Reentrant Spin Glass Transition Research Articles

Influence of external magnetic fields on the freezing temperature Tf of Ni 79Mn 21 alloys: Evidence for anisotropy rotation

DC magnetization measurements have been performed for Ni 79Mn 21 alloys in the temperature range of 4.2 to 50 K. Taking the demagnetizing field into account, the influence of an external magnetic field, H ext, on the re-entrant spin-glass transition temperature T f of this alloy has been investigated. It has been observed that T f is independent of H ext if H ext is sma ller than the demagnetizing field H D ( = NM s) where N is the demagnetizing factor; M s is the value of the saturation magnetization. However, for higher fields, T f is displaced towards lower temperatures. These results are interpreted in terms of anisotropy rotation based on the “domain-anisotropy” model.

NMR study of re-entrant spin-glass state in NiMn alloys

The temperature dependence of the average hyperfine field H̄ i and the nuclear spin-lattice relaxation time T 1 of 55Mn on three different types ( i = I, II and III) of Mn atoms in NiMn alloys containing 10 and 15 at % Mn have been measured. In 15 at % Mn alloy, H̄ III associated with Mn atoms having an antiparallel moment μ III increases abruptly at 12K, while H̄ I and H̄ II associated with Mn atoms having parallel moments μ I and μ II do not with decreasing temperature. On the other hand T −1 1 of 55Mn of all three types of Mn atoms are largely enhanced at the same temperature, 12 K. This behavior was not observed in 10 at % Mn alloy. These effects observed in 15 at % Mn alloy are considered to be due to the freezing of the transverse component of the antiparallel moment μ III due to the onset of the re-entrant spin-glass transition at 12 K.

Influence of an external magnetic field on the reentrant spin-glass transition temperature in a Cr75Fe25 alloy.

The influence of an external magnetic field ${B}_{0}$ on the reentrant spin-glass transition temperature ${T}_{G}$ of a ${\mathrm{Cr}}_{75}$${\mathrm{Fe}}_{25}$ alloy has been investigated by means of $^{57}\mathrm{Fe}$ M\"ossbauer-effect spectroscopy. A linear relationship in the (${B}_{0}$,T) plane has been observed which is interpreted theoretically in terms of a mean-field-theory model including nonvanishing local spontaneous magnetization.

Re-entrant spin glass transition in a randomly mixed insulating ferromagnet and antiferromagnet

The re-entrant spin glass (RSG) transition observed in the randomly mixed planar magnet with competing exchange interactions, Rb 2Mn 1- x Cr x Cl 4, is explained qualitatively by the Villain model. The temperature dependence of the anisotropy field which confines the spins in the c-plane plays an important role in the RSG transition.

A New Oxide Spin-Glass System of (1-x) FeTiO3–xFe2O3. IV. Neutron Scattering Studies on a Reentrant Spin Glass of 79FeTiO3–21Fe2O3Single Crystal

The spin correlation in a reentrant spin glass of 79FeTiO 3 –21Fe 2 O 3 has been studied by neutron scattering from a single-crystal. The spin correlation parallel and perpendicular to the c-axis has been separately discussed. It has been found that the squared Lorentzian type spin correlations between perpendicular components develop below the ferromagnetic transition temperature. The reentrant spin glass transition temperature defined as the temperature where the magnetization starts to decrease has been found to correspond to the temperature where the parallel (transverse) components appear and the system is devided into large domains with the canted spin structure.

Phase diagrams for dilute spin glasses

A generalised, dilute, infinite-ranged Ising spin-glass model is introduced and studied as a function of the concentration p and temperature T. The phase diagram is investigated and paramagnetic (P), ferromagnetic (F), spin glass (SG) and mixed (M) phases, meeting at a multicritical point (p*,T*), are identified. The P/F and P/SG phase boundaries are derived, and the F/M and M/SG boundaries are calculated close to (p*,T*). The condition for having a re-entrant spin-glass transition is derived. In non-zero magnetic field a p-dependent A-T instability line is obtained. The authors apply their results to the insulator EuxSr1-xS, it is predicted to exhibit re-entrant behaviour.

Mössbauer Study of Reentrant Spin-Glass Pd1-x-yFexMny: Evidence for Coexistence of Spin-Glass and Ferromagnetic Orderings

The Mössbauer study has been made on the reentrant spin-glass state of Pd 0.881 Fe 0.027 Mn 0.092 and Pd 0.930 Fe 0.015 Mn 0.055 . The anomalous increase of the average hyperfine field \bar H hf , found in some alloys with the reentrant spin-glass transition, was clearly observed below the spin-glass transition temperature T g . This can be explained as freezing of the transverse spin component at T g . From the variation of the Mössbauer absorption intensity ratios with applied field, it has been shown that Fe spins behave partly ferromagnetic and partly like a spin-glass. We consider that this fact is an evidence for the coexistence of the spin-glass and ferromagnetic orderings. A model to explain our results has been proposed. It has been also shown that the spin-glass state is microscopically not much affected by magnetic fields up to 5 kOe, the maximum value examined.

Re-Entrant Spin-Glass Behavior of the Randomly Mixed Insulating Ferromagnet and Antiferromagnet, Rb2Mn(1-x)CrxCl4

An ac susceptibility measurement and a polarized neutron experiment have been performed on the random mixture, Rb 2 Mn (1- x ) Cr x Cl 4 of an insulating ferromagnet Rb 2 CrCl 4 and an insulating antiferromagnet Rb 2 MnCl 4 . The susceptibility of the mixed crystals rich in Cr atoms increases sharply at the Curie Temperature and then shows a drop-off at a lower temperature, indicating a double transition. The polarization of the neutron beam transmitted through the sample exhibits drastic changes at the two transition temperatures. The experimental results are interpreted by models recently proposed to explain re-entrant spin-glass transition.

Magnetism in Eu-based amorphous alloys from local and bulk investigations

The magnetic properties of Eu2+ (4f7 electronic configuration) based amorphous alloys Eu1-xXx, where X=Mg, Zn, Cd and Al and x approximately=0.3, have been investigated by studying local moments from 151Eu Mossbauer spectroscopy and bulk magnetisation in low AC and high DC fields. The divalent 4f7 state of Eu atoms implies vanishing interactions with crystal fields. The magnetic properties are then assumed to be depicted by localised 4f7 moments interacting via RKKY interactions, in view of the pure s (Mg, Zn, Cd) or sp (Al) character of the valence electron shells of the components. Amorphous Eu1-xAlx (x=0.225, 0.30 and 0.40) are concentrated spin glasses (mictomagnets). Amorphous Eu0.70Zn0.30 (TC=133K) and Eu0.75Cd0.25 (TC=134K) reveal all the properties of soft ferromagnets in the presence of some distribution of the exchange interaction, resulting from the disorder. Amorphous Eu0.70Mg0.30 exhibits a double magnetic transition, i.e. from paramagnetic to ferromagnetic, at TC=131K and from ferromagnetic to spin glass at TSG approximately=52K. The latter re-entrant spin-glass transition is consistently characterised both from AC susceptibility and from the anomalous temperature dependence of the hyperfine field distribution. Amorphous Eu0.70Mg0.30 is concluded as representing an example of a cluster spin glass (with intercluster frustration) whereas the amorphous Eu1-xAlx alloys would present short-range frustration.