Sign Reversal Of Magnetization Research Articles

Magnetization sign reversal, spin-glass-like state and Griffiths-like phase driven by B-site disorder in double perovskite Gd2CrMnO6

The crystal structure and magnetic order of the double perovskite Gd2CrMnO6 have been investigated systematically by employing magnetization and ESR measurement for the first time. Structure analysis revealed that the Gd2CrMnO6 crystallizes in the adopted B-site disorder orthorhombic structure with space group of Pbnm. Magnetization measurements indicated that the system possesses a long-range antiferromagnetic ordering at TN = 40 K. In Gd2CrMnO6, the magnetization sign reversal was observed below Tcomp = ∼ 27 K due to the Dzyaloshinskii-Moriya antisymmetric interaction of Cr3+-O2--Mn3+ and the different sublattice of Gd3+ and Cr3+/Mn3+. The competing magnetic interaction is greatly enhanced by FM 3d-4f interaction and should be responsible for the Griffiths-like phase (TG ∼ 260 K) and spin-glass-like state.

Intertwined magnetization and exchange bias reversals across compensation temperature in YbCrO3 compound

We have investigated the origin of magnetization and exchange bias (EB) reversals in the $\mathrm{YbCr}{\mathrm{O}}_{3}$ compound at the magnetization compensation temperature, ${T}_{\mathrm{COMP}}$ of 16.5 K by dc magnetization, ac susceptibility, neutron diffraction (ND), neutron depolarization, specific heat, and dielectric measurements. A weak magnetization $({M}_{\mathrm{Cr}})$ is observed below the N\'eel temperature ${T}_{\mathrm{N}}$ (\ensuremath{\sim}120 K) in dc magnetization, which is consistent with a canted antiferromagnetic (AFM) state due to ordering of ${\mathrm{Cr}}^{3+}$ moments. Specific heat data exhibit a \ensuremath{\lambda}-shaped peak at ${T}_{\mathrm{N}}$. Further, a monotonic increase of ac susceptibility at low temperatures and the Schottky anomaly in the specific heat data account for the polarized nature of the ${\mathrm{Yb}}^{3+}$ moment $({M}_{\mathrm{Yb}})$ under the molecular field of the AFM ${\mathrm{Cr}}^{3+}$ sublattice. Our ND study has confirmed a finite polarized ${\mathrm{Yb}}^{3+}$ ordered moment, and the ${G}_{\mathrm{z}}$-type AFM ordering of ${\mathrm{Cr}}^{3+}$ moments below ${T}_{\mathrm{N}}$. The temperature variations of the lattice constants $a$ and $b$ show a crossover from positive to negative thermal expansion (NTE) across the ${T}_{\mathrm{COMP}}$ while cooling. Below ${T}_{\mathrm{COMP}}$, the separation between Cr-Cr atoms lying in the $ab$ plane increases with decrease in temperature, which corroborates with the observed NTE of the lattice constants. In the present compound, the sign change of the net magnetization arising out of the AFM coupled polarized ${\mathrm{Yb}}^{3+}$ $({M}_{\mathrm{Yb}})$ and the ferromagnetic ${\mathrm{Cr}}^{3+}$ $({M}_{\mathrm{Cr}})$ sublattice moments results in the sign reversal of magnetization. Interestingly, anomalous behavior of the coercive field with its minimum value at $T\ensuremath{\sim}{T}_{\mathrm{COMP}}$ is observed. EB also changes sign at $T\ensuremath{\sim}{T}_{\mathrm{COMP}}$. Moreover, the temperature variation of the real part of the dielectric constant reveals an anomaly at ${T}_{\mathrm{COMP}}$, indicating a weak magnetodielectric coupling in the $\mathrm{YbCr}{\mathrm{O}}_{3}$ compound. A training effect analysis ensures the conventional nature of the observed EB. Neutron depolarization study sheds light on the temperature-dependent domain magnetization with its zero value at the ${T}_{\mathrm{COMP}}$. The presence of the observed important phenomena viz. magnetization and EB reversals in a single-phase compound suggests their possible use in making magnetization switching, spin-value, thermomagnetic, and other spintronic devices.

Neutron diffraction evidence for local spin canting, weak Jahn–Teller distortion, and magnetic compensation in Ti1−xMnxCo2O4 spinel

A systematic study using neutron diffraction and magnetic susceptibility is reported on Mn substituted ferrimagnetic inverse spinel Ti1−xMnxCo2O4 in the temperature interval 1.6 K T 300 K. Our neutron diffraction study reveals cooperative distortions of the TO6 octahedra in the Ti1−xMnxCo2O4 system for all the Jahn–Teller active ions T = Mn3+ , Ti3+ and Co3+ , having the electronic configurations 3d1, 3d4 and 3d6, respectively which are confirmed by the x-ray photoelectron spectroscopy. Two specific compositions (x = 0.2 and 0.4) have been chosen in this study because these two systems show unique features such as; (i) noncollinear Yafet–Kittel type magnetic ordering, and (ii) weak tetragonal distortion with c/a < 1, in which the apical bond length dc(TB-O) is longer than the equatorial bond length dab(TB-O) due to the splitting of the eg level of Mn3+ ions into and . For the composition x = 0.4, the distortion in the TBO6 octahedra is stronger as compared to x = 0.2 because of the higher content of trivalent Mn. Ferrimagnetic ordering in Ti0.6Mn0.4Co2O4 and Ti0.8Mn0.2Co2O4 sets in at 110.3 and 78.2 K, respectively due to the presence of unequal magnetic moments of cations, where Ti3+ , Mn3+ , and Co3+ occupy the octahedral, whereas, Co2+ sits in the tetrahedral site. For both compounds an additional weak antiferromagnetic component could be observed lying perpendicular to the ferrimagnetic component. The analysis of static and dynamic magnetic susceptibilities combined with the heat-capacity data reveals a magnetic compensation phenomenon (MCP) at TCOMP = 25.4 K in Ti0.8Mn0.2Co2O4 and a reentrant spin-glass behaviour in Ti0.6Mn0.4Co2O4 with a freezing temperature of ∼110.1 K. The MCP in this compound is characterized by sign reversal of magnetization and bipolar exchange bias effect below TCOMP with its magnitude depending on the direction of external magnetic field and the cooling protocol.

Magnetism in an antiferromagnetic Ising nanoribbon

The phase diagrams and magnetizations of an antiferromagnetic Ising nanoribbon are investigated by using the effective-field theory with correlations. The numerical results show that the magnetic properties in the nanoribbon may exhibit some different behaviors, depending on whether the applied transverse field takes zero value or a finite value. In particular, the reentrant phenomena and the ferrimagnetic behaviors have been found in the both cases, while some differences are observed. It has been discussed that the sign reversal of magnetization is possible, when a transverse field is applied to the system.

Magnetization sign reversal, exchange bias, and Griffiths-like phase in orthorhombic perovskite Pr2FeMnO6

Abstract The perovskite Pr2FeMnO6 has been synthesized by citrate-gel combustion method. The material has an orthorhombic crystal structure with Pbnm space group. The presence of Fe3+ and Mn3+ cations in the material are confirmed by XPS analysis. A magnetization sign reversal is observed for the material at low-temperatures in low applied magnetic fields. When the applied field or temperature is increased, the negative magnetization got diminished. Such a sign reversal of magnetization is observed for the material as a result of the interaction between components of paramagnetic Pr3+ and Mn3+ moments opposite to the component of the ferromagnetic Fe3+ moment or the anti-aligned Fe-rich regions to that of Mn-rich regions containing with Pr3+. Negative exchange bias is also exhibited by Pr2FeMnO6 below 200 K which can be ascribed to the Dzyaloshinskii-Moriya interaction and magnetic exchange anisotropy. A high-temperature magnetic transition at TC = 576 K is identified for the material from the thermomagnetic data. From the detailed analysis of the thermomagnetic data, the presence of ferromagnetic short-range correlations is observed far above the TC, which suggests a Griffiths-like phase with Griffiths temperature at TG = 681 K.

Effects of a Transverse Field in Two Mixed-Spin Ising Bilayer Films.

The magnetic properties (phase diagrams and magnetizations) of two mixed-spin Ising bilayer films with a transverse field are investigated by the use of the effective field theory with correlations. The systems consist of two magnetic atoms where spin-1/2 atoms are directed to the z-direction and only spin-1 atoms are canted from the z-direction by applying a transverse field. We examined how magnetization sign reversal can be realized in the system, due to the effects of the transverse field on the spin-1 atoms. The compensation point phenomena are found in both systems, depending on the selections of physical parameters. However, the reentrant phenomena are found only for one of the two systems.

Sign reversal of magnetization and exchange bias in Ni(Cr1−xAlx)2O4 (x=0–0.50)

Ni(Cr1-xAlx)2O4 (x=0–0.50) samples were prepared in single phase form by using sol-gel method and their structural and magnetic properties were studied. Al substitution transforms the crystal structure of NiCr2O4 from tetragonal cell with space group I41/amd to cubic cell of Fd3¯m space group. Magnetization measurements by varying the temperature and magnetic field were carried out to investigate the interesting magnetization reversal and exchange bias behaviors. Magnetization reversal is observed for x=0.10 sample with a magnetic compensation temperature of 40K and it is explained by considering different temperature dependences of magnetic moments of the two sublattices. Shifting of magnetic hysteresis loops towards the negative magnetic field axis and hence the presence of negative exchange bias field is observed for x=0.15 sample. The x=0.10 sample exhibits the tunable positive and negative exchange bias field. Exchange bias in these samples is explained considering the anisotropic exchange interaction between the ferrimagnetic and the antiferromagnetic components of magnetic spins. However, the sign reversal of exchange bias field is due to the change in domination of one ferrimagnetic sublattice over the other with variation in temperature. Both normal and inverse magnetocaloric effects are observed for x=0.10 sample.

Tunable Exchange Bias and Bipolar Switching of Magnetization Near Room Temperature

Temperature-induced sign reversal of magnetization in the vicinity of room temperature is reported in a single-phase spinel compound of Ni(Cr0.70Fe0.30)2O4. The magnetic compensation temperature is 358 K. The mechanism of magnetization reversal is explained by considering the different temperature dependences of sublattice magnetization. Bipolar switching of magnetization at room temperature is demonstrated by just varying the magnetic field from + 200 to + 2050 Oe, i.e., without changing the direction of the magnetic field. Tunable positive and negative exchange bias fields are observed in the vicinity of room temperature with a maximum value of 1 kOe.

Magnetic compensation, field-dependent magnetization reversal, and complex magnetic ordering inCo2TiO4

The complex nature of magnetic ordering in the spinel Co2TiO4 is investigated by analyzing the temperature and magnetic field dependence of its magnetization (M), specific heat (C-p), and ac magnetic susceptibilities chi' and chi ''. X-ray diffraction of the sample synthesized by the solid-state reaction route confirmed the spinel structure whereas x-ray photoelectron spectroscopy shows its electronic structure to be Co2TiO4 = [Co2+][Co3+ Ti3+]O-4. From analysis of the temperature dependence of the dc paramagnetic susceptibility, the magnetic moments mu(A) = 3.87 mu(B) and mu(B) = 5.19 mu B on the A and B sites are determined with mu(B) in turn yielding mu(Ti3+) = 1.73 mu(B) and mu(Co3+) = 4.89 mu(B). Analysis of the dc and ac susceptibilities combined with the weak anomalies observed in the C-p vs T data shows the existence of a quasi-long-range ferrimagnetic state below T-N similar to 47.8K and a compensation temperature T-comp similar to 32 K, the latter characterized by sign reversal of magnetization with its magnitude depending on the applied magnetic field and the cooling protocol. Analysis of the temperature dependence of M (field cooled) and M (zero field cooled) data and the hysteresis loop parameters is interpreted in terms of large spin clusters. These results in Co2TiO4, significantly different from those reported recently in isostructural Co2SnO4 = [Co2+][Co2+ Sn4+]O-4, warrant further investigations of its magnetic structure using neutron diffraction.

Sign reversal of magnetization in Mn substituted SmCrO3

Single phase samples of orthorhombic SmCr1−xMnxO3 compounds were prepared for x=0 to 0.50. Analysis of X-ray diffraction patterns shows a systematic increase in lattice parameters with increase in Mn concentration. The phenomenon of magnetization reversal is observed for x=0.10–0.30 samples with a maximum magnetic compensation temperature of 126K. The mechanism of magnetization reversal is explained by considering the competition between the paramagnetic moments of Mn3+ and Sm3+ ions under the influence of negative internal field due to antiferromagnetically ordered Cr3+ ions and the canted ferromagnetic component of Cr3+ ions. For x≥0.40, the samples exhibit ferromagnetic like behavior.

ChemInform Abstract: The Phenomenon of Negative Magnetization and Its Implications

AbstractReview: 257 refs.

Phase relationship, structural and magnetic properties of Nd-deficient Nd0.95−xCaxMnO2.93±δ

Phase relationships in Nd-deficient solid solutions Nd0.95−xCaxMnO2.93±δ (x=0.00, 0.05, 0.10, 0.15, 0.20) were investigated in the temperature range T=800–1100°C in air and under reduced oxygen partial pressure (at T=1000°C). Phase diagrams in the coordinates “Temperature-calcium content” and “Po2-calcium content” were constructed. The boundaries of two-phase regions on the phase diagrams were defined.The oxidation mechanism and the stability conditions for the perovskite structure were determined.The magnetic properties of single phase samples with x=0, 0.1, 0.2 have been studied as a function of temperature and magnetic field. The observed magnetic anomalies: magnetization sign reversal and spin-reorientation transitions are compatible with the coexistence of AFM and FM phases, clusters of different nature, quasi heterogeneity (presence of clusters enriched/depleted with neodymium or manganese oxide). Quadrupole centers are considered as a source of spin inversion phenomena.

Sign reversal of magnetization and tunable exchange bias field in NdCr1−xFexO3 (x=0.05–0.2)

Abstract Magnetization reversal and tunable exchange bias behavior are observed in NdCr 1− x Fe x O 3 compounds for x =0.05–0.20. The magnetic compensation temperature ( T comp ) is found to increase with increase in Fe concentration and its maximum value is 198 K for x =0.15 sample. The observed magnetization reversal is explained by considering the competition between the weak ferromagnetic component of Cr 3+ ions and the paramagnetic moments of Nd 3+ and Fe 3+ ions under the influence of negative internal magnetic field. The exchange anisotropy between the above two components of magnetic moments give rise to tunable positive and negative exchange bias fields. The sign reversal of exchange bias field also coincides with T comp . Bipolar switching of magnetization is demonstrated at T comp by just varying the positive magnetic field.

Sign Reversal of Magnetization and Ferromagnetism in NdCr 1−x Mn x O 3 (x= 0 to 0.50)

Mn-doped NdCrO 3 samples were prepared in single-phase form. The samples exhibit antiferromagnetic (AFM) transition along with canted ferromagnetic (FM) component up to the doping concentration of x= 0.3 in NdCr 1−xMn xO3 and beyond that they show ferromagnetic behavior. The field-cooled magnetization as a function of temperature for x= 0.2 sample shows an interesting behavior of magnetization reversal for applied field H≤ 1000 Oe. The maximum compensation temperature is found to be 156 K for H= 50 Oe. The magnetization reversal is explained by considering the paramagnetic moment of Nd 3+ and Mn 3+ ions under the influence of negative internal field.

Sign reversal of magnetization and exchange bias field in LaCr0.85Mn0.15O3

The sign reversal of magnetization is observed in LaCr0.85Mn0.15O3 compound and the maximum magnetic compensation temperature (Tcomp) was at around 100 K. We have also observed negative and positive values of exchange bias field (HEB) having sign reversal at around Tcomp. The value of HEB could be tuned from −2.1 kOe to + 2.6 kOe with change in temperature. The competition between the magnetic moment due to the canted ferromagnetic component of Cr3+ ions and the paramagnetic component of doped Mn3+ ions under the negative internal field gives rise to magnetization reversal. The origin of sign reversal of HEB is discussed in detail.