Inverse Magnetocaloric Effect in Tetragonal FePt1xRhx Compound
Pallab Bag* and R Rawat
UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore -452001, India
*
Corresponding author’s e-mail: pallab@csr.res.in, Tel.: +91-731-2762267; Fax: +91-731-2465437
Abstract
We present transport and thermal characterization in FePt1(x = 0.2 - 0.24) compound associate a first order
antiferromagnetic (AFM) – ferromagnetic (FM) transition,
through resistivity () and specific heat (CP) measurements.
We observed latent heat associated with AFM - FM transition
comparable to cubic FeRh system. For 8 T change of magnetic
field it shows large change of magnetic entropy 5.7 J/kg-K and
magnetoresistance -22% at AFM-FM transition.
xRhx
Keywords: First order phase transition, magnetoresistance
and magnetocaloric effect.
Introduction
The tetragonal FePt and cubic FeRh alloys are
extensively studied due to their large perpendicular
magnetic anisotropy [1] and appearance of first order
AFM - FM transition [2], respectively. The AFM - FM
transition (TN) in FeRh system is very sensitive to
compositions, external pressure (P) and magnetic field
(H) etc. [3, 4] and shows large magnetocaloric effect
(MCE) [5] and magnetoresistance (MR) [3, 4, 6].
However there are few studies on AFM - FM transition
in tetragonal FePt1-xRhx (x = 0.20 - 0.24), accompanied
with iso-structural transition and change in electrical
resistivity [7, 8]. Here we present MCE and MR studies
on AFM-FM transition in tetragonal Fe-Pt-Rh system.
To the best of our knowledge these are the first report
on specific heat measurement in these systems.
transition with a latent heat of ~ 2.8k J/kg. It decreases
with increasing x. The value of latent heat associated at
TN is comparable to that in FeRh [5, 9], which shows
giant MCE. One typical isothermal magnetic entropy
change and magnetoresistance for present system is
shown in figure 1 (b) and (c), respectively. For 8T
magnetic field change it shows ~ -22% MR and ~ 5.7
J/kg-K ΔS above room temperature (~ 318 K). Even
though the latent heat associated with AFM-FM
transition is comparable to cubic FeRh system the
observed MCE is significantly lower. This could be due
to smaller dTN/dT in the present system (~ 3 K/T)
compared to (~ 8 K/T) for FeRh [5, 9].
Fig. 1: [a] Temperature dependence of resistivity and
specific heat for FePt0.76Rh0.24 compound in the absence
of magnetic field. Temperature dependence of [b] ΔS
and [c] MR at 8 T magnetic fields.
Results and discussion
Acknowledgment
Temperature dependence of resistivity (ρ)
measured during cooling and subsequent warming
showed hysteretic change in ρ which indicates first
order AFM - FM transition. One such typical curve is
shown for x = 0.24 composition. The variation of TN
with x is found to be consistent with earlier reports [7].
Extent of hysteresis (HW) and transition width (TW) is
found to be increase with x. This is consistent with our
study on Pd doped FeRh under simultaneous application
of H and P where we addressed that as the transition
temperature decreases the TW and HW increases
irrespective of H and P [4]. Figure 1 (a) also shows
corresponding CP vs T curve measured during warming.
Broad peak at ~ 330K can be associated with AFM-FM
We thank P Kushwaha for his suggestions and
discussion during the course of this work.
References
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