain-modified characteristics induced by different substrates, which has been investigated by magnetic curves, SMR, anisotropic magnetoresistance, and Hall effect measurements. [ABSTRACT FROM AUTHOR]

Thin films of Bi1.05La0.05FeO3 (BLFO) have been deposited on a CaRuO3 buffering layer on SrTiO3 using pulsed laser deposition. Then, a Pt thin layer was in situ sputtered on the surface of BLFO. The crystallization characteristic and surface morphology of the BLFO layer were checked. Spin transporting behaviors of the Pt/BLFO structure were investigated at room temperature. Interestingly, a magnetoresistance effect was observed at the interface of the Pt/BLFO bilayer. The spin mixing conductance at the interface between BLFO and Pt was estimated after a corrections of Pt thickness. This implies that the manipulation of spin–orbit coupling is possible at the interface of a single-phase multiferroic (e.g., BLFO) and a heavy metal (e.g., Pt). [ABSTRACT FROM AUTHOR]

Magnetism control has a variety of applications in magnetic storage and spintronic devices. Instead of the control of direct magnetoelectric coupling via strain, voltage, and Dzyaloshinskii-Moriya interaction, the polarization-dependent coupling in multiferroic materials such as BiFeO3 is employed for the electric-field control of magnetizations in this work. A perpendicular magnetic anisotropy (PMA) has been realized in a BiFeO3/Al2O3/Pt/Co/Pt multiferroic structure at room temperature. Interestingly, a distinct change of coercivity field (∼400%) has been observed in the structure with opposite polarization directions, which can be attributed to the different oxidation degree at the Pt/Co interface. This spontaneous polarization-controlled switching not only provides us a platform to study the interfacial effect in multiferroic heterostructures but also paves the way to manipulate PMA or even spin orbit torque through oxygen vacancies. [ABSTRACT FROM AUTHOR]

We demonstrate the negative spin Hall magnetoresistance (SMR) observed in antiferromagnetic Cr2O3/Ta bilayers at low temperature. The SMR signals are changed from the positive to negative magnitude when monotonously reducing the temperature from 300 K to 50 K. The positive and negative SMR signals are expected to be associated with the two different ways for injection of the spin current, into the boundary ferromagnetic region and the bulk antiferromagnetic region of α-Cr2O3 (0001), respectively. The slopes of the abnormal Hall curves exhibit the same sign with the SMR signal. From the SMR ratio under 3 T, the spin mixing conductance at the Cr2O3/Ta interface is estimated to be 1.12 × 1014 Ω−1·m−2, which is comparable to the one observed in the Y3Fe5O12(YIG)/Pt structure and our early results of the Cr2O3/W structure. [ABSTRACT FROM AUTHOR]

The spin Hall magnetoresistance (SMR) effect is studied in a magnetoelectric Cr2O3/heavy-metal W heterostructure. The Cr2O3 film is confirmed as the α-phase, and its Néel temperature is determined. A clear SMR behavior is observed at the interface of Cr2O3/W. A nearly 0.1% SMR ratio is achieved under a magnetic field of 9 T, which is larger than the reported value in the SrMnO3/Pt structure. A systematic study on the variations of SMR as functions of the magnetic field and its angle is performed. Our results indicate that the antiferromagnetic magnetoelectric Cr2O3/W structure has a promising prospect application in future spintronic devices. [ABSTRACT FROM AUTHOR]

In this letter, we fabricated Co2FeAl films with perpendicular-to-plane magnetic anisotropy by cosputtering with terbium (Tb). The as-prepared (Tb+Co2FeAl) films (TCFA) consists of nanocrystalline L21 Co2FeAl and amorphous alloy of Tb(Co, Fe, and Al). The coercivity field (Hc) of the TCFA films is adjustable from 200 to 800 Oe. After annealing, the Hc decreases to 70 Oe. A perpendicularly magnetized spin valve with the TCFA films as free and reference layers shows a current-perpendicular-to-plane magnetoresistance of 1.8% at room temperature. Our result opens a way to fabricate perpendicularly magnetized full-Heusler alloys and makes it possible to realize faster and simple structured magnetic storage bits in the future. [ABSTRACT FROM AUTHOR]

Ferroelectric K0.5Na0.5NbO3 (KNN) thin film was epitaxially grown on La0.67Sr0.33MnO3 (LSMO) buffered LaAlO3 substrate by pulse laser deposition. The crystallographic structure of KNN/LSMO was confirmed by x-ray diffraction. Interestingly, a dielectric relaxor feature was found in the temperature range 200–350 °C. The activation energies for relaxation and conduction of the films were found to be 1.87 and 0.63–0.71 eV, respectively. The mechanism for dielectric relaxation in KNN/LSMO structure was discussed under a thermally activated process. The remnant polarization and coercive field of the films were 21.3 μC/cm2 and 91 kV/cm, respectively. [ABSTRACT FROM AUTHOR]

Large Ca0.28Ba0.72Nb2O6 (CBN-28) single crystals exhibit saturated ferroelectric hysteresis loops under an electric field of 115 kV/cm along the [001] direction. Their spontaneous polarization, remanent polarization and coercive field are 35.3 μC/cm2, 32.2 μC/cm2, and 38.1 kV/cm, respectively. The dielectric constant and dielectric loss tan δ of the crystals are 195 and 0.32 at 10 kHz, respectively. A diffused dielectric anomaly with relaxor characteristic was observed in the range of 325-500 °C at low frequencies, while the CBN-28 crystals experienced a first-order normal-relaxor ferroelectric phase transition around 252 °C on heating. A broad dielectric loss peak appears around 120 °C and it is interpreted in terms of the migration of oxygen vacancies. The conductance activation energy was determined to be 1.33 eV in the high temperature regime (500–560 °C). [ABSTRACT FROM AUTHOR]

A Raman scattering study of the vibrational modes in K2Al2B2O7 crystals has been performed at room temperature. The vibrational modes are classified by the nuclear site group analysis method and the internal vibrational modes are assigned to vibrations of the BO3 triangle and AlO4 tetrahedron. [ABSTRACT FROM AUTHOR]

Mössbauer spectrum was collected in Fe[sup 3+] doped cubic LiMn[sub 2]O[sub 4] (LiFe[sub 0.1]Mn[sub 1.9]O[sub 4]) by using [sup 57]Fe as the radiation source. In the model of the crystal-field theory, the energy gaps between different d orbitals, ΔE(b[sub 1g]-a[sub 1g]) and ΔE(b[sub 2g]-e[sub g]), characterize the strength of the Jahn–Teller effect in the crystal. A relationship between the Mössbauer quardrupole splitting and the energy gaps was established, based on which both ΔE(b[sub 1g]-a[sub 1g]) and ΔE(b[sub 2g]-e[sub g]) of the [MnO[sub 6]] octahedron in LiFe[sub 0.1]Mn[sub 1.9]O[sub 4] are estimated to be about 0.41 and 0.30 eV, respectively. Electronic structure of LiMn[sub 2]O[sub 4] was studied theoretically via ab initio calculation based on the density-functional theory. Calculation shows that a gap about 0.28 eV between the filled Mn d bands is equivalent to ΔE(b[sub 2g]-e[sub g]). It also shows that the first unoccupied states are dominated by Mn 3d contribution essentially from both a[sub 1g] and b[sub 1g] of Mn d states. Distance between the two peaks in the first unoccupied band was used to calculate ΔE(b[sub 1g]-a[sub 1g]), which is about 0.36 eV. The Mössbauer quardrupole splitting characterizes Jahn–Teller distortion and its effect on the fine structure of Mn 3d bands. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]