Stress vibration / damping during initial elastic stage

Hello all,

I have done a compression test of CuZr alloy at T=700 K, and the stress-strain curve shows a systematic vibration for strain less than 2% and dies away for larger strain. I thought this vibration was due to temperature fluctuation before it reaches the set temperature, but the temperature reached the set value at step=2000.

It was also noted that the vibration amplitude decreases as T decreases and vanishes at low T. I was wondering why. Thanks.

------------------------------ input script ----------------

units metal
boundary p p p
atom_style atomic
read_data geoin.lmp
pair_style eam/fs
pair_coeff * * ${home}/code/lammps/potentials/Cu-Zr_2.eam.fs Cu Zr
velocity all create 700 49284359 rot yes dist gaussian
fix fnpt all npt temp 700 700 0.2 x 0.0 0.0 2.0 # vacuum along y, compression along z
fix fcompress all deform 10 z erate -0.0001 remap v
compute truetemp all temp/deform
compute stress all pressure truetemp
thermo 1000
thermo_style custom step temp c_truetemp pe ke etotal vol lx ly lz press
timestep 0.002
... # some output commands here
run 1000000