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Antiferromagnetic spin phase transition in nuclear matter with effective Gogny interaction  [PDF]
A. A. Isayev,J. Yang
Physics , 2004, DOI: 10.1103/PhysRevC.70.064310
Abstract: The possibility of ferromagnetic and antiferromagnetic phase transitions in symmetric nuclear matter is analyzed within the framework of a Fermi liquid theory with the effective Gogny interaction. It is shown that at some critical density nuclear matter with D1S effective force undergoes a phase transition to the antiferromagnetic spin state (the opposite direction of neutron and proton spins). The self--consistent equations of spin polarized nuclear matter with D1S force have no solutions, corresponding to the ferromagnetic spin ordering (the same direction of neutron and proton spins) and, hence, the ferromagnetic transition does not appear. The dependence of antiferromagnetic spin polarization parameter as a function of density is found at zero temperature.
On the Competition between Ferromagnetic and Antiferromagnetic States in Sr$_2$MnMoO$_6  [PDF]
I. V. Solovyev
Physics , 2002, DOI: 10.1016/S0304-8853(03)00498-0
Abstract: It is argued that the magnetic behavior of Sr$_2$MnMoO$_6$ is determined by the existence of two total energy minima corresponding to the metallic ferromagnetic and insulating antiferromagnetic states, which may be nearly degenerate depending on the magnitude of the breathing distortion.
Monte Carlo simulations of ordering in ferromagnetic-antiferromagnetic bilayers  [PDF]
Shan-Ho Tsai,D. P. Landau,Thomas C. Schulthess
Physics , 2003, DOI: 10.1063/1.1447868
Abstract: Monte Carlo simulations have been used to study phase transitions on coupled anisotropic ferro/antiferromagnetic (FM/AFM) films of classical Heisenberg spins. We consider films of different thicknesses, with fully compensated exchange across the FM/AFM interface. We find indications of a phase transition on each film, occuring at different temperatures. It appears that both transition temperatures depend on the film thickness.
Subtle competition between ferromagnetic and antiferromagnetic order in a Mn(II) - free radical ferrimagnetic chain  [PDF]
E. Lhotel,V. Simonet,E. Ressouche,B. Canals,D. B. Amabilino,C. Sporer,D. Luneau,J. Veciana,C. Paulsen
Physics , 2006, DOI: 10.1103/PhysRevB.75.104429
Abstract: The macroscopic magnetic characterization of the Mn(II) - nitronyl nitroxide free radical chain (Mn(hfac)2(R)-3MLNN) evidenced its transition from a 1-dimensional behavior of ferrimagnetic chains to a 3-dimensional ferromagnetic long range order below 3 K. Neutron diffraction experiments, performed on a single crystal around the transition temperature, led to a different conclusion : the magnetic Bragg reflections detected below 3 K correspond to a canted antiferromagnet where the magnetic moments are mainly oriented along the chain axis. Surprisingly in the context of other compounds in this family of magnets, the interchain coupling is antiferromagnetic. This state is shown to be very fragile since a ferromagnetic interchain arrangement is recovered in a weak magnetic field. This peculiar behavior might be explained by the competition between dipolar interaction, shown to be responsible for the antiferromagnetic long range order below 3 K, and exchange interaction, the balance between these interactions being driven by the strong intrachain spin correlations. More generally, this study underlines the need, in this kind of molecular compounds, to go beyond macroscopic magnetization measurements.
Competition of Ferromagnetic and Antiferromagnetic Order in the Spin-1/2 XXZ Chain at Finite Temperature  [PDF]
K. Fabricius,A. Klümper,B. M. McCoy
Physics , 1998,
Abstract: An analytical study is presented of the crossover in the gapless attractive XXZ chain from antiferromagnetic to ferromagnetic behaviour at low to high temperature, respectively. In particular, an analytic formula for the crossover in the long distance asymptotics and explicit results for the nearest-neighbour longitudinal correlation are obtained. We also provide results for the specific heat and magnetic susceptibility for various anisotropies.
Experimental evidence for competition of antiferromagnetic and ferromagnetic correlations in HgCr2S4  [PDF]
V. Tsurkan,J. Hemberger,A. Krimmel,H. -A. Krug von Nidda,P. Lunkenheimer,S. Weber,V. Zestrea,A. Loidl
Physics , 2006, DOI: 10.1103/PhysRevB.73.224442
Abstract: A detailed study of poly- and single crystalline samples of the normal spinel HgCr2S4 is reported. The structural refinement reveals enhanced values of the atomic displacements suggesting closeness to a structural instability. Magnetization, electron-spin resonance and specific-heat studies document strong ferromagnetic fluctuations close to 50 K and the occurrence of complex antiferromagnetic order at TN = 22 K. We found highly unconventional behavior resembling properties of a non-collinear antiferromagnet and soft ferromagnet dependent on temperature and magnetic field. Even weak external magnetic fields disturb the antiferromagnetic order and strongly enhance the ferromagnetic correlations. The conductivity shows an insulating character with non-monotonous temperature behavior and a metal-to-insulator like transition at 80 K well above the magnetic transition. The observed anomalies are related to bond frustration due to competing magnetic exchange interactions between the Cr ions.
Crossover from antiferromagnetic to ferromagnetic ordering in semi-Heusler alloys Cu1-xNixMnSb with increasing Ni concentration  [PDF]
Madhumita Halder,S. M. Yusuf,Amit Kumar,A. K. Nigam,L. Keller
Physics , 2012, DOI: 10.1103/PhysRevB.84.094435
Abstract: The magnetic properties and transition from an antiferromagnetic (AFM) to a ferromagnetic (FM) state in semi Heusler alloys Cu1-xNixMnSb, with x < 0.3 have been investigated in details by dc magnetization, neutron diffraction, and neutron depolarization. We observe that for x < 0.05, the system Cu1-xNixMnSb is mainly in the AFM state. In the region 0.05 \leq x \leq 0.2, with decrease in temperature, there is a transition from a paramagnetic to a FM state and below ~50 K both AFM and FM phases coexist. With an increase in Ni substitution, the FM phase grows at the expense of the AFM phase and for x > 0.2, the system fully transforms to the FM phase. Based on the results obtained, we have performed a quantitative analysis of both magnetic phases and propose a magnetic phase diagram for the Cu1-xNixMnSb series in the region x < 0.3. Our study gives a microscopic understanding of the observed crossover from the AFM to FM ordering in the studied semi Heusler alloys Cu1-xNixMnSb.
Ising-like Spin Anisotropy and Competing Antiferromagnetic - Ferromagnetic Orders in GdBaCo_{2}O_{5.5} Single Crystals  [PDF]
A. A. Taskin,A. N. Lavrov,Yoichi Ando
Physics , 2003, DOI: 10.1103/PhysRevLett.90.227201
Abstract: In RBaCo_{2}O_{5+x} compounds (R is rare earth), a ferromagnetic-antiferromagnetic competition is accompanied by a giant magnetoresistance. We study the magnetization of detwinned GdBaCo_{2}O_{5.5} single crystals, and find a remarkable uniaxial anisotropy of Co^{3+} spins which is tightly linked with the chain oxygen ordering in GdO_{0.5} planes. Reflecting the underlying oxygen order, CoO_2 planes also develop a spin-state order consisting of Co^{3+} ions in alternating rows of S=1 and S=0 states. The magnetic structure appears to be composed of weakly coupled ferromagnetic ladders with Ising-like moments, which gives a simple picture for magnetotransport phenomena.
Detection of antiferromagnetic ordering in heavily doped LaFeAsO1-xHx pnictide superconductors using nuclear-magnetic-resonance techniques  [PDF]
N. Fujiwara,S. Tsutsumi,S. Iimura,S. Matsuishi,H. Hosono,Y. Yamakawa,H. Kontani
Physics , 2013, DOI: 10.1103/PhysRevLett.111.097002
Abstract: We studied double superconducting (SC) domes in LaFeAsO1-xHx by using 75As- and 1H-nuclear magnetic resonance techniques, and unexpectedly discovered that a new antiferromagnetic (AF) phase follows the double SC domes on further H doping, forming a symmetric alignment of AF and SC phases in the electronic phase diagram. We demonstrated that the new AF ordering originates from the nesting between electron pockets, unlike the nesting between electron and hole pockets as seen in the majority of undoped pnictides. The new AF ordering is derived from the features common to high-Tc pnictides: however, it has not been reported so far for other high-Tc pnictides because of their poor electron doping capability.
Evidence of ferromagnetic short-range correlations in cubic La1-xSrxMnO3-δ (x=0.80, 0.85) above antiferromagnetic ordering  [PDF]
Aga Shahee,Kiran Singh,R. J. Choudhary,N. P. Lalla
Physics , 2015, DOI: 10.1002/pssb.201451552
Abstract: We report the existence of ferromagnetic correlations (FMC) in paramagnetic (PM) matrix of cubic La1-xSrxMnO3-{\delta} (x = 0.80, 0.85) well above its coupled structural, magnetic and electronic phase transitions. The dc-magnetization vs temperature [M(T)] behaviour under different magnetic fields (from 100 Oe to 70 kOe) shows the presence of short range magnetic correlations up to (TFMC ~) 365 K, far above the antiferromagnetic ordering temperatures (TN =) 260 K and 238 K for x=0.80 and 0.85, respectively. More importantly the observed short-range FMC survive even up to 70 kOe, which indicates their robust nature. The temperature region between TN to TFMC is dominated by the presence of correlated ferromagnetic (FM) entities within the PM matrix and stabilized due to A-site chemical disorder. Our results further illustrate that for the studied compositions, the oxygen off-stoichiometry does not have any significant effect on the nature and strength of these FM entities; however, FM interactions increase in the oxygen deficient samples. These compositions are the unique examples, where the presence of FMC is observed in an undistorted basic cubic perovskite lattice well above TN and therefore are novel to understand the physics behind the colossal magneto-resistance effect.
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