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The magnetic and structural properties of YΜn 2 are strongly influenced by introduction of hydrogen (deuterium) in the structure, however, it only slightly modifies the noncollinear antiferromagnetic structure of the compound. The temperature dependences of the NMR relaxation times T1 and Τ2 of deuterium and the zero-field relaxation of muons in YΜn2 D x were measured at temperatures above the magnetic ordering temperature TN. The corresponding relaxation rates are described by the empirical expres- The C15 Laves phase compound YΜn2 and its hydrides (deuterides) have very intriguing properties above their magnetic ordering temperature TN. The NMR relaxation times Τι and Τ2 of deuterium and the muon depolarisation rate λ of these materials exhibit a critical divergence as TN is approached from above [1][2][3]. It is interesting that their temperature dependence above TN can be described by nearly the same function of temperature Τ where δ = (Τ -TN )/TN is the reduced temperature, the exponent n depends linearly on the deuterium concentration x and the constant prefactor of course depends on the quantity under consideration. The dependence of n on x is shown in Fig. 1. We call the behaviour described by Eq. (1) "quasicritical" , because the function F(δ) has a singularity when Τ approaches the critical temperature TN but on the other hand the true critical exponent should not depend on the chemical composition of the material but only on the model Hamiltonian [4]. Thus we have to look for another formula which would explain this behaviour. It is clear that spin fluctuations play an important role in the vicinity of the temperature where the (867)

The NMR investigations of YMn 2 D x (xϭ0.65,1.0,1.5,2.0,2.5͒ deuterides are presented and discussed. The observations of 2 D spin echo signals were made for the samples in the paramagnetic state in the temperature ranges close above their magnetic ordering temperatures. The temperature dependencies of 2 D resonance frequency, T 1 and T 2 relaxation times at the ordering temperature show a divergence which is dependent on the deuterium concentration. It is shown that the mechanisms of conduction electron interaction and of dipolar or orbital interactions are responsible for the observed relations between Knight shift and the susceptibility. The observed concentration dependent relaxation rates are explained on the basis of extended theory of spin fluctuations.

Zero- and longitudinal-field muon spin relaxation techniques have been used to study spin fluctuations in and compounds in the temperature range 10 - 300 K. The temperature dependence of the asymmetry parameter indicates a first-order transition to ferrimagnetism at and 260 K for and , respectively. In contrast the depolarization rate exhibits a critical divergence, characteristic of a continuous transition, as is approached from above. These features are consistent with those observed for the parent compound and indicate that the character of the spin fluctuations in the paramagnetic state changes little with deuterium loading, despite marked modifications to the low-temperature, magnetically ordered state. provides evidence of significant spin fluctuations below , while slight deviations from predicted behaviour indicate further structural or magnetic transitions in the ordered state.

In this paper the dynamics of the magnetization reversal process in perpendicularly biased [20 Å Pt/5 Å Co] 3 /t Å Pt/100 Å IrMn/20 Å Pt multilayers with different Pt insertion layer thickness (0 Å ≤ t ≤ 12 Å) is studied. The insertion of 1 Å thick Pt enhances the exchange bias field (H ex ) and for t > 3 Å H ex decreases exponentially with increasing Pt layer thickness. We show by magnetization relaxation measurements and direct observation of magnetic domains that magnetization reversal takes place by the nucleation of isolated cylindrical domains with a different nucleation site density in the forward and backward branches of the hysteresis loop. All the results were quantitatively analyzed using the Fatuzzo model for the dynamics of domain reversal processes. The activation energies for magnetization reversal by domain nucleation and domain propagation were determined.