First-order magnetic phase transition in FeRh–Pt thin films

Abstract

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.

Temperature-dependent transport properties of FeRh

“…Furthermore, if the AFM to FM transition is induced by an applied magnetic field, a pronounced magnetoresistance (MR) effect is found experimentally with a measured MR ratio ∼ 50% at room temperature [2][3][4]. The temperature of the metamagnetic transition as well as the MR ratio can be tuned by addition of small amounts of impurities [2,[5][6][7][8]. These properties make FeRh-based materials very attractive for future applications in data storage devices.…”

Microstructure and magnetic properties of FeRh thin films with Pt doping

“…This first-order magnetic phase transition is sensitive to the Fe-Rh composition and preparation conditions, therefore there is a large variation in the FM to AFM transition temperature (T tr~3 20-370 K) reported by various groups [5,9,10]. FeRh-X alloys, where the Rh particles are partially replaced by X (Pd, Pt, Ir) ones, cause a large decrease or increase in the critical transition temperature compared to that of FeRh (about 330 K).…”

“…FeRh thin films have recently attracted much attention because of their potential applications in ultra high-density magnetic recording [3][4][5]. These interesting characteristics of this alloy system are thought to arise due to a first-order magnetostructural phase transition from an antiferromagnetic (AFM) to ferromagnetic (FM) state, which is also accompanied by a structural distortion [6], when heated beyond a critical transition temperature (T tr ).…”

“…Ordered B2-type (CsCl) Fe-Rh alloy and its nearby compositions have been the subject of extensive theoretical and experimental studies due to their various interesting magnetic properties, such as the magnetocaloric effect, the elastocaloric effect, giant magnetostriction and giant magnetoresistance occurring close to room temperature [1][2][3][4][5]. FeRh thin films have recently attracted much attention because of their potential applications in ultra high-density magnetic recording [3][4][5].…”

Kinetics of first order magnetostructural transition in single crystalline FeRh thin film

“…[1][2][3] This interest is primarily due to the observation that the near-equiatomic phase of FeRh possesses a chemically ordered CsCl-type structure which exhibits an abrupt antiferromagnetic (AFM) to ferromagnetic (FM) transition with heating to a transition temperature of around 350K in the bulk and thin film forms . [1][2][3] .…”