Magnetic study of low-temperature phase of UCu2Ge2

Magnetization and phase sensitive AC susceptibility was measured for the annealed and as-cast samples of ferromagnetic UCu₂Ge₂, $T_C=107K$. Special attention was paid to the low temperature range, $T<50K$, which is interesting due to the magnetization decrease and frozen AC response. The hysteresis loops showed a remanence of ≈87% and a fast, thermally activated decrease in the coercivity field. Thermoremanent magnetization at 4.3 K decayed with the relaxation time ≈1110³ s. The strong increase of the ${\chi }_{AC}$ with the amplitude of the driving field was observed. All these results point to a very large anisotropy of the compound at the lowest temperatures. Phase transition to the randomly canted ferromagnetic phase at $T\approx 55K$ was detected in the measurement of the third order non-linear susceptibility. It is concluded that the origin of the transition is the strong temperature dependence of magnetic anisotropy.     

Magnetic phase transitions and phase diagrams of DyMn2Ge2

The experimental studies of magnetic phase transitions in the layered tetragonal intermetallic compound DyMn₂Ge₂ are continued. The existence of spontaneous phase transitions is confirmed by the results of measurements of the temperature dependences of lattice parameters and the initial magnetic susceptibility. The measurements in strong (up to 50 T) and ultrastrong (up to 150 T) fields revealed two new field-induced magnetic transitions. The inclusion of the exchange interaction between next-to-nearest layers of manganese and the crystal field effects for the rare-earth subsystem along with the antiferromagnetic exchange interaction of nearest Mn layers has made it possible to describe the magnetic properties of DyMn₂Ge₂ in a wide range of magnetic fields. The parameters of these interactions are determined from a comparison of the experimental and theoretical magnetization curves and H-T phase diagrams.     

Magnetic phase diagram of UCoAl

Temperature T and pressure P dependences of the Landau coefficients for UCoAl are discussed by taking into account the magneto-volume effects and anisotropic spin fluctuations based on the Landau–Ginzburg theory. The P-dependence of the mean square amplitude of spin fluctuations is also discussed. A magnetic phase diagram is obtained with the parameters estimated from the observed magnetization curves under high pressures. The P-dependences of the characteristic temperatures T₀ and T_max, where the metamagnetic transition disappears and the susceptibility reaches a maximum, are estimated and compared with the observed results.     

Magnetic phase diagram of layered cobalt dioxide LixCoO2

The magnetism of LixCoO2 (LCO), which has a similar structure to NaxCoO2 (NCO), has been investigated by muon-spin spectroscopy and susceptibility measurements using samples with x=0.1-1 prepared by an electrochemical reaction. In the x range below 0.75, LCO was found to be Pauli paramagnetic down to 1.8 K, suggesting an intermediate- or weak-coupling regime, although disordered local moments, with volume fractions below approximately 20%, appear at low T for LCO with x > or = 0.5. The phase diagram and interactions of LCO are thus strikingly different from NCO, while the differences cannot be explained simply by structural differences between the two systems.     

Magnetic phase diagram for CuMn

To study the magnetic phases of CuMn, we carry out a generalized perturbation expansion of the band energy across the composition range. We obtain the pair energy using the orbital peeling technique of Burke, based on the tight-binding linear muffin-tin orbital and augmented space recursion methods. We analyze the phases of the system by studying the probability distribution of the local staggered occupation ’fields’ within a mean-field approach. We show that our predicted phase boundaries agree well with experimental results.     

Magnetic phase diagram in a quasi-two-dimensional electron gas

Using spin density functional theory within the framework of the local spin density approximation with Perdew-Zunger type exchange-correlation energy, ferromagnetism in a quasi-two-dimensional electron gas (Q-2DEG) is studied. The electronic and magnetic structures of a thin film are calculated as a function of film thickness and electron density. Ferromagnetism in the Q-2DEG is found to appear at a higher electron density than in the three-dimensional electron gas. Unless a film is very thin, with decreasing electron density, a magnetic phase transition occurs from a spin-unpolarized fluid to a Wigner film with surface magnetism, in which the spin polarization localizes only in the neighborhood of surfaces. Further decreasing density induces another transition to a fully spin-polarized ferromagnetic Wigner film.     

Magnetic phase diagram of spinel spin-glasses

The article by Villain [Z. Phys. B — Condensed Matter33, 31 (1979)] is discussed and a modified magnetic phase diagram is suggested for the spinel system (AB₂O₄) in which theA andB sites are partially (or completely) occupied by magnetic atoms. This diagram takes into account the antiferromagnetic exchange interactionsJ _AA,J _BB andJ _AB between nearest neighbor cations of various types. Regions of paramagnetic, antiferromagnetic, ferrimagnetic and possible spin glass behaviour are indicated on the diagram.Supported by the National Science Foundation under Grant ISP-80-11451     

Magnetic phase diagram and crystal fields of superconducting ErNi2B2C

We have measured the specific heatc _p in magnetic fields and the resistance of the antiferromagnetically ordered borocarbide superconductor ErNi₂B₂C. From our data we show that the superconductivity at 10.6 K coexists with antiferromagnetic order beginning at 5.8 K, and we determine the magneticB-T phase diagram. The specific heat in zero field gives additional information about the crystalline electric field (CEF) splitting. We show that the low-temperature specific heat is dominated by several low-lying CEF doublets with the first excited level at about 10 K, while the splitting of the next two levels is about 50 to 100 K.     

Magnetic phase diagram of single-layer CrBr3

We theoretically provide a magnetic phase diagram for the single-layer (SL) CrBr₃, which could be effectively tuned by both strain engineering and charge doping in SL-CrBr₃. Through systematical first-principles calculations and Heisenberg model Hamiltonian simulations, three different magnetic phases in SL-CrBr₃, which are off-plane ferromagnetic, in-plane ferromagnetic and in-plane Néel-antiferromagnetic phases, are found in the strain and charge doping regimes we studied. Furthermore, our results show that higher order Heisenberg exchange parameters and anisotropy exchange parameters should be taken into account for accurately illustrating the magnetic phase transition in SL-CrBr₃. As a result, we find from the SpinW simulation that the Curie temperature is about T_c=38.4 K, which is well consistent with the experimental result 34 K[Nano Lett. 19 3138 (2019)]. The findings here may be confirmed in future experiments, and may be useful for the potential applications of SL-CrBr₃ in spintronics field.     

Magnetic phase diagram of frustrated spin-chain compounds

The magnetic ordering in frustrated triangular lattices of Ising chains is discussed. It is shown that the differences in the low-temperature CsCoCl₃, Ca₃Co₂O₆, and Sr₅Rh₄O₁₂ phases are related to the interaction between the next-to-nearest pairs of chains, which partially lifts the degeneracy of the ground state of the 2D antiferromagnet Ising model. In zero magnetic field and at low temperature, a stripe structure arises in the new compound Sr₅Rh₄O₁₂.     

Magnetic phase diagram of a random mixture of Jahn-Teller ions

A magnetic model of a random mixture containing Jahn-Teller ions, in which several kinds of exchange interactions between the Jahn-Teller ions and between the Jahn-Teller and non-Jahn-Teller ions are assumed, is proposed and studied by using the distribution function method. It is shown that a spin glass phase occurs when these exchange interactions have different signs. Our model would be applicable to a mixture Rb₂Cr_xMn_1-xCl₄ in which the spin glass phase has been observed.     

Magnetic phase diagram of frustrated spin-chain compounds

Generalizations of Glauber dynamics on the triangular lattice of Ising chains are considered. Magnetic moment relaxation and the response to an AC magnetic field in Ca₃Co₂O₆ are investigated. It is shown that all of the main features of the dynamics of a frustrated lattice of spin chains can be described qualitatively in the framework of an extended two-dimensional model.     

Magnetic phase diagram of a ferromagnet-antiferromagnet bilayer with a rough interface

The thickness-roughness phase diagram of a thin ferromagnetic film on an antiferromagnetic substrate is studied in the case where the roughness of the interface between the layers causes frustration of the exchange interaction between them. It is shown that the inclusion of single-ion anisotropy makes the phase diagram significantly more complicated in comparison with that calculated within the exchange approximation. The evolution of a new type of domain walls caused by frustrations is traced with an increase in the film thickness and the width of the atomic steps on the film-substrate interface.     

Magnetic phase diagram for a random three-dimensional Ising point-dipole lattice

JETP Letters - It is shown, within the framework of the generalized mean-field theory, that the ground state of a system of Ising point dipoles randomly filling the sites of a three-dimensional...     

Magnetic transition phase diagram of cobalt clusters electrodeposited on HOPG: Experimental and micromagnetic modelling study

The magnetic transition from mono- to multidomain magnetic states of cobalt clusters electrodeposited on highly oriented pyrolytic graphite electrodes was studied experimentally using Magnetic Force Microscopy. From these images, it was found that the critical size of the magnetic transition is dominated by the height rather than the diameter of the aggregate. This experimental behavior was found to be consistent with a theoretical single-domain ferromagnetic model that states that a critical height limits the monodomain state. By analyzing the clusters magnetic states as a function of their dimensions, magnetic exchange constant and anisotropy value were obtained and used to calculate other magnetic properties such as the exchange length, magnetic wall thickness, etc. Finally, a micromagnetic simulation study correctly predicted the experimental magnetic transition phase diagram.