The structural and magnetic phase transition in FeRh thin films are investigated. The ͑001͒ oriented single crystal FeRh thin films fabricated onto MgO ͑100͒ substrate possess lattice parameter a smaller than c, because of the compressive stress along the a axis from MgO substrate. With increasing annealing temperature, paramagnetic FeRh thin films transform into ferromagnetic and then antiferromagnetic-ferromagnetic ͑AF-FM͒ stages. The transition temperature of AF-FM increases with annealing temperature, while the thermal hysteresis width decreases. The M-H loops of the film annealed at 700°C show an opening at high magnetic fields during the transition state. Note that the opening in M-H loops disappears when AF phase has transformed into FM phase. The origin of the opening is not known but possibly due to the combination of hysteresis loops of FM and AF phases, where FM phase is soft magnetic and the AF phase FeRh shows a hysteresis behavior with coercivity due to the reduction of magnetic anisotropy at high temperatures. The abrupt change of coercivity along the perpendicular direction during the AF-FM transition suggests that a stress-induced magnetic anisotropy exists in FeRh thin films due to the volume expansion in the phase transition process.

In this paper the propagation of small amplitude surface waves guided by a layer with a finite thickness on an incompressible half-space is studied. The layer and half-space are both assumed to be initially stressed. The combined effect of initial stress and finite deformation on the speed of Rayleigh waves is analyzed and illustrated graphically. With a suitable simple choice of constitutive law that includes initial stress, it is shown that in many cases, as is to be expected, the effect of a finite deformation (with an associated pre-stress) is very similar to that of an initial stress (without an accompanying finite deformation). However, by contrast, when the finite deformation and initial stress are considered together independently with a judicious choice of material parameters different features are found that don't appear in the separate finite deformation or initial stress situations on their own.

The first-order anti-ferromagnetic (AFM)-ferromagnetic (FM) phase transition in ordered FeRh alloy with CsCl structure is known to take place at about 100C. 1 This transition is accompanied by a unit cell volume expansion of 1%-2%, a reduction in resistivity, and a large entropy change. 2 The transition temperature is sensitive to composition, thus can be tuned by doping additives such as Pt or Ir to above 200C. 3 However, the physical mechanism of the transition mechanism is not well understood. FeRh (100−X) Pt X thin films (0≦X≦15) were deposited onto (100)MgO substrate by an e-beam technique using Fe, Rh, and Pt targets at substrate temperature around 450 °C. The film thickness was around 50 nm. The as-deposited films were annealed in vacuum at 800 °C for 2 h to obtain chemically ordered CsCl structure. The XRD and theφscan patterns of FeRh (100−X) Pt X thin films confirm they are of single crystalline of the ordered CsCl structure. The temperature dependent magnetization curves for FeRh (100−X) Pt X thin films with X are shown in Fig. 1. The transition temperature shifts to high temperature while the width of thermal hysteresis decreases, and there is little thermal hysteresis when X=15. The magnetization curves under different applied magnetic fields H during heating and cooling processes are shown in Figs. 2(a) and (b) for Fe 50 Rh 50 and (Fe 50 Rh 50) 95 Pt 5 thin films, respectively. As H increases, the transition temperatures during heating and cooling processes all decreased linearly. With X, (dT/dH) reduces from-8.6 to-3.3 K/T. This means that the effect of magnetic field is to stabilize the FM phase and consequently decrease the transition temperature. However, the effect of H on the AFM/FM phase transition is restrained by the addition of Pt. The result of this applied magnetic field dependence on transition temperature in FeRh (100−X) Pt X thin films is similar to the behavior observed in FeRh nanoparticles, FeRh (100−X) Pt X thin films, bulk FeRh alloys, and Ru-doped CeFe 2 alloys. 3-6 According to the magnetic Clausius-Clapeyron equation,3 the total entropy change (FeRh (100−X) Pt X S) associated with the magnetic phase transition was calculated., which is shown in Figure 3. The entropy change (△S) lat contributed by the lattice distortion is also plotted using the equation (△S) lat =3ɑ(△ V/V)κD, where ɑ is the thermal expansion coefficient, (△ V/V) is a relative volume change, κvolume compressibility, and D density. It is seen that △S is much larger than (△ S) lat. This result suggests that the lattice entropy change is not a determining factor for the first-order AFM-FM phase transition in FeRh-based alloys, but the entropy change originates from a change in the magnetic moments on Rh atoms between the AFM and FM states at the phase transition.

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A systematic investigation of structural and magnetic properties of FePt/FeRh bilayers has been carried out. The transition temperature of single FeRh layer is higher than that of FePt/FeRh bilayer. A sharp decrease in coercivity is observed at transition temperature for FePt/FeRh bilayer. The thickness FePt dependence of exchange bias field and unidirectional anisotropy constant are discussed. Of interest is the exchange bias effect that appears in FePt/FeRh bilayer and the unidirectional anisotropy constant, which is very large ͑up to 0.8 erg/ cm 2 ͒, suggesting that this system can be applied for spin-valve sensors and heat assisted magnetic recording medium. It may also provide some useful information for better understanding of the mechanism of exchange bias.